1. Translation

2. Purpose: Translation is the process by which proteins are made
Location: On the ribosome

3. About Proteins Polypeptide chain
Composed of amino acids held together by peptide bonds.
Met
Val
Phe
Gly
Tyr
Amino Acids

4. About Proteins Polypeptide chain
Composed of amino acids held together by peptide bonds.
Met
Val
Phe
Gly
Tyr
Peptide Bonds

5. The Genetic Code
The mRNA is read in sets of three nucleotides = CODONS
The code always begins with a “Start” codon = AUG (methionine)
The code ends with one of three “Stop” codons (UAA, UAG, UGA) which do not code for an amino acid
ALL organisms use the same amino acids and the same genetic code

6. Reading codons:

7. The Ribosome
Consists of two subunits – a large subunit and a small subunit
The two subunits join together to read the mRNA
Has three binding sites for tRNA – A (1st), P (2nd) and E (3rd)

8. Translation
Before translation can occur, mRNA must be transcribed from the DNA in the nucleus
The mRNA transcript is then processed
poly-A tail
methylated cap
Introns removed and exon spliced together

9. Translation - Initiation
An initiator tRNA is loaded onto the small ribosome subunit
The small ribosome subunit attaches to the 5’ end of the mRNA
The small ribosome subunit travels along the mRNA looking for a START codon

10. Translation – Initiation (cont.)
- When a START codon is encountered, the large ribosome subunit attaches to the small subunit
- Initiation Complex – formed when the two ribosome subunits attach to the mRNA

11. Translation - Elongation
-The mRNA molecule moves between the ribosome subunits.
The mRNA is read and anti-condons on tRNA are matched with codons on mRNA
Amino acids are placed in the correct sequence

12. Translation – Elongation (cont.)
Enzymes catalyze the formation of peptide bonds between the amino acids

13. Translation - Termination
- When a stop codon is reached (UAA, UAG, UGA) the ribosome ends the translation.
Stop codons do not code for amino acids

14. Translation – Termination (cont.)
Release factors (proteins) bind to the ribosome and trigger enzyme activity that detaches the mRNA and the polypeptide chain from the ribosome

16. The Central Dogma