This document provides an overview of DNA, RNA, and protein synthesis. It begins by discussing Griffith's experiments which discovered transformation and the experiments of Avery, MacLeod and McCarty which identified DNA as the transforming factor. It then describes the structure of DNA as a double helix based on evidence from Chargaff, Franklin and the model proposed by Watson and Crick. The document outlines DNA replication and how the DNA double helix unwinds and uses each strand as a template to produce two new DNA molecules. It concludes by explaining how DNA is transcribed into mRNA which is then translated into proteins, the basic process by which genes direct the traits of organisms.
GENETIC MATERIAL refers to the material of which genes are made up of. It includes both DNA and RNA. Though in most of the organism DNA is playing this role, but in certain viruses RNA is storing all the genetic information of the individual. Here we are discussing about the discovery and property of these genetic material.
GENETIC MATERIAL refers to the material of which genes are made up of. It includes both DNA and RNA. Though in most of the organism DNA is playing this role, but in certain viruses RNA is storing all the genetic information of the individual. Here we are discussing about the discovery and property of these genetic material.
DNA caries genetic information of organisms. This presentation covers the discovery of DNA as genetic material, structure of DNA, Nucleotides and nucleosides. Watson and crick DNA model.
Introduction to Genetic Material, Physical and Chemical properties of the same and various types of coiling mechanisms as well as information about chromosomal and extra-chromosomal DNA.
Circulating cell free DNA is a potential tumor marker in a non-invasive blood test for the treatment and evaluation of cancer and recurrence monitoring. As circulating tumor DNA is often present at low frequencies within circulating cell free DNA, targeted sequencing on the Ion Torrent™ platform is an optimal tool or mutation detection with very little sample input required. Here, we demonstrate a complete workflow from isolation through molecular characterization of circulating tumor DNA. We have optimized a protocol using magnetic beads to isolate circulating cell free DNA. This protocol is easily automated to process up to 192 samples a day. It is also easily scalable for any input volume and can elute in volumes down to 15 μL resulting in no loss of low frequency alleles. We demonstrate comparable performance between this bead based isolation and column based isolation. We have completed molecular characterization of circulating cell free DNA using the multiplexing capabilities of AmpliSeq™ and the Ion PGM™. With the Ion AmpliSeq™ Cancer Hotspot Panel v2, we performed targeted sequencing of 50 genes of interest, covering 2800 COSMIC mutations. We demonstrate good reproducibility of amplicon representation as well as allelic frequencies. Through saturation studies and subsampling, we have determined the limit of detection of hotspots circulating cell free DNA on the Ion PGM™ to be below 1%. We further demonstrate proof of principle of this workflow on circulating cell free DNA and matched FFPE samples. Our results verify the accuracy and ease of our workflow. This protocol, from isolation through targeted sequencing, will not only result in a simple sample preparation for circulating cell free DNA but also facilitate rapid mutation detection to advance cancer research.
DNA caries genetic information of organisms. This presentation covers the discovery of DNA as genetic material, structure of DNA, Nucleotides and nucleosides. Watson and crick DNA model.
Introduction to Genetic Material, Physical and Chemical properties of the same and various types of coiling mechanisms as well as information about chromosomal and extra-chromosomal DNA.
Circulating cell free DNA is a potential tumor marker in a non-invasive blood test for the treatment and evaluation of cancer and recurrence monitoring. As circulating tumor DNA is often present at low frequencies within circulating cell free DNA, targeted sequencing on the Ion Torrent™ platform is an optimal tool or mutation detection with very little sample input required. Here, we demonstrate a complete workflow from isolation through molecular characterization of circulating tumor DNA. We have optimized a protocol using magnetic beads to isolate circulating cell free DNA. This protocol is easily automated to process up to 192 samples a day. It is also easily scalable for any input volume and can elute in volumes down to 15 μL resulting in no loss of low frequency alleles. We demonstrate comparable performance between this bead based isolation and column based isolation. We have completed molecular characterization of circulating cell free DNA using the multiplexing capabilities of AmpliSeq™ and the Ion PGM™. With the Ion AmpliSeq™ Cancer Hotspot Panel v2, we performed targeted sequencing of 50 genes of interest, covering 2800 COSMIC mutations. We demonstrate good reproducibility of amplicon representation as well as allelic frequencies. Through saturation studies and subsampling, we have determined the limit of detection of hotspots circulating cell free DNA on the Ion PGM™ to be below 1%. We further demonstrate proof of principle of this workflow on circulating cell free DNA and matched FFPE samples. Our results verify the accuracy and ease of our workflow. This protocol, from isolation through targeted sequencing, will not only result in a simple sample preparation for circulating cell free DNA but also facilitate rapid mutation detection to advance cancer research.
DNA is a double helical structure that transfers the genetic information from one generation to another. it consists of two strands with the four nucleotide basis .The four nucleotides contains adenine, cytosine, guanine, thymine .These four nuclic basis are such arranged and coiled with the help of hydrogen bonds and forms the helical structure of DNA. In RNA the thymine is replaced with uracil. Here you will learn the replication ,transcription and translation process in DNA.
