W1- Lecture 4.2- Molecular Bio Of The Gene

Question 1

Describe how the 5’ end of the mRNA is capped

Answer 1

The addition of methylated G nucleotide by removal of a phosphate by a phosphatase
addition of a GMP via a guananyl transferase
the addition of a methyl group via a methyl transferase

The 3’ end is cleaved at a specific site and a poly( – A tail of up to 200 nucleotides )added by a polymerase.

Then splicing can take place

Question 2

Why is mRNA capped ?

Answer 2

So it isn’t degraded/ can survive

So it can be recognised by ribosomes and can make essential proteins for bodily functions.

Question 3

RNA splicing produces what from pre-mRNA

Answer 3

Mature mRNA

Question 4

Name 5 types of alternate splicing

+

Answer 4

Exon skipping/inclusion 
Alternate 3’ splice sites 
Alternate 5’ splice sites 
Mutually exclusive exons 
Intron retention

Question 5

Describe how translation/ gene expression can be Controlled via half life of mRNA ?

Answer 5

By many ribosomes attaching to an mRNA over time it degrades.
This is its half life
By having a half life the cell can regulate gene expression

Question 6

Describe the first step of translation

translation initiation

Answer 6

tRNA carrying a methionine associates with a small ribosomal in association with eukaryotic initiation factor 2 ( eIF2)

The small ribosomal unit recognises the a 5’ end of a mRNA capped with two additional initiation factors eIF4G and eIF4E, and scans along the mRNA for a start codon (AUG)
Then allows are subunit to bind

Question 7

Describe the second step of translation (elongation ) in 4 stages

Answer 7

An aminoacyl – tRNA binds to the A site and the tRNA molecule at the E site is released

Carboxyl end of the polypeptide chain is uncoupled from the tRNA in the P site and joined by a peptide bond to the amino acid attached to the new tRNA molecule in the A site via a peptide transferase enzyme.

Large ribosomal sub unit steps one codon along the mRNA

Small ribosomal subunit steps one codon along so that the new peptidyl –tRNA in the A site moves to the P site as and the tRNA that occupied the P site of the ribosome moves 1 codon along the mRNA molecule and becomes the new E –site. This generates a new A site

Question 8

What factors is translation eleongation driven by ?

Answer 8

Driven by Elongation factors EF1 and EF2

Question 9

Describe translation termination

Answer 9

Protein synthesis stops when the ribosome encounters a stop codon (UAA, UAG, UGA).
Cytoplasmic release factors bind to the stop codon and free the carboxyl end of the growing polypeptide chain.

Question 10

RNA splicing missed out

Answer 10

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