Module 10 Part 1 Flashcards

Question 1

Q

Which of the following statements about the preparatory phase of glycolysis is incorrect?

a. It forms a compound that can be readily cleaved into phosphorylated trioses.
b. This is where reduced nicotinamide adenine dinucleotide is generated.
c. It traps glucose in the cell by means of phosphorylation.
d. One of its intermediates is a branching point for other carbohydrate metabolism pathways.

Answer

A

b. This is where reduced nicotinamide adenine dinucleotide is generated.

Option A: 4th step in the preparatory phase. It is catalyzed by the enzyme aldolase.
Option C: 1st step, and is catalyzed by glucokinase (glycolysis in the liver) or hexokinase (glycolysis in other cells).
Option D: Glucose-6-Phosphate, apart from glycolysis, is also utilized in glycogen synthesis and pentose phosphate pathway. It is also an intermediate in gluconeogenesis to produce glucose.
Option B: The reduction of nicotinamide adenine dinucleotide occurs in the payoff phase when Glyceraldehyde-3-Phosphate (G-3-P) is catalyzed by G-3-P dehydrogenase to produce 1,3-Bisphosphoglycerate and NADH.

Reference: Dr. Van Haute’s video lectures on Carbohydrate Metabolism

Question 2

Q

Sorbitol does not cause osmolysis in this tissue because of the presence of the enzyme sorbitol dehydrogenase, which converts it to fructose, thus preventing sorbitol accumulation.

a. Renal glomeruli
b. Peripheral nerves
c. Lens
d. Seminal vesicles

Answer

A

d. Seminal vesicles

Sorbitol accumulation is common in the renal glomeruli (option A), peripheral nerves (option B), and lens (option C), thus osmolysis in these areas commonly occur.
On the other hand, sorbitol dehydrogenase is present in the liver, ovaries, and seminal vesicles (option D). This allows the production of fructose from glucose. Fructose is the carbohydrate energy source of spermatozoa found in the seminal vesicles.

Reference: Dr. Van Haute’s lecture on Pentose Phosphate Pathway and Alternative Carbohydrate Metabolism Pathways

Question 3

Q

The fate of glucose-6-phosphate depends on the need for NADPH, ribose-5-phosphate, and ATP. What is the typical scenario wherein much more ribose-5-phosphate than NADPH is needed?

a. Critical illness
b. Normal metabolic activity
c. Aerobic exercise
d. Adipose tissue
e. Actively dividing cells

Answer

A

e. Actively dividing cells

The fate of glucose-6-phosphate wherein ribose-5-phosphate is much more than NADPH occurs in actively dividing cells. This is because actively dividing cells need more pentose sugars to manufacture nucleic acids.

Reference: Dr. Michael Van Haute’s lecture on Pentose Phosphate Pathway and Alternative Carbohydrate Metabolism Pathways

Question 4

Q

The following statements correctly describe the uronic acid pathway, EXCEPT

a. Glucuronide produced from this pathway is used for detoxification, steroid excretion, and bilirubin metabolism.
b. This pathway does not lead to formation of ATP.
c. It catalyzes the conversion of glucose to glucuronic acid, ascorbic acid, and pentoses in humans.
d. It is an alternative oxidative pathway for glucose.

Answer

A

c. It catalyzes the conversion of glucose to glucuronic acid, ascorbic acid, and pentoses in humans

“Uronic acid pathway catalyzes the conversion of glucose to glucuronic acid, ascorbic acid, and pentoses.”

However in humans, non-human primates, and guinea pigs, there is a block in the pathway specifically in the part for synthesizing ascorbic acid. This is due to the absence of L-gulonolactone oxidase on the said species.

Reference: Dr. Michael Van Haute’s lecture on Pentose Phosphate Pathway and Alternative Carbohydrate Metabolism Pathways

Question 5

Q

5.Glutamate decarboxylase requires which of the following to be able to synthesize GABA?

a. Cobalamin
b. Vitamin B1
c. Vitamin B6
d. Biotin

Answer

A

c. Vitamin B6

Vitamin B6 is vital in GAD (glutamic acid decarboxylase) that catalyzes the synthesis of GABA from glutamate

Vitamin B6 functions in several transaminase and decarboxylation reactions.

GABA (Gamma-Aminobutyric Acid)
derived from glutamate
enzyme: Glutamate decarboxylase or glutamic acid decarboxylase
glutamate decarboxylase requires Vitamin B6

Reference: Doc Jan Monzon’s video lecture on Specialized products and derivatives from amino acids

Question 6

Q

Which of the following glycolytic pathway kinases is the SAME corresponding enzyme catalyzing the reverse direction (i.e., gluconeogenesis)?

a. Pyruvate kinase
b. Phosphofructokinase-1
c. Glucokinase
d. Hexokinase
e. Phosphoglycerate kinase

Answer

A

e. Phosphoglycerate kinase

Phosphoglycerate kinase is a reversible step, makes use of the same enzyme for glycolysis and gluconeogenesis.
1,3- Bisphosphoglycerate ↔ 3-Phosphoglycerate

Glycolysis is tightly controlled by these 3 IRREVERSIBLE steps in glycolysis
Hexokinase/ Glucokinase
Phosphofructokinase-1
Pyruvate kinase

Reference: Doc Michael Van Haute’s PPT on Carbohydrate Metabolism

Question 7

Q

Constipated individuals typically have stools with a darker shade of brown because of which enzyme/process?

a. Oxidation
b. Glucuronidase
c. Glutathione transfer
d. Glucuronide transfer

Answer

A

a. Oxidation

Food, after absorbing minerals in the small intestine, passes along the colon. The colon absorbs water from the food forming the stool. Excess absorption of water makes the stool dry and hard. In a constipated person, the stool stays much longer in the colon leading to an oxidation Hence, a darker shade of brown color of the stool.

Reference: Doc Jan Monzon’s Review Session

Question 8

Q

8.Abundance of which of the following will lead to allosteric activation of the rate-limiting step of the urea cycle?

a. Urea
b. Citrulline
c. Glutamate
d. Arginine

Answer

A

c. Glutamate

Glutamate and acetyl-CoA synthesize N-acetylglutamate, which is an allosteric activator. N-acetylglutamate activates the Carbamoyl Phosphate Synthetase I (CPS I), the rate-limiting step of the urea cycle.

Reference: Doc Jan Monzon’s lecture on Protein Metabolism

Question 9

Q

In skeletal muscle during strenuous exercise (moving towards anaerobic) and in other tissues during arterial circulation compromise, which two metabolic processes happen together?

a. Glycogenolysis and glycolysis
b. Glycogenolysis and gluconeogenesis
c. Glycolysis and Kreb’s cycle
d. Gluconeogenesis and fatty acid β-oxidation

Answer

A

a. Glycogenolysis and glycolysis.

The body is experiencing a lot of work, depleting all the available carbohydrates as a source of energy.

Glycogenolysis - breakdown of glycogen in order to replenish glucose.
Glycolysis - utilizes the available carbohydrate to sustain the energy demand of the body due to strenuous exercise.

Reference: Doc Jan Monzon’s lectures on Carbohydrate Metabolism

Question 10

Q

Which of the following will most likely occur in a 35-year-old male who is fond of eating red meat and drinking whey protein shakes without really working out?

a. Accumulation of ornithine in the liver
b. Increased transport of alanine into the muscles
c. Increased ammonia load in the liver
d. Increased transport of alanine from the muscles

Answer

A

c. Increased ammonia load in the liver

Eating high amounts of red meat would increase a person’s proteins which are “supposedly” utilized by the muscles to increase muscle mass.

Due to the neglect of using the muscles through exercise, proteins are not used enough to aid in muscle bulking, thus excessive proteins are brought to the liver. It is in the liver where the uric cycle occurs producing more ammonia than usual, thus increasing ammonia load in the liver.

Reference: Doc Jan Monzon’s lecture on Protein Metabolism

Question 11

Q

11.In patients with significant mood disorders, serotonin is rapidly cleared and broken down releasing tryptophan. In the liver, which of the following pathways is this amino acid destined for?

a. Gluconeogenesis
b. Both of the choices
c. Ketogenesis

Answer

A

b. Both of the choices

Gluconeogenesis with reference to the hydroxylation of tryptophan, is subsequent with the decarboxylation and formation of serotonin (page 316)

Ketogenesis, on the other hand in response with its process resulting from decreased insulin breaks down amino acids and affects the rate of serotonin breakdown and release of tryptophan in the liver. (page 192)

Reference: Harper’s Illustrated Biochemistry 30th Edition

Question 12

Q

12.A 62-year-old man is presented at the ER with decreased sensorium. AST and ALT are elevated. He is jaundiced with multiple bruises on his trunk, arms and legs. The breath smells of ammonia. To decrease the ammonia levels in his blood, we may reduce the following, EXCEPT for?

a. Amount of protein in the diet
b. Overall protein breakdown from stressors
c. Ammonia-fixing bacteria in the colon
d. Glutamine levels in the brain

Answer

A

d. Glutamine levels in the brain.

