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Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint® Lecture Slides forEssential Biology, Second Edition & Essential Biology with Physiology
Neil Campbell, Jane Reece, and Eric Simon
Presentation prepared by Chris C. Romero
CHAPTER 10CHAPTER 10
Molecular Biology of the GeneFigures 10.1 – 10.5
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• DNA
THE STRUCTURE AND REPLICATION OF DNA
– Was known as 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 are nucleic acids
DNA and RNA: Polymers of Nucleotides
– They consist of chemical units called nucleotides
– The nucleotides are joined by a sugar-phosphate backbone Fig. 10.3 to Fig. 10.5, p. 174-5
– Nucleic acids consist of long chains (polymers) of chemical units (monomers).
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Figure 10.2
Phosphate group Nitrogenous base
Sugar
Nucleotide
Polynucleotide Sugar-phosphate backbone
Nitrogenous base(A,G,C, or T)
Thymine (T)
Phosphategroup
Sugar(deoxyribose)
DNA nucleotide
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• The four nucleotides found in DNA
– Differ in their nitrogenous bases
– Are thymine (T), cytosine (C), adenine (A), and guanine (G)
• RNA has uracil (U) in place of thymine.
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• James Watson and Francis Crick determined that DNA is a double helix.
Watson and Crick’s Discovery of the Double Helix
Figure 10.3a(a) James Watson and Francis Crick
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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.
Figure 10.3b
(b) Rosalind Franklin
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• The model of DNA is like a rope ladder twisted into a spiral.
Figure 10.4Twist
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• Detailed representations of DNA
– Notice that the bases pair in a complementary fashion.
Figure 10.5
Hydrogen bond
(a) (b) (c)
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• When a cell or organism reproduces, a complete set of genetic instructions must pass from one generation to the next Fig. 10.6, p. 176.
DNA Replication
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• Watson and Crick’s model for DNA suggested that DNA replicated by a template mechanism.
Figure 10.6
Parental (old)DNA molecule
Daughter(new) strand
DaughterDNA molecule(double helices)
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• DNA can be damaged by ultraviolet light
– The enzymes and proteins involved in replication can repair the damage.
Figure 10.7
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• DNA replication
– Begins at specific sites on a double helix
– Proceeds in both directions
Figure 10.8
Origin ofreplication
Origin ofreplication
Origin ofreplication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
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• An organism’s genotype, its genetic makeup is the sequence of nucleotide bases in DNA
How an Organism’s DNA Genotype Produces Its Phenotype
– The phenotype is the organism’s specific traits
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• DNA specifies the synthesis of proteins in two stages
– Transcription
– Translation
Figure 10.9. P. 177
DNANucleus
Transcription
RNA
Translation
ProteinCytoplasm
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• The one gene–one protein hypothesis states that the function of an individual gene is to dictate the production of a specific protein
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• The information, or “language,” in DNA is ultimately translated into the language of polypeptides
From Nucleotide Sequence to Amino Acid Sequence: An Overview
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• What is the language of nucleic acids?
– In DNA, it is the linear sequence of nucleotide bases
Figure 10.10
DNA molecule
Translation
Polypeptide
Gene 1
Gene 2
Gene 3
DNA strand
Transcription
RNA
Codon
Amino acid
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• When DNA is transcribed, the result is an RNA molecule
• RNA is then translated into a sequence of amino acids in a polypeptide. Translation is the conversion of the nucleic acid language into the polypeptide language. P. 178.
• Like nucleic acids, polypeptides are polymers, but the monomers that make them up are the 20 amino acids common to all organisms.
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• What is the correspondence between the nucleotides of an RNA molecule and the amino acids of a polypeptide?
• If A, T, G, C coded for only one amino acid: 4 of 20
• If they code in combinations of two lettered words: 42= 16 of 20 amino acids
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• Triplets of bases
– Specify all the amino acids
– The triplets are called codons, Fig. 10.10, p. 178.
