honors bio - chapter 10

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

PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Honors Bio - Chapter 10

Molecular Biology of the Gene


Viruses - infect cells

- Gave us some of the earliest evidence that genes are made of DNA


10.1 Experiments showed DNA was the genetic material

Frederick Griffith 1928

a. Tried to make a vaccine for pneumoniab. Used mice and two strains of bacteria:

- one harmless (“R type”)- one pathogenic (“S type”)

c. Live R alone and dead S alone did not cause immune response

d. Mixed live R with dead S


Live R (‘rough’) no diseaseLive S (‘smooth’) pneumonia

Mix Live R and dead S pneumonia


What happened to Griffith’s mice?Mice treated with live R and dead S

- got sick and died- had live type S bacteria in them!

Where did the live S come from?

Griffith’s Conclusion: Something from dead S cells transformed live R cells into live S


Griffith’s conclusionSomething from dead S cells transformed

living R cells into living S cells


Avery, McLeod, and McCartey Problem: What substance from dead S transformed live R into live S?

Experiment: Grow live R and dead S in cultures- each culture has a different enzyme whichdestroys one type of molecule- carbs, lipids, proteins, RNA, or DNA

- Which enzyme stops transformation?


Only bacteria grown in DNAase did not transformConclusion: DNA is the transforming material


The Hershey-Chase experiment 1952Background: Viruses change host cells - produce more virus

Problem: Is it the protein coat? Or the DNA?

Experiment: grow bacteria in culture, add phage virus tagged with radioactive isotope

- use sulfur proteins (capsid) are radioactive

- use phosphorus phage DNA is radioactive

Let phage infect bacteria – where is radioactivity?


Hershey-Chase Experiment

Grow bacteria in culture with tagged

phage. Virus infects bacteria

Is radioactivity in the liquid (phage),

or in the cells (bacteria)?

Centrifuge separates cells

from culture liquid

Blender shakes phage loose from

bacterial cells.


Hershey-Chase ResultsPhage tagged with phosphorus bacterial cells became radioactive

Conclusion: phage DNA entered cells, but protein did not


Bacteriophage

Virus Life Cycle

Figure 10.1A


10.3 Finding the structure of DNA

Rosalind Franklin’s X-ray picture of DNA crystal shows double helix

Watson & Crick, 1953


DNA polynucleotide

A

C

T

G

T

Sugar-phosphate backbone

Phosphate group

Nitrogenous base

SugarA

C

T

G

T

Phosphategroup

O

O–

OO P CH2

H3C C

C

C

CN

C

N

H

H

O

O

C

O

O

H

C H H

H

C

H

Nitrogenous base(A, G, C, or T)

Thymine (T)

Sugar(deoxyribose)

DNA nucleotide

DNA nucleotide

10.2 DNA and RNA are polymers of nucleotides

Figure 10.2A


DNA has four kinds of nitrogen bases

Purines have two nitrogen-carbon rings (A and G) Pyrimidines have one ring (T and C)

CC

C

CC

C

O

N

C

H

H

ONH

H3C

H H

H

H

N

N

N

H

OC

H HN

H C

N

N N

N

C

CC

C

H

H

N

N

H

C

CN

C HN

CN

H C

O

H

H

Thymine (T) Cytosine (C) Adenine (A) Guanine (G)

PurinesPyrimidines

Figure 10.2B


RNA is also a nucleic acid

– Has ribose sugar

– Has uracil instead of thymine base

Nitrogenous base (A, G, C, or U)

Phosphategroup

O

O–

OO P CH2

HC

C

C

CN

C

N

H

H

O

O

C

O

O

H

C H H

OH

C

H

Uracil (U)

Sugar(ribose)Figure 10.2C

3 kinds of RNA


Three kinds of RNAMessenger RNA (mRNA)– carries code from DNA in nucleus to ribosome

Ribosomal RNA (rRNA) – makes up ribosome, along with proteins

Transfer RNA (tRNA) – carries one amino acid to ribosome and matches to mRNA code


