Homework 13 Flashcards
(16 cards)
When blood sugar levels are high in a nondiabetic, insulin normally inhibits which pathways in liver cells?
Gluconeogenesis and glycogen degradation
When blood sugar levels are high in a nondiabetic, insulin normally inhibits which pathways in muscle cells?
Fatty acid oxidation
Insulin is a signal that indicates a fed state. Which of the following functions does insulin promote?
I. an increase in gluconeogenesis
II. the biosynthesis of macromolecules
III. an increase in fuel storage
IV. the uptake of fuel molecules in some cells
II, III, and IV are functions promoted by insulin
Which of the following statements about skeletal muscle cells is/are TRUE?
I. Skeletal muscle cells can use glucose, fatty acids, and ketone bodies as a source of fuel.
II. Glycogen degradation and synthesis rates are equal in skeletal muscle cells.
III. Skeletal muscle cells respond to glucagon by performing gluconeogenesis.
I only
Which of the following statements about liver is/are TRUE?
I. Liver’s preferred fuel source under most physiological conditions is glucose.
II. Liver is responsible for stabilizing blood glucose levels.
III. Liver cells respond to glucagon by performing gluconeogenesis.
II and III only
Which statement, if any, correctly describes a similarity between glucagon and insulin signaling pathways?
I. Both signaling pathways always produce an increase in metabolic enzyme activity.
II. In both pathways, hormone binding induces a conformational change in the membrane receptor.
III. Stimulating the signaling pathway for both hormones eventually activates a kinase.
IV. None of the above correctly describes a similarity.
II
In a cell, ___ levels of ATP will inhibit PFK-1 by binding to a subunit’s ____ site and stabilizing the ____ .
High, allosteric, T form
In a cell, high levels of F-2,6-BP will ___ PFK-1 by binding to a subunit’s ___ site and stabilizing the ___.
Stimulate, allosteric, R form
Which of the following statements is FALSE?
I. Insulin decreases gluconeogenesis in the liver and increases glucose uptake and glycolysis in muscle.
II. Phosphofructokinase-1 is an enzyme target of glucagon signaling.
III. Glycogen phosphorylase is an enzyme target of insulin signaling but not of glucagon signaling.
IV. Glucagon increases protein kinase A activity in the liver in response to the fasting state.
III
In liver, glucagon stimulates glycogen breakdown. Although you might expect glucagon to stimulate oxidation of this glucose to make energy, instead glucagon inhibits glycolysis and stimulates gluconeogenesis in liver. Why?
A primary function of liver is to increase blood glucose concentration when glucagon is present.
Glucose-6-phosphatase is enzyme in glycogen degradation and in gluconeogenesis whose substrate is glucose-6-phosphate. If an individual possesses a glucose-6-phosphatase deficiency, what would happen to their blood glucose levels?
Blood glucose levels would be chronically low because dephosphorylation of glucose-6-phosphate is decreased.
Which of the following statements about glycogen metabolism is TRUE?
A. Glucose is the only energy source that skeletal muscle and liver cells can use.
B. Maximal rates of glycogen breakdown and synthesis are about equal in the liver.
C. The maximal rate of glycogen breakdown is significantly higher than the maximal rate of glycogen synthesis when skeletal muscle cells are active.
D. A and B, but not C.
E. B and C, but not A.
F. A, B, and C are true statements.
E.
Glucagon signaling leads to ___ of pyruvate kinase by a(n) ___.
Phosphorylation, kinase
Glucagon acts on liver cells and initiates gluconeogenesis. The major effect of glucagon is to increase cyclic adenosine monophosphate ( cAMP ) levels in the liver cells, which in turn phosphorylate the pyruvate kinase that increases the concentration of phosphoenolpyruvate by decreasing the concentration of pyruvate. This inhibition of pyruvate kinase is due to the fact that the phosphorylated form of the enzyme is far less active than the dephosphorylated form.
Which of the following statements correctly compares glycogen synthesis and degradation?
I. Glycogenesis occurs in liver cells, but not in skeletal muscle cells.
II. Glycogenesis is a catabolic pathway while glycogenolysis is an anabolic pathway.
III. ATP is required for both glycogenesis and glycogenolysis to occur.
IV. Both glycogenesis and glycogenolysis are exergonic processes in a cell.
IV.
Glycogen synthase is an enzyme important for making glycogen. In response to glucagon, glycogen synthase is?
Inactivated by phosphorylation
Which of the following statements helps explain why insulin stimulates glycolysis in liver cells?
A. Liver cells use glucose to produce ATP for its own needs when there is an abundance.
B. Liver cells use glucose oxidation reactions to produce acetyl-CoA, which is then used to synthesize fatty acids to store energy.
C. Liver cells use the glycolysis pathway to store excess glucose as glycogen.
D. A and B, but not C.
E. A, B and C all help explain.
D.