– Codons in figure 10.11, p. 179 are triplets found in RNA
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• The genetic code is the set of rules relating nucleotide sequence to amino acid sequence
The Genetic Code
Figure 10.11
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Transcription: From DNA to RNA
• In transcription
– Genetic information is transferred from DNA to RNA
– An RNA molecule is transcribed from a DNA template
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Figure 10.13a
RNApolymerase
RNA nucleotides
Newly madeRNA Direction of
transcription Templatestrand of DNA
(a) A close-up view of transcription
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• Transcription of an entire gene
Figure 10.13b
RNA polymerase
DNA of gene
PromoterDNA Initiation Terminator
DNA
RNAElongation
Area shownin part (a)
TerminationGrowingRNA
Completed RNA
RNApolymerase(b) Transcription of a gene
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• The “start transcribing” signal is a nucleotide sequence called a promoter
Initiation of Transcription
• The first phase of transcription is initiation
– RNA polymerase attaches to the promoter
– RNA synthesis begins
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• The second phase of transcription is elongation
RNA Elongation
– The RNA grows longer
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• The third phase of transcription is termination
Termination of Transcription
– RNA polymerase reaches a sequence of DNA bases called a terminator
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• The eukaryotic cell processes the RNA after transcription
The Processing of Eukaryotic RNA
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• RNA processing includes
– Adding a cap and tail
– Removing introns
– Splicing exonstogether
Figure 10.14
DNA
RNAtranscriptwith capand tail
mRNA
Exon Intron ExonIntron Exon
Cap
Introns removed Tail
Exons spliced together
Coding sequence
Nucleus
Cytoplasm
TranscriptionAddition of cap and tail
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• Translation
Translation: The Players
– Is the conversion from the nucleic acid language to the protein language
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• mRNA
Messenger RNA (mRNA)
– Is the first ingredient for translation
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• tRNA
Transfer RNA (tRNA)
– Acts as a molecular interpreter
– Carries amino acids
– Matches amino acids with codonsin mRNA using anticodons
Figure 10.15
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
AnticodonAnticodon
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• Ribosomes
Ribosomes
– Are organelles that actually make polypeptides, p. 183
– Are made up of two protein subunits
– Contain ribosomal RNA (rRNA)
Figure 10.16a
tRNAbinding sites
P site A site
P A
Largesubunit
mRNAbindingsite
Smallsubunit
(a)
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• A fully assembled ribosome holds tRNA and mRNA for use in translation
Figure 10.16b
Next amino acidto be added topolypeptide
Growingpolypeptide
mRNA
tRNA
(b)
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• Translation is divided into three phases
Translation: The Process
– Initiation
– Elongation
– Termination
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• The first phase brings together
Initiation
– The mRNA
– The first amino acid with its attached tRNA
– The two subunits of the ribosome
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• An mRNA molecule has a cap and tail that help it bind to the ribosome
Figure 10.17
Start of genetic message
CapEnd
Tail
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• The process of initiation
Figure 10.18.1
Met
Initiator tRNA
mRNA
Large ribosomalsubunit
Start codon
Small ribosomalsubunit
Initiation P site
A site
1
2
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• Step 1, codon recognition
Elongation
– The anticodon of an incoming tRNA pairs with the mRNA codon
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• Step 2, peptide bond formation
– The ribosome catalyzes bond formation between amino acids. That is, peptide bonds form between amino acids. P. 184
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• Step 3, translocation
– A tRNA leaves the P site of the ribosome
– The ribosome moves down the mRNA
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Polypeptide
Amino acid
P site
AnticodonmRNA A site
Codons
Elongation
2
3 Translocation
Codon recognition
Peptide bond formation
• The process of elongation
Figure 10.19
mRNAmovement
New peptidebond
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• Elongation continues until the ribosome reaches a stop codon
