Question

A) Two separate GTP hydrolysis reactions are involved in translation elongation. What are the differences between these two steps? For each step, predict the consequences of a mutation that causes GTP hydrolysis to be a) faster and b) slower.

B) Amino acid building blocks are chemically and structurally diverse and also more chemically reactive compared to nucleotides. Draw and explain three or four relevant chemical structures to demonstrate this point.

C) Why is protein structure difficult to predict simply by looking at a primary amino acid sequence?

Answer 1

As we can see in the above diagram first GTP hydrolysis occurs when t RNA binds to matching codon and the second hydrolysis of GTP occurs when m RNA shifts forward by a codon. More details are given here-

First step in the elongation-

Binding of the second aminoacyl t- RNA. The second aminoacyl t-RNA enters bound to Ef-Tu which contains bound GTP. Binding of the second aminoacyl t -RNA to the A site in the ribosome is accompanied by the hydrolysis of the GTP to GDP and Pi and Ef tu GDP complex leaves the ribosome. The bound GDP is released when the EF-Tu-GDP complex binds to EF-Ts and EF-Ts and EF- Ts is subsequently released when another molecule of GTP becomes bound to EF-Tu. This recycles Ef- Tu and permits it to bind another amino acyl t RNA.

Now if the mutation occurs that causes GTP to be faster or slower, binding of t RNA won`t occur and the shifting also would not occur properly. In short, elongation would not occur because GTP hydrolysis takes it own time to proceed.

B. Amino acids are 20 in number whereas nucleotides are 4 in number. Hence amino acids are more diverse than nucleotides. Also due to the presence of a variety of R groups present in 20 different amino acids and a reactive amino and carboxyl groups make them more reactive than nucleotides.

c.It is difficult to judge a structure of a protein by looking at its primary structure that is the structure which involves the sequence of amino acids because this primary structure acquires a secondary structure and tertiary structure like beta or alpha helix according to the various interactions like hydrogen bonds,Vanderwall forces and hydrophobic interactions. Tertiary and secondary structures are difficult to predict.