To fix levels of ammonia in blood, glutamine synthase fixes ammonia as glutamine in the Liver and Kidneys. (page 292)

Reference Harper’s Illustrated Biochemistry 30th Edition

Question 13

Q

13.A patient taking isoniazid for tuberculosis has sub-optimal heme synthesis due to the lack of?

a. activated succinate required in the rate-limiting step.
b. All of the choices
c. .glycine required in the rate-limiting step.
d. the co-factor required for the rate-limiting step.

Answer

A

d. the co-factor required for the rate-limiting step

Isoniazid’s mechanism of action includes inhibiting ALAS2 which is an essential component of the rate limiting step for heme synthesis

References:https://www.sciencedirect.com/science/article/pii/S0925443916302939

Question 14

Q

14.In the hepatocyte, carbon skeletons of catabolized amino acids will typically serve as substrates or intermediates for the following, EXCEPT:

a. Urea cycle
b. Ketogenesis
c. Fatty acid synthesis
d. Gluconeogenesis

Answer

A

c. fatty acid synthesis

Urea cycle - amino groups must enter this cycle to avoid accumulation and subsequent brain damage

Ketogenesis - Ketogenic AAs (Leu, Lys) give rise exclusively to ketones (Acetyl CoA is ketogenic)

Gluconeogenesis - Nearly all AAs except LL are glucogenic

Fatty Acid Synthesis - typically occurs only if the ketogenesis and gluconeogenesis is unneeded aka when the individual is well/overnourished

Reference Harper’s Illustrated Biochemistry 30th Edition, p. 236

Question 15

Q

15.The non-oxidative phase of the pentose phosphate pathway has the following characteristics, EXCEPT

a. It rearranges different sugars for entry into the glycolytic pathway.
b. This phase is responsible for the reduction of glutathione needed to neutralize reactive oxygen species (ROS).
c. It is responsible for recycling excess pentoses.
d. The steps in this phase are reversible.

Answer

A

b. This phase is responsible for the reduction of glutathione needed to neutralize reactive oxygen species.

Reference: Doc Van Haute’s Handout - Alternative Carbohydrate Metabolism Pathways

Question 16

Q

16.A 4-month-old boy is being evaluated for seizures, psychomotor retardation, and hypotonia. Extensive diagnostic work-up reveals elevated serum lactate, pyruvate, and keto-acid levels. Based on the clinical presentation, pyruvate carboxylase activity (measured using fibroblasts from a skin biopsy) is found to be markedly decreased. This enzyme is normally used by our bodies to directly synthesize which of the following molecules?

a. α-Ketoglutarate
b. Oxaloacetate
c. Pyruvate
d. Malate

Answer

A

b. Oxaloacetate.

Pyruvate produces oxaloacetate via pyruvate carboxylase. In order to activate this reaction, acetyl-CoA, formed from pyruvate, activates pyruvate carboxylase.

This means that acetyl-CoA, an allosteric activator, automatically ensures the provision of oxaloacetate, by activating pyruvate carboxylase

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st edition.). New York: Mcgraw-Hill Education.

Question 17

Q

17.An infant diagnosed of phenylketonuria has been lost to follow-up. Although the family avoided phenylalanine in the diet for the infant, the child still became similar to the picture below with below-average IQ and is classically labeled as a “cretin”.

This is most likely due to:

a. lack of tyrosine supplementation.
b. concurrent tetrahydrobiopterin deficiency.
c. lack of vitamin B12 supplementation.
d. lack of iodine in the diet.

Answer

A

a. Lack of tyrosine supplementation

For conditions such as phenylketonuria dietary restriction of the amino acid that are not metabolized normally. For this case, phenylalanine is restricted.

However, two amino acids, cysteine and tyrosine, can be synthesized in the body, but only from essential amino acid precursors—cysteine from methionine and tyrosine from phenylalanine. The dietary intakes of tyrosine thus affects the requirements for phenylalanine.

Tyrosine is also required in the diet if phenylalanine intake is inadequate or if an individual is congenitally deficient in an enzyme required to convert phenylalanine to tyrosine, which is the phenylketonuria.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st edition.). New York: Mcgraw-Hill Education.

Lieberman M., & Peet A. (2018). Mark’s Basic Medical Biochemistry, A Clinical Approach (5th Edition). Philadelphia : Wolters Kluwer.

Question 18

Q

18.A 42-year-old male has just walked 3 kilometers from work to home. During this time, alanine from his muscles is transported to the liver to become glucose. The intermediates required for this to happen are?

a. Glutamate then glutamine
b. Succinate then succinyl-CoA
c. Pyruvate then oxaloacetate
d. Aspartate then asparagine

Answer

A

c. Pyruvate then oxaloacetate

Transamination of α-alanine forms pyruvate. Alanine serves as a carrier of ammonia and of the carbons of pyruvate from skeletal muscle to liver via the Cori cycle. Similarly, transamination of oxaloacetate forms aspartate.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st edition.). New York: Mcgraw-Hill Education.

Question 19

Q

In the normal, healthy adult, the most abundant amino acids that enter the liver from other tissues are

a. Alanine and glutamine.
b. Glycine and alanine.
c. Glutamate and glutamine.
d. Aspartate and asparagine.

Answer

A

a. Alanine and glutamine.

Free amino acids, particularly alanine and glutamine, are released from muscle into the circulation. Alanine is extracted primarily by the liver, and glutamine is extracted by the gut and the kidney, both of which convert a significant portion to alanine. Glutamine also serves as a source of ammonia for excretion by the kidney. The kidney provides a major source of serine for uptake by peripheral tissues, including liver and muscle. Branched-chain amino acids, particularly valine, are released by muscle and taken up predominantly by the brain. Alanine is a key gluconeogenic amino acid. The rate of hepatic gluconeogenesis from alanine is far higher than from all other amino acids. The capacity of the liver for gluconeogenesis from alanine does not reach saturation until the alanine concentration reaches 20 to 30 times its normal physiologic level.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st edition.). New York: Mcgraw-Hill Education.

Question 20

Q

Low activity of this enzyme is implicated as one of the reasons for physiologic jaundice in newborn babies.

a. Galactose 1-P uridyltransferase
b. UDP-glucuronyltransferase
c. UDP-Glucose pyrophosphorylase
d. UDP-Glucose dehydrogenase

Answer

A

a. Galactose 1-P uridyltransferase

Inability to metabolize galactose occurs in the Galactosemias, which may be caused by inherited defects of galactokinase, uridyl transferase, or 4-epimerase, through deficiency of uridyl transferase is best known. Galactose is a substrate for aldose reductase, forming galactitol, which accumulates in the lens of the eye, causing cataract. The condition is more severe if it is the result of a defect in the uridyl transferase since galactose-1-phosphate accumulates and depletes the liver of inorganic phosphate.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st edition.). New York: Mcgraw-Hill Education.

Question 21

Q

21.A 54-year-old man is found to be hypertensive with fasting hyperglycemia. The rest of the metabolic work-up revealed hyperuricemia and hyperlipidemia. Which of the following is MOST accurate regarding the metabolism of proteins in his case?

a. More non-essential amino acids are used for gluconeogenesis
b. Less creatinine is produced from skeletal muscle breakdown
c. Less amino acids are mobilized in the blood from the liver
d. More essential amino acids are used for protein synthesis

Answer

A

a. More non-essential amino acids are used for gluconeogenesis

Hyperglycemia in the patient might be due to insulin resistance because of Diabetes Mellitus. Therefore, the body is not able to utilize glucose, leading to pseudo fasting state. Thus, gluconeogenesis will be activated.

During the fasted state, the pyruvate is diverted into GLUCONEOGENESIS.The liver releases the newly formed glucose to the blood for the other tissues to take up. Alanine, a non-essential amino acid, gets released from the skeletal muscle and processed in the liver for gluconeogenesis.

Reference: Doc Jan Monzon’s Protein and Amino Acid Metabolism PPT Handout

Question 22

Q

22.A 6-year-old boy fond of eating paint chips from the walls of their old house is admitted after a generalized convulsion. His presentation is most likely due to

a. severe anemia.
b. accumulation of false neurotransmitters.
c. accumulation of porphyrins in the brain.
d. reduced ALA formation.

Answer

A

b. Accumulation of false neurotransmitters.

Delta-Amino acid (ALA) is toxic to the brain because it can act as a false neurotransmitter disrupting GABA transmission.
On formation of Porphobilinogen, enzyme ALA dehydrogenase/ Porphobilinogen synthase is inhibited by lead. Lead poisoning leads to increased levels of ALA due to the enzyme block-> NEUROLOGIC SYMPTOMS (e.g. mental retardation in kids.)

Reference: Doc Jan Monzon’s Protein and Heme Metabolism PPT Handout

Question 23

Q

23.In the classic type of Maple Syrup Urine Disease, dysfunction of which organ due to increased BCAAs and BCKAs presents early in life leading to fatal complications?

a. Pancreas
b. Kidneys
c. Liver
d. Brain

Answer

A

d. Brain

Maple Urine Syrup Disease is an autosomal recessive deficiency of branched-chain α-keto acid dehydrogenase (BCKD). There is a block leading to the accumulation of branch chain amino acids (BCAA) and their respective keto acids. When this accumulate, they are not broken down properly which will cause cellular dysfunction. Patients with MSUD are at risk for organ dysfunction and mental retardation.

NOTE: MSUD is a lifelong problem because 30-40% of muscle mass is derived from BCAA. If they accumulate BCAAs, it can cause CNS or nervous system damage.

Reference: Doc Jan Monzon’s lecture

Question 24

Q

24.A neonate is born severely jaundiced. Neonatal sepsis is diagnosed. Which of the following is most likely TRUE regarding the patient?

a. The neonate is at risk for severe CNS complications.
b. There is increased turnover of bilirubin from heme from RBCs because of the infection.
c. All of the choices.
d. The neonatal liver is not yet capable of optimal conjugation of bilirubin.

Answer

A

c. All of the choices

Higher levels signs and symptoms of toxicity occur, and are related to the degree to which the central nervous system (CNS) is affected.
Increased production: Fetal erythrocytes have a higher rate of turnover; per kilogram, newborn infants produce twice the daily adult amount of bilirubin.
This normal process occurs when the neonatal liver is not able to conjugate the amount of bilirubin being produced. Total bilirubin level usually peaks on the 3rd day of life with values of 86-103 umol/L and then slowly declines over the first week.

Reference: Yaworski, A. (2015). Neonatal hyperbilirubinemia | McMaster Pathophysiology Review. Pathophys.org. http://www.pathophys.org/neonatal-hyperbilirubinemia/

Question 25

Q

In the active skeletal muscle, alanine is a breakdown product and is brought to the liver to become glucose. Glucose is then shipped back to the muscle. While alanine is being re-synthesized in the muscle, what else happens?

a. Glutamate is formed and is used as an amino group carrier.
b. 2-Oxoglutarate enters the Krebs cycle to produce more ATP.
c. Glucose is stored as glycogen.
d. Glutamine is formed from glutamate to release ammonia.

Answer

A

b. 2-Oxoglutarate enters the Krebs cycle to produce more ATP.
d. Glutamine is formed from glutamate to release ammonia.

Reference: https://www.researchgate.net/profile/Rob-Cairns/publication/311882673/figure/fig2/AS:646460806819840@1531139675033/The-potential-roles-of-IDH1-in-liver-During-prolonged-fasting-the-breakdown-of-skeletal.png

Question 26

Q

If ketogenesis is already occurring in a patient with leucine and lysine being the substrates, which of the following is most likely present or ongoing?

a. Systemic impairment of protein function
b. Excess of non-essential amino acids for gluconeogenesis
c. Severe lack of carbohydrates in the diet
d. Widespread destruction of the liver

Answer

A

a. Systemic impairment of protein function

Ketone bodies are a normal way to get energy from lipids (not water-soluble) through your blood. Ketone bodies are soluble so they can travel from the liver where they’re made throughout your body. The problem is just when you can’t keep up. During times of starvation or heavy prolonged exercise, the liver starts running out of OAA because you’re not feeding the pathway from sugar. And without OAA you can’t get acetyl-CoA into the pathway, so it instead takes the alternate ketone route. The ketones released can be taken in by cells throughout your body (even in your brain) and there’s enough OAA there (at least initially) to use it.

References: Bibel, B. (2020, December 13). Leucine, ketogenic amino acids. Retrieved February 12, 2021, from https://thebumblingbiochemist.com/365-days-of-science/leucine-ketogenic-amino-acids/

Question 27

Q

27.A 32-year-old man has had tuberculous infection of the intestines that led to eventual necrosis and resection. The resected specimen is shown below.

The patient, after 5 years, eventually complains of difficulty of breathing, light-headedness and tingling sensations on his lower extremities. Synthesis of which of the following amino acids is most significantly impaired in his case?

a. Glutamate
b. Tyrosine
c. Methionine
d. Glycine

Answer

A

c. Methionine
Anemia is consistent with the patient's shortness of breath and fatigue, and certain types of anemia can be associated with paresthesia. Therefore, anemia is the most likely diagnosis of the given differential diagnosis. Anemias due to vitamin B12 or folate deficiency, chemotherapeutic agents, or myelodysplasia are commonly the result of impaired DNA synthesis and are typically characterized by large immature red blood cells and hyper segmented neutrophils.
The MMA (Methylmalonic Acid)and homocysteine levels are used to confirm the diagnosis of vitamin B12 deficiency, especially in the setting of concurrent folate deficiency. In vitamin B12 deficiency, the MMA and homocysteine levels are both elevated. Only the homocysteine level is elevated in folate deficiency.
Methionine is the precursor of homocysteine, a sulfur amino acid intermediate in the methylation and transsulfuration pathways. Folate and B12 deficiencies result in low methionine and SAM and in high homocysteine, because they inhibit the regeneration of methionine from homocysteine
References: Tweet, M. S., & Polga, K. M. (2010). 44-year-old man with shortness of breath, fatigue, and paresthesia. Mayo Clinic Proceedings. Mayo Clinic, 85(12), 1148–1151.

Question 28

Q

28.The cofactor of pyruvate dehydrogenase that contributes to the structure of the high-energy molecule that is created in this particular step is derived from or dependent on which vitamin?

a. Riboflavin
b. Pantothenic acid
c. Thiamine
d. Biotin
e. Niacin

Answer

A

b. Pantothenic acid

Pantothenic acid (B5) is required for coenzyme A formation which is a cofactor of pyruvate dehydrogenase.

Reference: Doc VH’s lecture

Question 29

Q

29.The degradation of glycogen in the LIVER normally produces which of the following?

a. Only glucose-1-phosphate
b. More glucose-1-phosphate than glucose
c. More glucose than glucose-1-phosphate
d. Equal amounts of glucose and glucose-1-phosphate

Answer

A

b. More glucose-1-phosphate than glucose

Glycogen phosphorylase catalyzes the rate-limiting step in the degradation of glycogen. In glycogenolysis, the phosphorolytic cleavage of the 1 → 4 linkages of glycogen yields glucose-1-phosphate. Glucose-6-phosphate can be formed from glucose-1-phosphate via the enzyme phosphoglucomutase. In the liver, but not muscle, glucose-6-phosphatase hydrolyzes glucose-6-phosphate to glucose and is exported into the blood leading to an increase in the blood glucose concentration.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st edition.). New York: Mcgraw-Hill Education.

Question 30

Q

A 27-year-old man completes a 10K race and drinks a 16-oz bottle of sugar-containing drink. This drink transiently raises his blood glucose and triggers a release of insulin. The released insulin subsequently increases glucose absorption by skeletal muscle. Which of the following pathways is most likely principally involved in this latter process?

a. PI3K-Akt pathway
b. Phospholipase C pathway
c. Adenylate cyclase pathway
d. MAPK pathway

Answer

A

a. PI3K-Akt pathway

The PI3K-Akt pathway is principally involved in the internalization of glucose from the blood by the skeletal muscle which is mediated by insulin via a tyrosine kinase receptor. This is done by increasing the expression of glucose transporters (GLUTs) on the cell surface.

Reference: Dr. Michael Nicolaus Q. Van Haute’s video lecture

Question 31

Q

31.In skeletal muscle during strenuous exercise (moving towards anaerobic) and in other tissues during arterial circulation compromise, which two metabolic processes happen together?

a. Glycogenolysis and glycolysis
b. Glycolysis and Krebs cycle
c. Gluconeogenesis and fatty acid β-oxidation
d. Glycogenolysis and gluconeogenesis

Answer

A

a. Glycogenolysis and glycolysis

Glycolysis is the main pathway of glucose metabolism. It can occur either aerobically or anaerobically

Glycogenolysis is the process of breaking down glycogen. Muscle glycogen provides a source of glucose-6-phosphate for glycolysis in response to the need of ATP in muscle contraction.

Reference: Chapter 17 & 18, Harper’s 13th Ed.

Question 32

Q

32.On the same day, one pediatrician sees two children with a hereditary defect in fructose metabolism. The physician reminds the first set of parents to maintain their child on a low-fructose, low-sucrose diet. He tells the second set of parents that their child is unlikely to experience any symptoms from the disorder, despite the fact that fructose was detected in the child’s blood and urine. What action describes the function of the enzyme that is deficient in the first child?

a. It converts glyceraldehyde to glyceraldehyde-3-phosphate.
b. It converts glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.
c. It converts fructose-1-phosphate to dihydroxyacetone phosphate and glyceraldehyde.
d. It converts fructose to fructose-1-phosphate.

Answer

A

c. It converts fructose-1-phosphate to dihydroxyacetone phosphate and glyceraldehyde

Aldolase B catalyzes the cleavage of Fructose-1-Phosphate to D-glyceraldehyde and Dihydroxyacetone phosphate.

Aldolase B is the rate limiting enzyme of fructose metabolism because it has low affinity for Fructose-1-Phosphate. High levels must be accumulated for this reaction to move forward.

Reference: Doc Micheal Van Haute’s Lecture on Pentose Phosphate Pathway and Alternative Carbohydrate Metabolism Pathway.

Question 33

Q

33.The rate of ATP production from glycolysis is about 100 times faster than in oxidative phosphorylation, however it cannot sustain the metabolic needs of the tissues under anaerobic conditions because

a. the NADH produced from glycolysis cannot be used to generate ATP.
b. this requires an infinite supply of glycogen.
c. pyruvate becomes a metabolic dead end during anaerobic conditions.
d. oxidative phosphorylation beats glycolysis by sheer ATP numbers alone.

Answer

A

b. This requires an infinite supply of glycogen .

Rate of ATP production from glycolysis is 100x faster than from oxidative phosphorylation. This particularly true with skeletal muscle which has its own glycogen stores.

However, glycogen stores are rapidly depleted.

Reference: Dr. Van Haute’s Lecture on Carbohydrate Metabolism: Glycolysis

Question 34

Q

A 5-year-old girl with hereditary spherocytosis has been lost to follow up and returns with right upper quadrant (RUQ) pain. She is not jaundiced but bilirubin is elevated with indirect bilirubin being the predominantly increased fraction. Which of the following is the most likely cause?

a. Untreated hemolytic anemia
b. Acute liver injury
c. Pigment stone formation
d. Hypoalbuminemia

Answer

A

a. untreated hemolytic anemia

Indirect bilirubin (unconjugated) is the difference between total bilirubin and direct bilirubin.

Common causes of higher indirect indirect bilirubin include:
Hemolytic anemia
Bleeding into the skin caused by injury
Bleeding in the lung caused by a blood clot
A gene problem that causes slightly higher indirect bilirubin levels without other signs or symptoms of disease

Reference: University of Rochester Medical Center - Health Encyclopedia

Question 35

Q

Which of the following will most likely occur in a 35-year-old male who is fond of eating red meat and drinking whey protein shakes without really working out?

a. Accumulation of ornithine in the liver
b. Increased transport of alanine from the muscles
c. Increased ammonia load in the liver
d. Increased transport of alanine into the muscles

Answer

A

c. Increased ammonia load in the liver

The accumulation of excess protein in the body could lead to a hypercatabolic state and an increase in protein breakdown. As a result, this could lead to a high nitrogen turnover that increases ammonia load to the liver.

Reference: Doc Jan Monzon’s Lecture on Protein Breakdown, Nitrogen Turnover, & Urea Cycle.

Question 36

Q

Glycerol enters glycolysis through which glycolytic pathway intermediate?

a. Dihydroxyacetone phosphate
b. Pyruvate
c. Succinyl-CoA
d. Glyceraldehyde-3-phosphate

Answer

A

a. Dihydroxyacetone phosphate

Glycerol can be phosphorylated by glycerol kinase (which uses ATP) to form glycerol-3-phosphate, which can in turn enter the gluconeogenic pathway via oxidation to DHAP. DHAP, however, is a glycolysis intermediate, not glycerol-3-phosphate (should not be confused with glyceraldehyde-3-phosphate)

Succinyl-CoA, on the other hand, is the glycolysis entry point for propionate, which is a minor noncarbohydrate source of carbons for gluconeogenesis in humans.

Pyruvate, is the glycolysis entry point for lactate (via lactate dehydrogenase in the presence of NAD+) and glucogenic amino acids like alanine (via transamination reactions involving a-ketoglutarate)

Reference: Batch 2023 Biochemistry Evals 4 ratio on Carbohydrate Metabolism.

Question 37

Q

37.Which of the following conditions, when not satisfied, will basically negate all the efforts of gluconeogenesis in an energy-wasteful manner.

a. Inactivation of pyruvate dehydrogenase
b. Activation of pyruvate carboxylase
c. Induction of phosphoenolpyruvate carboxykinase
d. Inactivation of pyruvate kinase

Answer

A

d. Inactivation of pyruvate kinase

Pyruvate kinase is the enzyme involved in the last step of glycolysis, converting PEP to pyruvate. If it is not inactivated, all the PEP that was synthesized during gluconeogenesis will just get reconverted back to pyruvate, causing a net loss of energy.

Reference: Batch 2023 Biochemistry Evals 4 ratio on Carbohydrate Metabolism.

Question 38

Q

38.The biochemical basis of seasonal affective disorder is that that depressive or mood symptoms arise from decreased

a. entry of tryptophan into the brain.
b. breakdown of serotonin into its metabolites.
c. serotonin stores from increased melatonin production.
d. production of melatonin from serotonin.

Answer

A

c. serotonin stores from increased melatonin production

“People with SAD may also have difficulty with overproduction of melatonin. Melatonin is a hormone produced by the pineal gland that responds to darkness by causing sleepiness. As winter days become darker, melatonin production increases and, in response, those with SAD feel sleepy and lethargic.”

Since melatonin is derived from serotonin, increased production of melatonin would mean that a decrease in serotonin stores is expected.

Reference: Melrose S. (2015). Seasonal Affective Disorder: An Overview of Assessment and Treatment Approaches. Depression research and treatment, 2015, 178564. https://doi.org/10.1155/2015/178564

Question 39

Q

39.A 42-year-old male has just eaten from a buffet restaurant. Which of the following metabolic processes is likely highly active in his current state?

a. Glycolysis and amino acid synthesis
b. Entry of amino acids into the Krebs cycle
c. Glucose-alanine cycle
d. Gluconeogenesis and amino acid breakdown

Answer

A

a. Glycolysis and amino acid synthesis

Glycolysis is dominant in the fed state in which glucose is abundant.
Most amino acids are deaminated to produce alpha keto acids. In a fed state, alpha keto acids can be used to synthesize triacylglycerol.

Reference: Harper’s Illustrated Biochemistry. 13th Edition
Doc Jan Monzon’s Powerpoint

Question 40

Q

40.A 40-year-old female is seen in the ER due to severe right upper quadrant (RUQ) pain and jaundice. She has a history of gallstones. Lipase, amylase, aspartate transaminase (AST), alanine transaminase (ALT) are normal while γ-glutamyl transferase (GGT) is elevated. Total bilirubin is elevated with direct bilirubin being the predominantly increased fraction. She most likely has a gallstone obstructing the

a. ampulla of Vater.
b. common bile duct.
c. right and/or left hepatic duct.
d. cystic duct.

Answer

A

b. Common bile duct

Bile secretion:

Right hepatic duct + Left hepatic duct = Common hepatic duct + Cystic duct = Common Bile Duct

Reference: Batch 2024 Trans of Liver, HBT and Gallbladder

Question 41

Q

41.The main function of the pentose phosphate pathway is to

a. supply pentoses and NADPH.
b. give the cell an alternative pathway should glycolysis fail.
c. supply energy.
d. provide a mechanism for the utilization of the carbon skeletons of excess amino acids.
e. supply NADH.

Answer

A

a. Supply pentoses and NADPH

PPP provides a way for cells to oxidize glucose to generate NADPH and provides a way to synthesize pentose sugars.

References: Doc VH’s handout

Question 42

Q

42.The rate-limiting step of the pentose phosphate pathway is catalyzed by what enzyme?

a. Transaldolase
b. 6-Phosphogluconate dehydrogenase
c. Transketolase
d. Glucose 6-phosphate dehydrogenase

Answer

A

d. Glucose 6-phosphate dehydrogenase

G6PD is the first step of PPP. It is rate-limiting and is regulated allosterically and feedback inhibited by NADPH.

References: Doc VH’s handout

Question 43

Q

43.A patient diagnosed with thiamine deficiency exhibited fatigue and muscle cramps. The muscle cramps have been related to an accumulation of metabolic acids. Which of the following metabolic acids is most likely to accumulate in thiamine deficiency?

a. Oxaloacetic acid
b. Isocitric acid
c. Pyruvic acid
d. Succinic acid
e. Malic acid

Answer

A

c. Pyruvic acid

Reference: Batch 2022 Biochemistry Evals 5 ratio on Carbohydrate Metabolism.

Question 44

Q

44.Profound deficiency in selenium from the diet among Chinese living in a certain province will accelerate cardiovascular disease mainly due to

a. depletion of collagen.
b. build-up of free radicals.
c. insulin resistance.
d. altered lipid metabolism.

Answer

A

b. Build up of Free Radicals

Most commonly deficiency of Selenium

Accelerated atherosclerosis (bec enzymes mentioned help clear free radicals, if a lot of free radical induced damage to blood vessels)
Lead to heart attack, aneurysm, arterial occlusive disease, gangrene

References: Doc Jan Monzon’s PPT and Batch 2024 Trans

Question 45

Q

45.After an intense workout, a gym goer complains of muscle aches. He then drinks a supplement of creatine and branched-chain amino acids (BCAAs). The turnover of his BCAAs in his muscle would require which of the following?

a. Vitamins B6 and B12
b. Vitamins B1, B2 and B3
c. Vitamin B12 and folate
d. Folate and biotin

Answer

A

b. Vitamins, B1, B2 and B3

B Vitamins are critical for amino acid metabolism and can become depleted when you take high doses of the BCAAs. BCAA metabolism requires Thiamin (B1), Riboflavin (B2), Niacin (B3), and Pantothenic acid (B5). These enzymes are limiting factors in BCAA metabolism. if there is megadosing BCAAs during training, it will eventually be affected.

References: Poliquin. (2015). Pros and Cons of BCAA supplements. Retrieved form: https://main.poliquingroup.com/ArticlesMultimedia/Articles/Article/1394/The_Pros_Cons_of_BCAA_Supplements.aspx

Question 46

Q

46.Blood glucose is tightly regulated after a meal by an enzyme found in muscle tissues. This enzyme catalyzes one of the steps in the pathway to convert glucose to glycogen. In addition, this process is subject to feedback inhibition by glucose-6-phosphate. Which of the following enzymes is being described?

a. Hexokinase
b. Pyruvate kinase
c. Pyruvate dehydrogenase
d. Phosphofructokinase-1
e. Glucokinase

Answer

A

a. Hexokinase

The processes that usually follow after a meal (or entering the FED state) relate to the breakdown or usage of glucose, e.g., glycolysis or glycogenesis. These pathways in muscle tissue begin with a transfer of a phosphate group from ATP to a glucose molecule that has just entered the cell.

This irreversible reaction produces glucose-6-P, which commits it to metabolism, because the product glucose-6-P cannot leave the cell anymore.

An inhibitor of hexokinase is the product it forms, which is glucose-6-P, which makes sense. If glucose-6-P is being produced but does not enter glycolysis or another pathway, it accumulates and can decrease the activity of hexokinase so there is no overproduction of glucose-6-P

General rule of thumb: Most enzymes are inhibited by their products or the final products of the entire pathway.

References: Mark’s Basic Medical Biochemistry, 4th ed.

Question 47

Q

47.Which of the following steps in gluconeogenesis occurs only in the liver (and kidneys)?

a. Fructose-1,6-bisphosphate → fructose-6-phosphate
b. Pyruvate → phosphoenolpyruvate
c. 3-Phosphoglycerate → 1,3-bisphosphoglycerate
d. Glucose-6-phosphatase → glucose

Answer

A

d. Glucose-6-phosphatase → glucose

During fasting, two mechanisms that the liver can execute are: glycogenolysis and gluconeogenesis

The production of glucose from gluconeogenesis (Greek: gluco, glucose; neo, new; genesis,creation) requires an enzyme in the last step, which is glucose-6-phosphatase.

This is related to the first reaction of glycolysis as seen in no. 46, where we commit glucose into entering metabolism by adding a phosphate group to it. However, take note that although it looks like the reverse of hexokinase / glucokinase, it is not the reverse of it. (It is not the reverse because in glucose-6-phosphatase, ATP is not generated in this step)

References: Mark’s Basic Medical Biochemistry, 4th ed.

Question 48

Q

48.A 52-year-old man is admitted due to a bout of blood vomitus. Endoscopy revealed bleeding varices from the left gastric vein. This is his general appearance.

This patient is in

a. physiologic positive nitrogen balance.
b. normal nitrogen balance.
c. pathologic positive nitrogen balance.
d. negative nitrogen balance.

Answer

A

c. pathologic positive nitrogen balance.

Positive balance means more nitrogen is retained. under positive there are 2 types:
Physiologic: pregnancy and puberty (growth spurt)
Pathologic: excretion is imparied in liver failure and renal failure

Negative balance means more nitrogen is broken down. example of these are severe malnutrition, wasting (trauma, malignancy), post -operative cases, and hypercatabolic states

References: Doc Jan Monzon’s PPT

Question 49

Q

49.A first-year medical student is under a lot of stress due to her upcoming biochemistry examination. She knows that physiological stress leads to release of endogenous glucocorticoids, which increases her blood glucose levels. To raise glucose levels, glucocorticoids activate the enzyme phosphoenolpyruvate carboxykinase (PEPCK) to generate which of the following products?

a. Pyruvate
b. Acetyl-CoA
c. Malate
d. Oxaloacetate
e. Phosphoenolpyruvate

Answer

A

e. Phosphoenolpyruvate

In gluconeogenesis, phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate.

References: Harpers Illustrated Biochemistry 31st Ed. p.173

Question 50

Q

50.In times of high demand of collagen, glycine is produced in greater amounts. This may affect the availability of which essential amino acid?

a. Methionine
b. Phenylalanine
c. Threonine
d. Serine

Answer

A

c. Threonine

Glycine, Proline ,and Lysine (an essential amino acid) are the 3 main amino acids composing collagen.If there is an extensive wound, extensive surgery requiring a lot of wound healing and a lot of collagen then there is also an increased demand of glycine and proline.

Threonine is one of the essential amino acids, when this is broken down, it can yield glycine and since it is essential, the availability of this will affect glycine .

Reference: Doc Jan Monzon’s Lecture on Biosynthesis of Non- Essential Amino Acids

Question 51

Q

51.The following are statements describing the fed and fasting states. Which of them is correctly stated?

a. Muscle can release glucose into the circulation from its glycogen reserves in the fasting state.
b. The liver contains an isoenzyme of hexokinase, called glucokinase, which is especially important in the fed state.
c. Glucose 6-phosphatase is mainly active in muscle in the fasting state.
d. Because hexokinase has a low Km, its activity in the liver increases as the concentration of glucose in the portal blood increases.

Answer

A

b. The liver contains an isoenzyme of hexokinase, called glucokinase, which is especially important in the fed state.

The liver, in keeping with the role as a monitor of blood - glucose levels, possess a specialized isozyme of hexokinase called glucokinase that is not inhibited by the glucose 6 - phosphate. Glucokinase phosphorylates glucose only when it is abundant because it has about 50 - fold affinity of glucose than does hexokinase.

Reference: Berg, J.M., Tymoczko, J.L., Stryer, L. (2002).The Glycolytic Pathway is Tightly Controlled. Biochemistry (5th Ed.) Section 16. 2.3 .https://www.ncbi.nlm.nih.gov/books/NBK22395/

Question 52

Q

52.A 38-year-old man collapses while running a marathon and is brought to the ER. His wife states that he is not in shape but still decided to run. Arterial blood gas analysis on room air shows PO2 of 100 mmHg (normal), PCO2 of 42 mmHg (normal), and pH of 7.30 (low). Further evaluation reveals metabolic acidosis. Increased activity of which of the following biochemical pathways is the basis for the clinical findings?

a. Citric acid cycle
b. Pentose phosphate shunt
c. β-Oxidation of fatty acids
d. Anaerobic glycolysis
e. Mitochondrial oxidative phosphorylation

Answer

A

d. Anaerobic glycolysis

During intense exercise, oxygen demands of skeletal muscles exceed oxygen supply; hence (1) oxidation of NADH in the ETC, and (2) ATP production by oxidative phosphorylation are inhibited.

As such, the muscles rely on anaerobic glycolysis, and pyruvate is converted to lactate by lactate dehydrogenase as NADH is oxidized. This reaction generates NAD+ which allows glycolysis to proceed, and ATP is generated by substrate-level phosphorylation.

Serum lactate level then becomes elevated causing a decrease in blood pH leading to metabolic acidosis.

Reference: Batch 2023 Evals 04 Carbohydrate Metabolism.

Question 53

Q

53.A newly-advertised herbal tea drink boasts of high taurine content. Which of the following benefit/s is/are expected from this drink?

a. Increase CNS activity and function
b. Hastens antimicrobial killing with free radicals
c. Improved cholesterol levels
d. All of the choices

Answer

A

c. Improved cholesterol levels

Taurine, a special amino acid from cysteine, has potential metabolic benefits. It can reduce bad cholesterol (i.e., LDL and VLDL) by downregulating the hepatic production of apolipoprotein B100 needed by VLDL and LDL.

Reference: Batch 2024 Trans 07 Specialized Products and Derivatives from Amino Acids, p. 3

Question 54

Q

54.After an overnight fast, which of the following is most likely true regarding the patient’s serum?

a. There is increased alanine transported to the liver.
b. There is decreased activity of the urea cycle.
c. There is increased glucose transported into the portal vein.
d. There is increased protein synthesis in the hepatocytes.

Answer

A

a. There is increased alanine transported to the liver.

“In the fasting state, there is a considerable output of alanine from skeletal muscle, far in excess of the amount in the muscle proteins that are being catabolized. It is formed by transamination of pyruvate produced by glycolysis of muscle glycogen, and is exported to the liver, where, after transami- nation back to pyruvate, it is a substrate for gluconeogenesis.”

Reference: Harper’s Illustrated Biochemistry (30th ed) Section IV Metabolism of Carbohydrates, pp. 190-191

Question 55

Q

55.With activation of protein kinase A (via the adenylate cyclase pathway) by the catecholamine epinephrine, which of the following subsequent events SHOULD NOT occur?

a. Conversion of glycogen synthase to the active state
b. Activation of glycogen phosphorylase kinase
c. Phosphorylation of glycogen phosphorylase
d. Breakdown of glycogen to glucose-1-phosphate

Answer

A

a. Conversion of glycogen synthase to the active site.

Epinephrine is a hormone/neurotransmitter that functions as the ‘fight-or-flight’ of a person. When this is released, the system will trigger the rapid degradation of glycogen because glucose is needed for energy production.

Conversion of glycogen synthase will be counterproductive in this situation.

References: Batch 2023 Evals 04 Carbohydrate Metabolism.

Question 56

Q

56.Industrial fluoride poisons the enolase enzyme of glycolysis. As a consequence, which high-energy molecule is not formed?

a. Phosphoenolpyruvate
b. The first ATP molecule
c. 3-phosphoglycerate
d. 1,3-BPG

Answer

A

a. Phosphoenolpyruvate

The enzyme enolase in the glycolytic pathway is needed for the conversion of 2-phosphoglycerate to high-energy molecule phosphoenolpyruvate (PEP). Poisoning this enzyme will fail to produce phosphoenolpyruvate (PEP)

References: Batch 2023 Evals 04 Carbohydrate Metabolism and Doc VH’s lecture on Carbohydrate Metabolism.

Question 57

Q

57.Where do the carbon skeletons of ARGININE go? (A-F)

a. D
b. A
c. C
d. B
e. E
f. F

Answer

A

c. C

References: Doc Jan’s lecture video

Question 58

Q

58.A chronic kidney disease patient with muscle wasting is being given keto-acid analogues. His muscle mass improved after some time. This is most likely due to replenishment of which of the following?

a. Arginine, Glutamine, Asparagine
b. Alanine, Glutamine, Methionine
c. Glycine, Proline, Lysine
d. Valine, Leucine, Isoleucine

Answer

A

d. Valine, Leucine, Isoleucine.

Leu, Val, Phe, Ile, Met, Lys, Tyr, Thr, Trp, His - these AA belong to ketoanalogues.

a. Arg, Glu, Asn - not included ketoanalogues
b. Ala, Glu - not included in ketoanalogues
c. Gly, Pro - not included in ketoanalogues

References: Doc Jan’s lecture video

Question 59

Q

59.Fatty acid biosynthesis requires a good amount of NADPH. This particular scenario exemplifies the mode wherein the demand for NADPH is much higher than the demand for ribose 5-phosphate. Which phases of the pentose phosphate pathway are activated in this mode?

a. Both the oxidative and non-oxidative phase
b. The non-oxidative phase only
c. The oxidative phase only
d. Neither the oxidative nor the non-oxidative phase

Answer

A

a. Both the oxidative and non-oxidative phase

In cases such as fatty acid biosynthesis where more NADPH is needed than ribose 5-phosphate, both oxidative and non-oxidative phases are required. Oxidative phase produces NADPH while the non-oxidative phase converts ribulose 5-phosphate to glucose 6-phosphate to produce more NADPH.

Reference: Marks’ Basic Medical Biochemistry 5th Ed.

Question 60

Q

60.Glutamate in the brain cannot be transported directly from an astrocyte to the neuron since it is an excitatory neurotransmitter. Instead, it has to be converted into glutamine first in the astrocyte, then reconverted back to glutamate within the neuron. This process makes the brain utilize plenty of

a. pyruvate.
b. ammonia.
c. vitamin B6.
d. ATP

Answer

A

d. ATP

Conversion of glutamate to glutamine needs enzyme glutamine synthetase. Remember that synthetase reactions need ATP.

Reference: Doc Jan Monzon’s PPT

Question 61

Q

61.Which of the following is a direct consequence of breakdown of heme?

a. Creation of bilirubin
b. All of the choices
c. Production of carbon dioxide
d. Liberation of iron

Answer

A

d. Liberation of Iron

As heme is broken down to bilirubin, the process directly yields CARBON MONOXIDE and liberates IRON for storage and future use. This process occurs with the presence of oxygen and NADPH. Thus, resulting in biliverdin which is further reduced by biliverdin reductase to ultimately converted to bilirubin.

Conversion of heme to bilirubin by reticuloendothelial cells can be observed visually as the purple color of the heme in a hematoma slowly converts to the yellow pigment of bilirubin.

Creation of bilirubin - incorrect; it is not directly produced.

Reference: Harper’s Illustrated Biochemistry. 13th Edition Doc Jan Monzon’s Powerpoint

Question 62

Q

62.Glutamate may be formed in the hepatocytes from other amino acids by transfer of amino groups. This process would be impaired if the person lacks which of the following?

a. Vitamin B1
b. Biotin
c. Folate
d. Vitamin B6

Answer

A

d. Vitamin B6

Glutamate collects the nitrogen from most amino acids
except lysine, threonine, proline and hydroxyproline. It acts as the collector because it is the only amino acid that undergoes oxidative deamination at a rapid enough rate to clear the body from excess nitrogen.

NOTE: Most if not all transamination reactions (transaminase enzyme) rely on pyridoxal phosphate (Vit B6) as coenzyme/ cofactor.

› Transamination will not work if a person had Vit B6
deficiency
› Clinical scenario: Patient undergoes tuberculosis therapy which requires isoniazid (Isoniazid depleted Vit
B6) - result to difficulty in dealing with tuberculosis but also with nitrogen accumulation in the body because all these
transamination processes will be LESS efficient.

Reference: Doc Jan Monzon’s Lecture

Question 63

Q

63.Where do the carbon skeletons of the SERINE go? (A-F)

a. A
b. C
c. F
d. B
e. E
f. D

Answer

A

a. A

Serine is derived from 3-phosphoglycerate which is an intermediate in the glycolytic pathway. Since pyruvate is the final product of glycolysis in aerobic settings, the carbon skeleton of serine will ultimately end up to pyruvate.

References: Doc Jan’s lecture video

Question 64

Q

64.A 62-year-old man with anorexia, nausea and vomiting comes in due to worsening jaundice. The most recent vomitus is greenish in color. Direct bilirubin is markedly elevated while indirect bilirubin is only mildly elevated. Which of the following is the most likely diagnosis?

a. Pancreatic tumor located in the pancreatic head
b. Severe malnutrition leading to hypoalbuminemia
c. Severe hemolytic anemia
d. Progressive hepatic failure (cirrhosis)

Answer

A

a. Pancreatic tumor located in the pancreatic head

Pancreatic tumor located in the pancreatic head results in an obstruction of the biliary tree. This leads to post-hepatic jaundice (aka obstructive jaundice) and explains the elevated direct/conjugated bilirubin of the patient.

References: Doc Jan’s lecture video

Answer 65

A

b. Reduction of oxidized glutathione to protect against superoxides.

In red blood cells the pentose phosphate pathway provides NADPH for the reduction of oxidized glutathione catalyzed by glutathione reductase, a flavoprotein containing FAD. Reduced glutathione removes H2O2 in a reaction catalyzed by glutathione peroxidase, an enzyme that contains the selenium analogue of cysteine (selenocysteine) at the active site.

References: Harper’s Illustrated Biochemistry. 28th Edition

Answer 66

A

d. He may develop severe joint paints later on.

Alkaptonuria was first recognized and described in the 16th century. The defect is lack of homogentisate oxidase. The urine darkens on exposure to air due to oxidation of excreted homogentisate. Late in the disease, there is arthritis and connective tissue pigmentation (ochronosis) due to oxidation of homogentisate to benzoquinone acetate, which polymerizes and binds to connective tissue.

Reference: Harper’s Illustrated Biochemistry. 28th Edition

Answer 67

A

d. Cytoplasm

In this setting,of ischemia (oxygen-deprivation), the patient’s acidosis is likely due to lactic acid production under anaerobic conditions. Glycolysis is the biochemical pathway in which glucose is oxidized to pyruvate within the cytosol. In anaerobic conditions, pyruvate is converted into lactic acid by lactate dehydrogenase, an enzyme located in the cytoplasm.

The other choices can be eliminated since pyruvate to lactic acid conversion under anaerobic condition does not happen because lactate dehydrogenase is not present in those regions.

Reference: 2023 Trans (Rationalization of Doc VH)

Answer 68

A

a. All of the choices.

On fatal arrythmias:
Sinus tachycardia is the most common cardiac consequence of epileptic seizures and may occur in up to 80% of seizures. It may be associated with palpitations, but not with clinical signs such as syncope. Ictal asystole and rarer ictal arrhythmias have also been suggested as a potential pathomechanism for Sudden Unexpected Death in Epilepsy (SUDEP).

References: Van der Lende M., Surges R., Sander J.W. (2016). Cardiac arrhythmias during or after epileptic seizures. Journal of Neurology, Neurosurgery & Psychiatry, 87, 69-74.

On myoglobinuria:
The typical clinical manifestations of Rhabdomyolysis (RM) are myalgia, muscle weakness, and myoglobinuria. Seizures as cause of RM are classified as belonging to the category of ‘internal factors’ that result from injury due to involuntary muscle overuse. One study that included 475 hospitalized RM patients found that seizures occurred in 32 (approximately 7%) patients, and was considered to subsequently result in RM. However, RM is more common in status epilepticus when compared with those having a single seizure attack.

References: Zhou J., Luo B., & Peng G. (2017). A single seizure attack induced rhabdomyolysis. Neurol India, 65, Suppl S1, 93-4.

On hyperkalemia:
The most serious manifestations of hyperkalemia are muscle weakness or paralysis, cardiac conduction abnormalities, and cardiac arrhythmias. Unlike other electrolyte alterations, hypokalemia or hyperkalemia rarely causes symptoms in the CNS, and seizures do not occur. The majority of patients with mild hypokalemia are asymptomatic and initial symptoms, when they occur, may be non-specific such as weakness or fatigue.

References: Baratloo, A., Rouhipour, A., Forouzanfar, M., Rahmati, F., & Hashemi, B. (2013). Hypokalemia-induced abnormal movements: case report. Trauma monthly, 18(3), 141–144. https://doi.org/10.5812/traumamon.12016

Answer 69

A

a. Succinate Dehydrogenase

Succinate dehydrogenase is bound to the inner mitochondrial membrane and the only dehydrogenase who uses FAD as its electron acceptor

The cofactor FAD is housed or built in one of the domains of succinate dehydrogenase, and its reducing equivalents get transferred from succinate on to FAD to form FADH2, succinate being converted to fumarate in the process.

Reference: Doc VH lectures and batch 2023 rationalization by Doc VH

Answer 70

A

a. 2-Oxogluterate

2-Oxoglutarate or 𝛂-Ketoglutarate directly forms the amino acid Glutamate via the enzyme glutamate dehydrogenase.

This process includes the removal of a ketone group, and replacing it with an amino group, after doing so, addition of an amino group will help to form it into a new amino acid via transamiantion.

Reference: Doc VH lectures and batch 2023 rationalization by Doc VH

Answer 71

A

a. Porphyria cutanea tarda

Porphyria cutanea tarda (PCT) classic presentation is that of blistering or vesicles becoming tense bullae on photosensitive fragile skin which then rupture leaving the skin with a slow-healing erosions and crusted lesions. PCT is associated with a reduction in hepatic uroporphyrinogen decarboxylase. A reduced enzyme-substrate affinity leads to an accumulation of porphyrinogens in the skin and tissues resulting in photosensitivity (spontaneous oxidation of porphyrinogens to porphyrins).

Reference: Doc Jan Monzon’s PPT - Heme Metabolism

Answer 72

A

c. Tumors of the adrenal medulla

Tyrosine is the precursor for:

catecholamine
thyroid hormones
melanin

Some tumors produce abnormal levels of catecholamines.

Reference: Doc Jan Monzon’s PPT - Biosynthesis of Nonessential Amino Acids

Answer 73

A

d. The glucosyl residue directly attached to glycogenin is nonreducing..

Only one glucosyl residue that has an anomeric carbon not
linked in the glycosidic bond.
found at the very beginning of the chain
attached to a protein called GLYCOGENIN.
All the other ends of the chain in the glycogen molecule
DO NOT HAVE free anomeric carbons =NONREDUCING ENDS

Glycogenin- protein that begins the production of a
glycogen molecule

Reference: Doc Jan Monzon’s PPT

Answer 74

A

c. Acetoacetate

Acetoacetate is an intermediate in Ketogenesis. When HMG-CoA has entered the mitochondria it undergoes reaction via the enzyme HMG-CoA Lyase and one Acetyl-CoA will be removed again and in the process it will produce Acetoacetate.

Acetoacetate – is one of the ketone bodies and can undergo
spontaneous degradation to form Acetone.

Reference: Doc VH lectures and batch 2023 rationalization by Doc VH

Answer 75

A

a. Protein phosphatase

Insulin activates tyrosine kinase receptors resulting in the phosphorylation and activation of protein kinase, followed by the protein phosphatase. The activated protein phosphatase will inactivate protein kinase and glycogen synthase, and activate glycogen synthase by removing the phosphate group.

Reference: Harper’s Illustrated Biochemistry (30th edition)

Answer 76

A

c. The patient has decreased lean muscle mass.

Urea and creatinine are excreted in urine; their serum
concentrations can be used as markers of renal function
because the serum concentration increases as renal function
deteriorates.(p.566)

Creatinine excretion is reasonably constant from day to day for any one individual, but varies between individuals because it depends mainly on muscle mass; creatinine is formed non-enzymically from creatine and creatine phosphate, most of which is in skeletal muscle (p.563).

Reference: Harper’s Illustrated Biochemistry (31st ed.)

Answer 77

A

b. Pyruvate dehydrogenase

Pyruvate dehydrogenase is inhibited by its products, acetyl-CoA, and NADH. It is also regulated by phosphorylation (catalyzed by a kinase) of three serine residues on the pyruvate dehydrogenase component of the multienzyme complex, resulting in decreased activity and by dephosphorylation (catalyzed by a phosphatase) that causes an increase in activity.

Reference: Harper’s Illustrated Biochemistry (30th ed) Chapter 17, Page 173

Answer 78

A

c. These cycles are used to convert malate to oxaloacetate and then to aspartate, at the same time reducing NAD+ to NADH for the electron transport chain.

This reaction refers to the Krebs cycle or the Citric Acid Cycle where malate is oxidized to oxaloacetate by malate dehydrogenase, which is linked to NAD+ reduction.

Reference: Harper’s Illustrated Biochemistry: Chapter 16, pp 153

Answer 79

A

b. Cysteine

PAPS or 3’-phospho-adenosine-5’-phosphosulfate is a
key by-product of cysteine metabolism which is an active sulfate. This is needed for the transfer of sulfate to the sugars of glycosphingolipid molecules and the sulfated glycosaminoglycans (e.g. heparan sulfate, chondroitin sulfate, keratan sulfate, dermatan sulfate).

Reference: Batch 2024, Module 10B, Trans 06 Protein Metabolism: Fate of Carbon Skeleton p.5.

Answer 80

A

b. Debrancher enzyme

The function of the debrancher or debranching enzyme is an important step in the mobilization or breakdown of glycogen stores. The process includes the ceasing of phosphorylase to cleave α-1,4-glycosidic linkages four glucosyl residues from an α-1,6-branch site. It has two catalytic activities: a transferase activity and a glucosidase which results in the release of free glucose.

Reference: Case Files Biochemistry Lange (2nd Ed) Page 182

Answer 81

A

d. Activation of protein kinase A, through the adenylate cyclase pathway, and phosphorylation of PFK-2

During the fed state, there is an abundance of glucose,
which eventually leads to an abundance of fructose 6-phosphate, as stated in the question. This intermediate allosterically activates the kinase function of PFK-2 (and inhibits its bisphosphatase function at the same time). PFK-2 then converts fructose 6-phosphate to fructose 2,6-bisphosphate, an intermediate that allosterically activates PFK-1 and inhibits fructose 1,6-bisphosphatase, consequently leading glucose down the pathway of glycolysis.

