Lecture 3b

Question 1

At the end of the gene, specific sequences when transcribed into RNA trigger what?

Answer 1

Transfer of enzymes to RNA

Question 2

What are the 2 cleavage factors?

Answer 2

CstF and CPSF

Question 3

What is PAP and PABP

Answer 3

Poly A Polymerase

Poly A Binding Protein

Question 4

What happens once message is cleaved?

Answer 4

Poly A Tail is added and transcription is terminated

Question 5

What is further extended in the last phase?

Answer 5

Poly A tail is extended and is important for mRNA stability and function

Question 6

What are the 3 differences between transcription between prokaryotes and eukaryotes

Answer 6

Chromatin (no nucleosomes in pro)
3 RNA polymerases (1 in pro)
RNA processing (pre-mRNA in euks and not in Pros)

Question 7

3 steps for pre-mRNA to mature mRNA

Answer 7

1. Addition of a 5’ cap
2. Addition of polyA tail
3. Removal of introns

Question 8

What is added to the 5’ end of pre-mRNA while still being transcribed and what enzyme is used to add this?

Answer 8

Guanyl transferase adds guanine nucleotide to the 5’ end

Question 9

When is 5’ capping initiated?

Answer 9

Once 20-30 nucleotides have been transcribed

Question 10

What is one reason the 5’ cap is needed

Answer 10

Required for translation initiation in euks

Question 11

Poly-A sequence is added by what and is important for what?

Answer 11

Poly A polymerase, PAP. For mRNA stability.

Question 12

The pre-mRNA contains what that signal the beginning and end of introns?

Answer 12

Consensus nucleotide sequences

Question 13

What are snRNAs

Answer 13

Small nuclear RNA molecules that are in the spliceosome

Question 14

snRNAs associate with other proteins to form what?

Answer 14

snRNPs

Question 15

What forms the spliceosome complex?

Answer 15

snRNPs

Question 16

why does intron splicing need to be precise?

Answer 16

Errors in splicing affects the reading frame for translation

Question 17

What is tRNA?

Answer 17

Highly stable RNA molecule which is the adapter molecule between the mRNA and peptide sequences

Question 18

What enzyme attaches the amino acid to the respective tRNA

Answer 18

Aminoacyl tRNA synthetase (aaRS)

Question 19

What are the 3 sites in the large ribsomal subunits?

Answer 19

E site, P site, A site

exit, peptidyl, aminoacyl

Question 20

Describe initiation of translation?

Answer 20

Euk initiation factors (eIF) associate with 5’7mG cap of mRNA, 40S ribosomal subunit and Met tRNA.
This complex searches for AUG codon to start.
Large ribosomal subunit (60S) then binds.
80S initiation complex is then formed

Question 21

Describe elongation translation

Answer 21

Met is the first amino acid, and this tRNA is in the P site.
The next tRNA sits in the A sire and the Met amino acid forms a peptide bond with the Amino Acid in the A site and the old tRNA moves onto the E site and exits

Question 22

Describe translation termination

Answer 22

Elongation occurs till a stop codon is encountered.

A release factor binds to the A site instead of a tRNA which prompts termination.

Question 23

mRNA sequence is decoded in sets of what?

Answer 23

3 nucleotides

Question 24

What makes a charged tRNA?

Answer 24

A tRNA with the respective amino acid attached

Question 25

what does the aaRS do?

Answer 25

Amincoacyl tRNA synthetase (aaRS) enzyme attaches the amino acid to respective tRNA.
Specific tRNA for each amino acid and vice vera.