More Related Content Similar to 10 lecture presentation0 (20) More from Uconn Stamford (20) 1. © 2010 Pearson Education, Inc.
DNA: STRUCTURE AND REPLICATION
• DNA:
– Was known to be a chemical in cells by the end of the nineteenth century
– Has the capacity to store genetic information
– Can be copied and passed from generation to generation
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DNA and RNA Structure
• DNA and RNA are nucleic acids.
– They consist of chemical units called nucleotides.
– The nucleotides are joined by a sugar-phosphate backbone.
Animation: Hershey-Chase Experiment
Animation: DNA and RNA Structure
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• The four nucleotides found in DNA differ in their nitrogenous
bases. These bases are:
– Thymine (T)
– Cytosine (C)
– Adenine (A)
– Guanine (G)
• RNA has uracil (U) in place of thymine.
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Watson and Crick’s Discovery of the Double
Helix
• James Watson and Francis Crick determined that DNA is a
double helix.
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• Watson and Crick used X-ray crystallography data to reveal the
basic shape of DNA.
– Rosalind Franklin collected the X-ray crystallography data.
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• The model of DNA is like a rope ladder twisted into a spiral.
– The ropes at the sides represent the sugar-phosphate backbones.
– Each wooden rung represents a pair of bases connected by hydrogen
bonds.
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• DNA bases pair in a complementary fashion:
– Adenine (A) pairs with thymine (T)
– Cytosine (C) pairs with guanine (G)
Animation: DNA Double Helix
Blast Animation: Hydrogen Bonds in DNA
Blast Animation: Structure of DNA Double Helix
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DNA Replication
• When a cell reproduces, a complete copy of the DNA must pass
from one generation to the next.
• Watson and Crick’s model for DNA suggested that DNA
replicates by a template mechanism.
Animation: DNA Replication Review
Animation: DNA Replication Overview
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• DNA can be damaged by ultraviolet light.
• DNA polymerases:
– Are enzymes
– Make the covalent bonds between the nucleotides of a new DNA strand
– Are involved in repairing damaged DNA
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• DNA replication in eukaryotes:
– Begins at specific sites on a double helix
– Proceeds in both directions
Animation: Origins of Replication
Animation: Leading Strand
Animation: Lagging Strand
19. THE FLOW OF GENETIC INFORMATION
FROM DNA TO RNA TO PROTEIN
• DNA functions as the inherited directions for a cell or organism.
• How are these directions carried out?
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20. How an Organism’s Genotype Determines Its
Phenotype
• An organism’s genotype is its genetic makeup, the sequence of
nucleotide bases in DNA.
• The phenotype is the organism’s physical traits, which arise from
the actions of a wide variety of proteins.
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• DNA specifies the synthesis of proteins in two stages:
– Transcription, the transfer of genetic information from DNA into an
RNA molecule
– Translation, the transfer of information from RNA into a protein
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From Nucleotides to Amino Acids: An Overview
• Genetic information in DNA is:
– Transcribed into RNA, then
– Translated into polypeptides
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• What are the rules for translating the RNA message into a
polypeptide?
• A codon is a triplet of bases, which codes for one amino acid.
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The Genetic Code
• The genetic code is:
– The set of rules relating nucleotide sequence to amino acid sequence
– Shared by all organisms
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• Of the 64 triplets:
– 61 code for amino acids
– 3 are stop codons, indicating the end of a polypeptide
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Transcription: From DNA to RNA
• Transcription:
– Makes RNA from a DNA template
– Uses a process that resembles DNA replication
– Substitutes uracil (U) for thymine (T)
• RNA nucleotides are linked by RNA polymerase.
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Initiation of Transcription
• The “start transcribing” signal is a nucleotide sequence called a
promoter.