Termination
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• The flow of genetic information in a cell
Review: DNA���� RNA���� Protein
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Figure 10.20
1
2
3
4
Amino acid attachment
5 Elongation
Initiation of translation
6 Termination
Transcription
RNA processing
RNA Polymerase
Nucleus
DNA
RNAtranscript
Intron
Tail
Intron
mRNA
CAP
tRN
A
Enzyme
Amino acid
Ribosomal subunits
Anticodon
Codon
Stop codon
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• In eukaryotic cells
– Transcription occurs in the nucleus
– Translation occurs in the cytoplasm
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• Transcription and Translation
– Are the processes whereby genes control the structures and activities of cells
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• A mutation
Mutations
– Is any change in the nucleotide sequence of DNA
Figure 10.21
Normal hemoglobin Sickle-cell hemoglobin
Glu Val
Normal hemoglobin DNA Mutant hemoglobin DNA
mRNA mRNA
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• Mutations within a gene
Types of Mutations
– Can be divided into two general categories
– Can result in changes in the amino acids in proteins
Figure 10.22a
mRNA
Protein Met Lys Phe Gly Ala
(a) Base substitution
Met Lys Phe Ser Ala
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• Insertions and deletions
– Can have disastrous effects
– Change the reading frame of the genetic message
Figure 10.22b
Met Lys Leu Ala His
(b) Nucleotide deletion
mRNA
Protein Met Lys Phe Gly Ala
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• Mutations may result from
Mutagens
– Errors in DNA replication
– Physical or chemical agents called mutagens
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• Although mutations are often harmful
– They are the source of the rich diversity of genes in the living world
– They contribute to the process of evolution by natural selection
Figure 10.23
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• Viruses sit on the fence between life and nonlife
VIRUSES: GENES IN PACKAGES
– They exhibit some but not all characteristics of living organisms
Figure 10.24
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• Bacteriophages, or phages
Bacteriophages
– Attack bacteria
Figure 10.25
Head
Tail
Tail fiber
DNA of virus
Bacterialcell
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• Phages have two reproductive cycles
Figure 10.26
Phage DNA
1
2
3
4
Phage DNA circularizes
New phage DNA andproteins are sythesized
5 Phage DNA inserts into the bacterialchromosome by recombination
Cell lyses,releasing phages
6 Lysogenic bacteriumreproduces normally,replicating the prophageat each cell division
7 Occasionally a prophagemay leave the bacterialchromosome
Bacterial chromosome (DNA)
Lytic cycle Lysogenic cycle
Prophage
Many cell divisions
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• Viruses that infect plants
Plant Viruses
– Can stunt growth and diminish plant yields
– Can spread throughout the entire plant
Figure 10.27
Protein RNA
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• The reproductive cycle of an enveloped virus, p. 190
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Figure 10.29
VIRUS
Entry1
2
3
4
Uncoating
RNA synthesisby viral enzyme
5 RNA synthesis(other strand)
Proteinsynthesis
6 Assembly
7
Exit
Viral RNA (genome)
Protein spike
Protein coatEnvelope
Plasma membrane of host cell
mRNA
New viral proteins
Template
New viral genome
Mumps virus, p.190
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• HIV is a retrovirus
HIV, the AIDS Virus, p. 192
– A retrovirus is an RNA virus that reproduces by means of a DNA molecule
– It copies its RNA to DNA using reverse transcriptase
Figure 10.30a
Envelope
Protein
Protein coat
RNA(two identical
strands)
Reversetranscriptase
(a) HIV
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23
4
5
6
DNA strand
Viral RNA Reverse transcriptase
Cytoplasm
Double-stranded DNA
Chromosomal DNA
Provirus DNA
Viral RNA and proteins
Nucleus
(b) The behavior of HIV nucleic acid in an infected cell
• How HIV reproduces inside a cell
Figure 10.30b
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• DNA and RNA: Polymers of Nucleotides
SUMMARY OF KEY CONCEPTS
Visual Summary 10.1
DNA
Polynucleotide
Nitrogenousbase
Phosphategroup
Nucleotide
Sugar
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• DNA Replication
Visual Summary 10.2
ParentalDNA molecule
IdenticaldaughterDNA molecules
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• Translation: The Players
Visual Summary 10.3
Largeribosomal
subunit
Amino acid
mRNA
tRNA
Anticodon
Codons
Small ribosomal subunit