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DNA is a highly complex, intricate and extraordinary macromolecule found within all living cells. DNA is a "biochemical noun" and can be defined as "...a self- .... In other words, DNA refers to the molecules inside cells that carry genetic information and pass it from one generation to the next. The scientific name for DNA .... Free Essays from 123 Help Me | acid (DNA) is a molecule, a material rather, that is present in almost all living organisms. It is self-replicating and is .... 17. 2. 2022 ... Dna is the genetic fabric which is present in all the cells of the body. This molecule present a few characteristics, as VNTR, special present .... 24. 4. 2020 ... Genetic ancestry testing holds the potential to identify the geographic origins of an individual's ancestors, ancestral lineages, and relatives, .... 25. 4. 2022 ... 2022 DNA Day Essay Contest: Full Essays · 1st Place: Man Tak Mindy Shie, Grade 12. Teacher: Dr. Siew Hwey Alice Tan School: Singapore .... DNA, or Deoxyribonucleic acid, is two self replicating biopolymer strands that contain biological information that is necessary for human life. DNA is what .... DNA, also known as deoxyribonucleic acid, is a genetic information-carrying molecule that is essential for the development, growth, and reproduction of all .... DNA stand for deoxyribonucleic acid. RNA stands for ribonucleic acid. They share some similarities, such as both being nucleic acids.. Free Essay: The Structure and Replication of DNA Introduction The ... The enzyme polymerase is used to add new nucleotides to the growing DNA strands.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
2. Objectives:
Summarize the relationship between genes and DNA
Describe the overall structure of DNA
Summarize the events of DNA replication
Relate the DNA molecule to chromosome structure
3. DNA
Think about this:
How do genes work?
What are they made of?
How do they determine the characteristics of an
organism?
Are genes single molecules?
4. Griffiths and
Transformation
Accidental discovery
Griffith had isolated two slightly different
strains, or types, of pneumonia bacteria from
mice.
S – smooth: Disease causing bacteria
R – Rough: Harmless strain
Oswald Avery also worked with
Pneumococcus
5. Griffith’s Experiments
After heating the disease-causing bacteria, why did Griffith test whether material
from the bacterial culture would produce new colonies in a petri dish?
6. Transformation
From the last test of his experiment, Griffith discovered that
somehow the heat-killed bacteria had passed their disease-
causing bacteria.
Griffith called this process transformation because one strain
of bacteria had apparently been changed permanently into
another.
He hypothesized that when the live, harmless bacteria and the
heat-killed bacteria were mixed, some factor was transferred
from the heat-killed cells into the live cells.
That factor, he hypothesized, must contain information that
could change harmless bacteria into disease-causing ones.
Since the ability to cause disease was inherited by the
transformed bacteria's offspring, the transforming factor might
be a gene.
7. Avery and DNA
What were they able to determine was the “transforming factor” and how?
8. Key Finding!
Avery and other scientists discovered that the
nucleic acid DNA stores and transmits the
genetic information from one generation of an
organism to the next.
Oswald Avery
Colin Munro
MacLeod Maclyn McCarty
11. Radioactive Markers
Grew phage viruses in two media radioactively
labeled with either
35S radioactive Sulfur isotope in their proteins
32P radioactive phosphorus isotope in their DNA
Infected bacteria with labeled phages
Why did they use Sulfur and Phosphorus as
markers?
Which radioactive marker was found inside the cell
Which molecule carries viral genetic information?
12. Conclusions
35S phage
Radioactive proteins stayed in supernatant
Viral protein DID NOT enter the bacteria
32P phage
Radioactive DNA stayed in pellet
Viral DNA DID enter bacteria
The point?
Confirmed DNA is the “transforming factor”
Hershey and Chase concluded that the genetic
material of the bacteriophage was DNA, not protein.
14. The Components &
Structure of DNA
How does DNA, or any molecule for that matter,
could do the three critical things that genes were
known to do:
First, genes had to carry information from one
generation to the next;
second, they had to put that information to work by
determining the heritable characteristics of
organisms; and
third, genes had to be easily copied, because all of a
cell's genetic information is replicated every time a
cell divides.
18. Chargaff’s Rules
discovered that the
percentages of guanine
[G] and cytosine [C] bases
are almost equal in any
sample of DNA.
the percentages of
adenine [A] and thymine
[T] bases are also almost
equal in any sample of
DNA.
Samples from all
organisms obey this rule
20. The Double Helix
Using clues from
Franklin's pattern,
within weeks
Watson and Crick
had built a
structural model
that explained the
puzzle of how
DNA could carry
information, and
how it could be
copied.
Watson and
Crick's model of
DNA was a
double helix, in
which two
strands were
wound around
each other.
21. Key Point
DNA is a double helix in which two strands are
wound around each other.
Each strand is made up of a chain of nucleotides.
The two strands are held together by hydrogen
bonds between adenine and thymine and between
guanine and cytosine.
22. Quick Quiz
The double helix structure of DNA was first described by
___________________.
The first major experiment that led to the discovery of
DNA as the genetic material was conducted by
__________. He used heat-killed bacteria in mice.
The scientist who identified the transforming agent in
Griffith’s famous experiment as DNA was _________.