• The first phase of transcription is initiation, in which:
– RNA polymerase attaches to the promoter
– RNA synthesis begins
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RNA Elongation
• During the second phase of transcription, called elongation:
– The RNA grows longer
– The RNA strand peels away from the DNA template
Blast Animation: Roles of RNA
Blast Animation: Transcription
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Termination of Transcription
• During the third phase of transcription, called termination:
– RNA polymerase reaches a sequence of DNA bases called a terminator
– Polymerase detaches from the RNA
– The DNA strands rejoin
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The Processing of Eukaryotic RNA
• After transcription:
– Eukaryotic cells process RNA
– Prokaryotic cells do not
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• RNA processing includes:
– Adding a cap and tail
– Removing introns
– Splicing exons together to form messenger RNA (mRNA)
Animation: Transcription
37. (b) Transcription of a gene
RNA polymerase
Completed RNA
Growing RNA
Termination
Elongation
Initiation Terminator DNA
Area shown in part (a) at left
RNA
Promoter DNA
RNA polymerase
DNA of gene
Figure 10.13b
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Translation: The Players
• Translation is the conversion from the nucleic acid language to
the protein language.
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Messenger RNA (mRNA)
• Translation requires:
– mRNA
– ATP
– Enzymes
– Ribosomes
– Transfer RNA (tRNA)
40. Transcription
Addition of cap and tail
Coding sequence
mRNA
DNA
Cytoplasm
Nucleus
Exons spliced together
Introns removed Tail
CapRNA
transcript
with cap
and tail
Exon Exon ExonIntronIntron
Figure 10.14
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Transfer RNA (tRNA)
• Transfer RNA (tRNA):
– Acts as a molecular interpreter
– Carries amino acids
– Matches amino acids with codons in mRNA using anticodons
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Ribosomes
• Ribosomes are organelles that:
– Coordinate the functions of mRNA and tRNA
– Are made of two protein subunits
– Contain ribosomal RNA (rRNA)
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• A fully assembled ribosome holds tRNA and mRNA for use in
translation.
45. Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNA
tRNA binding sites
Codons
Ribosome
(b) The “players” of translation(a) A simplified diagram
of a ribosome
Large
subunit
Small
subunit
P site
mRNA
binding
site
A site
Figure 10.16
47. Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNA
Codons
(b) The “players” of translation
Figure 10.16b
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Translation: The Process
• Translation is divided into three phases:
– Initiation
– Elongation
– Termination
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Initiation
• Initiation brings together:
– mRNA
– The first amino acid, Met, with its attached tRNA
– Two subunits of the ribosome
• The mRNA molecule has a cap and tail that help it bind to the
ribosome.
Blast Animation: Translation
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• Initiation occurs in two steps:
– First, an mRNA molecule binds to a small ribosomal subunit, then an
initiator tRNA binds to the start codon.
– Second, a large ribosomal subunit binds, creating a functional ribosome.
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Elongation
• Elongation occurs in three steps.
– Step 1, codon recognition:
– the anticodon of an incoming tRNA pairs with the mRNA codon at
the A site of the ribosome.
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– Step 2, peptide bond formation:
– The polypeptide leaves the tRNA in the P site and attaches to the
amino acid on the tRNA in the A site
– The ribosome catalyzes the bond formation between the two amino
acids
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– Step 3, translocation:
– The P site tRNA leaves the ribosome
– The tRNA carrying the polypeptide moves from the A to the P site
Animation: Translation
57. mRNA
P site
Peptide bond formation
Polypeptide
ELONGATION
Codon recognition
A
site
Codons
Anticodon
Amino acid
Figure 10.19-2
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Termination
• Elongation continues until:
– The ribosome reaches a stop codon
– The completed polypeptide is freed
– The ribosome splits into its subunits
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Review: DNA→ RNA→ Protein
• In a cell, genetic information flows from DNA to RNA in the
nucleus and RNA to protein in the cytoplasm.
