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