Translation - Polyribosomes & Targeting

Question 1

Polyribosomes

Answer 1

Several ribosomes that simultaneously translate 1 RNA molecule
- Most mRNA molecules are associated with them

Question 2

Transcription + translation & space + time

Answer 2

In bacteria - t+t are coupled in space and time
In eukaryotes - t+t are seperate

Question 3

What is protein targeting?

Answer 3

• Delivers protein to the correct cellular or extracellular location
• Proteins without a target sequence are targeted to cytoplasm

Question 4

What do N-terminal targeting sequences do?

Answer 4

• Direct proteins to nucleus, mitochondria, peroxisome or chloroplast

Question 5

What do N-terminal ER signal sequences do?

Answer 5

Target proteins to the rough endoplasmic reticulum during translation
- Can insert protein into membrane during synthesis
- Can go via golgi to membrane or lysosome

Question 6

Protein synthesis in neurons

Answer 6

• Is decentralised
• mRNAs are transported to remote locations within the neuron
• Proteins are made where they are needed

Question 7

The Wobble Hypothesis by Crick

Answer 7

• Some tRNAs can recognise more than one codon
• Codons recognised by the same tRNA vary at the 3rd position, the ‘wobble’ base

e.g. serine codons 5’UCC-3’ and 5’-UCU-3’ are recognised by anticodon tRNA 3’-AGG-5’

Question 8

Non-standard base paring

Answer 8

There is flexibility in base pairing of the tRNA to the 3rd position in the codon

e.g. G in the tRNA can recognise C or U

Question 9

Mutations in eIF2B lead to…

Answer 9

Neurodegenerative disorder VWM (leukoencephalopathy with vanishing white matter)
- Fatal disease that causes he brain to ‘melt away’

Question 10

Trinucleotide repeat expansion in eukaryotic release factor gene leads to…

Answer 10

Increased risk of several cancers (inc.breast + gastric cancer)