Chromosomes are structures that carry genes within cells. They are made of DNA tightly coiled around histone proteins. The number and structure of chromosomes varies between species. Genes are segments of DNA that code for proteins and control inheritance of traits. They are located on chromosomes and there can be thousands of genes in a single cell. DNA replication and gene expression ensure genes are passed from parents to offspring.
Chromosome structure and packaging of dnaDIPTI NARWAL
Chromosome structure : classification based upon centromere position, autosomes and allosomes
Morphology of chromosome: chromatids, chromomeres, telomeres, sister chromatids
packaging of DNA: nucleosome model
functions of Chromosomes
Cell DivisionCell Division in ProkaryotesBinary FissionDefMaximaSheffield592
Cell Division
Cell Division in Prokaryotes
Binary Fission
Definition
Bacterial cells divide by a method of asexual reproduction known as binary fission. Fission means splitting. So in the process the genetic material is replicated, the cell grows larger and then splits into two.
Genetic Material of the Bacterial Cell
The genetic information of a bacterial cell exists as a single, circular, double-stranded DNA molecule. Bacterial cells are prokaryotic cells; they lack a nucleus. The DNA of the bacterial cell is not surrounded by and enclosed within a nuclear membrane. It lies free within the protoplasm of the bacterial cell. Although the bacterial cell lacks a nucleus, the area of the cell protoplasm where the nucleus is found is called the nucleoid.
Prior to the Division of the Cell the DNA must be Doubled
Prior to the division of the bacterial cell, the DNA must be replicated, producing two copies that can be equally distributed to each of the two daughter cells. Replication of the DNA at a specific site on the DNA molecule called the origin of replication. The replication enzymes copy the DNA of both strands, moving around the circular DNA in both directions simultaneously until a specific site of termination is reached. When these enzymes have proceeded all the way around the circle of DNA, the cell possesses two copies of the genome. These “daughter” genomes are attached side-by-side to the plasma membrane.
Elongation of the Cell and Segregation of DNA to Opposite Ends of the Cell
As the DNA replicates, the cell elongates. The two circular molecules of DNA now separate and move apart toward opposite ends of the cell.
Fission of the Cell into two Daughter Cells
After the DNA molecules have been segregated to opposite ends of the cell, the bacterial cell will divide to form two daughter cells. Then a group of proteins that will operate together to separate the cell into two assemble at the site of separation. A key component of this group of division machinery proteins is the protein FtsZ. FtsZ proteins begin the separation process by forming a ring in the middle of the cell. Other components of the division apparatus then join the FtsZ ring, forming new plasma membrane that separates the cytoplasm into the two cells. This is followed by the formation of cell wall material in the separation zones. The result of the process of binary fission is two cells, each with its own circular, double stranded, DNA molecule.
The cell will now begin to split into two cells by a process called septation. This occurs as a septum forms in the middle of the cell. A protein called FtsZ forms a ring in the middle of the cell. As this process proceeds, the cell lays down new plasma membrane and cell wall materials in the zone between the attachment sites of the two daughter genomes. A new plasma membrane grows between the genomes; eventually, it reaches all the way into the center of the cell, dividing it in two. B ...
Chromosome structure and packaging of dnaDIPTI NARWAL
Chromosome structure : classification based upon centromere position, autosomes and allosomes
Morphology of chromosome: chromatids, chromomeres, telomeres, sister chromatids
packaging of DNA: nucleosome model
functions of Chromosomes
Cell DivisionCell Division in ProkaryotesBinary FissionDefMaximaSheffield592
Cell Division
Cell Division in Prokaryotes
Binary Fission
Definition
Bacterial cells divide by a method of asexual reproduction known as binary fission. Fission means splitting. So in the process the genetic material is replicated, the cell grows larger and then splits into two.
Genetic Material of the Bacterial Cell
The genetic information of a bacterial cell exists as a single, circular, double-stranded DNA molecule. Bacterial cells are prokaryotic cells; they lack a nucleus. The DNA of the bacterial cell is not surrounded by and enclosed within a nuclear membrane. It lies free within the protoplasm of the bacterial cell. Although the bacterial cell lacks a nucleus, the area of the cell protoplasm where the nucleus is found is called the nucleoid.
Prior to the Division of the Cell the DNA must be Doubled
Prior to the division of the bacterial cell, the DNA must be replicated, producing two copies that can be equally distributed to each of the two daughter cells. Replication of the DNA at a specific site on the DNA molecule called the origin of replication. The replication enzymes copy the DNA of both strands, moving around the circular DNA in both directions simultaneously until a specific site of termination is reached. When these enzymes have proceeded all the way around the circle of DNA, the cell possesses two copies of the genome. These “daughter” genomes are attached side-by-side to the plasma membrane.
