CSIR NET 2024 | Life Science: Molecules and their interactions relevant to Biology | 6 April

Titin, which has a molecular weight of 3 x 10⁶ daltons, is the largest polypeptide yet described. Titin molecules extend from muscle thick filaments to the Z disc; they are thought to act as springs to keep the thick filaments centered in the sarcomere. Titin is composed of a large number of repeated immunoglobulin (Ig) sequences of 89 amino acids, each of which is folded into a domain about 4 nm in length. You suspect that the spring like behavior of titin is caused by the sequential unfolding (and refolding) of individual Ig domains. You test this hypothesis using the atomic force microscope, which allows you to pick up one end of a protein molecule and pull with an accurately measured force. For a fragment of titin containing seven repeats of the Ig domain, this experiment gives the saw tooth force-versus extension curve shown in Figure.
 
When the experiment is repeated in a solution of 8 M urea (a protein denaturant), the peaks disappear, and the measured extension becomes much longer for a given force. If the experiment is repeated after the protein has been cross-linked by treatment with glutaraldehyde, once again the peaks disappear but the extension becomes much smaller for a given force.
On basis of above observation which is correct conclusion:

During an all-out sprint, muscles metabolize glucose anaerobically producing a high concentration of lactic acid, which lowers the pH of the blood and of the cytosol and contributes to the fatigue sprinters experience well before their fuel reserves are exhausted. The main blood buffer against pH changes is the bicarbonate/CO2 system.
 
To improve their performance, what would you advise sprinters?

Consider a system at pH 7.4 (physiological pH).
For simplicity sake, assume that the only buffer in the system is phosphoric acid and ignore all but the dissociation constant near 7.4, that is, 7.21.
At this pH, the other hydrogen ions on phosphoric acid will play a relatively minor role in regulating pH. In this particular system, the concentration of [H2PO4-] and [HPO4 2-] will be:
Given= [antilog 0.21=1.6]

Which of the following statements about trans fatty acids is false

A histidine side chain is known to have an important role in the catalytic mechanism of an enzyme; however it not clear that which state is required for enzymatic activity.
To answer this question you measure enzyme activity over a range of pH, with the result shown in figure.

Which form of histidine is required for enzyme activity?