The structure of DNA

• Two polynucleotide strands double helix

Figure 10.3C Twist


• Form between complementary bases• A with T (2 H bonds), and G with C (3 H bonds)

Figure 10.3D

G C

T A

A T

G

G

C

C

A T

GC

T A

T A

A T

A T

G C

A T

O

O

OH–O

P

O O–O

PO

OO

P– O

– O OP

OO

O

OH

H2C

H2C

H2C

H2C

O

O

O

O

O

O

O

O

PO–

O–

O–

O–

OH

HO

O

O

O

P

P

P

O

O

O

O

O

O

O

O

T A

G C

C G

A T

CH2

CH2

CH2

CH2

Hydrogen bond

Basepair

Ribbon model Partial chemical structure Computer model

Hydrogen bonds hold two strands together


10.4 DNA REPLICATION

10.4 Depends on specific base pairing• Starts with the separation of DNA strands• Then enzymes use each strand as a template

• Assemble new nucleotides into complementary strands

Figure 10.4A

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A

T

A T

C G

AC

T

A

Parental moleculeof DNA

Both parental strands serve as templates

Two identical daughtermolecules of DNA

Nucleotides


DNA replication: For cell division• Starts in several places

at once• Each original strand is

template for a new strand (“semi-conservative”

• Proceeds until entire strands are duplicated

• Copies stay together at centromere


10.5 Replication begins at several sites (origins) • “bubbles” elongate and merge

Figure 10.5A

Origin of replication

Two daughter DNA molecules

Parental strand

Daughter strand

Bubble


Figure 10.5B

P

P

P

P

P

P

P

P

HO

OH

A

C

G

T

T

C

G

A

2 134

5

15 4

32

5 end 3 end

3 end 5 end

Go in opposite directions

DNA strands are antiparallel

DNA works in only one direction

-- from 5’ to 3’


• Enzyme DNA polymerase

• Leading Strand: one daughter strand synthesized as a continuous piece

• Lagging strand: other strand a series of short pieces, joined by enzyme DNA ligase

Figure 10.5C

3

53

53

5

53

Daughter strandsynthesizedcontinuously

Daughter strandsynthesizedin pieces

Parental DNA

DNA ligase

DNA polymerasemolecule

Overall direction of replication

Leading and lagging strands


Gene Expression = Protein Synthesis

10.6 The DNA genotype is expressed as proteins, which are the molecular basis for phenotypic traits

• Information in an organism’s genotype– Is carried in the sequence of its DNA bases

• A particular gene (linear sequence of many nucleotides) has code for one polypeptide

Gene info – From DNA to RNA to protein


1. DNA of a gene is transcribed into RNA

2. RNA is then translated into the polypeptide

Figure 10.6A

DNA

Transcription

RNA

Protein

Translation

Two stages in gene expression


mRNA synthesis - writes the gene onto a messenger molecule

RNApolymerase

RNA nucleotides

Direction of transcription Template

Strand of DNA

Newly made RNA

TC

AT C C A A T

T

GG

CC

AATTGGAT

G

U

C A U C C AA

U

Stage 1: Transcription – in nucleus

DNA unzips

mRNA leaves nucleus

ONE gene on one side of DNA is

copied


• Helicase enzyme unwinds part of DNA

• RNA nucleotides line up along one strand of the DNA, following the base pairing rules

• RNA polymerase joins nucleotides

• Single-stranded messenger RNA (mRNA) forms

• Finished RNA detaches from DNA

• DNA strands rejoin and rewind


Transcription of a geneRNA polymerase

DNA of gene

PromoterDNA Terminator

DNA

Area shownIn Figure 10.9A

GrowingRNA

Completed RNARNApolymerase

Figure 10.9B

1 Initiation

2 Elongation

3 Termination


Transcription – writes DNA code onto mRNA


• Before leaving nucleus

• Noncoding segments (introns) are spliced out

– And a cap and a tail are added to the ends

Exon Intron Exon Intron ExonDNA

Cap TranscriptionAddition of cap and tail

RNAtranscript with capand tail

Introns removedTail

Exons spliced together

mRNA

Coding sequence Nucleus

Cytoplasm

Figure 10.10

RNA processing


10.7 Genetic information is written in three-base sets called codons”

• A codon specifies one amino acid

• Sequence of codons = sequence of amino acids

• Primary structure of a protein

The DNA “code”


