Translation

Question 1

How many different types of Amino acids are there?

Answer 1

20 (22)

Question 2

What are the stop codons?

Answer 2

UAA, UAG and UGA

Question 3

What is the codon for Methionine? What aspect of Methionine differs between the normal amino acid and the initiator?

Answer 3

AUG

The normal Met-tNA differs from the initiator Met-tRNA

Question 4

How is translation initiated?

Answer 4

Initiation factors bind to the small subunit of the ribosome and travels along the mRNA until the initiating AUG codon is encountered. Once encountered the large subunit of the ribosome attaches.

Question 5

What is the start codon in Bacteria?

Answer 5

N-formylmethionine.

Question 6

Give the schematic of translation

Answer 6

1. The small subunit along with the initiating factors bound to it, moves along the mRNA stand from the 5’ UTR.
2. Once it encounters the initiating AUG codon, the large subunit attaches.
3. Additional ribosomes can add to the mRNA. As a result there is more than one ribosome in different stages of translation on one mRNA molecule. This is known as a polysome.
4. Once it reaches the stop codon, the ribosome dissociates and the mRNA protein is released.

Question 7

What helps ensure the AUG is the initiating AUG?

Answer 7

The context - i.e. the nucleotides around it

Question 8

What enzyme is used to break up the mRNA molecule in which a premature stop codon? What is the process known as?

Answer 8

RNAses

Nonsense mediated decay

Question 9

What is the family of enzymes that attaches an amino acid to tRNA molecules?

Answer 9

Aminoacyl tRNA syntheses

Question 10

In which position is the anticodon found on a tRNA molecule?

Answer 10

The bottom of the anticodon loop?

Question 11

Why are 61 different synthetases needed?

Answer 11

Anticodons on tRNA molecules can recognise codons even if they do not pair using complementary base pairing rules. Wobble decrease the number of RNA molecules and sythetases that are required for protein synthesis.

Question 12

How many sites are there on a ribosome?

Answer 12

3: A site (aminoacyl tRNA site)
P site (Peptidyl site)
E Site (Exit site)

Question 13

What site does the tRNA molecule first enter? What does it do after that?

Answer 13

A site. The amino acid of the tRNA molecule in the A site forms a peptide bond with the amino acid sequence of the tRNA molecule in the P site. As a result, this means the tRNA molecule in the P site has no amino acids and the length of amino acids, now on the tRNA molecule of the A site, has increased by one. The ribosome moves up one codon. The E site is now held by the empty tRNA site. The P site now hold the chain of amino acids and the A site is empty. The tRNA molecule in the E site exits and the whole thing happened again until the stop codon is reached.

Question 14

How does termination occur?

Answer 14

When the stop codon is reached, releasing factors bind. The polypeptide chain is released from the ribosome and the ribosome dissociates.

Question 15

How do ribosomes in eukaryotes compare to those in prokaryotes? What is the unit?

Answer 15

Eukaryotes: 80S Ribosome. Made up of a 60S unit and a 40S unit.
Prokaryotes: 70S ribosomes made up of a 50S unit and a 30S unit.
The unit is the rate of sedimentation when under centrifugal force.

Question 16

What is the symbiotic theory?

Answer 16

Mitochondrion were once their own prokaryotic organism and were engulfed by a eukaryote. This is as the ribosomes in mitochondria are of a similar size and function to those in bacteria.

Question 17

What are the implications of the symbiotic theory?

Answer 17

Some drugs that target ribosomes in bacteria may also effect mitochondria in healthy cells.