10 lectures ppt

7/16/2019 10 Lectures PPT

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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for

Biolog y: Concepts and Connect ions, Fi f th Edi t ion

– Campbell , Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 10

Molecular Biology of the

Gene




10.2 DNA and RNA are polymers of nucleotides

• Nucleic acids are polynucleotides made of longchains of nucleotide monomers

– Nitrogenous bases

• Single-ring pyrimidines: thymine (T),

cytosine ( C)

• Double-ring purines: adenine (A), guanine

(G)

– Sugar-phosphate backbone




• DNA and RNA are identical except for two

things

– Nitrogenous bases

• DNA: A, C, G, T

• RNA: A, G, C, U

– Sugars

•DNA: deoxyribose

• RNA: ribose

Animation: DNA and RNA Structure

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_02DNAandRNAStructure_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_02DNAandRNAStructure_A.html



LE 10-2a

Sugar-phosphate backbone Phosphate group Nitrogenous base

Sugar

DNA nucleotide

DNA polynucleotide DNA nucleotide

Sugar

(deoxyribose)

Thymine (T)

Nitrogenous base

(A, G, C, or T)Phosphate

group

A

C

T

G

T T

G

T

C

A



LE 10-2b

Thymine (T) Cytosine (C) Pyrimidines

Adenine (A) Purines

Guanine (G)



LE 10-2c

Phosphate

group

Nitrogenous base

(A, G, C, or U)

Sugar

(ribose)

Uracil (U)



LE 10-2dKey

Hydrogen atom

Phosphorus atom

Carbon atom Nitrogen atom Oxygen atom


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10.3 DNA is a double-stranded helix

• James Watson and Francis Crick worked outthe three-dimensional structure of DNA, based

on X-ray crystallography by Rosalind Franklin

• DNA consists of two polynucleotide strandswrapped around each other in a double helix

– Sugar-phosphate backbones are on the

outside and nitrogenous bases on the inside

Animation: DNA Double Helix

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_03D_DNADoubleHelix_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_03D_DNADoubleHelix_A.html


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– Each base pairs with a complementary

partner

• A with T, and G with C

– Hydrogen bonds between the bases hold

the strands together

• The Watson-Crick model of DNA suggested a

molecular explanation for genetic inheritance

LE 10 3



LE 10-3c

Twist

LE 10 3d



LE 10-3d

Hydrogen bond Base

pair

Ribbon model Partial chemical structure Computer model

G C T A

A T

T A

C C

G G

G C

T T

T T

A A A

A

G C A T

A

C

T

G

C G

A T




DNA REPLICATION

10.4 DNA replication depends on specific base pairing

•

The Watson-Crick model of DNA structure suggesteda mechanism for its replication

– DNA strands separate

– Enzymes use each strand as a template toassemble new nucleotides into complementary

strands

• The mechanism of DNA replication is

semiconservative

– Each new double helix consists of one old and one

new strand

LE 10 4



LE 10-4a

Parental

molecule

of DNA

Both parental

strands serve

as templates

Two identical

daughter molecules

of DNA

T

Nucleotides

C G A

G C A

A T

T

A

A

A C

C C

T

T

G G

A C

A A A

A

A

A

C C C

C G

T G

T T

T

T G

T

T T

G G




• DNA replication is a complex process

– Some of the helical DNA molecule mustuntwist

Animation: DNA Replication Overview

LE 10 4b

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_04DNAReplicatOverview_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_04DNAReplicatOverview_A.html



LE 10-4b

G C T A

A T G

G C C

C




10.5 DNA replication: A closer look

• DNA replication begins at specific sites (originsof replication) on the double helix