These scientists preformed an experiment to
demonstrate that DNA is the genetic material in viruses.
______________________
This scientist’s X-ray diffraction data helped Watson and
Crick solve the structure of DNA.
_____________________
24. DNA & Chromosomes
Prokaryotic cells
lack nuclei and
many of the
organelles found in
eukaryotes.
Their DNA
molecules are
located in the
cytoplasm.Most prokaryotes have a single circular DNA
molecule that contains nearly all of the cell's genetic
information.
25. Eukaryotic DNA
Eukaryotic DNA is generally located in the cell nucleus in the form of a number of
chromosomes.
The number of
chromosomes
varies widely from
one species to the
next.
26. DNA Length
The chromosome
of the prokaryote E.
coli, which can live
in the human colon
(large intestine),
contains 4,639,221
base pairs.
27. Chromosome Structure
Eukaryotic chromosomes
contain both DNA and
protein, tightly packed
together to form a
substance called
chromatin.
Chromatin consists of
DNA that is tightly coiled
around proteins called
histones
28.
29.
30. DNA Replication
During DNA replication, the DNA molecule separates into two strands, then
produces two new complementary strands following the rules of base pairing.
Each strand of the double helix of DNA serves as a template, or model, for the
new strand.
31.
32. Complete the Strand
Complete the Strand with the complimentary bases
T A C G T T C G G G T A T A T T
33.
34.
35.
36.
37.
38. DNA Proofreading
DNA polymerase proof reads the DNA strands as it adds
new nucleotides.
The DNA polymerase can only add a new nucleotide if
the previous nucleotide is correctly paired to its
complementary base.
If an error is found, the DNA polymerase goes back and
removes the incorrect nucleotide, adding a correct one
so that it may then proceed along the strand.
The DNA polymerase's proof reading ability limits errors
in DNA replication to about one in 1 billion nucleotides.
39. Recap, Please!
Step 1: Helicase separates DNA strands
Step 2: SSBs Coat Single stranded DNA and RNA
Primase synthesizes RNA primers
Step 3: Polymerase Extends the DNA strand
Sliding clamps increase processivity
Step 4: RNase H removes the RNA primer, Polymerase
fills the gap & Ligase connects short DNA strands
40. Dissecting the Steps in DNA Replication
Strands are separated
Helicase unwinds the DNA double helix
The point where the DNA is separated into single strands and
new DNA will be synthesized is known as the Replication
Fork
Single Strand Binding Proteins (SSBs) quickly coat the
newly exposed single strand. Why?
They bind loosely to the DNA and are displaced when the
polymerase enzymes begin synthesizing the new DNA
strands.
Now that they are separated, the new DNA strands can
act as templates for the production of two new
complimentary DNA strands
42. The Players
Helicase – made of 6 proteins arranged in a ring shape unwinds the
DNA double helix into two individual strands.
Single Strand Binding proteins (SSBs) – tetramers that coat the single
stranded DNA preventing the DNA from reannealing to form double
stranded DNA.
Primase – an RNA polymerase that synthesizes the short RNA primers
needed to start the replication process.
DNA polymerase – Bean shaped enzyme that strings nucleotides
together to form a DNA strand.
The Sliding Clamp – an accessory protein that helps hold the DNA
polymerase on to the DNA strand during replication
RNase H – removes the RNA primers that previously began the
synthesis.
DNA Ligase – links short stretches of DNA together to form one long
continuous strand of DNA.
43. Some questions for you…
Why is DNA replication essential to life?
How often/fast does replication occur?
What nucleotides are complimentary Pairs?
What pairs with Guanine?
What pairs with Cytosine?
What pairs with Adenine?
What pairs with Thymine?
What pairs with Uracil?
44. Quick Quiz
Match the enzyme with
the function:
A. Helicases
B. Ligase
C. DNA Polymerase
D. RNA Polymerase
E. Primase
1. Joins Okazaki
fragments together
2. unwinds and unzips the
parent DNA molecule
3. add short segments of
RNA primers to each DNA
strand
4. Adds the appropriate
nucleotides to the new
DNA strands
45. Objectives
How is the code of DNA translated into messenger
RNA?
How is messenger RNA transcribed into a protein?
Describe how to make a protein (beginning with a a
gene).
46. Bodies Cells DNA
Bodies are made up of cells
All cells run on a set of instructions
spelled out in DNA
47. DNA Cells Bodies
How does DNA code for cells &
bodies?
How are cells and bodies made from the
instructions in DNA?
48. DNA Proteins
Cells Bodies
DNA has the information to build proteins
genes
49. How do proteins do all
the work
Proteins
Proteins run living organisms
Enzymes
Control all chemical reactions in living organisms
Structure
All living organisms are built out of proteins
50. Cell Organization
DNA
DNA is in the ____________
Genes = instructions for making proteins
Want to keep it there = protected
Locked in the “vault”
51.
52.
53.
54.
55. Types of RNA
There are three main types of RNA: messenger
RNA, ribosomal RNA, and transfer RNA.
56.
57.
58.
59. How does RNA polymerase
“know” where to start and stop
making an RNA copy of DNA?
