Honors Bio - Chapter 10
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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
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Viruses - infect cells
- Gave us some of the earliest evidence that genes are made of DNA
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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
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Live R (‘rough’) no diseaseLive S (‘smooth’) pneumonia
Mix Live R and dead S pneumonia
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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
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Griffith’s conclusionSomething from dead S cells transformed
living R cells into living S cells
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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?
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Only bacteria grown in DNAase did not transformConclusion: DNA is the transforming material
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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?
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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.
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Hershey-Chase ResultsPhage tagged with phosphorus bacterial cells became radioactive
Conclusion: phage DNA entered cells, but protein did not
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Bacteriophage
Virus Life Cycle
Figure 10.1A
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10.3 Finding the structure of DNA
Rosalind Franklin’s X-ray picture of DNA crystal shows double helix
Watson & Crick, 1953
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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
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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
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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
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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
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The structure of DNA
• Two polynucleotide strands double helix
Figure 10.3C Twist
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• 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
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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
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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
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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
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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’
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• 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
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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
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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
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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
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• 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
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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
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Transcription – writes DNA code onto mRNA
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• 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
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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”
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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
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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
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UUG
All organisms use the same code
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“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
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1. Ribosome attaches to mRNA
2. Transfer RNA (tRNA) brings amino acids to ribosome
How RNA helps
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• 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
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10.12 Ribosomes build polypeptides• Made of proteins and ribosomal RNA (rRNA)
tRNAmolecules
mRNA Small subunit
Growingpolypeptide
Largesubunit
Figure 10.12A
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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
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10.12 Ribosomes build polypeptides
TRANSLATION: decode message to make protein
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Translation1. Begins at “start” codon
2. Amino acids are set in sequence, according to the code on mRNA
3. Ends at “stop” codon
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10.13 A start (“initiation”) codon marks the start of an mRNA message
Start of genetic message
End
Figure 10.13A
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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
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Elongation
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Transcription
Translation
mRNA
Polypeptide
DNA
tRNA
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Polypeptide
P site
mRNA Codons
mRNAmovement
Stopcodon
NewPeptidebond
Anticodon
Aminoacid
A site
Figure 10.14
1 Codon recognition
2 Peptide bondformation
3 Translocation
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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
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Genetic information: DNA to RNA to protein
Sequence of codons primary structure of protein
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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
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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
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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
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• 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
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– 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
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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
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The lac operon
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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
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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
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Eukaryotic Gene Regulation
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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
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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
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