65. Transcription RNA polymerase
mRNA DNA
Intron
Nucleus
mRNA
Intron
Tail
Cap
RNA processing
tRNA
Amino acid
Amino acid
attachment
EnzymeATP
Initiation
of translation
Ribosomal
subunits
Figure 10.20-4
66. Transcription RNA polymerase
mRNA DNA
Intron
Nucleus
mRNA
Intron
Tail
Cap
RNA processing
tRNA
Amino acid
Amino acid
attachment
EnzymeATP
Initiation
of translation
Ribosomal
subunits
Elongation
Anticodon
Codon
Figure 10.20-5
67. Transcription RNA polymerase
mRNA DNA
Intron
Nucleus
mRNA
Intron
Tail
Cap
RNA processing
tRNA
Amino acid
Amino acid
attachment
EnzymeATP
Initiation
of translation
Ribosomal
subunits
Elongation
Anticodon
Codon
Termination
Polypeptide
Stop
codon
Figure 10.20-6
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• As it is made, a polypeptide:
– Coils and folds
– Assumes a three-dimensional shape, its tertiary structure
• Several polypeptides may come together, forming a protein with
quaternary structure.
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• Transcription and translation are how genes control:
– The structures
– The activities of cells
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Mutations
• A mutation is any change in the nucleotide sequence of DNA.
• Mutations can change the amino acids in a protein.
• Mutations can involve:
– Large regions of a chromosome
– Just a single nucleotide pair, as occurs in sickle cell anemia
71. © 2010 Pearson Education, Inc.
Types of Mutations
• Mutations within a gene can occur as a result of:
– Base substitution, the replacement of one base by another
– Nucleotide deletion, the loss of a nucleotide
– Nucleotide insertion, the addition of a nucleotide
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• Insertions and deletions can:
– Change the reading frame of the genetic message
– Lead to disastrous effects
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Mutagens
• Mutations may result from:
– Errors in DNA replication
– Physical or chemical agents called mutagens
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• Although mutations are often harmful, they are the source of
genetic diversity, which is necessary for evolution by natural
selection.
78. mRNA and protein from a normal gene
Inserted
(c) Nucleotide insertion
Figure 10.22c
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VIRUSES AND OTHER NONCELLULAR
INFECTIOUS AGENTS
• Viruses exhibit some, but not all, characteristics of living
organisms. Viruses:
– Possess genetic material in the form of nucleic acids
– Are not cellular and cannot reproduce on their own.
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Bacteriophages
• Bacteriophages, or phages, are viruses that attack bacteria.
Animation: Phage T2 Reproductive Cycle
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• Phages have two reproductive cycles.
(1) In the lytic cycle:
– Many copies of the phage are made within the bacterial cell, and
then
– The bacterium lyses (breaks open)
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(2) In the lysogenic cycle:
– The phage DNA inserts into the bacterial chromosome and
– The bacterium reproduces normally, copying the phage at each cell
division
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Plant Viruses
• Viruses that infect plants can:
– Stunt growth
– Diminish plant yields
– Spread throughout the entire plant
Animation: Phage T4 Lytic Cycle
Animation: Phage Lambda Lysogenic and Lytic Cycles
87. Phage
Phage DNA
Phage injects DNA
Phage
attaches
to cell.
Bacterial
chromosome (DNA)
Phage DNA
circularizes.
Phages assemble
OR
New phage DNA and
proteins are synthesized.
LYTIC CYCLE
Cell lyses,
releasing
phages.
Figure 10.26-1
88. Phage
Phage DNA
Phage injects DNA
Phage
attaches
to cell.
Bacterial
chromosome (DNA)
Phage DNA
circularizes.
Phages assemble
OR
New phage DNA and
proteins are synthesized.
LYTIC CYCLE
Cell lyses,
releasing
phages.
LYSOGENIC
CYCLE
Phage DNA is inserted into
the bacterial chromosome.
Many cell divisions
Prophage
Occasionally a
prophage
may leave the bacterial
chromosome.