Like many stories in science, the discovery of the molecular nature of the gene began with an investigator who was actually looking for something else. In 1928, British scientist Frederick Griffith was trying to figure out how bacteria make people sick. More specifically, Griffith wanted to learn how certain types of bacteria produce a serious lung disease known as pneumonia.
Griffith's Experiments Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Inferring After heating the disease-causing bacteria, why did Griffith test whether material from the bacterial culture would produce new colonies in a petri dish?
Transformation is the process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria
In 1944, Avery and MacLeod, and McCarty purified the transforming principle of Fred Griffith's earlier experiment with pneumococcus bacteria. By a process of elimination, these scientists showed that DNA was the factor that caused genetic transformation.
They made an extract, or juice, from the heat-killed bacteria. They then carefully treated the extract with enzymes that destroyed proteins, lipids, carbohydrates, and other molecules, including the nucleic acid RNA. Transformation still occurred. Obviously, since these molecules had been destroyed, they were not responsible for the transformation.
Avery and the other scientists repeated the experiment, this time using enzymes that would break down DNA. When they destroyed the nucleic acid DNA in the extract, transformation did not occur.
There was just one possible conclusion. DNA was the transforming factor.
They collaborated in studying viruses, nonliving particles smaller than a cell that can infect living organisms.
Bacteriophage: virus that infects bacteria
They collaborated in studying viruses, nonliving particles smaller than a cell that can infect living organisms.
Bacteriophage: virus that infects bacteria
Hershey and Chase reasoned that if they could determine which part of the virus—the protein coat or the DNA core—entered the infected cell, they would learn whether genes were made of protein or DNA. To do this, they grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (35S). This was a clever strategy because proteins contain almost no phosphorus and DNA contains no sulfur. The radioactive substances could be used as markers. If 35S was found in the bacteria, it would mean that the viruses' protein had been injected into the bacteria. If 32P was found in the bacteria, then it was the DNA that had been injected. Click the article at right for more information on radioisotopes.
Nucleotide: monomer of nucleic acids made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base
There are four kinds of nitrogenous bases in DNA. Two of the nitrogenous bases, adenine (AD-uh-neen) and guanine (GWAH-neen), belong to a group of compounds known as purines. The remaining two bases, cytosine (SY-tuh-zeen) and thymine (THY-meen), are known as pyrimidines. Purines have two rings in their structures, whereas pyrimidines have one ring.
She used a technique called X-ray diffraction to get information about the structure of the DNA molecule. Franklin purified a large amount of DNA and then stretched the DNA fibers in a thin glass tube so that most of the strands were parallel. Then she aimed a powerful X-ray beam at the concentrated DNA samples, and recorded the scattering pattern of the X-rays on film. Franklin worked hard to make better and better patterns from DNA until the patterns became clear. The result of her work is the X-ray pattern shown below.
By itself, Franklin's X-ray pattern does not reveal the structure of DNA, but it does carry some very important clues. The X-shaped pattern in the photograph in the image below shows that the strands in DNA are twisted around each other like the coils of a spring, a shape known as a helix. The angle of the X suggests that there are two strands in the structure. Other clues suggest that the nitrogenous bases are near the center of the molecule.
At the same time that Franklin was continuing her research, Francis Crick, a British physicist, and James Watson, an American biologist, were trying to understand the structure of DNA by building three-dimensional models of the molecule. Their models were made of cardboard and wire. They twisted and stretched the models in various ways, but their best efforts did nothing to explain DNA's properties.
Then, early in 1953, Watson was shown a copy of Franklin's remarkable X-ray pattern. The effect was immediate. In his book The Double Helix, Watson wrote: “The instant I saw the picture my mouth fell open and my pulse began to race.”
When Watson and Crick evaluated their DNA model, they realized that the double helix accounted for many of the features in Franklin's X-ray pattern but did not explain what forces held the two strands together. They then discovered that hydrogen bonds could form between certain nitrogenous bases and provide just enough force to hold the two strands together.
hydrogen bonds can form only between certain base pairs—adenine and thymine, and guanine and cytosine. Once they saw this, they realized that this principle, called base pairing, explained Chargaff's rules.
Watson and Crick
Griffith
Avery
Hershey & Chase
Rosalind Franklin
DNA is present in such large amounts in many tissues that it's easy to extract and analyze.
Where are the genes that Mendel first described a century and a half ago?
Eukaryotic DNA is a bit more complicated. Many eukaryotes have as much as 1000 times the amount of DNA as prokaryotes.
This DNA is not found free in the cytoplasm.
Eukaryotic DNA is generally located in the cell nucleus in the form of a number of chromosomes.
The number of chromosomes varies widely from one species to the next. For example, diploid human cells have 46 chromosomes, Drosophila cells have 8, and giant sequoia tree cells have 22.
DNA molecules are surprisingly long. The chromosome of the prokaryote E. coli, which can live in the human colon (large intestine), contains 4,639,221 base pairs. The length of such a DNA molecule is roughly 1.6 mm, which doesn't sound like much until you think about the small size of a bacterium. To fit inside a typical bacterium, the DNA molecule must be folded into a space only one one-thousandth of its length.
