Download Chapter 17.

From Gene
to Protein
How Genes
Work
AP Biology
2007-2008
What do genes code for?

How does DNA code for cells & bodies?

how are cells and bodies made from the
instructions in DNA
DNA
AP Biology
proteins
cells
bodies
The “Central Dogma”
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Flow of genetic information in a cell

How do we move information from DNA to proteins?
DNA
AP Biology
RNA
protein
trait
1941 | 1958
Beadle & Tatum
one gene : one enzyme hypothesis
George Beadle
Edward Tatum
AP Biology
"for their discovery that genes act by
regulating definite chemical events"
a
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From gene to protein
nucleus
cytoplasm
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DNA
mRNA
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protein
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trait
AP Biology
Transcription
from
DNA language
to
RNA language
AP Biology
2007-2008
RNA


ribose sugar
N-bases
____________________
 ____________________
 ____________________
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____________________
lots of RNAs

DNA
AP Biology
mRNA, tRNA, rRNA, siRNA…
transcription
RNA
Transcription
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Making mRNA
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transcribed DNA strand = ___________________
enzyme
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__________________________
5
C
DNA
G
3
A
G
T
A T C
T A
53
A G C
A
T
C G T
A
C
T
3
G C A U C G U
C
G T A G C A
T
T
A
C
A G
C T
G
A
T
A
T
3
5
unwinding
rewinding
mRNA
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build
RNA
G
5
RNA polymerase
template strand
Initiation

________________________
binding site before beginning of gene
 __________________________________
 binding site for RNA polymerase

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Elongation
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Match RNA bases to DNA
bases on one of the DNA
strands
A
G
C
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G
G
U
U
C
A
AG
U
C
G
A
U
A
C
5'
RNA
A C C polymerase G
A
U
3'
T G G T A C A G C T A G T C A T CG T A C CG T
AP Biology
U
C
Termination

Eventually the RNA transcript is
released and the polymerase detaches
(complete mechanism still not fully
known)
AP Biology
Eukaryotic genes have junk!

Eukaryotic genes are not continuous
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___________ = the real gene

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expressed / coding DNA
___________ = the junk
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inbetween sequence
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence
AP Biology
mRNA splicing
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Post-transcriptional processing

eukaryotic mRNA needs work after transcription
______________________________
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______________________________
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edit out introns
______________________________
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intron = noncoding (inbetween) sequence
~10,000 base
eukaryotic DNA
exon = coding (expressed) sequence
pre-mRNA
primary mRNA
transcript
AP Biology
mature mRNA
transcript
~1,000 base
spliced mRNA
Splicing must be accurate
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No room for mistakes!

a single base added or lost throws off the
_______________________
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGUCCGAUAAGGGCCAU
AUG|CGG|UCC|GAU|AAG|GGC|CAU
Met|Arg|Ser|Asp|Lys|Gly|His
AP Biology
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGGUCCGAUAAGGGCCAU
AUG|CGG|GUC|CGA|UAA|GGG|CCA|U
Met|Arg|Val|Arg|STOP|
RNA splicing enzymes
snRNPs
snRNA
intron
exon
exon
5'
3'
spliceosome
5'
3'
lariat
5'
mature mRNA
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exon
5'
3'
exon
3'
excised
intron
Alternative splicing

_______________________________________

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AP Biology
when is an intron not an intron…
different segments treated as exons
More post-transcriptional processing

Need to protect mRNA on its trip from
nucleus to cytoplasm

enzymes in cytoplasm attack mRNA
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protect the ends of the molecule
________________________________
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________________________________
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3'
mRNA
5'
AP Biology
P
G P
P
A
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From gene to protein
nucleus
cytoplasm
transcription
DNA
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translation
mRNA
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protein
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a
ribosome
trait
AP Biology