Lysogenic bacterium
reproduces normally,
replicating the prophage
at each cell division.
Figure 10.26-2
89. Phage
Phage DNA
Phage injects DNA
Phage attaches
to cell.
Bacterial
chromosome (DNA)
Phage DNA circularizes.Phages assemble
New phage DNA and
proteins are synthesized.
LYTIC CYCLE
Cell lyses,
releasing
phages.
Figure 10.26a
90. Phage DNA
Phage injects DNA
Phage attaches
to cell.
Bacterial
chromosome (DNA)
Phage DNA
circularizes.
LYSOGENIC
CYCLE
Many cell divisions
Prophage
Occasionally a prophage
may leave the bacterial
chromosome.
Lysogenic bacterium
reproduces normally,
replicating the prophage
at each cell division.
Phage DNA is inserted into the
bacterial chromosome.
Phage
Figure 10.26b
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• Viral plant diseases:
– Have no cure
– Are best prevented by producing plants that resist viral infection
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Animal Viruses
• Viruses that infect animals are:
– Common causes of disease
– May have RNA or DNA genomes
• Some animal viruses steal a bit of host cell membrane as a
protective envelope.
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• The reproductive cycle of an enveloped RNA virus can be broken
into seven steps.
Animation: Simplified Viral Reproductive Cycle
99. Protein coat
mRNA
Protein spike
Plasma membrane
of host cell
Envelope
Template
New viral
genomeNew viral proteins
Exit
VirusViral RNA (genome)
Viral RNA
(genome)
Entry
Uncoating
Assembly
RNA synthesis
by viral enzyme
RNA synthesis
(other strand)
Protein
synthesis
Figure 10.29
100. Protein coat
Protein spike
Plasma membrane
of host cell
Envelope
Virus
Viral RNA (genome)
Viral RNA
(genome)
Entry
Uncoating
RNA synthesis
by viral enzyme
Figure 10.29a
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HIV, the AIDS Virus
• HIV is a retrovirus, an RNA virus that reproduces by means of a
DNA molecule.
• Retroviruses use the enzyme reverse transcriptase to synthesize
DNA on an RNA template.
• HIV steals a bit of host cell membrane as a protective envelope.
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• The behavior of HIV nucleic acid in an infected cell can be
broken into six steps.
Animation: HIV Reproductive Cycle
Blast Animation: AIDS Treatment Strategies
105. Reverse
transcriptase
HIV (red dots) infecting
a white blood cell
DNA
strand Chromosomal
DNA
Cytoplasm
Nucleus
Provirus
RNA
Viral RNA
Double
stranded
DNA
Viral
RNA
and
proteins
SEM
Figure 10.32
107. © 2010 Pearson Education, Inc.
• AIDS (acquired immune deficiency syndrome) is:
– Caused by HIV infection and
– Treated with drugs that interfere with the reproduction of the virus
109. Part of a T nucleotide
Thymine
(T)
AZT
Figure 10.33
110. © 2010 Pearson Education, Inc.
Viroids and Prions
• Two classes of pathogens are smaller than viruses:
– Viroids are small circular RNA molecules that do not encode proteins
– Prions are misfolded proteins that somehow convert normal proteins to
the misfolded prion version
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• Prions are responsible for neurodegenerative diseases including:
– Mad cow disease
– Scrapie in sheep and goats
– Chronic wasting disease in deer and elk
– Creutzfeldt-Jakob disease in humans
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• Avian flu:
– Infects birds
– Infected 18 people in 1997
– Since has spread to Europe and Africa infecting 300 people and killing
200 of them
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• If avian flu mutates to a form that can easily spread between
people, the potential for a major human outbreak is significant.
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• New viruses can arise by:
– Mutation of existing viruses
– Spread to new host species
Editor's Notes Figure 10.1 The chemical structure of a DNA polynucleotide.