DNA strand

Transcription

Translation

Polypeptide

RNA

Amino acid

Codon

A A A C C G G C A A A A

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

Gene 1

Gene 2

Gene 3

DNA molecule

Figure 10.7


Figure 10.8A

UUC

UGUUGC

UGA Stop

Met or start

Phe

Leu

Leu

Ile

Val Ala

Thr

Pro

Ser

Asn

Lys

His

Gln

Asp

Glu

Ser

Arg

Arg

Gly

CysTyr

G

A

C

U

U C A G

Thi rd

ba s

e

Second base

Firs

t bas

e

UUA

UUU

CUC

CUU

CUG

CUA

AUC

AUU

AUG

AUA

GUC

GUU

GUG

GUA

UCC

UCU

UCG

UCA

CCC

CCU

CCG

CCA

ACC

ACU

ACC

ACA

GCC

GCU

GCG

GCA

UAC

UAU

UAG Stop

UAA Stop

CAC

CAU

CAG

CAA

AAC

AAU

AAG

AAA

GAC

GAU

GAG

GAA

UGG Trp

CGC

CGU

CGG

CGA

AGC

AGU

AGG

AGA

GGC

GGU

GGG

GGA

U

C

A

G

U

C

A

G

U

C

A

G

U

C

A

G

UUG

All organisms use the same code


UUG

All organisms use the same code


“Central Dogma” = DNA to RNA to protein

Figure 10.8B

T A C T T C A A A A T C

A T G A A G T T T T A G

A U G A A G U U U U A G

Transcription

Translation

RNA

DNA

Met Lys PhePolypeptide

Startcondon

Stopcondon

Strand to be transcribed


1. Ribosome attaches to mRNA

2. Transfer RNA (tRNA) brings amino acids to ribosome

How RNA helps


• One amino acid attached to one end

• 3-base set on other end called “anticodon”

