Question 1

Glycogen phosphorylaseacts on the non-reducing ends of glycogen.

Accepted Answer

Glycogen phosphorylase is an enzyme that cleaves glucose molecules from the non-reducing ends of glycogen, releasing glucose-1-phosphate.

Question 2

Glycogen storage disease results in glycogen accumulation in the liver and kidneys. It can be controlled by changing the diet.

Accepted Answer

Glycogen storage disease is a genetic disorder that affects the body's ability to break down glycogen, leading to its accumulation in the liver and sometimes in the kidneys. The condition can be managed by controlling the diet and administering certain medications.

Question 3

Glycogenin is a protein scaffold for glycogen as well as an enzyme catalyzing extension of the glycogen primer.

Accepted Answer

Glycogenin is both a protein scaffold for glycogen and an enzyme that catalyzes the extension of the glycogen primer.

Question 4

UDP-glucose is a precursor of glycogen in all cells.

Accepted Answer

UDP-glucose is a precursor of glycogen primarily in liver and muscle cells, not in all cells.

Question 5

The brain normally uses both glucose and fatty acids as energy sources.

Accepted Answer

The brain primarily uses glucose as its main source of energy and has a limited ability to metabolize fatty acids directly.

Question 6

Under fasting conditions the liver increases its rate of gluconeogenesis to maintain blood glucose levels, but this can only be maintained for a few days before the rate decreases.

Accepted Answer

This is true. After a few days of fasting, the liver's glycogen stores become depleted and the rate of gluconeogenesis slows down, leading to decreased blood glucose levels. This is why prolonged fasting can be dangerous and lead to hypoglycemia.

Question 7

Two molecules of NADPH are generated for each molecule of glucose 6-phosphate that enters the pentose phosphate pathway.

Accepted Answer

During the oxidative phase of the pentose phosphate pathway, two molecules of NADPH are generated for every molecule of glucose 6-phosphate that enters the pathway. Therefore, the statement is true.

Question 8

Rapidly dividing cells generally have a high pentose phosphate pathway activity.

Accepted Answer

The pentose phosphate pathway plays a vital role in providing precursors for nucleotide synthesis in rapidly dividing cells. Therefore, they have a high pentose phosphate pathway activity to meet their metabolic demands.

Question 9

There are no branched polysaccharide chains in limit dextrin.

Accepted Answer

Limit dextrin contains branched polysaccharide chains, as it is a product of partial hydrolysis of amylopectin, which is a branched molecule.

Question 10

The enzymes transketolase and transaldolase of the pentose phosphate pathway are each very specific for only one substrate.

Accepted Answer

Both transketolase and transaldolase are able to catalyze reactions using a range of substrates, although they do show some specificity for certain molecules.

Question 11

The enzyme transketolase transfers 2-carbon units from ketose phosphates to aldose phosphates.

Accepted Answer

Transketolase is an enzyme that transfers 2-carbon units from ketose phosphates (e.g. fructose-6-phosphate, xylulose-5-phosphate) to aldose phosphates (e.g. glyceraldehyde-3-phosphate, erythrose-4-phosphate) in the non-oxidative phase of the pentose phosphate pathway.

Question 12

Since caffeine inhibits cAMP phosphodiesterase, too much coffee can result in the synthesis of too much glycogen.

Accepted Answer

Caffeine inhibits cAMP phosphodiesterase, which leads to an increase in cAMP levels. However, cAMP is not directly involved in glycogen synthesis, so the statement that too much coffee can result in the synthesis of too much glycogen is false.

Question 13

Glucose 1,6-bisphosphate is the primary starting substrate for the pentose phosphate pathway.

Accepted Answer

Glucose 6-phosphate is the primary starting substrate for the pentose phosphate pathway.

Question 14

Epinephrine can stimulate glycogen degradation while at the same time, lowering glycogen synthesis.

Accepted Answer

Epinephrine activates the enzyme glycogen phosphorylase, which breaks down glycogen into glucose. At the same time, it inhibits the enzyme glycogen synthase, which is responsible for forming glycogen from glucose. Therefore, epinephrine can both stimulate glycogen degradation and lower glycogen synthesis.

Question 15

Enzymes to regulate glycogen metabolism are always active when phosphorylated by protein kinases.

Accepted Answer

Enzymes that regulate glycogen metabolism can be either activated or inactivated by phosphorylation, depending on the specific enzyme. For example, glycogen phosphorylase is activated by phosphorylation, while glycogen synthase is inactivated by phosphorylation.

Quiz 12: Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism