Question

How many ATP and GTP molecules are required respectively for incorporation of 25 amino acids in peptide chains?
A. 20 ATP , 20 GTP
B. 25 ATP , 25 GTP
C. 50 ATP , 50 GTP
D. 25 ATP , 50 GTP

Answer 1

Hint: The main route for the disposal of amino acids is protein synthesis. By binding to specific molecules of transfer RNA, amino acids are activated and assembled by ribosomes into a sequence specified by messenger RNA which, in turn, has been transcribed from the DNA template. Between adjacent amino acids, peptide bonds are then formed.

Complete Answer:
- A chemical compound (nucleotide) that is incorporated into the growing RNA chain during RNA synthesis and used as an energy source during protein synthesis is GTP (also known as guanylyl imidodiphosphate, guanosine-5'-triphosphate, or guanosine triphosphate).
- The energy-carrying molecule adenosine triphosphate ( ATP) is present in the cells of all living organisms. ATP captures and releases chemical energy derived from the breakdown of food molecules to power other cellular processes. ATP then functions as a shuttle, transporting energy to areas where energy-consuming activities take place within the cell.
- An amino acid has to be added to the respective tRNA in order to be inserted into the peptide chain, so that it can be taken to the translational machinery as and when necessary by the mRNA codon. 1 ATP is used in this method of attachment to the tRNA, also called tRNA charging.
- 1 GTP is used to render the 30S complex of the ribosome in the initiation step of the translation process. 2 GTPs, 1 GTP for the positioning of the incoming tRNA and the other for the translocation of the ribosome for the continuation of the elongation process are used in the elongation stage of the translation.
- 1 GTP is used to release the newly formed polypeptide chain in the termination step of translation. So, 1 ATP and 4 GTP molecules are used for each single amino acid incorporated into the peptide chain.
- One GTP is hydrolyzed to GDP as each successive complex of amino acid-tRNA binds to the ribosome's A site.
- As the ribosome travels to each fresh codon in the mRNA, a second GTP is broken down to GDP. During amino acid activation, one ATP is hydrolysed to AMP. Thus, 3 high-energy molecules, one ATP and two GTP, are used to form each peptide bond.

The correct answer is option(D) 25 ATP , 50 GTP.

Note: The disposal of amino acids is regulated by protein synthesis, but a series of complex pathways often oxidise amino acids, some of which produce other useful small molecules. In the liver, nitrogen from amino acids is converted into urea and excreted in the urine. In plasma, amino acids flow naturally and are distributed throughout all tissues. For the transport of amino acids through cell membranes, a set of particular proteins are responsible.