Biochem

Question 1

Under starvation conditions which of the following substances is the preferred source of fuel for brain tissue?
A. Glucose
B. Fatty acids
C. Liver glycogen
D. Acetone
E. Acetoacetate (2 Acetyl-CoAs)

Answer 1

E. Acetoacetate (2 Acetyl-CoAs)

Question 2

In anaerobic glycolysis, how many net ATP molecules are synthesized?
E. 3
C. 2
D. 32
B.4

Answer 2

2

Question 3

Which enzyme activity deficiency in pentose phosphate pathway leads to the hemolysis of ervhroevtes?
A. Glucokinase
B. Hexokinase
C. Aldolase
D. Glucose-6 phosphate dehydrogenase
E. Pyruvate kinase

Answer 3

D. Glucose-6 phosphate dehydrogenase

Question 4

Degradation of ketogenic amino acids results in two-carbon fragments which may be formed into Ketone bodies or fatty acids. or oxidized to carbon dioxide and water by which metabolic
A. The TCA cycle
B. Gluconeogenesis
C The pentose phosphate pathway
D. 6-Oxidation
E. Glvcolvsis

Answer 4

A. The TCA cycle

Question 5

The initial step in cellular catabolism of amino acids is usually which mechanism?
A Loss of the acid functional group
B. Conversion of the acid group to an aldehyde group
C. Conversion of the acid group to an alcohol group
D. Esterification of the acid group with an alcohol
E. Deamination, or elimination of the nitrogen

Answer 5

E. Deamination, or elimination of the nitrogen

Question 6

Unlike many physiological substances, metabolism of ammonia is under very strict control due to which of the following?
A. Ammonia is relatively insoluble in water
B. Ammonia is a flammable gas
C. Ammonia reacts readily with acids and could cause acidosis
D. Ammonia is very toxic
E Ammonia could be consumed by intestinal bacteria if they were not held in check

Question 7

In byperammonemia, excess ammonia builds up in blood and threatens brain tissue.
Hyperammonemia may be treated by intravenous administration of arginine-glutamate. The arginine stimulates the ornithine cycle. converting ammonia to urea, and the glutamate helps by which reaction?
A. Taking urea away
B. Causing increased excretion of glutamic acid oxidase
C. Changing the pH of brain tissue
D. Decreasing protein synthesis
E. Trapping ammonia by forming glutamine

Answer 7

E. Trapping ammonia by forming glutamine

Question 8

Metabolism of fats and carbohydrates differs from nitrogen metabolism in what aspect?
A Nitrogen can be stored, far and carbohydrate can’t
B. Fat can be stored. nitrogen and carbohydrate can”
C. Fats and carbohydrate can be stored, nitrogen can’t
D. Carbohydrate can be stored, nitrogen and fat can’t
E. Nitrogen and fat can be stored, but carbohydrates can’t

Answer 8

C. Fats and carbohydrate can be stored, nitrogen can’t

Question 9

Which one is the precursor of the potent vasoconstrictor serotonin?
A. Histidine
B. Tyrosine
C. Tryptophan
D. Glycine
E. Glutamate

Answer 9

Tryptophan

Question 10

Which one of the following amino acids is purely ketogenic regarding the fate of carbon skeletons?
A. Isoleucine
B. Tyrosine
C. Alanine
D. Leucine
E. Gycine

Answer 10

Leucine

Question 11

Gluconeogenesis is not an exact reversal of glycolysis and different reactions are required to convert pyruvate to glucose. Which of the following incorrectly pairs a glycolytic enzyme with the gluconeogenic enzyme that catalyzes the “reverse” reaction?
A. phosphotructokinase-fructose 1.6 bisphosphatase
B. pyruvate kinase-pyruvate carboxylase
C. hexokinase-glucose 6-phosphatase
D. pyruvate kinase-phosphoenolpyruvate carboxykinase
E. pyruvate kinase-pyruvate dehydrogenase

Answer 11

pyruvate kinase-pyruvate dehydrogenase

Question 12

The carbon atoms of serine can appear in all of the following except one of them. Indicate which one is that?
A. Pyruvate
B. Leucine
C. Glycine
D. Sphingoruyelin
E. Phosphatidy| ethanolamine

Answer 12

D. Sphingoruyelin

Question 13

The two nitrogens in urea euter the urea synthesis
A. Both as ammonia
B. One as ammonia and one as the amide of glutamine
C. One as ammonia and one as the a-amino group of aspartate
D. One as ammonia and one as the a-amino go of glutamine
E Both as the amide of glutamine

Answer 13

One as ammonia and one as the a-amino group of aspartate

Question 14

A person suffering from phenylketonuria on consumption food containing high phenylalanine may lead to the accumulation of which of the following substances?
A. Phenylpyruvate
B. Phenylalanine
-C. Tyrosine
D. Isoleucine
E. Alanine

Answer 14

Phenylpyruvate

Question 15

Choose the correct answer.
The oxidation of fatty acids in healthy people:
A. does not change during the starve-feed cycle
B. is highest between meals and lower in the well-fe
C. only occurs between meals
D. onlv occurs in the well-fed state

Answer 15

B. is highest between meals and lower in the well-fe

Question 16

Which of the following incorrectly pairs a pathway with one of its regulated enzymes?
A. TCA cycle: fumarase
B. B-oxidation of fatty acids: caritine acyl transferase II (CAT II
C. Glycolysis: phosphoglycerate kinase
D. Fatty acid synthesis: acetyl CoA carboxylase
E. Urea cycle: carbamoyl-phosphate synthetase II (CPS I)

Answer 16

E. Urea cycle: carbamoyl-phosphate synthetase II (CPS I)

Question 17

Which of the following is an example of the oxidative deamination reaction taking part in amino acid metabolisms?
A. Glutamate - Hexanoic acid - NH;
B. Aspartate - a-Ketoglutarate - Oxaloacetate - Glutamate
C. Glutamate + a-Ketoglutarate + NH;
D. Aspartate - Hexanoic acid -* Glutamate - Oxaloacetate
E. Pyruvate - Glutamate -* Alanine - a-Ketoglutarate

Answer 17

Glutamate + a-Ketoglutarate + NH;

Question 18

Which carriers are used to transport the ammonia produced in muscle degradation of nitrogenated compounds through blood to the liver?
A. Alanine and glutamine
B. Urea and alanine
C. NH” and glufamate
D. Glutamate and glutamine
E. a-Ketoglutarate and urea

Answer 18

A. Alanine and glutamine

Question 19

Choose the correct answer for the necessary coenzy
A. Pyndoxal phosphate
B. Thiamine pyrophosphate
C Coenzyme A
D. Tetrahydrobiopterin
E. Folate

Answer 19

Pyndoxal phosphate

Question 20

Under starvation conditions which of the following substances is the preferred source of fuel for brain tissue?
A. Glucose
B. Fatty acids
C. Liver glycogen
D. Acetone
E. Acetoacetate (2 Acetyl-COAs)

Answer 20

E. Acetoacetate (2 Acetyl-COAs)

Question 21

All of the following statements about the enzymic complex that carries out the synthesis of
ATP during oxidative phosphorylation are correct except which one?
A. It is located on the matrix side of the inner mitochondrial membrane
B. It is inhibited by oligomycin
C. It can exhibit ATPase activity
D. It is inhibited by CO.
D. It can bind molecular 02

Answer 21

D. It can bind molecular 02