Protein synthesis 2 eukaryotes

Question 1

What is required for the small part of the ribosome (40s) to bind to the mRNA?

Answer 1

A binding site at the level of the cap, and presence of cap-binding proteins.

Question 2

While the 40s is moving along the untranslated region of the mRNA to the first AUG, what powers such movement?

Answer 2

ATP powered helicases

Question 3

What is the Kozak sequence?

Answer 3

a sequence right before the first codon, ending with AUG. Provides context for translation initiation

Question 4

Once the 40s subunit has found the first AUG and bound the first tRNA, what happens?

Answer 4

The initiation factors dissociate, allowing the large subunit (60s) to associate to it.

Question 5

Define EF-Tu

Answer 5

An elongation factor that is bound to a new tRNA to the A site. It temporarily prevents the peptidyl reaction to ensure correct pairing to the codon.

Question 6

Define EF-G

Answer 6

It binds the large subunit of the A-site and moves it up next to the 40s unit that has just shifted over one codon.

Question 7

What is the role of the release factor?

Answer 7

Bind to the A-site of the ribosome, and cause the last amino acid in the polypeptide to bind to water, getting rid of the reactive OH group.

Question 8

What is the role of the ribosome recycling factor

Answer 8

replaces the RF in the A site and causes the ribosome to dissociate by attracting EF-G.

Question 9

Define translation recoding in the context of selenocysteine.

Answer 9

Selenocysteine is linked to a tRNA that has a stop codon as its anticodon. it will bind when that stop codon is reached, and the mRNA downstream will form a “stem and loop” that allows a specific translation factor to allows this AA to be incorporated.

Question 10

What is transtional shift, a special case?

Answer 10

An occasional slip of the ribosome will allow passage of a stop codon, allowing for a different protein to be made from the same strand of mRNA.