AP Biology 2007-2008

From Gene to Protein

How Genes Work

AP Biology

mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

ribosome

trait

proteintranslation

AP Biology 2007-2008

Translation

fromnucleic acid language

toamino acid language

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How does mRNA code for proteins?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

Met Arg Val Asn Ala Cys Alaprotein

?

How can you code for 20 amino acids with only 4 nucleotide bases (A,U,G,C)?

4

4

20

ATCG

AUCG

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AUGCGUGUAAAUGCAUGCGCCmRNA

mRNA codes for proteins in triplets

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

Met Arg Val Asn Ala Cys Alaprotein

?

codon

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Cracking the code1960 | 1968

Crick determined 3-letter (triplet) codon system

WHYDIDTHEREDBATEATTHEFATRATWHYDIDTHEREDBATEATTHEFATRAT

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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

Why is thewobble good?

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How are the codons matched to amino acids?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

aminoacid

tRNA anti-codon

codon

5 3

3 5

3 5

UAC

MetGCA

ArgCAU

Val

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mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

ribosome

traitaa

proteintranslation

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Transfer RNA structure “Clover leaf” structure

anticodon on “clover leaf” end amino acid attached on 3 end

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Loading tRNA Aminoacyl tRNA synthetase (don’t need to know

name) enzyme which bonds amino acid to tRNA bond requires energy

ATP AMP bond is unstable so it can release amino acid at ribosome easily

activatingenzyme

anticodontRNATrp binds to UGG

condon of mRNA

Trp Trp Trp

mRNAA C CU GG

C=O

OHOH

H2OO

tRNATrp

tryptophan attached to tRNATrp

C=O

O

C=O

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Ribosomes Facilitate coupling of

tRNA anticodon to mRNA codon

Structure ribosomal RNA (rRNA) & proteins 2 subunits

large small E P A

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Ribosomes

Met

5'

3'

UUA C

A G

APE

A site (aminoacyl-tRNA site) holds tRNA carrying next amino acid to

be added to chain P site (peptidyl-tRNA site)

holds tRNA carrying growing polypeptide chain

E site (exit site) empty tRNA

leaves ribosome from exit site

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Building a polypeptide Initiation

brings together mRNA, ribosome subunits, initiator tRNA

Elongation adding amino acids based on

codon sequence

Termination end codon 123

Leu

Leu Leu Leu

tRNA

Met MetMet Met

PE AmRNA5' 5' 5' 5'

3' 3' 3'3'

U UA AAACC

CAU UG G

GUU

A AAAC

CC

AU UG GGU

UA

AAAC

CC

AU UG GGU U

A AACCA U UG G

G AC

ValSer

AlaTrp

releasefactor

AA A

CCU UGG 3'

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Translation

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Can you tell the story?

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Can you tell the story?

DNA

pre-mRNA

ribosome

tRNA

aminoacids

polypeptide

mature mRNA

5' GTP cap

poly-A tail

large ribosomal subunit

small ribosomal subunit

aminoacyl tRNAsynthetase

E P A

5'

3'

RNA polymerase

exon intron

tRNA