To get a rough idea of what this means, think of a large school backpack. Then, imagine trying to pack a 300-meter length of rope into the backpack! The DNA must be dramatically folded to fit within the cell.
The DNA in eukaryotic cells is packed even more tightly. A human cell contains almost 1000 times as many base pairs of DNA as a bacterium. The nucleus of a human cell contains more than 1 meter of DNA. How is so much DNA folded into tiny chromosomes? The answer can be found in the composition of eukaryotic chromosomes.
Eukaryotic chromosomes contain both DNA and protein, tightly packed together to form a substance called chromatin.
Chromatin consists of DNA that is tightly coiled around proteins called histones.
Chromatin is granular material visible within the nucleus; consists of DNA tightly coiled around proteins
Histones are protein molecule around which DNA is tightly coiled in chromatin
Together, the DNA and histone molecules form a beadlike structure called a nucleosome. Nucleosomes pack with one another to form a thick fiber, which is shortened by a system of loops and coils.
Eukaryotic Chromosome Structure
During most of the cell cycle, these fibers are dispersed in the nucleus so that individual chromosomes are not visible. During mitosis, however, the fibers of each individual chromosome are drawn together, forming the tightly packed chromosomes you can see through a light microscope in dividing cells. The tight packing of nucleosomes may help separate chromosomes during mitosis. There is also some evidence that changes in chromatin structure and histone-DNA binding are associated with changes in gene activity and expression.
What do nucleosomes do? Nucleosomes seem to be able to fold enormous lengths of DNA into the tiny space available in the cell nucleus. This is such an important function that the histone proteins themselves have changed very little during evolution—probably because mistakes in DNA folding could harm a cell's ability to reproduce.
Before a cell divides, it duplicates its DNA in a copying process called replication.
Replication is the copying process by which a cell duplicates its DNA
This process ensures that each resulting cell will have a complete set of DNA molecules.
Strands are separated
Helicase unwinds the DNA double helix.
The point where the DNA is separated into single strands and new DNA will be synthesized is known as the Replication Fork.
DNA replication takes place simultaneously at each fork. The mechanism of replication is identical at each fork.
Single Strand Binding Proteins (SSBs) quickly coat the newly exposed single strand. Why? They bind loosely to the DNA and are displaced when the polymerase enzymes begin synthesizing the new DNA strands.
Now that they are separated, the new DNA strands can act as templates for the production of two new complimentary DNA strands
SSBs coat the strand to prevent the single strands from snapping back together (Reannealing). It maintains them as separate strands.
Remember that the double helix consists of two antiparallel DNA strands with complimentary 5prime and 3prime strands running in opposite directions. Polymerase enzymes can synthesis nucleic acids strands only in the 5prime to 3prime direction hooking the 5prime phosphate group of an incoming nucleotide onto the 3prime hydroxyl group at the end of the growing nucleic acid chain.
Because the chain grows by extension off the 3prime hydroxyl group, strand synthesis is said to proceed in a 5prime to 3 prime direction.
Even when the strands are separated however, DNA Polymerase cannot simply begin copying the DNA.
DNA polymerase can only extend the nucleic acid chain but cannot start one from scratch. So how do we “fix this problem??
To give the DNA polymerase a place to start, an RNA polymerase called ? (Primase) first copies a short stretch of the DNA strand.
- Primase synthesizes RNA primers.
This creates a complimentary RNA segment up to 60 nucleotides long that is called a primer. Now DNA polymerase can copy the DNA strand.
Primers are necessary because DNA polymerase can only extend the nucleic acid chain but cannot start one from scratch.
The DNA polymerase starts at the 3prime end of the RNA primer, and using the original DNA strand as a guide begins to synthesize the new complimentary DNA strand.
- Each of the two new strands gets synthesized in the 5prime to 3 prime direction
- Two polymerase enzymes are required – one for each parental DNA strand.
Due to the antiparallel nature of the DNA strands, however, the polymerase enzymes on the two strands start to move in opposite directions.
One polymerase can remain on it’s DNA template and copy the DNA in one continuous strand. However, the other polymerase can only copy a short stretch of DNA before it runs into the primer of the previously sequenced fragment. It is therefore forces to repeatedly release the DNA strand and slide further upstream to begin extension from another RNA primer. What helps hold the DNA polymerase onto the DNA as the DNA moves through the replication machinery. (Sliding clamp). The sliding clamp makes the polymerase processive.
The continually synthesized strand is known as the leading strand and the strand that is synthesized in short pieces is the lagging strand. The short pieces separated by RNA primers in the lagging strand are called Okazaki Fragments.
Before the lagging strand DNA exits the replication factory, its RNA primers must be removed and the Okazaki fragments must be joined together to create a continuous DNA strand.
Next, the sequence gap created by the RNase H is then filled in by DNA polymerase which extends the 3prime end of the neighboring Okazaki fragment.
The First step is the removal of the RNA primer. RNase H which recognizes RNA-DNA hybrid helices degrades the RNA by hydrolyzing its phosphodiester bonds.
Finally the Okazaki fragments are joined together by DNA ligase which hooks together the 3prime end of one fragment to the 5prime phosphate group of the neighboring fragment in an ATP or NAD dependant reaction (This means that it requires energy).
