10. Gene Translation

Question 1

How many kinds and copies are there of rRNA, tRNA and mRNA in eukaryote cells?

Answer 1

rRNA few kinds but lot of copies of each kind, tRNA ~100 kinds with lots of copies and mRNA 100000s of kinds with few copies of each.

Question 2

What are the details of rRNA is found in prokaryotes?

Answer 2

3 rRNA + 56 proteins. 30s and 50s subunits. 70s ribosome.

Question 3

What are the details of rRNA found in eukaryotes?

Answer 3

4 rRNAs + 82 proteins. 40s and 60s subunits. 80s ribosome.

Question 4

What are the sizes of ribosomes in prokaryotes and eukaryotes respectively?

Answer 4

20nm and 32nm.

Question 5

What is the initiation codon?

Answer 5

AUG methionine.

Question 6

What are the termination codons?

Answer 6

UAA, UAG and UGA.

Question 7

What end do amino acids join to tRNA molecules? (5’ or 3’).

Answer 7

3’ end.

Question 8

Which bases can the base inosine recognise?

Answer 8

Uracil, cytosine and adenine.

Question 9

What is the wobble position?

Answer 9

5’base of anticodon and 3’base of codon that allows a single tRNA species to recognise more than one codon.

Question 10

What is involved in initiation of translation?

Answer 10

AUG codon recognised, special methionyl tRNA ribosome.

Question 11

What is involved in elongation of translation?

Answer 11

N to C chain growth, amino acyl tRNAs (charged tRNA as amino acids are bound to them).

Question 12

What is involved in termination of translation?

Answer 12

Stop codons.

Question 13

How is tRNA activated?

Answer 13

The amino acid and ATP attach to amino acyl-tRNA synthetase.
Pyrophosphate is cleaved off and this separates to two phosphate.
tRNA is joined to the molecule and AMP is cleaved off.
Amino acyl tRNA is released and amino acyl tRNA synthetase is also released.

Question 14

Describe the details of initiation in translation.

Answer 14

40S subunit binds USING GTP and moves 5’ to 3’ until it finds AUG start codon. ATP is used to bind it. The 60S subunit joins and GDP is released. The ribosome is fully functioning now.

Question 15

Describe the details of elongation in translation.

Answer 15

The complementary amino acyl tRNA binds using GTP. Another amino acyl tRNA comes over and the two amino acids form a peptide bond using peptidyl transferase. The ribosome moves along the nucleic acid. There is now an empty site for another amino acyl tRNA to bind to.

Question 16

Describe the details of termination of translation.

Answer 16

A stop codon is read in the A site. Water breaks the peptide bond and the chain stops growing, the stop codon is a competitor of the peptidyl transferase.

Question 17

What is polyribosome or polysome?

Answer 17

Lots of ribosome joined along the exposed mRNA strand.

Question 18

What are the three types of RNA in eukaryotes with their respective abundances?

Answer 18

rRNA >80%, tRNA ~15% and mRNA ~2%.