Transcript How Genes Work

How Genes Work

Genes on DNA are used to make RNA
 Transcription

RNA is used to make proteins
 Translation
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Information Flow

Transcription
 In

Translation
 In

the nucleus
the cytoplasm
Animation
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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RNA vs. DNA
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Both are linear
nucleotide polymers
RNA differs from DNA
 Single
stranded
 Ribose instead of
deoxyribose
 U base instead of T
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Three Types of RNA

Messenger RNA (mRNA)
 Encodes

Transfer RNA (tRNA)
 Aids

proteins
translation
Ribosomal RNA (rRNA)
 Used
to make ribosomes
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Transcription
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
DNA information is copied into RNA
Similar to replication with three differences:
 RNA polymerase
is used instead of DNA polymerase
 Only genes are transcribed not the entire genome
 RNA is made instead of DNA
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Transcription
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RNA polymerase starts at
promoter
Its complex unwinds DNA
It copies bases using
complimentary base
pairing (U v.s. T)
Moves down one strand
Stops at terminator
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Introns & Exons
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Eukaryotic cells have
non-coding regions in
genes (introns)
Removed after
transcription
Exons are connected
to produce the mature
mRNA
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The Genetic Code
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
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Translation of RNA
3 bases = 1 codon
1 codon = 1 amino
acid
© 2006 W.W. Norton & Company, Inc.
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The Genetic Code
Possible codons: 4 X 4 X 4 = 64
 20 possible amino acids
 Most amino acids have more than 1 codon
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 Degeneracy
of the code
 Why many mutations are silent (make no
protein change)
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Three codons code for no amino acid
 STOP
codons
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Translation
RNA sequence translated into protein
sequence
 Genetic code used like a dictionary
 Ribosome

 Holds
mRNA
 Links amino acids together
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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tRNA

Two binding sites:
 Amino
acid site
 Anticodon
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Amino Acid
Serine
Amino Acid
attachment
site
tRNA
Matches the Amino
acid with codon
Anticodon
Codon
mRNA
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Translation
Ribosome holds mRNA
 tRNA binds to first codon

 AUG
– start codon = methionine
Second tRNA binds to next codon
 Amino acids are linked
 Move to next codon
 Animation

© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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From Gene to Phenotype
Genes are inherited as DNA
 DNA is transcribed into RNA
 RNA is translated into protein
 Proteins give the organism traits

 Mutations
in DNA produce changes in traits
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Sickle Cell Anemia
Gene for hemoglobin
 One base pair
change
 Causes one amino
acid change
 Sickle Cell phenotype

© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Process Animation 13.1
The Flow of Genetic Information
in a Eukaryotic Cell
Macintosh
Windows
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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Process Animation 13.3
Translation
Macintosh
Windows
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
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