biochemistry guide

8/8/2019 Biochemistry Guide

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1) A 21 year-old man has muscle fatigue after strenuous exercise. He occasionally notes that his

urine is brown. His blood glucose is normal but the ischemic exercise test was abnormal. Which

enzyme is most likely deficient in this patient?

a) G6Pase

b) 1,4 glucosidase

c) liver phosphorylase

d) muscle phosphorylase

2) In the well fed state, the rate limiting set in the storage of glucose is

a) Adding G1P to the glycogen particle;

b) Activating the sugar molecule to UDP-glucose;

c) Catalyzing the 1-6 glycosidic linkage;

d) Adding the activated sugar to the glycogen particle.

3) A woman with insulin dependent diabetes was late for her tennis match and didn't have time to

eat breakfast. She injected her usual dose of insulin, normally administered 30 minutes before

breakfast. The insulin injection will

a) have little effect because her tissues are utilizing fatty acids under these conditions;

b) stimulate the transport of glucose into skeletal muscles and its conversion to glycogen;

c) decrease the concentration of fructose 2,6-bisphosphate in the liver;

d) increase the uptake of glucose into brain.

4) After only an hour of exercise, the tennis player became dizzy and explained to her friend whathad happened before she passed out. Her friend gave her some hard candy to eat. It would have

been a good idea to give her an injection of glucagon in order to:

a) stimulate the formation of blood glucose from muscle glycogen;

b) activate glycogenolysis in the liver;


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c) activate gluconeogenesis;

d) prevent muscle tissues from taking up glucose.

1. A 23 year old woman with systemic lupus erythematous requires corticosteroids to control the

disease. Steroids interact with their target cells by

a. activating transcription of specific genes

b. activating cytoplasmic protein kinases

c. binding to membrane bound receptors

d. using cAMP as an intracellular second message

2. All of the following statements about integral membrane proteins are true EXCEPT

a. they are associated with lipid in the membrane.

b. they can be transmembranous.

c. they are amphipathic.

d. they are symmetrically distributed within the membrane.

e. they are only removed from the membrane by drastic treatments.

1) A woman with insulin dependent diabetes was late for her tennis match and didn't have time to

eat breakfast. She injected her usual dose of insulin, normally administered 30 minutes before

breakfast. The insulin injection is likely to

a) have little effect because her tissues are already utilizing fatty acids;

b) stimulate the transport of glucose into skeletal muscles

c) decrease the concentration of fructose 2,6-bisphosphate in the liver;

d) increase the uptake of glucose into brain.

1. During glucose influx from the gut after a normal carbohydrate meal,

a. Muscle glycolysis goes up;


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b. the glucose saturation of liver glucokinase goes up;

c. red cell glycolysis goes up;

d. the AMP concentration goes up and activates liver PFK;

e. All of the above.

2. When exercising, a 19 year old man develops painful cramps that are associated with

myoglobinuria (presence of myoglobin in the urine, typically from muscle breakdown).

Administration of glucose did not alleviate the symptoms. Additional studies indicated that he has a

hemolytic anemia. The patient most likely has a deficiency in which of the following enzymes?

a. Branching enzyme

b. G6Pase

c. Alpha glucosidase

d. Liver phosphorylase

e. PFK

3. Glycolysis is a highly regulated pathway. Which one of the following statements isnot true?

a. The energy state of the cell (ATP, ADP, AMP) allosterically regulates PFK

b. Glucose-6-P is a feedback inhibitor of hexokinase

c. Increased levels of glucose in most cells greatly increase the rate of glycolysis

d. At low I/G, glycolysis is inhibited in the liver

2) In the fasting state, which of the following statements about glucagons best explains how the

hormone functions to maintain adequate blood glucose levels?

a) It activates adenylate cyclase in skeletal muscle

b) It facilitates glucose uptake into skeletal muscle

c) It increases in response to decreased blood glucose levels

d) It increases in response to increased blood glucose levels


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A 3 days old infant was admitted to the hospital because he had not regained consciousness after

an attack of seizures. Blood chemistry data on admission showed:

metabolite concentration

glucose, 1.5mM

HCO3- 25 mM

lactate 1.5 mMpyruvate 0.15mM

Subsequent fasting studies showed that he always became hypoglycemic at about 3.5 hours

following a feeding.

1) An oxidative challenge was performed by incubating erythrocytes with phenylhydrazine. The

recovery of reduced glutathione in erythrocytes from the patient was similar to that in erythrocytes

from a normal control. The diagnostic aim of the phenylhydrazine test was to

a) defect in PFK (phosphofructokinase);

b) defect in G6PD (glucose-6-phosphate dehydrogenase);

c) a defect in oxygen binding to hemoglobin;

d) None of the above.

2) Which of the following is not a function of the pentose pathway?

a) To generate reducing equivalents (NADPH) for reductive synthesis

b) To generate NADPH to maintain protein sulfhydryls in the reduced state

c) To generate pentoses (ribose) precursors for nucleic acid synthesis

d) To generate NADPH for the reduction of NAD+ to NADH

3) The blood chemistry and the outcome of the fasting study are consistent with:

a) Impaired glycogen metabolism;

b) Hyperinsulinism;

c) Defect in glucagon secretion;

d) All of the above.


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1) Some patients with erythrocytosis (excess RBCs) have a mutation that converts a lysine to alanine

at amino acid 82 in the subunit of hemoglobin. This particular lysine normally protrudes into the

central cavity of deoxyhemoglobin, where it participates in binding 2,3-bisphosphoglycerate (BPG).

Which of the following effects would you predict this mutation to have on the affinity of

hemoglobin for BPG and O2, respectively, in such patients?

a) Increase, Decrease

b) Increase, Increase

c) Decrease, Increase

d) Decrease, Decrease

2) A 52-year old man with chronic bronchitis requires continuous supplementary oxygen to

maintain adequate oxygen PO2. Which of the following would improve oxygen delivery to thepatients tissue?

a) Decreased arterial pH

b) Decreased red blood cell 2,3,BPG

c) Decreased temperature

d) Hyperventilation

4) A muscle biopsy revealed normal glycogen content, which suggests:

a) release of glucose from glycogen is normal;

b) conversion of alanine to glucose in muscle helped minimize the hypoglycemia;

c) infusions of alanine should be instituted immediately to supply gluconeogenic precursors;

d) If infusions of glucose were instituted immediately the patient would respond quickly and

favorably.

The physicians performed a glucagon test on the child about eight hours after a feeding and foundthat the amount of glucose released into the patient's blood was abnormally large.

1. Which one is a characteristic of phospholipids?

a. They must contain choline and glycerol


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b. They are not charged in the body

c. They are a major component of membranes

d. They are not soluble in water

2. Which ones(s) of the following are untrue about the processes of active and passive transport?

a. Primary active transport uses ATP directly for transport

b. Passive transport may occur using the energy of an electrochemical gradient

c. Facilitated diffusion is another form of active transport.

d. Active transport requires energy; passive transport does not

3. Which of the following groups of lipids are important constituents of cell membranes?

a. phospholipid, cholesterol, triglyceride

b. triglyceride, sphingomyelin, glucocerebroside

c. phospholipid, ganglioside, cholesterol

d. phospholipid, lysophospholipid, diglyceride

4. All of the following statements about lipid bilayer membranes are correct, EXCEPT

a. cholesterol can decrease the fluidity of a membrane.

b. water molecules can diffuse through a lipid bilayer.

c. Lipids can readily diffuse laterally in the membrane.

d. lipids can rotate end-over-end (Flip-Flop) easily.

e. all major components of a lipid membrane show asymmetric arrangement.

1) A 1-yr old boy has had progressive psychomotor retardation, which is associated with lactic

acidosis. The blood glucose and hemoglobin concentrations are both normal. The child most likely

has a deficiency in which of the following enzymes?


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a) PEPCK

b) Phosphofructokinase

c) Pyruvate dehydrogenase

d) Pyruvate kinase

1) A competiveInhibitors alters the rate of a reaction by

a) Decreasing the Vmax and decreasing Km.

b) Increasing the Vmax and increasing Km.

c) Increasing the Vmax without effecting Km

d) Increasing Km without effecting Vmax

e) Decreasing the Vmax without effecting Km

2) Which of the following statements about the velocity of an enzyme catalyzed reaction is most

accurate?

a) It increases as the temperature increases

b) It is always dependent on the substrate concentration

c) It is half the maximal value at its Km

d) It is initially slow but increases over time

2) A 2-year-old boy has a history of poor feeding and lethargy. He shows developmental delays and

is in the fifth percentile for growth. His parents say that he has had no problems sleeping through

the night but that he just doesnt have any energy. A muscle biopsy and histologic examination

show no apparent pathologic condition. Serum chemistry indicates severe lactic acidosis and

supplementation of his diet with a B multivitamin does not alleviate his condition. Which of the

following is the most likely diagnosis?

a) Pyruvate kinase deficiency

b) Pyruvate carboxylase deficiency

c) Thiamine deficiency


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5) The outcome of the patients glucagon test indicates that

a) the patient's liver contained an unusually large amount of glycogen;

b)the patient had a genetic deficiency of glycogen phosphorylase;

c) the patient had a genetic deficiency of glycogen synthase;

d)the patient had an abnormal G6Pase.

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