Figure 10.1a The chemical structure of a DNA polynucleotide.
Figure 10.1b The chemical structure of a DNA polynucleotide.
Figure 10.3a Discoverers of the double helix.
Figure 10.3b Discoverers of the double helix.
Figure 10.4 A rope-ladder model of a double helix.
Figure 10.5 Three representatives of DNA.
Figure 10.7 Multiple "bubbles" in replicating DNA.
Figure 10.8 The flow of genetic information in a eukaryotic cell. (Step 1)
Figure 10.8 The flow of genetic information in a eukaryotic cell. (Step 2)
Figure 10.8 The flow of genetic information in a eukaryotic cell. (Step 3)
Figure 10.10 Transcription of DNA and translation of codons.
Figure 10.10 Transcription of DNA and translation of codons.
Figure 10.13b Transcription
Figure 10.14 The production of messenger RNA (mRNA) in a eukaryotic cell.
Figure 10.15 The structure of tRNA
Figure 10.16 The ribosome.
Figure 10.16a The ribosome.
Figure 10.16b The ribosome.
Figure 10.17 A molecule of mRNA.
Figure 10.18 The initiation of translation
Figure 10.19 The elongation of a polypeptide. (Step 1)
Figure 10.19 The elongation of a polypeptide. (Step 2)
Figure 10.19 The elongation of a polypeptide. (Step 3)
Figure 10.19 The elongation of a polypeptide. (Step 4)
Figure 10.20 A summary of transcription and translation. (Step 1)
Figure 10.20 A summary of transcription and translation. (Step 2)
Figure 10.20 A summary of transcription and translation. (Step 3)
Figure 10.20 A summary of transcription and translation. (Step 4)
Figure 10.20 A summary of transcription and translation. (Step 5)
Figure 10.20 A summary of transcription and translation. (Step 6)
Figure 10.21 The molecular basis of sickle-cell disease.
Figure 10.22a Base substitution of mutations and their effects.
Figure 10.22b Nucleotide deletion of mutations and their effects.
Figure 10.22c Nucleotide insertion of mutations and their effects.
Figure 10.24 Adenovirus
Figure 10.24 Adenovirus
Figure 10.25 Bacteriophages (viruses) infecting a bacterial cell.
Figure 10.26 Alternative phage reproductive cycles. (Step 1)
Figure 10.26 Alternative phage reproductive cycles. (Step 2)
Figure 10.26a Alternative phage reproductive cycles.
Figure 10.26b Alternative phage reproductive cycles.
Figure 10.26c Alternative phage reproductive cycles.
Figure 10.27 Tobacco mosaic virus
Figure 10.27b Tobacco mosaic virus
Figure 10.27a Tobacco mosaic virus
Figure 10.28 An influenza virus.
Figure 10.29 The reproductive cycle of an enveloped virus.
Figure 10.29a The reproductive cycle of an enveloped virus.
Figure 10.29b The reproductive cycle of an enveloped virus.
Figure 10.31 HIV, the AIDS virus.
Figure 10.32 The behavior of HIV nucleic acid in an infected cell.
Figure 10.32a The behavior of HIV nucleic acid in an infected cell.
Figure 10.32b HIV infecting a white blood cell.
Figure 10.33 AZT and the T nucleotide.
Figure 10.34 Mad cow disease.
Figure 10.35 Rounding up ducks in Vietnam to help prevent the spread of the Avian flu virus.
Figure 10.UN1 Transcription orientation diagram
Figure 10.UN2 Translation orientation diagram
Figure 10.UN3 Summary: DNA and RNA Structure
Figure 10.UN3a Summary: DNA and RNA Structure
Figure 10.UN3b Summary: DNA and RNA Structure
Figure 10.UN4 Summary: DNA Replication
Figure 10.UN5 Summary: DNA to Protein
Figure 10.UN6 Summary: Translation: The Players
Figure 10.UN7 Summary: Mutations
