02_Lecture_Presentation.ppt on genes by prof lraymond

Copyright © 2009 Pearson Education, Inc.
PowerPoint Lectures for
Introduction to Biotechnology, Second Edition
William J.Thieman and Michael A.Palladino
Lectures by Lara Dowland
Chapter 2
An Introduction to Genes and
Genomes
Prof. Dr. Ekrem Gürel

Chapter Contents
• 2.1 A Review of Cell Structure
• 2.2 The Molecule of Life
• 2.3 Chromosome Structure, DNA Replication, and
Genomes
• 2.4 RNA and Protein Synthesis
• 2.5 Mutations: Causes and Consequences

2.1 A Review of Cell Structure
• Plasma Membrane – double-layer structure of
lipids and proteins that surrounds the outer surface
of cells
• Cytoplasm – inner contents of a cell between the
nucleus and plasma membrane
• Organelles – structures in the cell that perform
specific functions

• Prokaryotic Cells (include bacteria)
– No nucleus and no organelles

• Eukaryotic cells (plant cells, animal cells)
– Have a nucleus and many organelles
– Organelles
• Nucleus
• Mitochondria
• Endoplasmic reticulum
• Golgi apparatus

• Comparison of Prokaryotic and Eukaryotic Cells

2.2 The Molecule of Life
• Evidence that DNA is the Inherited Genetic Material
– 1869 Friedrich Miescher: “nuclein”
• Could not be broken down by proteases
• Had acidic properties: “nucleic acids”
– 1928 Frederick Griffith
• Two strains of Streptococcus pneumoniae
– Virulent smooth strain (S cells) and harmless rough
strain (R cells)
• Demonstrated transformation – the uptake of DNA by
bacterial cells

• Evidence that DNA Is the Inherited Genetic Material
– 1944 Oswald Avery, Colin MacLeod, and Maclyn
McCarty
• Purified DNA from large batches of Streptococcus
pneumoniae
• Experiment proved that DNA was the transforming factor in
the Griffith experiments

• DNA Structure
– Building block of DNA is the nucleotide
– Each nucleotide is composed of
• Pentose (5-carbon) sugar called deoxyribose
• Phosphate molecule
• A nitrogenous base
– The nitrogenous bases are the interchangeable
component of a nucleotide
• Each nucleotide contains one base
– Adenine (A), thymine (T), guanine (G) or cytosine (C)

• DNA Structure
– James Watson and Francis Crick revealed the definitive
structure of DNA
– “The Molecular Structure of Nucleic Acids: A Structure for
Deoxyribose Nucleic Acid” published in Nature on April
25, 1953

• DNA Structure
– Nucleotides are joined together to form long strands of
DNA and each DNA molecule consists of two strands
that join together and wrap around each other to form a
double helix
– Nucleotides in a strand are held together by
phosphodiester bonds
– Each strand has a polarity – a 5 end and a 3 end

• DNA Structure
– The two strands of a DNA molecule are held together by
hydrogen bonds
• Formed between complementary base pairs
• Adenine (A) pairs with thymine (T)
• Guanine (G) pairs with cytosine (C)
– The two strands are antiparallel because their polarity
is reversed relative to each other

2.3 Chromosome Structure, DNA
Replication, and Genomes
• Chromosome Structure
– Chromosomes – highly coiled and tightly condensed
package of DNA and proteins
• Occurs only during DNA replication
– Chromatin – strings of DNA and DNA-binding proteins
called histones
• State of DNA inside the nucleus when the cell is NOT
dividing

• Most human cells have two sets (pairs) of 23
chromosomes, or 46 chromosomes total
– Called homologous pairs
– Autosomes – chromosomes 1-22
– Sex chromosomes – chromosome pair # 23
• X and Y chromosomes
• Gametes (sex cells) contain a single set of 23
chromosomes (haploid number, n)

• Chromosome consists of two thin, rodlike
structures of DNA called sister chromatids
– Exact replicas of each other copied during DNA
replication
– During cell division, each sister chromatid is
separated

• DNA Replication
– Cells divide by a process called mitosis
• Sex cells divide by a slightly different process called
meiosis
– Mitosis
• One cell divides to form two daughter cells, each with an
identical copy of the parent cell DNA
• In order to accomplish this, the DNA of the parent cell must
be copied prior to mitosis

• Semiconservative Replication
– Replication occurs in such a manner that, after
replication, each helix contains one original (parental)
DNA strand and one newly synthesized DNA strand

