Chapter 31, Problem 1P

Interpretation Introduction

Interpretation:

The number of ATP equivalents consumption during the synthesis of the rhodanese polypeptide chain from its constituent amino acids needs to be determined.

Concept Introduction:

Amino acids are organic compounds containing amino as well as acidic groups. The general molecular formula of an amino acid is as follows:

  ${\text{H}}_{\text{2}}\text{N-CH}\left(R\right)-\text{COOH}$

Here, R refers to the different group for different amino acids. If there is more than one amino group present in an amino acid, they are considered as basic amino acids and if there is more than one carboxylic group, then they are considered as acidic amino acids.

Explanation of Solution

Elongation of the amino acid needs 4 ATP per amino acid. The initial step in elongating the polypeptide activates the amino acids and then it is connected to the tRNA. This procedure converts an ATP to an AMP, costing two phosphate groups. This is equal in hydrolyzing two ATPs in this step.

Subsequent, the “loaded” aminoacyl-tRNA is moved towards the ribosome’s A-site. This is achieved with the aid of the elongation factor EF-Tu and the GTP’s hydrolysis. The GTP hydrolysis is actively equal to hydrolyzing another ATP.

Lastly, the aminoacyl-tRNA is moved to the P-Site from A-site utilizing EF-G: GTP complex. Again, GTP is hydrolyzed to the GDP which is again equivalent to the single GTP hydrolysis. Thus, there are total 4 ATP equivalents per amino acids.

  $\text{295A}\text{.A}\times \text{4}\frac{\text{ATP}}{\text{A}\text{.A}\text{.}}=1180\text{ ATP}$

We now should consider termination and initiation. Initiation needs 2 ATP. One is in the form of GTP, for Met-tRNA_i binding to form the 40S pre-initiation complex, and another is in the form of ATP in forming the initiation complex. The Met-tRNA_i formation costs another 2 ATP.

Termination needs the hydrolysis of a single GTP. This means that for the amino acid, which is about 296 amino acids long, 4 ATP equivalents would be consumed within initiation, 1180 ATP equivalents are consumed during elongation, plus 1 ATP equivalent are consumed during termination. In this process, total 1185 ATP equivalents are provided.