LEC 6: Translation

Question 1

3-Stepped Process of Protein Synthesis

Answer 1

1. Synthesis of mRNA from DNA template
2. Migration of mRNA from nucleus to cytoplasm (the ribosome) where it will wait for another type of RNA (tRNA)
3. tRNA will bring amino acids which are complimentary to the codons on mRNA

Question 2

Transfer RNA (tRNA)

Answer 2

Functions to attach to a specific amino acid and bring that amino acid to the ribosome

• One end of the molecule attached to a specific amino acid
• The other end has an exposed sequence of 3-bases known as the anticodon

Question 3

How are Amino Acids loaded onto tRNA’s?

Answer 3

1. ATP and AA bind through active site on tRNA aminoacyl synthetase
2. AMP binds to enzyme-AA complex, 2 phosphate groups released
3. Activated AA transferred from tRNA synthetase to specific tRNA. AMP released
4. tRNA and AA released from tRNA synthetase for particicpation in translation

Question 4

tRNA Structure and Function

Answer 4

• 64 codons

- Secondary structure with hairpin loops

Question 5

Wobble Hypothesis

Answer 5

Non-standard base pairing at the third position allows for a limited flexibility in base pairing

• Codons of the same amino acid have the same nucleotides at the first and second positions
• Therefore, the 3rd base is somewhat redundant

Question 6

Role of Ribosomes

Answer 6

• Each ribosome consists of two subunits (rRNA and proteins) with binding sites for both tRNA and mRNA molecules

Question 7

3 Steps to Translation

Answer 7

1. Initiation: Initiation factors known bind to 5‘cap and guide it to the ribosome
2. Elongation: Peptide bond formation using ribozyme
3. Termination: Releasing factor binds STOP codon

Question 8

1. Initiation

Answer 8

• Ribosomes bind to the 5’ cap

- Move down the mRNA until a AUG codon is reached (codon for Methionine)

Question 9

2. Elongation

Answer 9

The ribosome has 2 sites for tRNA’s (P and A)

• The initial tRNA binds to the P site while the next tRNA binds to the A site
• The growing polypeptide chain of AA’s transfers to each successive tRNA as the previous is ejected from the E site

Question 10

3. Termination of Translation

Answer 10

When the ribosome reaches a stop codon, there is no tRNA that binds to it. Instead, proteins called “release factors” bind
- Code for no AA and all protein-coding regions end in a stop codon

Question 11

Peptide Bonds and Polypeptide Chains

Answer 11

All amino acids have an amino group (-NH2) group on one end, and an acid group (-COOH) on the other end.
- When polypeptides are synthesized, the acid group of one amino acid is attached to the amino group of the next amino acid, forming a peptide bond

Question 12

Inhibition of Protein Synthesis

Answer 12

• Tetracyclines
• Aminoglycosides
• Cycloheximide
• Ricin