RNA, Transcription And Translation

Question 0

What occurs during initiation in transcription?

Answer 0

• Transcription factors bind to recognition code
• Attracts RNA polymerase to separate DNA strands
• RNA nucleotides can now bind to template strand

Question 1

In transcription, what is the initiation code and where is it positioned?

Answer 1

5’ TATA 3’

It is upstream of the gene

Question 2

What occurs during elongation of transcription?

Answer 2

• RNA polymerase travels along the template strand, picking up base pairs
• It copies them onto the complementary RNA strand

Question 3

What happens in termination of transcription?

Answer 3

• mRNA adds a methyl-guanine cap to the 5’ end
• The cap is bonded with a 5’-5’ triphosphate linkage and this stabilises the mRNA
• A stop codon at the 3’ end activates cleavage of mRNA
• 3’ end is polyadenylated - TAILING

Question 4

When does splicing occur?

Answer 4

After transcription and before translation

Question 5

What do endo and exonucleases do?

Answer 5

• They are both used in splicing
• Endonuclease breaks within the polynucleotide
• Exonuclease degrades the polynucleotide from the 5’ or 3’ end

Question 6

What is the start product and end product of splicing

Answer 6

Pre-mRNA

Mature mRNA

Question 7

What is rRNA?

Answer 7

• Ribosomal RNA
• Used to bind to mRNA
• Provides a location for tRNA A

Question 8

What occurs during initiation of translation?

Answer 8

• At the 5’ cap of mRNA, the 40S subunit with Met-tRNA binds
• A start codon is recognised (5’AUG) which is specific to methionine only
• The 60S subunit then binds for elongation to occur

Question 9

What are the two sites on rRNA for tRNA to bind and what are their functions?

Answer 9

• P site: holds the peptide chain

- A site: accepts the tRNA

Question 10

What happens during elongation of translation?

Answer 10

Met-tRNA already occupies the P site.

Another aminoacetyl-tRNA enters the ribosome to occupy the A site which requires GTP

The Methionine forms a peptide bond with the next aminoacetyl-tRNA making the tRNA in the P site now uncharged

This tRNA now leaves and the ribosome moves along (translocation)

The binding of the two amino acids requires peptidyl transferase

Question 11

What happens during termination of translation?

Answer 11

• A stop codon is read on the mRNA.
• These codons could be UAA, UAG or UGA.
• There are no tRNA molecules which can bind to these
• The peptide and tRNA molecule are hydrolysed to release the protein into the cytoplasm

Question 12

What is the purpose of RNA maturation?

Answer 12

So that the molecule can be cleaved

Question 13

List the three major types of RNA and their proportions.

Answer 13

mRNA: ~2%
tRNA: ~15%
rRNA: ~80%

Question 14

State how many types and how many copies of each type there are of each type of RNA molecule

Answer 14

mRNA: 100,000s of types but few copies of each
tRNA: ~100 types but many copies of each
rRNA: few types but many copies of each