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”

Flow of genetic information in a cell

How do we move information from DNA to proteins?
DNA
RNA
protein
DNA gets
all the glory,
but proteins do
all the work!
AP Biology
trait
Metabolism taught us about genes

Inheritance of metabolic diseases
suggested that genes coded for enzymes
 each disease (phenotype) is caused by
non-functional gene product





lack of an enzyme
Tay sachs
PKU (phenylketonuria)
albinism
metabolic pathway
A

AP Biology enzyme 1
Am I just the
sum of my proteins?
disease
disease
disease
disease
B
C
D
E

enzyme 2

enzyme 3

enzyme 4
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"
Beadle & Tatum
X rays or ultraviolet light
Wild-type
Neurospora
create mutations
asexual
spores
Minimal
medium
spores
Growth on
complete
medium
positive control
Select one of
the spores
Test on minimal
medium to confirm
presence of mutation
negative control
Grow on
complete medium
Minimal media supplemented only with…
experimentals
Choline
Pyridoxine
Riboflavin
Minimal
Nucleic
Arginine
control
amino acid p-Amino
Niacin
Inositol acid Folic
supplements
acid
Thiamine
benzoic acid
AP Biology
a
a
From gene to protein
nucleus
cytoplasm
a
a
DNA
mRNA
a
a
a
a
a
a
a
a
a
a
a
protein
a
a
a
a
a
a
a
trait
AP Biology
Transcription
from
DNA nucleic acid language
to
RNA nucleic acid language
AP Biology
2007-2008
RNA


ribose sugar
N-bases
____________________
 ____________________
 ____________________



____________________
lots of RNAs

DNA
AP Biology
mRNA, tRNA, rRNA, siRNA…
transcription
RNA
Transcription

Making mRNA


transcribed DNA strand = ___________________
untranscribed DNA strand = ________________


synthesis of complementary RNA strand


same sequence as RNA
transcription bubble
enzyme

__________________________
5
C
DNA
G
3
A
G
T
A T C
T A
53
G
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
AP Biology
build
RNA
coding strand
5
RNA polymerase
template strand
RNA polymerases

3 RNA polymerase enzymes

RNA polymerase 1



______________________


AP Biology
transcribes genes into mRNA
RNA polymerase 3


only transcribes rRNA genes
makes ribosomes
only transcribes tRNA genes
each has a specific promoter sequence
it recognizes
Which gene is read?

________________________
binding site before beginning of gene
 __________________________________
 binding site for RNA polymerase
& transcription
factors


________________________

binding site far
upstream of gene
turns transcription
on HIGH
AP Biology

Transcription Factors

Initiation complex

___________________________________________




AP Biology
suite of proteins which bind to DNA
hormones?
turn on or off transcription
trigger the binding of RNA polymerase to DNA
Matching bases of DNA & RNA

Match RNA bases to DNA
bases on one of the DNA
strands
A
G
C
A
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
Eukaryotic genes have junk!

Eukaryotic genes are not continuous

___________ = the real gene


expressed / coding DNA
introns
come out!
___________ = the junk

inbetween sequence
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence
AP Biology
mRNA splicing

Post-transcriptional processing

eukaryotic mRNA needs work after transcription
______________________________

______________________________

edit out introns
______________________________


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
Discovery of exons/introns
Richard
Roberts
CSHL
Philip
Sharp
MIT
beta-thalassemia
AP Biology
1977 | 1993
adenovirus
common cold
Splicing must be accurate

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|
Whoa! I think
we just broke
a biological “rule”!
RNA splicing enzymes


_________________

________________

proteins
snRNPs
snRNA
intron
exon
exon
5'
_________________


several snRNPs
recognize splice
site sequence

spliceosome
5'
3'
cut & paste gene
No,
not smurfs!
“snurps”
AP Biology
3'
mature mRNA
lariat
5'
exon
5'
3'
exon
3'
excised
intron
Alternative splicing

_______________________________________


when is an intron not an intron…
different segments treated as exons
Starting to get
hard to
define a gene!
AP Biology
More post-transcriptional processing

Need to protect mRNA on its trip from
nucleus to cytoplasm

enzymes in cytoplasm attack mRNA

protect the ends of the molecule
________________________________

________________________________

3'
mRNA
5'
AP Biology
P
G P
P
A
a
a
From gene to protein
nucleus
cytoplasm
transcription
DNA
a
a
translation
mRNA
a
a
a
a
a
a
a
a
a
a
a
protein
a
a
a
a
a
a
a
ribosome
trait
AP Biology
Translation
from
nucleic acid language
to
amino acid language
AP Biology
2007-2008
How does mRNA code for proteins?
DNA
TACGCACATTTACGTACGCGG
4 ATCG
mRNA
4 AUCG
protein
AUGCGUGUAAAUGCAUGCGCC
?
Met Arg Val Asn Ala Cys Ala
20
AP Biology
How can you code for 20 amino acids
with only 4 nucleotide bases (A,U,G,C)?
mRNA codes for proteins in triplets
DNA
TACGCACATTTACGTACGCGG
codon
mRNA
AUGCGUGUAAAUGCAUGCGCC
?
protein
AP Biology
Met Arg Val Asn Ala Cys Ala
Cracking the code

