L6 Protein Synthesis

Question 1

How is mRNA made?

Answer 1

DNA is transcribed using RNA Polymerase to primary RNA TRANSCRIPT

Introns are then spliced out

5’ end has RNA cap, 3’ has Poly A cap

It is then exported out of the nucleus to be translated to a protein

Question 2

What is alternate splicing?

Answer 2

Alternative splicing allows for different proteins to be produced from one gene.

Diff proteins mag bind to mRNA so that it prevents splicing

Question 3

How many reading frames can any mRNA have?

Answer 3

3

A punctuator signal (Met) sets the correct reading frame

Question 4

What are the sites on a ribosome?

Answer 4

A- acceptor when tRNA binds
P- where peptide bond forms
e- ejector site

Question 5

What are the ribosomes constituted of?

Answer 5

2/3 RNA 1/3 protein

Rrna: overall structure, a p e sites, catalysed peptide bonds.

Question 6

How does translation occur?

Answer 6

Initiation tRNA (usually Met) to determine where translation begins
Elongation factors assemble with the ribosomal subunits when it forms in the mRNA

Initiator tRNA moves along mRNA searching for AUG

Once found, large ribosomal unit comes and translation begins

Question 7

How does selective translation occur?

Answer 7

Some proteins bind on mRNA and stop it from binding

Some RNAs localised to specific regions of cytoplasm

Question 8

What are some ways that mRNA may be localised to specific regions of cytoplasm?

Answer 8

Directed transport on cytoskeleton

Random diffusion and trapping

Generalised degradation in combination with local protection by trapping

Question 9

What role does poly a tail play in gene expression?

Answer 9

Removal of poly a sequence causes mRNA degradation (by deadenylase)

Proteins can bind to 3’ to prevent poly a removal

Proteins that need to be present for long time are more stable

Question 10

What are microRNAs

Answer 10

A class of noncoding RNA that degrade or block translation of mRNAs

Often arise from introns

They form a hairpin structure, cleave, and move to cytosol, interacts with Argonaute and create risc complex

May mop up low levels of inappropriate gene transcription

Matches with RNA

Extensive match: rapid degradation
Less extensive: binds and translation reduced

Question 11

What is the major diff between eukaryotes and prokaryotes protein synth?

Answer 11

In eukaryotes, coding regions of genes are interrupted