Question 1:

During translation, the identity of an amino acid attached to an incoming tRNA and added to the growing polypeptide is never checked. A proofreading step that hydrolyzed the previously formed peptide bond after an incorrect amino acid had been inserted into a growing polypeptide (analogous to the proofreading step of DNA polymerases) would be impractical. Why? 10 sentences max.

Question 2:

A new polypeptide of 320 amino acids has been found. Analysis of the protein shows that it has high homology to the hexokinase family of enzyme. Thus, this protein was renamed Hexokinase V. It has a much lower Km than any hexokinase and a much higher Vmax than any Hexokinase.

A. Estimate the approximate molecular weight (in daltons) of this protein. (hint: you may have to do some research)

B. Why might it be good or bad if this new Hexokinase was present in the liver? 10 sentences max.

Question 3:

Glycerol 3-phosphate is required for the biosynthesis of triacylglycerols. Adipocytes, specialized for the synthesis and degradation of triacylglycerols, cannot use glycerol directly because they lack glycerol kinase, which catalyzes the reaction:

How does adipose tissue obtain the glycerol 3-phosphate necessary for triacylglycerol synthesis?

Question 4:

The glutamine synthetase of E. coli is independently modulated by various products of glutamine metabolism (see Fig. 22-8). In this concerted inhibition, the extent of enzyme inhibition is greater than the sum of the separate inhibitions caused by each product. For E. coli grown in a medium rich in histidine, what would be the advantage of concerted inhibition?