DNA replication is carried out by a series of enzymes. These enzymes “unzip” a molecule of DNA. The unzipping occurs when the hydrogen bonds between the base pairs are broken and the two strands of the molecule unwind. Each strand serves as a template for the attachment of complementary bases.
DNA Replication
DNA replication involves a host of enzymes and regulatory molecules. You may recall that enzymes are highly specific. For this reason, they are often named for the reactions they catalyze. The principal enzyme involved in DNA replication is called DNA polymerase (PAHL-ih-mur-ayz) because it joins individual nucleotides to produce a DNA molecule, which is, of course, a polymer. DNA polymerase also “proofreads” each new DNA strand, helping to maximize the odds that each molecule is a perfect copy of the original DNA.
Strands are separated
Helicase unwinds the DNA double helix.
The point where the DNA is separated into single strands and new DNA will be synthesized is known as the Replication Fork.
DNA replication takes place simultaneously at each fork. The mechanism of replication is identical at each fork.
Single Strand Binding Proteins (SSBs) quickly coat the newly exposed single strand. Why? They bind loosely to the DNA and are displaced when the polymerase enzymes begin synthesizing the new DNA strands.
Now that they are separated, the new DNA strands can act as templates for the production of two new complimentary DNA strands
SSBs coat the strand to prevent the single strands from snapping back together (Reannealing). It maintains them as separate strands.
Remember that the double helix consists of two antiparallel DNA strands with complimentary 5prime and 3prime strands running in opposite directions. Polymerase enzymes can synthesis nucleic acids strands only in the 5prime to 3prime direction hooking the 5prime phosphate group of an incoming nucleotide onto the 3prime hydroxyl group at the end of the growing nucleic acid chain.
Because the chain grows by extension off the 3prime hydroxyl group, strand synthesis is said to proceed in a 5prime to 3 prime direction.
Even when the strands are separated however, DNA Polymerase cannot simply begin copying the DNA.
DNA polymerase can only extend the nucleic acid chain but cannot start one from scratch. So how do we “fix this problem??
To give the DNA polymerase a place to start, an RNA polymerase called ? (Primase) first copies a short stretch of the DNA strand.
- Primase synthesizes RNA primers.
This creates a complimentary RNA segment up to 60 nucleotides long that is called a primer. Now DNA polymerase can copy the DNA strand.
Primers are necessary because DNA polymerase can only extend the nucleic acid chain but cannot start one from scratch.
The DNA polymerase starts at the 3prime end of the RNA primer, and using the original DNA strand as a guide begins to synthesize the new complimentary DNA strand.
- Each of the two new strands gets synthesized in the 5prime to 3 prime direction
- Two polymerase enzymes are required – one for each parental DNA strand.
Due to the antiparallel nature of the DNA strands, however, the polymerase enzymes on the two strands start to move in opposite directions.
One polymerase can remain on it’s DNA template and copy the DNA in one continuous strand. However, the other polymerase can only copy a short stretch of DNA before it runs into the primer of the previously sequenced fragment. It is therefore forces to repeatedly release the DNA strand and slide further upstream to begin extension from another RNA primer. What helps hold the DNA polymerase onto the DNA as the DNA moves through the replication machinery. (Sliding clamp). The sliding clamp makes the polymerase processive.
The continually synthesized strand is known as the leading strand and the strand that is synthesized in short pieces is the lagging strand. The short pieces separated by RNA primers in the lagging strand are called Okazaki Fragments.
Before the lagging strand DNA exits the replication factory, its RNA primers must be removed and the Okazaki fragments must be joined together to create a continuous DNA strand.
Next, the sequence gap created by the RNase H is then filled in by DNA polymerase which extends the 3prime end of the neighboring Okazaki fragment.
The First step is the removal of the RNA primer. RNase H which recognizes RNA-DNA hybrid helices degrades the RNA by hydrolyzing its phosphodiester bonds.
Finally the Okazaki fragments are joined together by DNA ligase which hooks together the 3prime end of one fragment to the 5prime phosphate group of the neighboring fragment in an ATP or NAD dependant reaction (This means that it requires energy).
SSBs coat the strand to prevent the single strands from snapping back together (Reannealing). It maintains them as separate strands.
Remember that the double helix consists of two antiparallel DNA strands with complimentary 5prime and 3prime strands running in opposite directions. Polymerase enzymes can synthesis nucleic acids strands only in the 5prime to 3prime direction hooking the 5prime phosphate group of an incoming nucleotide onto the 3prime hydroxyl group at the end of the growing nucleic acid chain.
Because the chain grows by extension off the 3prime hydroxyl group, strand synthesis is said to proceed in a 5prime to 3 prime direction.
Even when the strands are separated however, DNA Polymerase cannot simply begin copying the DNA.
DNA polymerase can only extend the nucleic acid chain but cannot start one from scratch. So how do we “fix this problem??
To give the DNA polymerase a place to start, an RNA polymerase called ? (Primase) first copies a short stretch of the DNA strand.
- Primase synthesizes RNA primers.