Elongation of the Cell and Segregation of DNA to Opposite Ends of the Cell
As the DNA replicates, the cell elongates. The two circular molecules of DNA now separate and move apart toward opposite ends of the cell.
Fission of the Cell into two Daughter Cells
After the DNA molecules have been segregated to opposite ends of the cell, the bacterial cell will divide to form two daughter cells. Then a group of proteins that will operate together to separate the cell into two assemble at the site of separation. A key component of this group of division machinery proteins is the protein FtsZ. FtsZ proteins begin the separation process by forming a ring in the middle of the cell. Other components of the division apparatus then join the FtsZ ring, forming new plasma membrane that separates the cytoplasm into the two cells. This is followed by the formation of cell wall material in the separation zones. The result of the process of binary fission is two cells, each with its own circular, double stranded, DNA molecule.
The cell will now begin to split into two cells by a process called septation. This occurs as a septum forms in the middle of the cell. A protein called FtsZ forms a ring in the middle of the cell. As this process proceeds, the cell lays down new plasma membrane and cell wall materials in the zone between the attachment sites of the two daughter genomes. A new plasma membrane grows between the genomes; eventually, it reaches all the way into the center of the cell, dividing it in two. B ...
This presentation elaborates regarding introduction to genetics, chromosomes, DNA, RNA, Genetics of developmental disorders of teeth, Genetics of craniofacial disorders and syndromes, genetics of cleft lip and palate, malocclusion and dental caries
Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes
This presentation elaborates regarding introduction to genetics, chromosomes, DNA, RNA, Genetics of developmental disorders of teeth, Genetics of craniofacial disorders and syndromes, genetics of cleft lip and palate, malocclusion and dental caries
Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes Eukaryotic and Prokaryotic Chromosomes
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
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.
ISI 2024: Application Form (Extended), Exam Date (Out), EligibilitySciAstra
The Indian Statistical Institute (ISI) has extended its application deadline for 2024 admissions to April 2. Known for its excellence in statistics and related fields, ISI offers a range of programs from Bachelor's to Junior Research Fellowships. The admission test is scheduled for May 12, 2024. Eligibility varies by program, generally requiring a background in Mathematics and English for undergraduate courses and specific degrees for postgraduate and research positions. Application fees are ₹1500 for male general category applicants and ₹1000 for females. Applications are open to Indian and OCI candidates.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
2. Contents:
Chromosomes
➢ Chromosome’s composition
➢ Structure of chromosomes
➢ Types of chromosomes
➢ Number of chromosomes in different organisms,
➢ Chromosome’s size
Gene
➢ What is gene?
➢ Number of genes in different organisms
➢ Chemical structure of genes
➢ DNA Replication
➢ Gene expression
3. Chromosomes
➢ In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called
chromosomes which are carriers of genes.
➢ Each chromosome is made up of DNA tightly coiled many times around proteins called histones
that support its structure.
➢ Chromosomes were first described by Strasburger (1815), and the term ‘chromosome’ was first
used by Waldeyer in 1888 (Gr. Chrom- color, soma- body).
➢ They appear as rod-shaped dark stained bodies during the stages of cell division under light
microscope, otherwise they are not visible in an active nucleus due to high water contents.
4. Chromosome’s Composition
Major components of chromosomes are
1. DNA
2. RNA
3. Basic proteins of low molecular weights known
as “histones”.
4. Acidic proteins (non-histone proteins).
5. Chromosomes are made up of thin chromatic
threads called “chromatin fibers”.
5. • Interphase Chromosomes consists of about 30-40% DNA, 50-60% Proteins and 1-10%
RNA.
• Metaphase Chromosomes contain 15-20% DNA, 65-75% Proteins and 10-15% RNA.
• Chromatin fibers undergo folding, coiling and supercoiling during “prophase” so the
chromosomes become progressively thicker, smaller and visible.
• At the end of cell division these fibers unfold and extend as fine chromatin threads.
