Transcript The Body in Motion

Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 12
Gene Expression
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Early evidence indicating most
genes specify the structure of
proteins
• Garrod’s work on inborn errors of
metabolism in early 1900s
• Beadle and Tatum’s work with
Neurospora mutants in the 1940s
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 12 Gene Expression
An
“inborn error
of
metabolism”
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Mutations
affecting
biochemical
pathways
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Information flow from DNA to
protein
• Transcription
–RNA molecule complementary to the
template DNA strand synthesized
• Translation
–Polypeptide chain specified by messenger
RNA (mRNA) is synthesized
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Nucleotide
structure of
RNA
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Overview of transcription and translation
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Structure of RNA
• RNA
–Formed from nucleotide subunits
–Each nucleotide subunit contains ribose, a
base, and three phosphates
–Like DNA, RNA subunits are covalently
joined by a 5΄—3΄ linkage to form
alternating sugar-phosphate backbone
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Transcription
• Incoming nucleotides with three
phosphates pair with complementary
bases on the DNA strand
• RNA polymerase cleaves two
phosphates from each nucleotide and
covalently links the remaining
phosphate to the 3΄end of the RNA
chain
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 12 Gene Expression
Transcription
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 12 Gene Expression
Synthesis of mRNA
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Translation
• Polypeptide chain specified by the
mRNA is synthesized
–Initiation
–Repeating cycles of elongation
–Termination
• Each sequence of three nucleotide
bases in the mRNA constitutes a codon
• Requires tRNAs and cell machinery,
including ribosomes
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Three representations of a tRNA molecule
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Ribosome
structure
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Initiation of translation in bacteria
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Elongation cycle in translation
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Termination of translation
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Coupled transcription and
translation in bacteria
• Unlike eukaryotic cells, in bacterial cells
translation and transcription coupled
• Translation of the bacterial mRNA
molecule usually begins before the 3´ end
of the transcript is completed
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Coupled
transcription
and translation in
bacteria
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Retroviruses
• Flow of genetic information is reversed
by reverse transcriptase
–Enzyme associated with retroviruses
–Retroviruses synthesize DNA from an RNA
template
–Example of retrovirus is HIV-1, AIDS virus
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Infection cycle of an RNA tumor virus
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Mutations
• Base substitution mutations
–Often result from errors in base pairing
during replication
–Missense mutations
–Nonsense mutations
• Frameshift mutations
–One or two nucleotide pairs are inserted
into or deleted from the molecule
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
• Some mutations involve larger
DNA segments
• Due to change in chromosome structure
• Wide range of effects as they involve
many genes
–DNA sequences that “jump” into the middle
of a gene
–Known as transposons or transposable
genetic elements
–Most are retrotransposons
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Biology, Seventh Edition
CHAPTER 12 Gene Expression
Mutations
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