Question 1

Which factor directly results in the activation of glycogen synthase?

Accepted Answer

A)  binding of glucose-6-phosphate 
B)  dephosphorylation of multiple residues by phosphoprotein phosphorylase-1 (PP1) 
C)  phosphorylation of specific residues by casein kinase II (CKII) 
D)  phosphorylation of specific residues by glycogen synthase kinase-3 (GSK-3) 
E)  the presence of insulin 
A)  binding of glucose-6-phosphate 
B)  dephosphorylation of multiple residues by phosphoprotein phosphorylase-1 (PP1) 
C)  phosphorylation of specific residues by casein kinase II (CKII) 
D)  phosphorylation of specific residues by glycogen synthase kinase-3 (GSK-3) 
E)  the presence of insulin B

Question 2

Describe the process of glycogen breakdown in muscle. Include a description of the structure of glycogen, the nature of the breakdown reaction and the breakdown product, and the required enzyme(s).

Accepted Answer

Glycogen is a highly branched polysaccharide that serves as a storage form of glucose in the body, particularly in the liver and muscle cells. The structure of glycogen consists of a core protein called glycogenin, with glucose molecules attached in chains through alpha-1,4-glycosidic bonds and branching points created by alpha-1,6-glycosidic bonds.

The breakdown of glycogen in muscle cells, known as glycogenolysis, is a crucial process for providing energy during periods of high demand, such as exercise. This breakdown reaction is catalyzed by the enzyme glycogen phosphorylase, which cleaves glucose molecules from the non-reducing ends of the glycogen chains, releasing glucose-1-phosphate as the breakdown product. This process continues until the branching points are reached, at which point the enzyme debranching enzyme is required to remove the branching glucose molecule and allow further glycogen phosphorylase action.

The glucose-1-phosphate produced from glycogen breakdown can then be converted to glucose-6-phosphate and enter glycolysis to generate ATP for muscle contraction. This process allows for rapid mobilization of glucose stores in the form of glycogen to meet the energy demands of muscle cells.

Question 3

The glycogen-branching enzyme catalyzes:

Accepted Answer

A)  degradation of ($\alpha$1 $\rightarrow$  4) linkages in glycogen 
B)  formation of ($\alpha$1 $\rightarrow$ 4) linkages in glycogen. 
C)  formation of ($\alpha$1 $\rightarrow$  6) linkages during glycogen synthesis. 
D)  glycogen degradation in tree branches. 
E)  removal of unneeded glucose residues at the ends of branches. 
A)  degradation of ($\alpha$1 $\rightarrow$  4) linkages in glycogen 
B)  formation of ($\alpha$1 $\rightarrow$ 4) linkages in glycogen. 
C)  formation of ($\alpha$1 $\rightarrow$  6) linkages during glycogen synthesis. 
D)  glycogen degradation in tree branches. 
E)  removal of unneeded glucose residues at the ends of branches. C

Question 4

The flux control coefficient for an enzyme in a multistep pathway depends on the:

Accepted Answer

A)  concentration of the enzyme itself. 
B)  concentration of other enzymes in the pathway. 
C)  levels of regulatory molecules. 
D)  amounts of substrate molecules present at each step. 
E)  All of the answers are correct. 
A)  concentration of the enzyme itself. 
B)  concentration of other enzymes in the pathway. 
C)  levels of regulatory molecules. 
D)  amounts of substrate molecules present at each step. 
E)  All of the answers are correct.

Question 5

Explain why reactions that are far from equilibrium need to be regulated.

Accepted Answer

Reactions that are far from equilibrium

Question 6

To which enzyme in glycolysis is phosphoglucomutase MOST similar?

Accepted Answer

A)  phosphohexose isomerase 
B)  triosphosphate isomerase 
C)  phosphoglycerate mutase 
D)  enolase 
E)  phosphoglycerate kinase 
A)  phosphohexose isomerase 
B)  triosphosphate isomerase 
C)  phosphoglycerate mutase 
D)  enolase 
E)  phosphoglycerate kinase

Question 7

Which statement is NOT associated with controlling the rate of glycogen synthesis in hepatocytes?

Accepted Answer

A)  Insulin stimulates the translocation of GLUT 2 transporters to the plasma membrane. 
B)  Insulin induces the synthesis of hexokinase IV. 
C)  Glucagon inhibits the activity of glycogen synthase via covalent modification. 
D)  Insulin activates phosphorylase a phosphatase. 
E)  Epinephrine and insulin both result in the phosphorylation of the glycogen targeting protein GM. 
A)  Insulin stimulates the translocation of GLUT 2 transporters to the plasma membrane. 
B)  Insulin induces the synthesis of hexokinase IV. 
C)  Glucagon inhibits the activity of glycogen synthase via covalent modification. 
D)  Insulin activates phosphorylase a phosphatase. 
E)  Epinephrine and insulin both result in the phosphorylation of the glycogen targeting protein GM.

Question 8

Why is citrate, in addition to being a metabolic intermediate in aerobic oxidation of fuels, an important control molecule for a variety of enzymes?

Accepted Answer

Citrate plays a crucial role in cellular

Question 9

In the glycolytic path from glucose to pyruvate, three steps are practically irreversible. What are these steps, and how is each bypassed in gluconeogenesis? What advantages does an organism gain from having separate pathways for anabolic and catabolic metabolism? What are the disadvantages?

Accepted Answer

The three irreversible steps in the glyc

Question 10

Glycogen is converted to monosaccharide units by:

Accepted Answer

A)  glucokinase. 
B)  glucose-6-phosphatase 
C)  glycogen phosphorylase. 
D)  glycogen synthase. 
E)  glycogenase. 
A)  glucokinase. 
B)  glucose-6-phosphatase 
C)  glycogen phosphorylase. 
D)  glycogen synthase. 
E)  glycogenase.

Question 11

Which factor does NOT contribute to the regulation of enzymatic activity?

Accepted Answer

A)  protein phosphorylation 
B)  allosteric regulation 
C)  protein stability 
D)  mRNA stability 
E)  DNA stability 
A)  protein phosphorylation 
B)  allosteric regulation 
C)  protein stability 
D)  mRNA stability 
E)  DNA stability

Question 12

Both hexokinase IV and hexokinase I phosphorylate glucose at carbon-6. What properties of hexokinase IV make it important for maintaining stable blood sugar levels?

Accepted Answer

Hexokinase IV, also known as glucokinase

Question 13

What is a "futile cycle"? Give an example of a potential futile cycle in carbohydrate metabolism, and describe methods used by cells or organisms to avoid the operation of the futile cycle.

Accepted Answer

A "futile cycle" refers to a metabolic p

Question 14

An altered version of glycogen synthase is produced in the laboratory, with one of its amino acid residues substituted for another. Unlike normal glycogen synthase, the activity of the mutant protein is unaffected by glycogen synthase kinase-3. Which mutation is MOST likely to produce this effect?

Accepted Answer

A)  Cys $\rightarrow$ Ser 
B)  Ile $\rightarrow$ Thr 
C)  Ser $\rightarrow$ Ala 
D)  Cys $\rightarrow$ Met 
E)  Thr $\rightarrow$ Ser 
A)  Cys $\rightarrow$ Ser 
B)  Ile $\rightarrow$ Thr 
C)  Ser $\rightarrow$ Ala 
D)  Cys $\rightarrow$ Met 
E)  Thr $\rightarrow$ Ser

Question 15

Which enzyme is used in both glycolysis and gluconeogenesis?

Accepted Answer

A)  3-phosphoglycerate kinase 
B)  hexokinase 
C)  glucose 6-phosphatase 
D)  phosphofructokinase-2 
E)  pyruvate kinase 
A)  3-phosphoglycerate kinase 
B)  hexokinase 
C)  glucose 6-phosphatase 
D)  phosphofructokinase-2 
E)  pyruvate kinase

Question 16

Which statement is TRUE of glycogen synthase?

Accepted Answer

A)  Activation of the enzyme involves a phosphorylation. 
B)  It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain by formation of ($\alpha$1 $\rightarrow$  4) bonds. 
C)  It uses glucose-6-phosphate as donor of glucose units 
D)  It catalyzes addition of glucose residues at branch points by formation of ($\alpha$1 $\rightarrow$  6) bonds. 
E)  The enzyme has measurable activity only in liver. 
A)  Activation of the enzyme involves a phosphorylation. 
B)  It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain by formation of ($\alpha$1 $\rightarrow$  4) bonds. 
C)  It uses glucose-6-phosphate as donor of glucose units 
D)  It catalyzes addition of glucose residues at branch points by formation of ($\alpha$1 $\rightarrow$  6) bonds. 
E)  The enzyme has measurable activity only in liver.

Question 17

The rate of glycolysis is tightly regulated in all cells. Regulation is important to ensure that:

Accepted Answer

A)  cells energy needs met. 
B)  fuel is not wasted. 
C)  there are appropriate levels of intermediates required for other purposes. 
D)  fuel is not wasted and the cells energy needs are met. 
E)  All of the answers are correct. 
A)  cells energy needs met. 
B)  fuel is not wasted. 
C)  there are appropriate levels of intermediates required for other purposes. 
D)  fuel is not wasted and the cells energy needs are met. 
E)  All of the answers are correct.

