Question

1. Describe how the 43 S preinitiation complex forms for Eukaryotic protein synthesis.

2. How might the fact that mature mRNA having 3' poly A tails be used to isolate mature mRNA form eukaryotic genes.

3. The base analog 5-bromouracil is a thymine analog that causes transition mutations because it can easily interconvert between the keto and enol forms. Draw the base pair for 5-bromouracil and adenosine (keto) and 5-bromouracil and Guanosine (enol).

Answer 1

1) The initiation factors eIF-1 and eIF-3 bind to the 40S ribosomal subunit. This prevents premature re-association of 60s subunit and allows the pre-initiation complex to form.

binding of GTP to eIF-2 to form a binary complex. This binary complex is then bound to the initiator met-tRNA_i forming a ternary complex.

this ternary complex is then bound to the 40S subunit forming the 43S pre-initiation complex. this complex is stabilized by the eIF-3 and eIF-1.

after this cap of mRNA is bind with initiation factor eIF-4. eIF-4 is a complex factor. after ATP hydrolysis this complex is converted into active mRNA complex. poly A tail is also bind with poly A binding protein (PABP) to promote interaction with cap structure.

this mRNA is now bind with the 43S pre-initiation complex and converted into 48S initiation complex.

2) the fact that poly A tail is present in only mature mRNA and not in any other RNA or DNA helps in isolation of mRNA from rest of the RNA and DNA. the poly A tail is strongly bound with the poly T containing beads and can be purified.

3)