Transcription & Translation

Question 1

What happens in Initiation of Transcription?

Answer 1

Initiation code recognised
Transcription factors bind at this code, upstream of the gene, and attract RNA polymerase to start mRNA production.
RNA polymerase separates the DNA strands for the RNA nucleotides to bind along the template strand

Question 2

What happens in Elongation of Transcription?

Answer 2

RNA polymerase travels along the template strand, picking up base pairs and copying them onto a complimentary RNA strand.
This process continues until new RNA molecule – mRNA.

Question 3

What happens in Termination of Transcription?

Answer 3

Adds a methyl-guanine ‘cap’ to the 5’ end to stabilise the mRNA.
3’ end is polyadenylated - lots of Adenine nucleotides are added – known as tailing.

Question 4

Define Splicing

Answer 4

The pre-mature product of transcription is pre-mRNA with introns and exons. The introns are removed by endo/exo nucleases

Question 5

Describe mRNA

Answer 5

Around 2% of RNA
100,000 kinds
Few copies of each

Question 6

Describe rRNA

Answer 6

> 80% of RNA
Few kinds
Many copes of each
80S, 60S & 40S subunits (70S, 50S & 30S in bacteria)

Question 7

Describe tRNA

Answer 7

Around 15%
100 kinds
Many copies of each
Uncharged

Question 8

What happens in Initiation of Translation?

Answer 8

At the 5’ cap of the mRNA the 40S subunit binds. Starting codon recognised. The 60S subunit then binds for elongation to occur

Question 9

What happens in Elongation of Translation?

Answer 9

The rRNA has two sites for tRNA to bind:
The P site is for the site holding the peptide chain. The A site is for the site accepting the tRNA.
1 & 2 - tRNA occupies the P site and then another aminoacyl-tRNA enters the ribosome to occupy the A site (requires GTP).
3 & 4 - The Methionine forms a peptide bond with the next aminoacyl-tRNA making the tRNA in the P site now uncharged. This leaves and the ribosome moves along
Requires Peptidyl Transferase

Question 10

What happens in Termination of Translation?

Answer 10

The termination requires a stop codon to be read on the mRNA. There aren’t any tRNAs that can bind to these codons and so the peptide and tRNA are hydolysed to release the protein into the cytoplasm

Question 11

Define Gene

Answer 11

A unit of heredity

Question 12

What does Maturation of mRNA involve?

Answer 12

Capping
Polyadenylation
Splicing

Question 13

What is Capping?

Answer 13

Adds a methyl-guanine with a 5’-5’ triphophate linkage

Question 14

What is Polyadenylation?

Answer 14

Adds a series of Adenines to the end of the mRNA (tailing)

Question 15

What is Splicing?

Answer 15

Removes introns using Endonucleases and Exonucleases. Endonucleases can be non-specific or specific.

Question 16

What is meant by the triplet code being Degenerative?

Answer 16

There is more than one code per amino acid.

Question 17

How can the effect of a mutation vary?

Answer 17

Severity of the effect depends on the amount of difference in the protein caused
Premature or delayed stop codons will cause truncated/elongated proteins that may not function correctly if at all eg Haemoglobin