Question 18

The enzyme glycogen phosphorylase:

Accepted Answer

A)  catalyzes a cleavage of $\beta$ (1 $\rightarrow$ 4) bonds. 
B)  catalyzes a hydrolytic cleavage of$\alpha$ (1 $\rightarrow$  4) bonds. 
C)  is a substrate for a kinase. 
D)  uses glucose 6-phosphate as a substrate. 
E)  uses glucose as a substrate. 
A)  catalyzes a cleavage of $\beta$ (1 $\rightarrow$ 4) bonds. 
B)  catalyzes a hydrolytic cleavage of$\alpha$ (1 $\rightarrow$  4) bonds. 
C)  is a substrate for a kinase. 
D)  uses glucose 6-phosphate as a substrate. 
E)  uses glucose as a substrate.

Question 19

Which process is NOT an event in the signaling pathway from insulin to glycogen synthase kinase 3 (GSK3) inactivation?

Accepted Answer

A)  insulin binding to a tyrosine kinase receptor 
B)  activation of insulin receptor substrate-1 (IRS-1) by phosphorylation 
C)  phosphatidylinositol 3-kinase associating with IRS-1 generates phosphatidylinositol 3,4,5-triphosphate 
D)  protein kinase B being activated by a protein kinase known as PDK-1 
E)  protein kinase B phosphorylating GSK3, resulting in its activation 
A)  insulin binding to a tyrosine kinase receptor 
B)  activation of insulin receptor substrate-1 (IRS-1) by phosphorylation 
C)  phosphatidylinositol 3-kinase associating with IRS-1 generates phosphatidylinositol 3,4,5-triphosphate 
D)  protein kinase B being activated by a protein kinase known as PDK-1 
E)  protein kinase B phosphorylating GSK3, resulting in its activation

Question 20

Which statement is TRUE of glycogen synthase?

Accepted Answer

A)  It is activated by at least 11 different protein kinases. 
B)  It is activated by Ca2+ ions in skeletal muscle. 
C)  It catalyzes formation of ($\alpha$1-4) glycosidic bonds. 
D)  It uses glucose-1-phosphate as a substrate. 
E)  All of the statements are true true. 
A)  It is activated by at least 11 different protein kinases. 
B)  It is activated by Ca2+ ions in skeletal muscle. 
C)  It catalyzes formation of ($\alpha$1-4) glycosidic bonds. 
D)  It uses glucose-1-phosphate as a substrate. 
E)  All of the statements are true true.

Exam 15: Principles of Metabolic Regulation

Which factor directly results in the activation of glycogen synthase?

Describe the process of glycogen breakdown in muscle. Include a description of the structure of glycogen, the nature of the breakdown reaction and the breakdown product, and the required enzyme(s).

The glycogen-branching enzyme catalyzes:

The flux control coefficient for an enzyme in a multistep pathway depends on the:

Explain why reactions that are far from equilibrium need to be regulated.

To which enzyme in glycolysis is phosphoglucomutase MOST similar?

Which statement is NOT associated with controlling the rate of glycogen synthesis in hepatocytes?

Why is citrate, in addition to being a metabolic intermediate in aerobic oxidation of fuels, an important control molecule for a variety of enzymes?

In the glycolytic path from glucose to pyruvate, three steps are practically irreversible. What are these steps, and how is each bypassed in gluconeogenesis? What advantages does an organism gain from having separate pathways for anabolic and catabolic metabolism? What are the disadvantages?

Glycogen is converted to monosaccharide units by:

Which factor does NOT contribute to the regulation of enzymatic activity?

Both hexokinase IV and hexokinase I phosphorylate glucose at carbon-6. What properties of hexokinase IV make it important for maintaining stable blood sugar levels?

What is a "futile cycle"? Give an example of a potential futile cycle in carbohydrate metabolism, and describe methods used by cells or organisms to avoid the operation of the futile cycle.

An altered version of glycogen synthase is produced in the laboratory, with one of its amino acid residues substituted for another. Unlike normal glycogen synthase, the activity of the mutant protein is unaffected by glycogen synthase kinase-3. Which mutation is MOST likely to produce this effect?

Which enzyme is used in both glycolysis and gluconeogenesis?

Which statement is TRUE of glycogen synthase?

The rate of glycolysis is tightly regulated in all cells. Regulation is important to ensure that:

The enzyme glycogen phosphorylase:

Which process is NOT an event in the signaling pathway from insulin to glycogen synthase kinase 3 (GSK3) inactivation?

Which statement is TRUE of glycogen synthase?

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biological Membranes and Transport

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Protein Metabolism

Regulation of Gene Expression

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