1960 | 1968
Nirenberg & Khorana
Crick

determined 3-letter (triplet) codon system
WHYDIDTHEREDBATEATTHEFATRAT

Nirenberg (47) & Khorana (17)
determined mRNA–amino acid match
 added fabricated mRNA to test tube of
ribosomes, tRNA & amino acids



AP Biology
created artificial UUUUU… mRNA
found that UUU coded for phenylalanine
Marshall Nirenberg
1960 | 1968
Har Khorana
AP Biology
The code

Code for ALL life!


Code is redundant



several codons for
each amino acid
3rd base “wobble”
_______________



strongest support for
a common origin for
all life
AUG
methionine
_______________

AP Biology
UGA, UAA, UAG
How are the codons matched to
amino acids?
DNA
mRNA
3
5
5
3
TACGCACATTTACGTACGCGG
AUGCGUGUAAAUGCAUGCGCC
3
UAC
tRNA
amino
acid
AP Biology
Met
codon
5
GCA
Arg
CAU
Val
anti-codon
a
a
From gene to protein
nucleus
cytoplasm
transcription
DNA
a
a
translation
mRNA
a
a
a
a
a
a
a
a
a
a
a
protein
a
a
a
a
a
a
a
ribosome
aa
trait
AP Biology
Transfer RNA structure

“Clover leaf” structure
anticodon on “clover leaf” end
 amino acid attached on 3 end

AP Biology
Loading tRNA

__________________________________________


enzyme which bonds amino acid to tRNA
bond requires energy



ATP  AMP
bond is unstable
so it can release amino acid at ribosome easily
Trp C=O
OH
OH
Trp C=O
O
Trp
H2O
O
activating
enzyme
tRNATrp
anticodon
AP Biology
tryptophan attached
to tRNATrp
AC C
UGG
mRNA
tRNATrp binds to UGG
condon of mRNA
Ribosomes

Facilitate coupling of
tRNA anticodon to
mRNA codon


organelle or enzyme?
Structure
_____________________________
 _________________

AP Biology

_____________

_____________
E P A
Ribosomes

____________ (aminoacyl-tRNA site)


____________ (peptidyl-tRNA site)


holds tRNA carrying next amino acid to
be added to chain
holds tRNA carrying growing
polypeptide chain
Met
____________ (exit site)

AP Biology
empty tRNA
leaves ribosome
from exit site
U A C
A U G
5'
E
P
A
3'
Building a polypeptide

Initiation


Elongation


brings together mRNA, ribosome
subunits, initiator tRNA
adding amino acids based on
codon sequence
Termination

3 2 1
end codon
Leu
Val
Met
Met
Met
Met Leu
Ala
Leu
Leu
release
factor
Ser
Trp
tRNA
U AC
5'
C UGAA U
mRNA A U G
3'
E P A
AP Biology
5'
UAC GAC
A U G C U GAA U
5'
3'
U A C GA C
A U G C U G AAU
5'
3'
U AC G A C
AA U
AU G C U G
3'
A CC
U GG U A A
3'
Destinations:
Protein targeting



______________________

_____________________




start of a secretory pathway
AP Biology

secretion
nucleus
mitochondria
chloroplasts
cell membrane
cytoplasm
etc…
Can you tell
the story?
AP Biology
The Transcriptional unit
enhancer
exons
1000+b 20-30b
3'
TAC
transcriptional unit
5'
DNA
ACT
introns
5'
3'
5'
AP Biology
3'
Bacterial chromosome
Proteion
Synthesis in
Prokaryotes
Transcription
mRNA
Psssst…
no nucleus!
Cell
membrane
Cell wall
AP Biology
2007-2008
Prokaryote vs. Eukaryote genes

Prokaryotes
Eukaryotes
________________
_

 ________________
_
________________
_

 ________________
introns
_
come out!
________________
intron = noncoding (inbetween)
sequence
_
eukaryotic
 ________________
DNA
 ________________
_exon = coding (expressed) sequence
_

AP Biology
________________
_
________________
_
________________
_
________________
_


Translation in Prokaryotes

Transcription & translation are simultaneous
in bacteria
DNA is in
cytoplasm
 no mRNA
editing
 ribosomes
read mRNA
as it is being
transcribed

AP Biology
Translation: prokaryotes vs. eukaryotes

Differences between prokaryotes &
eukaryotes

time & physical separation between
processes


AP Biology
takes eukaryote ~1 hour
from DNA to protein
RNA processing
Any Questions??
What color would a smurf turn
if he held his breath?
AP Biology
2007-2008