1. AP Biology
Lecture #33
Translation

2. From gene to protein DNA mRNA protein trait nucleus cytoplasmaa
nucleus
cytoplasm
transcription
translation
DNA
mRNA
protein
ribosome
trait

3. from nucleic acid language to amino acid language
Translation
from nucleic acid language to amino acid language

4. How does mRNA code for proteins?
TACGCACATTTACGTACGCGG
DNA 4
ATCG
AUGCGUGUAAAUGCAUGCGCC
mRNA 4
AUCG ?
Met Arg Val Asn Ala Cys Ala
protein
How can you code for 20 amino acids with only 4 nucleotide bases (A,U,G,C)? 20

5. mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
codon
AUGCGUGUAAAUGCAUGCGCC
mRNA
AUGCGUGUAAAUGCAUGCGCC
mRNA ?
Met Arg Val Asn Ala Cys Ala
protein

6. Cracking the code WHYDIDTHEREDBATEATTHEFATRAT
1960 | 1968
Cracking the code
Nirenberg & Khorana
Crick
determined 3-letter (triplet) codon system
WHYDIDTHEREDBATEATTHEFATRAT
WHYDIDTHEREDBATEATTHEFATRAT
Nirenberg (47) & Khorana (17)
determined mRNA–amino acid match
added fabricated mRNA to test tube of ribosomes, tRNA & amino acids
created artificial UUUUU… mRNA
found that UUU coded for phenylalanine

7. Marshall Nirenberg
1960 | 1968
Har Khorana

8. The code Code for ALL life! Code is redundant Start codon Stop codons
strongest support for a common origin for all life
Code is redundant
several codons for each amino acid
3rd base “wobble”
Why is the wobble good?
Strong evidence for a single origin in evolutionary theory.
Start codon
AUG
methionine
Stop codons
UGA, UAA, UAG

9. How are the codons matched to amino acids?3 5
DNA
TACGCACATTTACGTACGCGG 5 3
mRNA
AUGCGUGUAAAUGCAUGCGCC
codon 3 5
UAC
Met
GCA
Arg
tRNA
CAU
Val
anti-codon
amino acid

10. From gene to protein DNA mRNA protein trait nucleus cytoplasmaa
nucleus
cytoplasm
transcription
translation
DNA
mRNA
protein
ribosome
trait

11. Transfer RNA structure
“Clover leaf” structure
anticodon on “clover leaf” end
amino acid attached on 3 end

12. 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
The tRNA-amino acid bond is unstable. This makes it easy for the tRNA to later give up the amino acid to a growing polypeptide chain in a ribosome.
Trp
C=O
Trp
Trp
C=O OH
H2O OH O
C=O O
activating
enzyme
tRNATrp A C C U G G
mRNA
anticodon
tryptophan attached to tRNATrp
tRNATrp binds to UGG codon of mRNA

13. Ribosomes Facilitate coupling of tRNA anticodon to mRNA codon
organelle or enzyme?
Structure
ribosomal RNA (rRNA) & proteins
2 subunits
large
small E P A

14. Ribosomes A site (aminoacyl-tRNA site) P site (peptidyl-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
Met A C 5' U A U G 3' E P A

15. Building a polypeptide1 2 3
Initiation
brings together mRNA, ribosome subunits, initiator tRNA
Elongation
adding amino acids based on codon sequence
Termination
end codon
Leu
Val
release
factor
Ser
Met
Met
Met
Met
Leu
Leu
Leu
Ala
Trp
tRNA C A G U A C U A C G A C A C G A C A 5' U 5' U A C G A C 5' A A A U G C U G U A U G C U G A U A U G C U G A A U 5' A A U
mRNA A U G C U G 3' 3' 3' 3' A C C U G G U A A E P A 3'

16. Protein targeting Signal peptide address label Destinations: secretion
nucleus
mitochondria
chloroplasts
cell membrane
cytoplasm
etc…
Signal peptide
address label
start of a secretory pathway

17. Can you tell the story? RNA polymerase DNA amino acids exon intron
tRNA
pre-mRNA
5' GTP cap
mature mRNA
aminoacyl tRNA synthetase
poly-A tail
large ribosomal subunit 3'
polypeptide 5'
tRNA
small ribosomal subunit E P A
ribosome