40 - protein synthesis

What directs a ribosome to translation start sites?

Shine-Dalgarno/Kozak sequence (prokaryote/eukaryote sequences, respectively)

Which part of the prokaryotic ribosome binds to the shine-dalgarno sequence?

30s subunit

What does the E.coli initiator tRNA have instead of the usual methionine?

fMet (modified methionine)

What are the three tRNA binding sites?

A - aminoacyl site, P - peptidyl site, E - exit site

What is the rate limiting step in translation initiation in bacteria?

Formation of 70s initiation complex

IF2 is regulated by ________

GTP/GDP

What are the 3 steps of elongation?

1. positioning of charge tRNA at A site

2. Formation of peptide bond at P site

3. Shifting of mRNA by 1 codon

What guides AA-tRNA to the A site?

EF-Tu

EF-Tu-GTP binds to all aa-tRNA molecules except for ______

fMet

Which enzyme catalyzes peptide bond formation?

peptidyl transferase

Which enzyme uses GTP hydrolysis to move the mRNA by one codon?

EF-G (elongation factor G)

How is eukaryotic translation initiation different from prokaryotic translation initiation?

• In eukaryotes, the initiator codon is always the first AUG from the 5’ mRNA end

• Eukaryotes have larger ribosomes

• Protein synthesis begins with methionine instead of fMet

Which subunit of a ribosome is recruited first in eukaryotic translation? What recruits it?

Small ribosomal subunit, recruited by 5’ cap

Where does eukaryotic protein synthesis occur?

Cytoplasm

What shape is mRNA?

Circular

Where does secretory pathway protein synthesis begin?

On free ribosomes in the cytosol

What does the N-terminal region of the primary protein structure contain?

Signal peptide

What does the signal recognition particle do?

Binds signal sequence and directs the complex to the ER in the secretion synthesis pathway

How is iron transport/storage regulated?

Stem loops structure in 5’ UTR binds IRE-binding protein when iron is absent to prevent translation, when iron is present it binds to the IRE-binding proteins and allows translation

What happens to the mRNA when there is no IRE-BP?

receptor mRNA is degraded

If a small RNA was complementary to a part of mRNA, what would happen to the mRNA?

It would be degraded

What is the use of micro RNA in translational regulation?

It helps cleave double stranded RNA