Question

1. Describe the differences between prokaryotic and eukaryotic translation initiation. How does the ribosome find the correct start codon and what proteins are involved in the process? please include the shine-dalgarno sequence in the answer.

2. Consider the following partial sequence of messenger RNA. The sequence below contains the code for a short, complete protein.

5 ́-UCCCCAGUCAUGGAGUCGUUAAUUAAAUGACCGGUGCGGAUCGUA - 3 ́

Using the codon chart (from your textbook or in the lecture slides), give the amino acid sequence of the protein that would be produced by translation of this mRNA. Label the amino and carboxyl ends of the resulting protein.

4. How are positive and negative regulation used to control induction of the E. coli lac operon? Include in your description the roles of glucose, CAP, cAMP, lactose, and the lac repressor.

Answer 1

Answer=

differences between prokaryotic and eukaryotic translation initiation

prokaryotic translation initiation	Eukaryotic translation initiation
1.Poly A tail is absent at the 5' end.	1.Poly A tail is present at the 5' end.
2.Ribosomal subunits are 30 S and 50S.	2.Ribosomal subunits are 40 S and 60S.
3.Shinedalgarno sequence is i.e. 5'UAAGGAGG 3' is present at the 5'end.	3.Shinedalgarno sequence ' is absent at the 5'end.
4.There are 3 initiation factors that are IF1,IF2 and IF3.	4.There is 9 initiation factors .
5.The first amino acid which is synthesized is N-formyl methionine.	5.The first amino acid which is synthesized is methionine.
6.Initiator tRNA is Met-tRNAf	6.Initiator tRNA is Met-tRNA.

the ribosome find the correct start codon is as follows =

In case of eukaryotes: Eukaryotes does not have purine rich sequence on the 5' side to distinguish initiator AUGs from internal ones.

- A 40 S ribosome attaches to the cap at the 5' end of eukaryotic mRNA and searches for an AUG codon by moving step by step in 3' direction.

-This scanning process is powered by helicases that hydrolyze ATP.

In prokaryotes : The small ribosomal subunit binds to the purine rich sequence which is present at 5'end .SD sequence is 5'UAAGGAGG 3'

SD sequence acts as a start site for protein synthesis.