Chromosomes during different stages of cell division
6. Histones
Histones are highly basic proteins that provide structural support for chromosomes. Each chromosome contains a
long molecule of DNA, which must fit into the cell nucleus. To do that, the DNA wraps around complexes of histone
proteins, giving the chromosome a more compact shape. They act as coils around which DNA winds to create
structural units called nucleosomes. Nucleosomes in turn are wrapped into 30 nm fibers that form tightly
packed chromatin. Histones prevent DNA from becoming tangled and protect it from damage. In addition, histones
play important roles in gene regulation and DNA replication. Without histones, unwound DNA in chromosome would
be very long. For example, each human cell has about 1.8 meters of DNA if completely stretched out; however, when
wound about histones, this length is reduced to about 90 micrometers (0.09 mm) of 30 nm diameter chromatin fibers.
There are five families of histones which are designated H1/H5 (linker histones), H2, H3, and H4 (core histones).
The nucleosome core is formed of two H2A-H2B dimers and a H3-H4 tetramer. The tight wrapping of DNA around
histones is to a large degree a result of electrostatic attraction between the positively charged histones and negatively
charged phosphate backbone of DNA.
7.
8. Structure of Chromosomes
Chromatid:
A chromosomes is made up of two strands which are identical to each other and these are called chromatids.
They are connected near the center. Chromatids are prepared when new cells are going to be made.
Centromere :
It is the primary constriction at the center to which the
chromatids or spindle fibers are attached. Its function is to enable movement
of the chromosome during the anaphase stage of cell division.
9. Continued
Chromatin: It is a complex of DNA and proteins that forms chromosomes within the nucleus of
eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser
structures. This prevents the strands from becoming tangled and also plays important roles in
reinforcing the DNA during cell division, preventing DNA damage, and regulating gene
expression and DNA replication.
Telomere: Telomere is the terminal region of each side of the chromosome.
10.
11. On the basis of the location of the centromere, chromosomes are classified into four types:
Metacentric Chromosomes: Metacentric chromosomes have the centromere present exactly in the center. Both the sections of
metacentric chromosomes are therefore of equal length. Example: Human chromosome 1 and 3 are metacentric.
Sub-metacentric Chromosomes: In Submetacentric chromosomes, the centromere is not present exactly at the center. The
centromere is slightly offset from the center. Both the sections are therefore not of equal length or are asymmetrical. Example:
Human chromosomes 4 to 12 are submetacentric.
Acrocentric Chromosomes: Acrocentric chromosomes have a centromere which is highly offset from the center. Therefore,
one of the strands is very long and one very short. Example: Human chromosomes 13,15, 21, and 22 are acrocentric.
Telocentric Chromosomes: In telocentric chromosomes, the centromere is present at the very end of the chromosome.
Telocentric chromosomes are present in species such as mice. Humans do not possess telocentric chromosomes.
Types of Chromosomes
12. Among many organisms that have separate sexes, there are two basic types of chromosomes:
❖ Autosomes (body Chromosomes)
❖ Allosomes (sex chromosomes)
Autosomes: Body chromosomes or non sex chromosomes (humans have 44 chromosomes in 22
pairs). Autosomes control the inheritance of all the characteristics except the sex-linked ones, which are
controlled by the sex chromosomes
Allosomes (Sex Chromosomes): XX or XY (23rd pair for humans) determines the sex of the offspring..
Humans have 22 pairs of autosomes and one pair of sex chromosomes.
Types of Chromosomes
13. Number of Chromosomes
Precise number of chromosomes is typical for a given species.
In any given asexually reproducing species, the chromosomes
number is always the same in all the cells of an organism.
While in sexually reproducing organisms, the number of
chromosomes in the body (somatic) cells typically is diploid (2n; a
pair of each chromosome).
While in the sex cells, or gametes the number of chromosomes is
haploid (1n). The haploid number is produced during meiosis.
14. No of Chromosomes in Different Organisms
The number of chromosomes does not correlate with the apparent complexity of an animal or a plant, in humans for
example, the diploid number is 2n = 46 (that is, 23 pairs), compared with 2n = 78, or 39 pairs, in the dog.
Organisms No. Of Chromosomes Organisms No. Of Chromosomes
Humans 46 Chimpanzee 48
Dog 78 Horse 64
Chicken 78 Goldfish 94
Fruit Fly 8 Mosquito 6
Horsetail 216 Round Worm 2
15. Chromosome Size
Unlike other cell organelles, the size of chromosomes vary significantly depending upon stages of
cell division.
Interphase: Chromosomes are longest & thinnest.
Prophase: Progressive decrease in their length accompanied with increase in thickness.
Anaphase: Chromosomes are smallest.
Metaphase: Chromosomes are easily observed and studied during metaphase when they are thick
small and well spread in the cell. The size of chromosomes in mitotic phase generally varies between
0.5 µ to 32 µ in length and between 0.2 µ to 3 µ in diameter.