– Proteins attach and separate the strands

– Replication proceeds in both directions,

creating replication bubbles

• Parent strands open, daughter strands

elongate

– Replication occurs simultaneously at many

sites

LE 10 5a



LE 10-5a

Origin of replication

Bubble

Parental strand Daughter strand

Two daughter DNA molecules




• DNA's sugar-phosphate backbones are

oriented in opposite directions

– The enzyme DNA polymerase adds

nucleotides at only the 3’ end

•One daughter strand is synthesized as acontinuous piece

• The other strand is synthesized as a series

of short pieces

• The two strands are connected by the

enzyme DNA ligase

LE 10-5b



LE 10-5b

3 end 5 end

5 end 3 end

P

4 A

T

C

G

HO

OH

P 1 3

2

5 P

P

P

P

C

G

P

P

A

T

P

4 3

1 2

5

LE 10-5c



LE 10-5cDNA polymerase

molecule

Parental DNA Daughter strand

synthesized

continuously

Daughter

strand

synthesized

In pieces

3

5

3

5

5

3

3

5

DNA ligase Overall direction of replication




Animation: Origins of Replication

Animation: Leading Strand

Animation: Lagging Strand

Animation: DNA Replication Review

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05A_OriginsOfReplicati_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05C_LeadingStrand_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05C_LaggingStrand_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05DNAReplicatReview_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05DNAReplicatReview_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05C_LaggingStrand_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05C_LeadingStrand_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_05A_OriginsOfReplicati_A.html



THE FLOW OF GENETIC INFORMATIONFROM DNA TO RNA TO PROTEIN

10.6 The DNA genotype is expressed as

proteins, which provide the molecular basis for

phenotypic traits

• The information constituting an organism's

genotype is carried in its sequence of DNA

bases

• A particular gene—a linear sequence of many

nucleotides—specifies a particular polypeptide





• The flow of genetic information

1. Transcription of the genetic information in DNAinto RNA

2. Translation of RNA into the polypeptide

•

Beadle-Tatum one gene-one enzyme hypothesis – Studies of inherited metabolic disorders in mold

suggested that phenotype is expressed through

proteins

– A gene dictates production of a specific enzyme

– The hypothesis has been restated to one gene-

one polypeptide




10.7 Genetic information written in codons is

translated into amino acid sequences

• Genetic information flows from DNA to RNA to

protein

• Nucleotide monomers represent letters in analphabet that can form words in a language

– Triplet code

• Three-letter words (codons)

• Each word codes for one amino acid in a

polypeptide

LE 10-7a



DNA molecule

Gene 1

Gene 2

Gene 3

A A A A A C C G G C

C C G G G U U U U U U U

A A DNA strand

Transcription

RNA

Translation

Polypeptide Amino acid

Codon




10.8 The genetic code is the Rosetta stone of life

• The genetic code specifies thecorrespondence between RNA codons and

amino acids in proteins

– Includes start and stop codons

– Redundant but not ambiguous

• Nearly all organisms use exactly the same

genetic code

LE 10-8a



Second base

UUU U C A G

G A A

C

U

U

U

C

A C

A

G

G U C A G

U

C

A

G

UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA

Leu

lle

AUG Met or

start GUU GUC GUA GUG

Val Ala

Thr

GCG GCA GCC GCU ACG ACA ACC ACU

Pro

CCG CCA CCC CCU UCG UCA UCC UCU

Ser Tyr Cys UAU

UAC UAA UAG CAU CAC CAA CAG

His

Gln

Stop Stop

UGU UGC UGA UGG Trp

Stop

Arg

CGU CGU CGA CGG

Asn

Lys

Asp

Glu Gly

Arg

Ser AAU AGU AAC AAA AAG GAU

GAG

AGC AGA AGG GGU GGC

GGG

Phe

Leu

GAC GAA GAG

GGA

LE 10-8b



Strand to be transcribed

Transcription

DNA T

A G T

A C T T

T T

A A

A A G

C

G

C

T T

T A A

A

A G U RNA

Translation Start

codon

A A U U G U U A G

Stop

codon

Phe Lys Met Polypeptide




10.9 Transcription produces genetic messages in

the form of RNA

• One DNA strand serves as a template for the

new RNA strand

• RNA polymerase constructs the RNA strand ina multistep process

– Initiation

• RNA polymerase attaches to the promotor

• Synthesis starts




• Elongation:

