Download AP Details for Protein Synthesis

AP Details for Protein Synthesis
2014
From gene to protein
Transcription
from
DNA nucleic acid language
to
RNA nucleic acid language
AP Biology
Transcription
• Making mRNA
– transcribed DNA strand = template strand
– untranscribed DNA strand = coding strand
• same sequence as RNA
– synthesis of complementary RNA strand
• transcription bubble
– Enzyme involved
• RNA polymerase
5
DNA
C
G
3
A
G
T
A T C
T A
A
G C
rewinding
5
A
T
C
G
T
A
C
T
3
G
C
mRNA
build RNA 53
G
coding strand
C
A
U C
G
U
G
T
A
C
A
G
RNA polymerase
T
T
A
A
C
T
A G
C T
G
A
T
3
5
unwinding
template strand
RNA polymerases
• 3 RNA polymerase enzymes
– RNA polymerase 1
• only transcribes rRNA genes
• makes ribosomes
– RNA polymerase 2
• transcribes genes into mRNA
– RNA polymerase 3
• only transcribes tRNA genes
– each has a specific promoter sequence it
recognizes
Which gene is read?
• Promoter region
– binding site before beginning of gene
– TATA box binding site
– binding site for RNA polymerase
& transcription
factors
– Enhancer region
– binding site for
activators (activate
genes)
– Silence region
– Binding site for
repressors (turns genes
off)
What are Transcription Factors?
• Initiation complex
– transcription factors bind to promoter region
• suite of proteins which bind to DNA
• 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
U
A
G
G
U
U
C
A
A G
C
C
G
A
U
A
C
5'
RNA
A C C polymerase
A
U
U
3'
G
T G G T A C A G C T A G T C A T C G T A C C G T
C
Eukaryotic genes have junk!
• Eukaryotic genes are not continuous
– exons = the real gene
• expressed / coding DNA
introns
come out!
– introns = the junk
• inbetween sequence
intron = noncoding (inbetween) sequence
eukaryotic DNA
exon = coding (expressed) sequence
mRNA splicing
• Post-transcriptional processing
– eukaryotic mRNA needs work after transcription
– primary transcript = pre-mRNA
– mRNA splicing
• edit out introns
– make mature mRNA transcript
intron = noncoding (inbetween) sequence
~10,000 base
eukaryotic DNA
exon = coding (expressed) sequence
pre-mRNA
primary mRNA
transcript
mature mRNA
transcript
~1,000 base
spliced mRNA
Splicing must be accurate
• No room for mistakes!
– a single base added or lost throws off the reading
frame
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGUCCGAUAAGGGCCAU
AUG|CGG|UCC|GAU|AAG|GGC|CAU
Met|Arg|Ser|Asp|Lys|Gly|His
AUGCGGCTATGGGUCCGAUAAGGGCCAU
AUGCGGGUCCGAUAAGGGCCAU
AUG|CGG|GUC|CGA|UAA|GGG|CCA|U
Met|Arg|Val|Arg|STOP|
RNA splicing enzymes
• snRNPs
– small nuclear RNA
• Spliceosome
snRNPs
snRNA
intron
exon
– several snRNPs 5'
– recognize splice site
sequence
• cut & paste gene
exon
3'
spliceosome
5'
3'
lariat
No,
not smurfs!
“snurps”
mature mRNA
5'
exon
5'
3'
exon
3'
excised
intron
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
• add 5 GTP cap
– Chemically modified molecule of GTP
– It facilitates the binding of mRNA to the ribosome and protects the mRNA
from being digested by ribonucleases – enzymes in cytoplasm that break
down RNA
• add 3’poly-A tail
– longer tail – 100-300 adenine nucleotides
– Assists in export of mRNA from nucleus
– Important in mRNA stability
3'
mRNA
5'
P P
G P
A
Translation
from
nucleic acid language
to
amino acid language
Radjewski
The code
• Code for ALL life!
– strongest support for a
common origin for all life
• Code is redundant
– several codons for each
amino acid
– 3rd base “wobble”

Start codon



AUG
methionine
Stop codons

UGA, UAA, UAG
Transfer RNA structure
• “Clover leaf” structure
– anticodon on “clover leaf” end
– amino acid attached on 3 end
Loading tRNA
• Aminoacyl tRNA synthetase
– 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
tryptophan attached
to tRNATrp
AC C
UGG
mRNA
tRNATrp binds to UGG
condon of mRNA
Building a polypeptide
• Initiation
– brings together mRNA, ribosome
subunits, initiator tRNA
• Elongation
– 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
5'
mRNA
UAC
AA U
A UGC UG
3'
E
P
A
5'
UA C G A C
A UG C U GA AU
5'
3'
U A C GA C
A U G C U G AA U
3'
5'
U A C G A CG A A U
AUG C U
3'
ACC
U GG UA A
3'
Protein targeting
• Signal peptide
– address label
Destinations:
secretion
nucleus
mitochondria
chloroplasts
cell membrane
cytoplasm
etc…
RNA polymerase
DNA
Can you tell the
story?
amino
acids
exon
intron
tRNA
pre-mRNA
5' GTP cap
mature mRNA
poly-A tail
large ribosomal subunit
aminoacyl tRNA
synthetase
3'
polypeptide
5'
small ribosomal subunit
tRNA
E P A
ribosome
Bacterial chromosome
Protein
Synthesis in
Prokaryotes
Transcription
mRNA
Psssst…
no nucleus!
Cell
membrane
Cell wall
AP Biology
Prokaryote vs. Eukaryote genes
• Prokaryotes
• Eukaryotes
– DNA in cytoplasm
– circular chromosome
– naked DNA
– no introns
– DNA in nucleus
– linear chromosomes
– DNA wound on histone
proteins
– introns vs. exons
introns
come out!
intron = noncoding (inbetween) sequence
eukaryotic
DNA
exon = coding (expressed) sequence
Translation in Prokaryotes
• Transcription & translation are simultaneous in
bacteria
– DNA is in
cytoplasm
– no mRNA
editing
– ribosomes
read mRNA
as it is being
transcribed
Translation: prokaryotes vs. eukaryotes
• Differences between prokaryotes &
eukaryotes
– time & physical separation between processes
• takes eukaryote ~1 hour
from DNA to protein
– no RNA processing
Any Questions??
What color would a smurf turn
if he held his breath?
AP Biology