Question

1. Assume you replaced the ara gene with the gene for amylase in the ara operon. What would be produced in the presence of arabinose?

2. How does Enterococcus grow without accumulating H2O2?

3. What sugar did Saccharomyces metabolize best?

4. Where is Saccharomyces found naturally? How does this correspond with its sugar-metabolizing capability?

Answer 1

1.  L-arabinose selectively inhibits intestinal sucrase(amylases) activity in an uncompetitive manner and suppresses the glycemic response after sucrose ingestion by inhibition of sucrase activity.

2. Mutation of an NADH oxidase-encoding gene eliminated nearly all NADH oxidase activity and reduced hydrogen peroxide production. Mutation of an NADH peroxidase-encoding gene resulted in the enhanced accumulation of hydrogen peroxide.

3. Lactose and starch.

4. They are found in the wild growing on the skins of grapes and other fruits. The metabolic networks employed for the metabolism of hexoses and disaccharides share the same pathways (most metabolic building blocks are derived from intermediaries of glycolysis, the tricarboxylic acid cycle (TCA), and the pentose phosphate pathway) and differ only in the initial basic steps of metabolism. However, significant changes could be observed when the metabolism of sugars is compared with that of the two-carbon compounds. In this case, the TCA, the pentose phosphate pathway together with gluconeogenesis and the glyoxylate cycle are essential for the provision of anabolic precursors.