16. Gene
Word Gene is derived from Greek word genos meaning generation/ birth/ gender. “It is the segment of DNA that has the
information (the code) for specific proteins. These proteins have different functions throughout the body and allow humans to
live, grow, and reproduce. In other words gene is a unit of hereditary information that occupies a fixed position (locus) on a
chromosome”. A single molecule of DNA has thousands of genes.
Genes are a set of instructions passed down from parents to offspring. They contain the information that determines a person’s
specific physical and biological traits, like hair color, eye color, and blood type.
➢In eukaryotes (such as animals, plants, and fungi), genes are contained within the cell nucleus. The mitochondria (in animals)
and the chloroplast (in plants) also contain small subsets of genes distinct from the genes found in the nucleus.
➢ In prokaryotes (organisms lacking a distinct nucleus, such as bacteria), genes are contained in a single chromosome that is
free-floating in the cell cytoplasm.
17. Genome
The genome is the total genetic material of an organism and includes both the genes and non-coding sequences.
Number of Genes in Different Organisms
The number of genes in an organism’s genome (the entire set of chromosomes) varies significantly between species.
For example, the human genome contains an estimated 20,000 to 25,000 genes, the genome of the bacterium
Escherichia coli houses precisely 5,416 genes. The smallest genomes occur in viruses, and viroids* (which act as a
single non-coding RNA gene). Conversely, plants can have extremely large genomes, with rice containing >46,000
protein-coding genes. The total number of protein-coding genes (the Earth's proteome) is estimated to be 5 million.
*infectious agents that consist only of naked RNA without any protective layer such as a protein coat.
18. Chemical Structure of Genes
Genes are composed of deoxyribonucleic acid (DNA), except in some viruses, which have genes consisting of
RNA. The sequence of bases along a strand of DNA determines the genetic code.
A DNA molecule is composed of two chains of nucleotides that wind about each other to resemble a twisted ladder.
The sides of the ladder are made up of sugars and phosphates, and the rungs are formed by bonded pairs of
nitrogenous bases. These bases are adenine (A), guanine (G), cytosine (C), and thymine (T). An A on one chain
bonds to a T on the other (thus forming an A–T ladder rung); similarly, a C on one chain bonds to a G on the other.
.
19. DNA Replication
DNA replicates by separating into two single strands, each of which serves as a template for a new
strand. If the bonds between the bases are broken, the two chains unwind, and free nucleotides within
the cell attach themselves to the exposed bases of the now-separated chains.
The free nucleotides line up along each chain according to the base-pairing rule—A bonds to T, C bonds
to G. This process results in the creation of two identical DNA molecules each containing one of the
original strands and one new strand and is the method by which hereditary information is passed from
one generation of cells to the next. The new strands are copied by the same principle of hydrogen-bond
pairing between bases that exists in the double helix. This replication is the key to the stable inheritance
of genetic traits.
20. Gene Expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene
product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype
(physical traits and structure of an organism e.g. eye color, height , body structure and its behavioral characteristics
etc.) as the final effect.
In all organisms, two steps are required to read the information encoded in a gene's DNA and produce the protein it
specifies. First, the gene's DNA is transcribed to messenger RNA (mRNA). Second, that mRNA is translated to
protein. RNA-coding genes must still go through the first step, but are not translated into protein. The process of
producing a biologically functional molecule of either RNA or protein is called gene expression, and the
resulting molecule is called a gene product.
21. Transcription and Translation
When the product of a particular gene is needed, the portion of the DNA molecule that contains that gene will split. Through the
process of transcription, a strand of RNA with bases complementary to those of the gene is created from the free nucleotides in the
cell (RNA has the base uracil [U] instead of thymine, so A and U form base pairs during RNA synthesis).
Transcription is performed by an enzyme called an RNA polymerase, which reads the template strand in the 3' to 5' direction and
synthesizes the RNA from 5' to 3'. This single chain of RNA, called messenger RNA (mRNA), then passes to the organelles called
ribosomes, where the process of translation, or protein synthesis, takes place. In prokaryotes, transcription occurs in the cytoplasm
while in In eukaryotes, transcription occurs in the nucleus, where the cell's DNA is stored.
During translation, a second type of RNA, transfer RNA (tRNA), matches up the nucleotides on mRNA with specific amino acids.
Each set of three nucleotides codes for one amino acid. The series of amino acids built according to the sequence of nucleotides
forms a polypeptide chain; all proteins are made from one or more linked polypeptide chains.