Download L06 - Biochemistry III

DNA Replication
• When a cell or organism reproduces, a complete set
of genetic instructions must pass from one
generation to the next
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Watson and
Crick’s model
for DNA
suggested
that DNA
replicated by
a template
mechanism
Parental (old)
DNA molecule
Daughter
(new) strand
Daughter
DNA molecule
(double helices)
Figure 10.6
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THE FLOW OF GENETIC INFORMATION
FROM DNA TO RNA TO PROTEIN
• DNA functions as the inherited directions for a cell
or organism
– How are these directions carried out?
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How an Organism’s DNA Genotype Produces Its
Phenotype
• An organism’s genotype, its genetic makeup is the
sequence of nucleotide bases in DNA
– The phenotype is the organism’s specific traits
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• What is the
language of
nucleic acids?
– In DNA, it is
the linear
sequence of
nucleotide
bases
DNA molecule
Gene 1
Gene 2
Gene 3
DNA strand
Transcription
RNA
Translation
Codon
Polypeptide
Amino acid
Figure 10.10
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• DNA specifies
the synthesis of
proteins in two
stages
Nucleus
DNA
Transcription
RNA
– Transcription
– Translation
Translation
Protein
Cytoplasm
Figure 10.9
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• When DNA is transcribed, the result is an RNA
molecule
• RNA is then translated into a sequence of amino
acids in a polypeptide
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Transcription: From DNA to RNA
• In transcription
– Genetic information is transferred from DNA to
RNA
– An RNA molecule is transcribed from a DNA
template
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
RNA nucleotides
RNA
polymerase
Newly made
RNA
Direction of
transcription
Template
strand of DNA
(a) A close-up view of transcription
Figure 10.13a
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Transcription
of an entire
gene
RNA polymerase
DNA of gene
Promoter
DNA
Initiation
RNA
Elongation
Terminator
DNA
Area shown
in part (a)
Termination
Growing
RNA
Completed RNA
(b) Transcription of a gene
RNA
polymerase
Figure 10.13b
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• RNA processing
includes
DNA
Cap
– Adding a cap
and tail
– Removing
introns
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Tail
Introns removed
Exons spliced together
mRNA
– Splicing exons
together
Coding sequence
Nucleus
Cytoplasm
Figure 10.14
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Transcription and translation
– Are the processes whereby genes control the
structures and activities of cells
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• Triplets of bases
– Specify all the amino acids
– Are called codons
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The Genetic Code
• The genetic code is the set of rules relating
nucleotide sequence to amino acid sequence
Figure 10.11
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• The genetic code is
shared by all
organisms
Figure 10.12
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Translation: The Players
• Translation
– Is the conversion from the nucleic acid language to
the protein language
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Messenger RNA (mRNA)
• mRNA
– Is the first ingredient for translation
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• An mRNA molecule has a cap and tail that help it
bind to the ribosome
Start of genetic message
Cap
End
Tail
Figure 10.17
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Transfer RNA (tRNA)
• tRNA
– Acts as a
molecular
interpreter
– Carries amino
acids
– Matches amino
acids with codons
in mRNA using
anticodons
Amino acid attachment site
Hydrogen bond
RNA
polynucleotide
chain
Anticodon
Anticodon
Figure 10.15
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• A fully
assembled
ribosome holds
tRNA and
mRNA for use
in translation
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNA
(b)
Figure 10.16b
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• The process
of elongation
Amino acid
Polypeptide
P site
Anticodon
mRNA
A site
Codons
1 Codon recognition
Elongation
2 Peptide bond formation
New peptide
bond
mRNA
movement
3 Translocation
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.19
Mutations
• A mutation
– Is any change in the nucleotide sequence of DNA
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Glu
Sickle-cell hemoglobin
Val
Figure 10.21
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Mutagens
• Mutations may result from
– Errors in DNA replication
– Physical or chemical agents called mutagens
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• DNA can be damaged by ultraviolet light
– The enzymes and proteins involved in replication
can repair the damage
Figure 10.7
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
VIRUSES: GENES IN PACKAGES
• Viruses sit on the fence between life and nonlife
– They exhibit
some but not all
characteristics
of living
organisms
Figure 10.24
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Bacteriophages
• Bacteriophages, or phages
– Attack bacteria
Head
Tail
Tail fiber
DNA of virus
Bacterial
cell
Figure 10.25
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Plant Viruses
• Viruses that infect plants
– Can stunt growth
and diminish
plant yields
Protein
RNA
– Can spread
throughout the
entire plant
Figure 10.27
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Protein spike
VIRUS
Protein coat
Envelope
Viral RNA
(genome)
Plasma
membrane
of host cell
mRNA
1
Entry
2
Uncoating
3
RNA synthesis
by viral enzyme
4 Protein
synthesis
5 RNA synthesis
(other strand)
Template
New viral genome
6
Assembly
New viral proteins
Exit
7
Figure 10.29
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings
Signaling between biomolecules
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
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• Gene therapy
Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings