Class 9: MCQ's on Carbohydrates and its Metabolism

Ans. c) Gluconeogenesis

Explanation: Gluconeogenesis, which literally means "new glucose creation", is a pathway by which the body creates glucose (glucose is needed for energy). Liver and kidneys are the main site of Gluconeogenesis. The metabolic pathways that result in the production of glucose are: glycerol, lactate, pyruvate, alanine, and glutamine. If a person's diet does not contain carbohydrates, then gluconeogenesis will occur to provide them with glucose since they are the only nutrients that can be metabolised within this pathway.

Ans. a) Liver

Explanation: Gluconeogenesis is a metabolic process that takes place in the liver and certain cells in the kidneys and is responsible for maintaining the blood glucose concentration during periods of fasting (usually overnight). It is the simultaneous formation of glucose and alanine from non-carbohydrate sources such as lactate or glycerol in the liver and kidney cortex. The breakdown process for the liver and kidney cortex involves converting certain precursors into intermediates called keto acids.

Ans. d) Lysine or leucine

Explanation: Degradation of lysine and leucine is an important source of the acetyl-CoA used in the synthesis of gluconeogenesis glycogen. The above idea of gluconeogenesis means only leucine or lysine is the substrate which can be used for gluconeogenesis , as these amino acids produce only acetyl-CoA upon degradation. Animals cannot carry out gluconeogenesis by two acetyl hydrates of acetyl-CoA.

Ans. a) Pyruvate carboxylase

Explanation: Pyruvate carboxylase is an enzyme that catalyses the synthesis of oxaloacetate from pyruvate. The reverse reaction is catalysed by pyruvate carboxykinase. The reaction proceeds in two steps: a slow irreversible step that serves as an energy-conserving measure, and a fast second step which produces oxaloacetate.

Ans. b) False

Explanation: The process of gluconeogenesis begins in the liver. The liver cells of mammals, including humans and rodents, have glucose 6-phosphatase that is essential for gluconeogenesis. The absence of glucose 6-phosphatase enzyme in animal muscle and brain explains why these organs cannot carry out the process of gluconeogenesis.

Ans. c) Muscle and liver

Explanation: Glycogen is produced in liver and muscle tissue. Muscle glycogen along with blood glucose stores are crucial for energy supply during exercise. The liver plays a vital role in glucose production through glycogenolysis using glucagon hormone as a stimulus; on the other hand, the muscles store an excess of glycogen until they are used.

Ans. c) UDP - glucose

Explanation: Glycogen synthase acts to catalyse the reaction that converts uridine triphosphate and glucose 1-phosphate to UDP-glucose and glycogen when coupled with energy in the form of ATP. The addition of UDP-glucose into glycogen is known as elongation.

Ans. c) Glycogenin

Explanation: Glycogen is an important energy storage compound in animal and plant cells. In order to incorporate the next glucosyl residue into the chain, a primer is needed to bridge the gap between the terminal glucose of the last glucosyl residue and the first glucose of the next one. Glycogenin, a small protein from bacteria, can act as such a primer via its priming action.

Ans. a) Branching enzyme

Explanation: Branching enzyme adds a branch at four residues away from the existing branch. This specific enzyme is an allosteric enzyme in which it is primarily responsible for the production of glycogen, a polymer of glucose that is stored in the form of insoluble (branching enzyme). This enzyme catalyses the synthesis of branches in glycogen.

Ans. b) Glucagon

Explanation: The secretion of glucagon is activated by low blood glucose concentration (<70 mg/dl), whereas its synthesis is stimulated by the presence of amino acids. Glycogenolysis and gluconeogenesis are accelerated with the increase in hepatic glucose production, as well as after insulin administration, which makes glucagon a counter-regulatory hormone for insulin.