– RNA synthesis continues

– RNA strand peels away from DNA template

– DNA strands come back together in

transcribed region

• Termination

– RNA polymerase reaches a terminator sequence at the end of the gene

– Polymerase detaches

LE 10-9a



RNA

polymerase RNA nucleotides

Template

strand of DNA Direction of

transcription

Newly made RNA

A A C C

C C A

G T T

U A

G T A

LE 10-9b



RNA polymerase

Initiation

Promoter

DNA Terminator

DNA

Area shown

In Figure 10.9A

Initiation

Elongation

Termination Growing

RNA

Completed RNA RNA

polymerase

DNA of gene




Animation: Transcription

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_09TranscriptionIntro_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_09TranscriptionIntro_A.html




10.10 Eukaryotic RNA is processed before

leaving the nucleus

• The RNA that encodes an amino acid

sequence is messenger RNA (mRNA)

• In prokaryotes, transcription and translationboth occur in the cytoplasm

• In eukaryotes, RNA transcribed in the nucleus

is processed before moving to the cytoplasmfor translation




• RNA Splicing

– Noncoding segments called introns are cutout

– Remaining exons are joined to form a

continuous coding sequence

– A cap and a tail are added to the ends

LE 10-10



Exon Exon Exon Intron Intron

Cap DNA

RNA

transcript

with cap

and tail

mRNA

Coding sequence Nucleus

Cytoplasm

Exons spliced together

Tail Introns removed

Transcription

Addition of cap and tail




10.11 Transfer RNA molecules serve as interpreters

during translation

• Transfer RNA (tRNA) molecules match the right amino

acid to the correct codon

• tRNA is a twisted and folded single strand of RNA

– Anticodon loop at one end recognizes a particular

mRNA codon by base pairing

– Amino acid attachment site is at the other end

• Each amino acid is joined to the correct tRNA by a

specific enzyme

LE 10-11a



Amino acid attachment site

Hydrogen bond

RNA polynucleotide chain

Anticodon

LE 10-11bAmino acid



Anticodon

Amino acid

attachment site




10.12 Ribosomes build polypeptides

• A ribosome consists of two subunits

– Each is made up of proteins and ribosomal

RNA (rRNA)

• The subunits of a ribosome

– Hold the tRNA and mRNA close together in

binding sites during translation

– Allow amino acids to be connected into a

polypeptide chain

LE 10-12a



tRNA

molecules Growing

polypeptide

Largesubunit

Small

subunit mRNA

LE 10-12btRNA-binding sites



tRNA-binding sites

Largesubunit

Small

subunit

mRNA

binding

site

LE 10-12c



Growing

polypeptide

mRNA

Codons

tRNA

Next amino acid

to be added to

polypeptide




10.13 An initiation codon marks the start of an

mRNA message

• The initiation phase of translation

– Brings together mRNA, a specific tRNA,

and the two subunits of a ribosome

– Establishes exactly where translation will

begin

• Ensures that mRNA codes are translated in

the correct sequence




• Initiation is a two-step process

– Step 1

• mRNA binds to a small ribosomal subunit

• Initiator tRNA, carrying the amino acid Met,

binds to the start codon

– Step 2

•

A large ribosomal subunit binds to the smallone, forming a functional ribosome

• Initiator tRNA fits into one binding site; the

other is vacant for the next tRNA

LE 10-13a



Start of genetic message

End

LE 10-13b



C

Initiator tRNA P site

mRNA Start codon

Small ribosomal

subunit

A site

Large

Ribosomal

subunit

C A U A A U

U G A G U




10.14 Elongation adds amino acids to the

polypeptide chain until a stop codon terminates

translation

• Once initiation is complete, amino acids are

added one by one in a three-step elongation

process

1. Codon recognition

2. Peptide bond formation

3. Translocation

• Elongation continues until a stop codon reaches

the ribosome's A site, terminating translation

LE 10-14Amino

id



Polypeptide P site

mRNA

A site

Codons Anticodon

acid

Condon recognition

Peptide bond

formation New

peptide

bond

Translocation

Stop

codon

mRNA

movement




Animation: Translation

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_14TranslationIntro_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_14TranslationIntro_A.html




10.15 Review: The flow of genetic information in

the cell is DNA RNA protein

• The sequence of codons in DNA, via the

sequence of codons in RNA, spells out the

primary structure of a polypeptide

1. Transcription of mRNA from a DNA

template

2. Attachment of amino acid to tRNA

3. Initiation of polypeptide synthesis

4. Elongation

5. Termination

LE 10-15DNA Transcription



mRNA RNA

polymerase mRNA is

transcribed from a

DNA template.

Each amino acid

attaches to its proper tRNA with the help of a

specific enzyme and ATP.

Translation Amino acid

mRNA

Enzyme

ATP

Anticodon Large

ribosomal

subunit Initiator

tRNA

Start Codon Small

ribosomalsubunit

U A A U

C G

Initiation of

polypeptide synthesis

The mRNA, the first

tRNA, and the ribosomal

Sub units come together.

Stop codon

A succession of tRNAs

add their amino acids to

the polypeptide chain

as the mRNA is moved

through the ribosome,

one codon at a time.

Growingpolypeptide

New peptidebond forming

mRNA

Polypeptide

Codons

Elongation

Termination The ribosome recognizes

a stop codon. The poly-

peptide is terminated

and released.

tRNA




10.16 Mutations can change the meaning of

genes

• Mutation: any change in the nucleotide

sequence of DNA

– Caused by errors in DNA replication or recombination, or by mutagens

– Can involve large regions of a chromosome

or a single base pair

– Can cause many genetic diseases, such as

sickle-cell disease

LE 10-16a



Normal hemoglobin DNA

mRNA

C T T

A A G

Normal hemoglobin Glu

mRNA

C

G

A

Sickle-cell hemoglobin Val

Mutant hemoglobin DNA

A

T

U




• Two general categories of genetic mutations

–

Base substitutions replace one base withanother

• Most are harmful but may occasionally have

no effect or be beneficial

– Base insertions or deletions alter the

reading frame

• Result is most likely a nonfunctioning

polypeptide

• Mutagenesis caused by spontaneous error or

a physical or chemical mutagen

LE 10-16bNormal gene



Base substitution

Protein mRNA

Base deletion

Missing

Met

Met

Met Lys

Lys

Lys Phe Gly Ala

Ala Phe

Ala

Ser

Leu His

A

A A A A

A A A

A

A A A A A U U U U

U U U U

U U U U G G G G G

G G G G

C C

C C

G G G G G C C

U

MICROBIAL GENETICS




10.17 Viral DNA may become part of the host

chromosome

• Viruses are infectious particles consisting of

nucleic acid enclosed in a protein capsid

• Viruses depend on their host cells for thereplication, transcription, and translation of

their nucleic acid

– DNA enters host bacterium, circularizes,and enters one of two pathways




– Lytic cycle

•

Host produces more viruses

• Host cell lyses (breaks open) to release new

viruses




– Lysogenic cycle

•

Phage DNA inserted by recombination intothe host chromosome; is now a prophage

• Prophages replicated each time host cell

divides; passed on to generations of

daughter cells

• Does not destroy host

•

Environmental signal may trigger switchfrom lysogenic to lytic cycle

LE 10-17



Phage

Phage DNA

Attaches

to cell

Cell lyses,

releasing phagesPhage injects DNA

Lytic cycle

Phages assemblePhage DNA

circularizes

New phage DNA and

proteins are synthesized

Bacterial

chromosome

OR

Lysogenic cycle

Prophage

Many cell

divisions

Lysogenic bacterium repro-

duces normally, replicating the

prophage at each cell division

Phage DNA inserts into the bacterial

chromosome by recombination




Animation: Simplified Viral Reproductive Cycle

Animation: Phage T4 Lytic Cycle

Animation: Phage Lambda Lysogenic and Lytic Cycles

CONNECTION

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_17SimpViralReproCycle_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_17PhageT4LyticCycle_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_17LysogenicLyticCycles_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_17LysogenicLyticCycles_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_17PhageT4LyticCycle_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_17SimpViralReproCycle_A.html




10.18 Many viruses cause disease in animals

• Structure of a virus that invades animal cells

– Genetic material may be RNA (examples:

flu, HIV) or DNA (examples: hepatitis,

herpes)

– Protein coat

– Sometimes a membranous envelope with

glycoprotein spikes

• The envelope helps the virus enter and leave

the host cell during its reproductive cycle

LE 10-18aMembranous

envelope



envelope

RNA

Protein

coat

Glycoprotein spike

LE 10-18bVIRUS

Viral RNA Glycoprotein spike P t i t



(genome) Protein coat Envelope

Entry Plasma membrane

of host cell

Uncoating Viral RNA

(genome) RNA synthesis

by viral enzyme RNA synthesis

(other strand)

Template mRNA Protein

synthesis

New

viral proteins

New viral

genome Assembly

Exit

CONNECTION




10.19 Plant viruses are serious agricultural pests

• Most plant viruses

– Have RNA genomes

– Enter their hosts via wounds in the plant's

outer layers

– May spread throughout the plant through

plasmodesmata

• There is no cure for most plant viruses

LE 10-19



RNA

Protein

CONNECTION




10.20 Emerging viruses threaten human health

•Emerging viruses have appeared suddenly or have recently come to the attention of

scientists

– Examples: HIV, SARS, Ebola, West Nile

• Processes contributing to emergence

– Mutation

– Contact between species

– Spread from isolated populations




10.21 The AIDS virus makes DNA on an RNA

template

• HIV, the AIDS virus, is a retrovirus

– Flow of genetic information is RNA _ DNA

– Inside a cell, HIV uses its RNA as a

template for making DNA

– The enzyme reverse transcriptase catalyzes

reverse transcription

Animation: HIV Reproductive Cycle

LE 10-21a

Envelope

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_21HIVReproCycle_A.html

http://localhost/var/www/apps/conversion/tmp/scratch_15/Media/10_21HIVReproCycle_A.html



p

Glycoprotein

Proteincoat

RNA

(two identicalstrands)

Reverse

transcriptase

LE 10-21b



Viral RNA

DNA

strand Double-

stranded

DNA

Viral

RNA

and

proteins

C YTOPLASM NUCLEUS

Chromosomal

DNA Provirus

DNA

RNA




10.22 Bacteria can transfer DNA in three ways

•Bacteria can transfer genes from cell to cell byone of three processes

– Transformation: the uptake of foreign DNA

from the surrounding environment

– Transduction: transfer of bacterial genes by

a phage

– Conjugation: union of two bacterial cells andthe transfer of DNA between them

LE 10-22a

DNA enters



cell

Fragment of

DNA from

another

bacterial cell

Bacterial chromosome

(DNA)

LE 10-22bPhage



Fragment of DNA from

another bacterial cell

(former phage host)

LE 10-22cMating bridge



Recipient cell

(“female”)

Sex pili

Donor cell

(“male”)




• Once new DNA is in a bacterial cell, part of it

may integrate into the recipient's chromosome

– Occurs by crossing over between the two

molecules

–

Leaves the recipient with a recombinantchromosome

LE 10-22d



Donated DNA Crossovers Degraded DNA

Recombinant

chromosome Recipient cell’s

chromosome




10.23 Bacterial plasmids can serve as carriers for

gene transfer

• The F factor is a piece of bacterial DNA

– Carries genes for things needed for

conjugation

– Contains an origin of replication

– Can transfer chromosomal DNA by

integrating into the donor bacterium's

chromosome or entering the cell as a

plasmid

LE 10-23aF factor (integrated)

Male (donor)



Male (donor)

cell

Origin of F

replication

Bacterial

chromosome

F factor starts replication

and transfer of chromosome

Recipient cell

Only part of the

chromosome transfers

Recombination can occur

LE 10-23bF factor (plasmid)



Cell now male

Plasmid completes

transfer and circularizes

F factor starts replication

and transfer

Bacterial

chromosome

Male (donor)

cell




• Plasmids

– Small circular DNA molecules separatefrom the bacterial chromosome

– Can serve as carriers for the transfer of

genes

LE 10-23c



Plasmids

C o l o r i z e

d T E M 2 , 0

0 0

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