Download Saboteurs Inside Our Cells

Saboteurs Inside Our Cells
• The invasion and damage of
cells by the herpesvirus can
be compared to the actions
of a saboteur intent on
taking over a factory
– The herpesvirus hijacks the
host cell’s molecules and
organelles to produce new
copies of the virus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Viruses provided
some of the earliest
evidence that genes
are made of DNA
• Molecular biology
studies how DNA
serves as the
molecular basis of
heredity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
1
THE STRUCTURE OF THE GENETIC
MATERIAL
10.1 Experiments showed that DNA is the genetic
material
• The Hershey-Chase
experiment showed
that certain viruses
reprogram host
cells to produce
more viruses by
injecting their DNA
Head
DNA
Tail
Tail
fiber
Figure 10.1A
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• The Hershey-Chase Experiment
1
Mix radioactively
labeled phages with
bacteria. The phages
infect the bacterial
cells.
Phage
2
Agitate in a blender
to separate phages
outside the bacteria
from the cells and
their contents.
Radioactive
protein
Bacterium
DNA
3
Centrifuge the mixture
so bacteria form a
pellet at the bottom of
the test tube.
4
Empty
protein shell
Measure the
radioactivity in
the pellet and
liquid.
Radioactivity
in liquid
Phage
DNA
Batch 1
Radioactive
protein
Centrifuge
Pellet
Batch 2
Radioactive
DNA
Radioactive
DNA
Figure 10.1B
Centrifuge
Pellet
Radioactivity
in pellet
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• Phage reproductive cycle
Phage attaches
to bacterial cell.
Phage injects
DNA.
Phage DNA directs host
cell to make more phage
DNA and protein parts.
New phages assemble.
Cell lyses and releases
new phages.
Figure 10.1C
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10.2 DNA and RNA are polymers of nucleotides
• DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
Figure 10.2A
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3
• DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Adenine (A)
Pyrimidines
Guanine (G)
Purines
Figure 10.2B
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• RNA is also a nucleic acid
– RNA has a slightly different sugar
– RNA has U instead of T
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
Figure 10.2C, D
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4
10.3 DNA is a double-stranded helix
• James Watson and Francis Crick worked out
the three-dimensional structure of DNA, based
on work by Rosalind Franklin
Figure 10.3A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The structure of DNA consists of two
polynucleotide strands wrapped around each
other in a double helix
1 chocolate coat,
Blind (PRA)
Figure 10.3C
Twist
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• Hydrogen bonds between bases hold the
strands together
– Each base pairs with a complementary partner
– A pairs with T
– G pairs with C
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• Three representations of DNA
Hydrogen bond
Ribbon model
Partial chemical structure
Computer model
Figure 10.3D
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DNA REPLICATION
10.4 DNA replication depends on specific base
pairing
• In DNA replication, the strands separate
– Enzymes use each strand as a template to
assemble the new strands
A
A
Nucleotides
Parental molecule
of DNA
Both parental strands serve
as templates
Two identical daughter
molecules of DNA
Figure 10.4A
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THE FLOW OF GENETIC INFORMATION
FROM 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 bases
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• A specific gene specifies a polypeptide
– The DNA is transcribed into RNA, which is
translated into the polypeptide
DNA
TRANSCRIPTION
RNA
TRANSLATION
Protein
Figure 10.6A
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10.7 Genetic information written in codons is
translated into amino acid sequences
• The “words” of the DNA “language” are triplets
of bases called codons
– The codons in a gene specify the amino acid
sequence of a polypeptide
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Gene 1
Gene 3
DNA molecule
Gene 2
DNA strand
TRANSCRIPTION
RNA
Codon
TRANSLATION
Polypeptide
Figure 10.7
Amino acid
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10.8 The genetic code is the Rosetta stone of life
• Virtually all
organisms
share the same
genetic code
Figure 10.8A
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• An exercise in translating the genetic code
Transcribed strand
DNA
Transcription
RNA
Start
codon
Translation
Polypeptide
Stop
codon
Figure 10.8B