• Anticodon is complement to a specific codon

Amino acidattachment site

AnticodonFigure 10.11B, C

Transfer RNA


10.12 Ribosomes build polypeptides• Made of proteins and ribosomal RNA (rRNA)

tRNAmolecules

mRNA Small subunit

Growingpolypeptide

Largesubunit

Figure 10.12A


The ribosome• Holds tRNA and mRNA close together

• Helps bond form between amino acids

Largesubunit

mRNA-binding site

Smallsubunit

tRNA-binding sites

Growing polypeptide

Next amino acid to be added to polypeptide

mRNA

tRNA

Codons

Figure 10.12B, C


10.12 Ribosomes build polypeptides

TRANSLATION: decode message to make protein


Translation1. Begins at “start” codon

2. Amino acids are set in sequence, according to the code on mRNA

3. Ends at “stop” codon


10.13 A start (“initiation”) codon marks the start of an mRNA message

Start of genetic message

End

Figure 10.13A


Initiation codon = Start

Peptide bond forms between two

amino acids

tRNA bring amino acids in sequence of

code on mRNA

Elongation – polypeptide grows as amino acids join

Termination codon = Stop

tRNA released


Elongation

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Transcription

Translation

mRNA

Polypeptide

DNA

tRNA


Polypeptide

P site

mRNA Codons

mRNAmovement

Stopcodon

NewPeptidebond

Anticodon

Aminoacid

A site

Figure 10.14

1 Codon recognition

2 Peptide bondformation

3 Translocation


10.15 Review: The flow of genetic information in the cell is DNARNAprotein

– Sequence of bases in DNA

sequence of codons in mRNA

primary structure of a polypeptide

DNA mRNA tRNA amino acids protein


Genetic information: DNA to RNA to protein

Sequence of codons primary structure of protein


Polypeptide

Transfer RNAs

tRNA anticodons

mRNA codons

Peptide bonds join amino acids into a polypeptide

Sequence of amino acids determines 3-D shape of protein


Polypeptide

TranscriptionDNA

mRNA

RNApolymerase

Amino acid Translation

tRNA

Enzyme

Anticodon

ATP

InitiatortRNA

Largeribosomalsubunit

Start Codon

Codons

mRNA

Stop codon

Smallribosomalsubunit

Growingpolypeptide

New peptidebond forming

mRNA

Figure 10.15

Summary of transcription and translation

mRNA is transcribed from a DNA template.1

Each amino acidattaches to its propertRNA with the help of aspecific enzyme and ATP.

2

Initiation ofpolypeptide synthesisThe mRNA, the first tRNA,and the ribosomal subunits come together.

3

Elongation4A succession of tRNAsadd their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time.

5The ribosome recognizes a stop codon. The poly-peptide is terminated and released.

Termination


10.16 Mutations can change the meaning of genes

• Mutations are changes in the DNA base sequence

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

C T T C A T

Normal hemoglobin

Mutant hemoglobin DNA

G A A G U A

Sickle-cell hemoglobin

Normal hemoglobin DNA

Glu Val

mRNA mRNA

Figure 10.16A


• Substituting, inserting, or deleting nucleotides alters a gene

– With varying effects on the organismNormal gene

mRNA

Base substitution

Base deletion Missing

Met Lys Phe Gly Ala

Met Lys Phe Ser Ala

Met Lys Leu Ala His

A U G A A G U U U G G C G C A

A U G A A G U U U A G C G C A

A U G A A G U U G G C G C A U

U

Protein

Figure 10.16B


– Substituting, inserting, or deleting nucleotides alters a gene

– With varying effects on the organismNormal gene

mRNA

Base substitution

Base deletion Missing

Met Lys Phe Gly Ala

Met Lys Phe Ser Ala

Met Lys Leu Ala His

A U G A A G U U U G G C G C A

A U G A A G U U U A G C G C A

A U G A A G U U G G C G C A U

U

Protein

Figure 10.16B

10.16 Mutations change the words in the code

Normal amino acid sequence

Point mutation = one base changed one amino acid changed

Frame shift = one base deleted all following codons are altered


Ch. 11- What turns genes ON and OFF?In bacteria, control genes are next to code genes

Lac operon – gene is OFF when lactose absent

- ON when lactose presentRepressor protein on DNA blocks RNA polymerase - Lactose removes repressor transcription


The lac operon


The trp Operon – for tryptophan• Tryptophan keeps gene turned off

• When tryptophan is low, gene turns onPromoter

DNA

Activerepressor

Inactiverepressor

Lactose

Activerepressor

Tryptophan

Inactiverepressor

lac operon trp operon

Operator Genes

Figure 11.1C


Ch. 11 Gene Control in EukaryotesControl genes are NOT near code genes

- may be on different chromosomes

Many proteins interact to help mRNA form

• Transcription Factors


Eukaryotic Gene Regulation


DNA packing helps regulate gene expression

DNA has to unwind from histones to be transcribed

DNA doublehelix (2-nm

diameter)

Histones

Linker“Beads ona string”

Nucleosome(10-nm diameter)

Tight helical fiber(30-nm diameter)

Supercoil(300-nm diameter)

Metaphase chromosome

700nm

TEM

TEM

Figure 11.4

Variety of regulatory proteins interact with DNA

and with each other

11.4 Control in Eukaryotes


Coding genes and regulatory genes are NOT located together on chromosomes

Complex signaling and interaction in cell

Transcription Factors

Enhancers

Groups of genes, often on different chromosome

honors bio - chapter 10

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