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Genetic Code and Translation
Outline
The Breaking of the Genetic Code Examples of two experimental approaches
Concepts and Terms related to genetic code Wobble Degeneracy isoaccepting
Translation prokaryote eukaryotes
The Genetic Code and Translation
The Breaking of the Genetic Code
Experiments that “broke the genetic code”
1. Cell Free experiments Applied to the Homopolymer experiment
2. Known RNA sequences and ribosomal bound tRNA
All these experiments used a cell free system.
1 23
4
ppt. protein5
1. Overview
Cell free system
1 hot amino acid
19 cold amino acids
translation
20X each a different “hot amino acid
Application of experimental design
+
2. Known mRNA sequences + Ribosomal bound tRNA
This is transfer RNA
Anti-codon
Amino acid
Now link this idea toThe genetic code table
Transfer RNA
Amino Acid
ribosome
Codon of mRNAMix with
Isolate ribosome bound tRNA Analyze amino acid
2. EXPERIMENT
Close up of a possible result:
Genetic Code Table1968
Degeneracy & mRNA
Wobble
Isoaccepting & tRNAs
Different tRNAs accept same amino acid!
The process of translation
mRNA sequences
We will approach our discussion of translation as a “Nonoverlapping Code”
Steps of Translation
1. Binding of amino acids to tRNA
2. Initiation
3. Elongation
4. Termination
5. Peptide Release
6. Protein modification
Step 1 Binding of amino acid to tRNA
It takes two steps to “charge” the tRNA
Amino acid+ATPtRNA is charged
Aminoacyl-tRNA-synthetase
Up close view of “charged” tRNA
Step 2: Initiation of Translation
IF3
Bacterial Initiation
30S
70S
Note 3 ribosomal sites E P A
E A
Kozak
Eukaryotic Initiationkey differences
3. ELONGATION: look at the “EPA” sites
Peptidyl transferase
Up close view of translation
Elongation continues on ribosomes
Termination and Release
UAAUAGUGA
Steps 4 and 5:
Animation of Translation
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html
See chapter 15
6.
Lipoprotein
Glycoprotein
Many antibiotics target prokaryotic translation.
Antibiotics and Translation
Tetracyclines
Chloramphenicol
Streptoymycin
Erythromycin
Bind and block bacterial ribosomes “A” site
Binds to large subunit; blocks peptide formation
Blocks initiation step
Blocks translocation step
Review: The Structure and Function of Proteins
Amino Acids-R groups
Nonpolar, aliphatic
Polar, uncharged
Aromatic
Positively charged
Negatively charged
Protein: Levels of structural organization
For your review:Summary of important steps involved in translation
1.
2.
3.
4.
5.
6. Protein Modifications
Eukaryotic translation is very similar except:
More IF’s
Kozak sequence
5’CAP
3’poly-A tail