This creates a complimentary RNA segment up to 60 nucleotides long that is called a primer. Now DNA polymerase can copy the DNA strand. The DNA polymerase starts at the 3prime end of the RNA primer, and using the original DNA strand as a guide begins to synthesize the new complimentary DNA strand.
- Each of the two new strands gets synthesized in the 5prime to 3 prime direction
- Two polymerase enzymes are required – one for each parental DNA strand.
Due to the antiparallel nature of the DNA strands, however, the polymerase enzymes on the two strands start to move in opposite directions.
One polymerase can remain on it’s DNA template and copy the DNA in one continuous strand. However, the other polymerase can only copy a short stretch of DNA before it runs into the primer of the previously sequenced fragment. It is therefore forces to repeatedly release the DNA strand and slide further upstream to begin extension from another RNA primer. What helps hold the DNA polymerase onto the DNA as the DNA moves through the replication machinery. (Sliding clamp). The sliding clamp makes the polymerase processive.
The continually synthesized strand is known as the leading strand and the strand that is synthesized in short pieces is the lagging strand. The short pieces separated by RNA primers in the lagging strand are called Okazaki Fragments.
Before the lagging strand DNA exits the replication factory, its RNA primers must be removed and the Okazaki fragments must be joined together to create a continuous DNA strand.
The First step is the removal of the RNA primer. RNase H which recognizes RNA-DNA hybrid helices degrades the RNA by hydrolyzing its phosphodiester bonds.
Next, the sequence gap created by the RNase H is then filled in by DNA polymerase which extends the 3prime end of the neighboring Okazaki fragment. Finally the Okazaki fragments are joined together by DNA ligase which hooks together the 3prime end of one fragment to the 5prime phosphate group of the neighboring fragment in an ATP or NAD dependant reaction (This means that it requires energy).
The major types of proteins, which must work together during the replication of DNA, are illustrated, showing their positions.
When DNA replicates, many different proteins work together to accomplish the following steps:
The two parent strands are unwound with the help of DNA helicases.
Single stranded DNA binding proteins attach to the unwound strands, preventing them from winding back together.
The strands are held in position, binding easily to DNA polymerase, which catalyzes the elongation of the leading and lagging strands. (DNA polymerase also checks the accuracy of its own work!).
While the DNA polymerase on the leading strand can operate in a continuous fashion, RNA primer is needed repeatedly on the lagging strand to facilitate synthesis of Okazaki fragments. DNA primase, which is one of several polypeptides bound together in a group called primosomes, helps to build the primer.
Finally, each new Okazaki fragment is attached to the completed portion of the lagging strand in a reaction catalyzed by DNA ligase.
Tetramer - A tetramer is a protein with four subunits (tetrameric).
DNA carries the information for making all of the cell's proteins. These proteins implement all of the functions of a living organism and determine the organism's characteristics. When the cell reproduces, it has pass all of this information on to the daughter cells.
Before a cell can reproduce, it must first replicate, or make a copy of, its DNA.
Different types of cells replicated their DNA at different rates. Some cells constantly divide, like those in your hair and fingernails and bone marrow cells. Other cells go through several rounds of cell division and stop (including specialized cells, like those in your brain, muscle and heart). Finally, some cells stop dividing, but can be induced to divide to repair injury (such as skin cells and liver cells). In cells that do not constantly divide, the cues for DNA replication/cell division come in the form of chemicals. These chemicals can come from other parts of the body (hormones) or from the environment.
The double helix structure explains how DNA can be copied, but it does not explain how a gene works. In molecular terms, genes are coded DNA instructions that control the production of proteins within the cell. The first step in decoding these genetic messages is to copy part of the nucleotide sequence from DNA into RNA, or ribonucleic acid. These RNA molecules contain coded information for making proteins.
You can think of an RNA molecule as a disposable copy of a segment of DNA. In many cases, an RNA molecule is a working copy of a single gene. The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or even thousands of RNA molecules.
RNA molecules have many functions, but in the majority of cells most RNA molecules are involved in just one job—protein synthesis. The assembly of amino acids into proteins is controlled by RNA.
Most genes contain instructions for assembling amino acids into proteins. The RNA molecules that carry copies of these instructions are known as messenger RNA (mRNA) because they serve as “messengers” from DNA to the rest of the cell.
Proteins are assembled on ribosomes, shown in the model below. Ribosomes are made up of several dozen proteins, as well as a form of RNA known as ribosomal RNA (rRNA).
During the construction of a protein, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA. These RNA molecules are known as transfer RNA (tRNA).
RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA, a process called transcription. Transcription requires an enzyme known as RNA polymerase that is similar to DNA polymerase.
During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
How does RNA polymerase “know” where to start and stop making an RNA copy of DNA? The answer to this question begins with the observation that RNA polymerase doesn't bind to DNA just anywhere. The enzyme will bind only to regions of DNA known as promoters, which have specific base sequences. In effect, promoters are signals in DNA that indicate to the enzyme where to bind to make RNA. Similar signals in DNA cause transcription to stop when the new RNA molecule is completed.
