molecular biology of the gene - arizona state …pbaluch/courses/bio100/dna.pdfessential biology,...

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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


• 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.


• 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


• 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.


• 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


• The model of DNA is like a rope ladder twisted into a spiral.

Figure 10.4Twist


• 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


• 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)


• 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



Parental strand

Daughter strand

Bubble

Two daughter DNA molecules


• 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


• 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


• The information, or “language,” in DNA is ultimately translated into the language of polypeptides

From Nucleotide Sequence to Amino Acid Sequence: An Overview


• 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.


• 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


• 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


Transcription: From DNA to RNA

• In transcription

– Genetic information is transferred from DNA to RNA

– An RNA molecule is transcribed from a DNA template


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


• 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


• 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


• The eukaryotic cell processes the RNA after transcription

The Processing of Eukaryotic RNA


• 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


• mRNA

Messenger RNA (mRNA)

– Is the first ingredient for translation


• 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)


• 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)


• 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


• An mRNA molecule has a cap and tail that help it bind to the ribosome

Figure 10.17

Start of genetic message

CapEnd

Tail


• 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


• Step 2, peptide bond formation

– The ribosome catalyzes bond formation between amino acids. That is, peptide bonds form between amino acids. P. 184


• 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


• 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


• In eukaryotic cells

– Transcription occurs in the nucleus

– Translation occurs in the cytoplasm


• 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


• 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


• 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


• 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


• 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


• 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


• 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


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


• 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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1

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


• DNA and RNA: Polymers of Nucleotides

SUMMARY OF KEY CONCEPTS

Visual Summary 10.1

DNA

Polynucleotide

Nitrogenousbase

Phosphategroup

Nucleotide

Sugar


• 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

molecular biology of the gene - arizona state …pbaluch/courses/bio100/dna.pdfessential biology,...

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