Chapter 20 Self-test questions

. Which of the following statements about the regulation of a metabolic pathway is correct?

Most metabolic pathways are not regulated.

Regulation of metabolic pathways always involves changing the amount of enzymes.

Metabolic regulation always depends on control by hormones.

Most metabolic pathways are regulated.

. Which of the following correctly exhibits an example of metabolic control?

In cases where the direction of a metabolic pathway has to be reversed the pathway is controlled at an irreversible step.

Regulatory changes in a pathway always occur slowly over periods of several hours or more.

Enzymes which are controlled are always those which catalyse the first reaction of the pathway.

Most enzyme control mechanisms are irreversible.

. Which of the following statements about the control of enzyme activity by phosphorylation is correct?

Phosphorylation of an enzyme is not a reversible process since it is a covalent modification.

Phosphorylation of an enzyme occurs by protein phosphatases.

Phosphorylation of an enzyme is an intracellular process and cannot occur in response to external signals.

Phosphorylation of an enzyme results in a conformational change.

. Which of the following statements about the integration of fat and carbohydrate metabolism control is correct?

High insulin/glucagon ratio inhibits lipogenesis in liver.

High insulin/glucagon ratio activates lipolysis in muscle

Low insulin/glucagon ratio activates lipolysis in adipocytes.

Insulin-dependent glucose transporters are recruited to their functional membrane site when insulin levels are low.

. Which type of metabolic fuel is utilised for generating glucose under conditions of severe starvation?

Glycogen.

Fats.

Starch.

Amino acids.

. Liver glycogen is used in fasting to provide glucose for use by other tissues including the brain. Muscle glycogen is not. What is the explanation for this?

Muscle does not have a debranching enzyme.

Muscle cannot degrade glycogen further than glucose-1-phosphate.

Muscle lacks glucose-6-phosphatase.

The liver provides all the glucose necessary for metabolism and there is no need for muscle to do the same.

. Which is true of brain metabolism in starvation?

The brain can only use glucose as fuel.

Up to a quarter of the energy requirement of the brain can come from fatty acids.

Up to half the energy requirement of the brain can be met by ketone bodies.

The brain can use glucogenic amino acids for energy.

. Which of the following statements about the control of enzyme activity by phosphorylation is correct?

Enzyme control by phosphorylation is irreversible.

Phosphorylation of enzymes is carried out by phosphoprotein phosphatases.

Phosphorylation of enzymes only occurs at specific tyrosine residues.

Phosphorylation of an enzyme results in a conformational change.

. Which of the following statements about the control of muscle glycogen phosphorylase is correct?

Muscle glycogen phosphorylase is allosterically activated by cAMP.

Muscle glycogen phosphorylase is allosterically activated by ATP.

Muscle glycogen phosphorylase normally exists in the a form.

Muscle glycogen phosphorylase is activated by phosphorylation by an active phosphorylase kinase.

. Which of the following statements about the control of glycogen synthase are correct? Please select all that apply.

Glycogen synthase kinase 3 is inactivated by a protein phosphatase.

Glycogen synthase kinase 3 is activated in the presence of insulin.

PKA and glycogen synthase kinase 3 phosphorylate glycogen synthase at different sites.

The phosphorylation by glycogen synthase kinase 3 is inhibited by insulin.

Insulin activates protein kinase B which phosphorylates glycogen synthase.

. What is the significance of irreversible reactions in metabolic pathways?

They provide enough free energy for the pathway to proceed.

They do not need activation energy as they are spontaneous.

Futile cycles are prevented.

They prevent the conversion of lactate into glucose in skeletal muscle.

. How is the signal produced by the second messenger cAMP terminated?

Phosphodiesterase cleaves cAMP to AMP.

The catalytic subunit of protein kinase A is inactivated by phosphorylation.

Adenylate cyclase is inhibited by the G protein subunits.

Phosphorylase kinase inhibits adenylate cyclase.

Chapter 20 Self-test questions

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