Like a writer's first draft, many RNA molecules require a bit of editing before they are ready to go into action. Remember that an RNA molecule is produced by copying DNA. Surprisingly, the DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins. The DNA sequences that code for proteins are called exons because they are “expressed” in the synthesis of proteins. When RNA molecules are formed, both the introns and the exons are copied from the DNA. However, the introns are cut out of RNA molecules while they are still in the nucleus. The remaining exons are then spliced back together to form the final mRNA as shown in the figure below.
T
The genetic code is read three letters at a time, so that each “word” of the coded message is three bases long. Each three-letter “word” in mRNA is known as a codon, as shown in the figure below. A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide.
Codon A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid.
Because there are four different bases, there are 64 possible three-base codons (4 × 4 × 4 = 64). The figure at right shows all 64 possible codons of the genetic code. As you can see, some amino acids can be specified by more than one codon. For example, six different codons specify the amino acid leucine, and six others specify arginine.
There is also one codon, AUG, that can either specify methionine or serve as the initiation, or “start,” codon for protein synthesis. Notice also that there are three “stop” codons that do not code for any amino acid. Stop codons act like the period at the end of a sentence; they signify the end of a polypeptide, which consists of many amino acids.
There is also one codon, AUG, that can either specify methionine or serve as the initiation, or “start,” codon for protein synthesis. Notice also that there are three “stop” codons that do not code for any amino acid. Stop codons act like the period at the end of a sentence; they signify the end of a polypeptide, which consists of many amino acids.
The sequence of nucleotide bases in an mRNA molecule serves as instructions for the order in which amino acids should be joined together to produce a polypeptide. However, anyone who has tried to assemble a complex toy knows that instructions generally don't do the job themselves. They need something to read them and put them to use. In the cell, that “something” is a tiny factory called the ribosome.
The decoding of an mRNA message into a polypeptide chain (protein) is known as translation. Translation takes place on ribosomes. During translation, the cell uses information from messenger RNA to produce proteins.
A. Messenger RNA is transcribed in the nucleus, then enters the cytoplasm and attaches to a ribosome.
B. Translation begins at AUG, the start codon. Each tRNA has an anticodon whose bases are complimentary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.
C. Like an assembly line worker who attaches one part to another, the ribosome forms a peptide bond between the first and second amino acids, methionine and phenylalanine. At the same time, the ribosome breaks the bond that had held the first tRNA molecule to its amino acid and releases the tRNA molecule. The ribosome then moves to the third codon, where a tRNA molecule brings it the amino acid specified by the third codon.
D. The polypeptide chain continues to grow until the ribosome reaches a stop codon on the mRNA molecule. When the ribosome reaches a stop codon, it releases the newly formed polypeptide and the mRNA molecule, completing the process of translation.
Gregor Mendel might have been surprised to learn that most genes contain nothing more than instructions for assembling proteins, as shown in the figure at right. He might have asked what proteins could possibly have to do with the color of a flower, the shape of a leaf, a human blood type, or the sex of a newborn baby.
Assembling Proteins
The answer is that proteins have everything to do with these things. Remember that many proteins are enzymes, which catalyze and regulate chemical reactions. A gene that codes for an enzyme to produce pigment can control the color of a flower. Another gene produces an enzyme specialized for the production of red blood cell surface antigen. This molecule determines your blood type. Genes for certain proteins can regulate the rate and pattern of growth throughout an organism, controlling its size and shape. In short, proteins are microscopic tools, each specifically designed to build or operate a component of a living cell.
Now and then cells make mistakes in copying their own DNA, inserting an incorrect base or even skipping a base as the new strand is put together. These mistakes are called mutations, from a Latin word meaning “to change.”
Mutations are changes in the genetic material.
Gene mutations involving changes in one or a few nucleotides are known as point mutations, because they occur at a single point in the DNA sequence. Point mutations include substitutions, in which one base is changed to another, as well as insertions and deletions, in which a base is inserted or removed from the DNA sequence.
Substitutions usually affect no more than a single amino acid.
The effects of insertions or deletions can be much more dramatic. Remember that the genetic code is read in three-base codons. If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings are shifted for every codon that follows, as shown in the figure at right. Changes like these are called frameshift mutations because they shift the “reading frame” of the genetic message. By shifting the reading frame, frameshift mutations may change every amino acid that follows the point of the mutation. Frameshift mutations can alter a protein so much that it is unable to perform its normal functions.
Chromosomal mutations involve changes in the number or structure of chromosomes. Such mutations may change the locations of genes on chromosomes, and may even change the number of copies of some genes.
Deletions involve the loss of all or part of a chromosome, while duplications produce extra copies of parts of a chromosome. Inversions reverse the direction of parts of chromosomes, and translocations occur when part of one chromosome breaks off and attaches to another.
In contrast, beneficial mutations may produce proteins with new or altered activities that can be useful in changing environments. One such mutation produces resistance to HIV, the virus that causes AIDS.
Plant and animal breeders often take advantage of such beneficial mutations. For example, when a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms. The condition in which an organism has extra sets of chromosomes is called polyploidy. Polyploid plants are often larger and stronger than diploid plants. Important crop plants have been produced in this way, including bananas and many citrus fruits.
The lac genes are turned off by repressors and turned on by the presence of lactose.