Steps in DNA Replication
1. Unwinding the DNA
– Helicase enzyme breaks the hydrogen bonds holding the two
DNA strands together; “unzips” DNA
– DNA binding proteins hold the strands apart
– Separation of strands occurs in regions called origins of
replication
2. Adding short segments of RNA
– Primase enzyme adds RNA primers
– RNA primers start the replication process

Steps in DNA Replication
3. Copying the DNA
– DNA polymerase enzyme binds to the
RNA primers
– Uses nucleotides to synthesize complementary strands
of DNA
– Always works in one direction – 5’ to 3’ direction

2.4 RNA and Protein Synthesis
• Transcription – genes are copied (transcribed)
from DNA code to RNA code
• Translation – RNA code is read into a protein

• Transcription
– Occurs only in genes
– RNA polymerase unwinds DNA helix and copies one
strand of DNA into RNA
• Binds to a promotor region
• Copies DNA in a 5’ to 3’ direction into RNA
• Uses nucleotides
– Adenine, uracil, guanine, and cytosine
– A-U, C-G

• Transcription
– At end of gene, RNA polymerase encounters the
termination sequence
• RNA polymerase and newly formed strand of RNA are
released from DNA molecule
– RNA strand is called a messenger RNA (mRNA)
– Multiple copies of mRNA are transcribed from each gene
during transcription

• mRNA Processing
– Initial mRNA produced is the primary transcript
• Immature and not fully functional
– A series of modifications before primary transcripts are
ready for protein synthesis
• RNA splicing
• Polyadenylation
• Addition of a 5’ cap

• How Is mRNA read?
– Genetic code – universal language of genetics used by
virtually all living organisms
• Works in three nucleotide units of mRNA called codons
• Each codon codes for a single amino acid
• One amino acid may be coded for by more than one codon
• Start codon
• Stop codons

• Translation
– Occurs in the cytoplasm
– Function of each type of RNA
• mRNA – exact copy of the gene; carries the genetic code
from nucleus to the cytoplasm
• rRNA – component of ribosomes, the organelles
responsible for protein synthesis
• tRNA – transports amino acids to ribosome

Translation
1. Initiation – small ribosome subunit binds to 5’ end of
mRNA
– Moves along the mRNA until the start codon is found
2. Elongation – tRNAs, carrying the correct amino acid,
enter the ribosome, one at a time, as the mRNA code
is read
3. Termination – ribosome encounters the stop codon
– Newly formed protein is released

• Basics of Gene Expression Control
– Gene expression refers to the production of mRNA by a
cell
• All cells of an organism contain the same genome,
so how and why are skin cells different from brain
cells or liver cells?
– Because cells can regulate or control the genes they
express

– Gene regulation is how genes can be turned on and off
in response to different signals

– Transcriptional regulation – controlling the amount of
mRNA transcribed from a particular gene
• Certain sequences found in the promotor region
– TATA box and CAAT box
• RNA polymerase cannot bind to promotor region without
presence of transcription factors
• Enhancer sequences bind to regulatory proteins called
activators

– Micro RNA (miRNA) regulate gene expression by
“silencing” gene expression through blocking translation
of mRNA or by causing degradation of mRNA

– Bacteria use operons to regulate gene expression
• Organization of bacterial genes
• Clusters of several related genes located together and
controlled by a single promotor
• Operator – region within promotor
– Can use operons to regulate gene expression in
response to their nutrient requirements
• lac operon

2.5 Mutations: Causes and Consequences
• Mutation – change in the nucleotide sequence of DNA
– Major cause of genetic diversity
– Can also be detrimental
• Types of Mutations
– Point mutations
• Silent mutations
• Missense mutations
• Nonsense mutations
• Frameshift mutations

• Gene mutations can be inherited or acquired
– Inherited mutations are those passed on to offspring
through gametes
– Acquired mutations occur in the genome of somatic cells
• Are not passed along to offspring

• Mutations are a major cause of genetic diversity
– Human genomes are approximately 99.9% identical
• 0.1% differences in DNA between individuals, or one base
out of every thousand
– Roughly 3 million differences between different
individuals
• Most have no obvious effects; other mutations strongly
influence cell functions, behavior, and susceptibility to
genetic diseases

02_Lecture_Presentation.ppt on genes by prof lraymond

More Related Content

Similar to 02_Lecture_Presentation.ppt on genes by prof lraymond

Recently uploaded

02_Lecture_Presentation.ppt on genes by prof lraymond