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10.9 Transcription produces genetic messages in
the form of RNA
RNA
polymerase
RNA nucleotide
Direction of
transcription
Figure 10.9A
Newly made RNA
Template
strand of DNA
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10
RNA polymerase
• In transcription, the
DNA helix unzips
– RNA nucleotides line
up along one strand
of the DNA following
the base pairing rules
– The single-stranded
messenger RNA peels
away and the DNA
strands rejoin
DNA of gene
Promoter
DNA
Terminator
DNA
Initiation
Elongation
Area shown
in Figure 10.9A
Termination
Growing
RNA
Completed RNA
RNA
polymerase
Figure 10.9B
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10.11 Transfer RNA molecules serve as
interpreters during translation
• In the cytoplasm, a
ribosome attaches
to the mRNA and
translates its
message into a
polypeptide
• The process is aided
by transfer RNAs
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Figure 10.11A
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• Each tRNA molecule has a triplet anticodon on
one end and an amino acid attachment site on
the other
Amino acid
attachment
site
Anticodon
Figure 10.11B, C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.12 Ribosomes build polypeptides
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
molecules
P site
A site
Growing
polypeptide
Large
subunit
tRNA
P
mRNA
binding
site
A
mRNA
Codons
mRNA
Small
subunit
Figure 10.12A-C
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10.13 An initiation codon marks the start of an
mRNA message
Start of genetic message
End
Figure 10.13A
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• mRNA, a specific tRNA, and the ribosome
subunits assemble during initiation
Large
Ribosomal
subunit
Initiator tRNA
P site
A site
Start
codon
mRNA
Small ribosomal
subunit
1
2
Figure 10.13B
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10.14 Elongation adds amino acids to the
polypeptide chain until a stop codon
terminates translation
• The mRNA moves a codon at a time relative to
the ribosome
– A tRNA pairs with each codon, adding an amino
acid to the growing polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Amino acid
Polypeptide
A
site
P site
Anticodon
mRNA
1
Codon recognition
mRNA
movement
Stop
codon
New
peptide
bond
Figure 10.14
3
2
Peptide bond
formation
Translocation
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10.15 Review: The flow of genetic information in
the cell is DNA→RNA→protein
• The sequence of codons in DNA spells out the
primary structure of a polypeptide
– Polypeptides form proteins that cells and
organisms use
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Summary of
transcription
and
translation
TRANSCRIPTION
DNA
mRNA
RNA
polymerase
Stage 1 mRNA is
transcribed from a
DNA template.
Amino acid
TRANSLATION
Enzyme
Stage 2 Each amino
acid attaches to its
proper tRNA with the
help of a specific
enzyme and ATP.
tRNA
Initiator
tRNA
mRNA
Anticodon
Large
ribosomal
subunit
Start
Codon
Small
ribosomal
subunit
Stage 3 Initiation of
polypeptide synthesis
The mRNA, the first
tRNA, and the
ribosomal subunits
come together.
Figure 10.15
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New
peptide
bond
forming
Growing
polypeptide
Codons
Stage 4 Elongation
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.
mRNA
Polypeptide
Stop Codon
Stage 5 Termination
The ribosome recognizes
a stop codon. The polypeptide is terminated and
released.
Figure 10.15 (continued)
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10.16 Mutations can change the meaning of genes
• Mutations are changes in the DNA base
sequence
– These are caused by errors in DNA replication
or by mutagens
– The change of a single DNA nucleotide causes
sickle-cell disease
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Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
Figure 10.16A
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• Types of mutations
NORMAL GENE
mRNA
Protein
Met
Lys
Phe
Gly
Ala
Lys
Phe
Ser
Ala
BASE SUBSTITUTION
Met
Missing
BASE DELETION
Met
Lys
Leu
Ala
His
Figure 10.16B
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10.21 The AIDS virus makes DNA on an RNA
template
• HIV is a retrovirus
Glycoprotein
Envelope
Protein
coat
RNA
(two identical
strands)
Reverse
transcriptase
Figure 10.21A
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10.22 Virus research and molecular genetics are
intertwined
• Virus studies help
establish molecular
genetics
• Molecular genetics helps
us understand viruses
– such as HIV, seen here
attacking a white blood
cell
Figure 10.22
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