Reference: Batch 23 Ratio

Answer 82

A

a. Transport of bilirubin to the liver

Bilirubin is transported to the liver bound to serum albumin. Patients with decreased protein levels (in this case, protein-losing enteropathy) tend to have decreased albumin levels as well. As a consequence, of low albumin levels, decreased amounts of bilirubin (B1) are transported to the liver and the rest remains in the blood which will then cause Jaundice.

Reference: Doc Jan Monzon’s Lecture and Heme Metabolism PPT.

Answer 83

A

d. Gluconeogenesis

The viral infection causes liver cells damage causing AST and ALT to leak out of the cell to the bloodstream, making them not available to be utilized in the gluconeogenesis in the liver.

AST- is involved in converting glutamate to oxaloacetate which is both an intermediate in TCA and Gluconeogenesis.
ALT- converts alanine to pyruvate, which is used in gluconeogenesis during the fasted state.

Reference: Doc Monzon’s Lecture video and Batch 2024’s Protein Metabolism trans (Part 1 & 3)

Answer 84

A

d. NADH : NAD+
Alcohol metabolism favors an increase in NADH to NAD+ ratio which is true in a drinking binge.
The abundance of NADH favors the reduction of pyruvate to lactate.
The ethanol mediated increase in NADH causes the gluconeogenic precursors to be diverted into alternate pathways resulting in the decrease in the synthesis in glucose. It is common in alcoholics and among those who binge drink to not eat anything nutritive, and thus they have depleted liver glycogen stores.
The gluconeogenesis will be impaired, metabolism of ethanol in such circumstances can precipitate HYPOGLYCEMIA which can produce behaviors associated with alcohol intoxication such as agitation, impaired judgement and combativeness
Pyruvate- is a substrate in gluconeogenesis
Hypoglycemia- blood sugar is lower than normal.
Reference: Doc VH’s Lecture Video and Handout (Carbohydrate Metabolism Part III: Pentose Phosphate Pathway and Alternative Carbohydrate Metabolism Pathways) and Siopao (Batch 2024): PART 3

Answer 85

A

c. Inferior mesenteric vein

Distribution of ammonia production are as follows: intestine (mostly from colon) - 50%; kidney - 40%; RBCs - 5% and muscles - 5%.

From the figure above, ammonia & ammonium ions are produced in the left half of the transverse colon, splenic flexure & descending colon. These parts of the colon initially drains into the left colic vein which is a tributary of the inferior mesenteric vein.
Reference: Chapter 14. ammonia and urea. Barrett K.E.(Ed.), (2014). Gastrointestinal Physiology, 2e. McGraw-Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=691&sectionid=45431415

Answer 86

A

a. GAPDH

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is the enzyme that catalyzes the sixth step of glycolysis. This reaction is the combination of GAPDH and an inorganic phosphate (Pi) that leads to the formation of 1,3-Biphosphoglycerate.

Hexokinase - catalyzes the first step of glycolysis; used to convert glucose to glucose-6-phosphate

Phosphoglycerate Mutase - catalyzes the eight step of glycolysis; used to form 3-Phosphoglycerate to 2-Phosphoglycerate

Phosphofructokinase-1 (PFK-1) - catalyzes the third step of glycolysis; conversion of Fructose-6-phosphate to Fructose-1,6-bisphosphate; rate limiting step; first committed step of glycolysis; regulated enzyme

Reference: Doc VH’s Lecture Video and Handout (Carbohydrate Metabolism Part I: Glycolysis and Gluconeogenesis)

Answer 87

A

c. Glutamine - essential for maintaining resting vascular tone.

Catalyzed by nitric oxide synthase, Arginine is converted to l-ornithine and nitric oxide, an intracellular signaling molecule that serves as a neurotransmitter, smooth muscle relaxant, and vasodilator.

Nitric Oxide - The major vasodilator that maintains vascular tone, alongside other dilators and constrictor substances.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st ed., p. 308). New York: Mcgraw-Hill Education.

Answer 88

A

c. It is a large, highly branched heteropolysaccharides.

The reason why the Glycogen was designed to be branched is for its rapid degradation and rapid synthesis. It allows enzymes to work on several chains simultaneously from the multiple nonreducing ends, therefore resulting in a large amount of glucose-1 phosphate released in a short period of time.

Reference: Doc VH’s lecture

Answer 89

A

c. Acetyl-CoA
Ethanol to Acetyl-CoA
1st step: Ethanol is first oxidized in the liver to acetaldehyde by cytosolic alcohol dehydrogenase.
2nd step: Acetaldehyde is further oxidized to acetate by mitochondrial acetaldehyde dehydrogenase
3rd step: Much of the acetate produced from ethanol leaves the liver to blood stream to muscle, where it is converted to ACETYL-COA, which can be used to provide energy via the Krebs cycle
Acetyl-CoA may also be formed in the liver and used as a precursor for lipid biosynthesis.
Acetyl-CoA- is an oxidized by series of enzymes that make up the cyclical series of reactions called the Krebs Cycle
Reference: Doc VH’s Lecture Video and Handout (Carbohydrate Metabolism Part III: Pentose Phosphate Pathway and Alternative Carbohydrate Metabolism Pathways )

Answer 90

A

b. Ribose-5-phosphate can be recycled back to glucose-6-phosphate via the non-oxidative phase to produce more NADPH via the oxidative phase

Reference: Lieberman, M., Peet, A., & Chansky, M. (2018). Pathways of Sugar Metabolism: Pentose Phosphate Pathway, Fructose, and Galactose Metabolism. In Marks’ basic medical biochemistry: A clinical approach (4th ed., p. 535. 539). Philadelphia: Wolters Kluwer.

Answer 91

A

a. Production of gastric acid.
b. Biliverdin, a product of heme catabolism, is an antioxidant and as such performs a significant role when heme oxygenase is induced by stress. (Devlin, 2011, p. 798)

c. At least half of the common drugs that we ingest are metabolized by isoforms of cytochrome P450. (Rodwell et al., 2018, p. 557)
d. Heme proteins are ubiquitous in biology and serve diverse functions, including oxygen transport and storage (e.g. hemoglobin and myoglobin). (Rodwell et al., 2018, p. 305)

References:
Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., &
Weil, P. A. (2018). Harper’s Illustrated Biochemistry (31st
ed.). McGraw Hill Education.
Devlin, T. M. (2011). Textbook of Biochemistry with Clinical
Correlations (7th ed.). John Wiley & Sons, Inc.

Answer 92

A

a. GAP and fructose-6-P.

Reference:
Van Haute, M. Q. (2021). Carbohydrate Metabolism 3a: Pentose
Phosphate Pathway

Answer 93

A

d. Aldehyde dehydrogenase.

Deficiency in aldehyde dehydrogenase results in the accumulation of acetaldehyde, which is produced from the metabolism of alcohol by alcohol dehydrogenase.

Reference: Doc VH’s lecture

Answer 94

A

b. Kidney.

a. RBC is not an organ.
c. Functions as a blood filter and the graveyard of erythrocytes. It is not involved in gluconeogenesis.

d. Gluconeogenesis occurs mainly in the liver under fasting conditions. Under extreme conditions of starvation, gluconeogenesis can also occur in the renal cortex

Reference: Doc VH’s lecture

Answer 95

A

a. Under anaerobic conditions, pyruvate does not form because glycolysis does not occur.

Under anaerobic conditions, glycolysis still occurs and pyruvate is still formed, but instead of being converted into acetyl-CoA to enter TCA (which can’t proceed), it is converted to lactate by the enzyme lactate dehydrogenase.

Reference: Carbohydrate Metabolism Part 1 2024 Trans

Answer 96

A

b. Biotin and cobalamin

The Methionine pathway shared with Valine, Isoleucine and others will lead to Propionyl-CoA.

Propionyl-CoA will become Succinyl-CoA to enter the TCA cycle. In the TCA cycle leading up to oxaloacetate, this can enter gluconeogenesis, making Methionine a glucogenic amino acid.

Vitamins required for methionine are biotin and cobalamin aka Vitamin B12.

Reference: Protein Metabolism Part 3 2024 Trans

Answer 97

A

d. Pyruvate Dehydrogenase

Many Alcoholics are thiamine deficient (both because of poor diet and also because alcohol inhibits thiamine absorption. Pyruvate dehydrogenase is inhibited leading to the accumulation of pyruvate. Thus, these metabolic defects cause neurological disturbances as shown by the patient’s symptoms.

Reference: Harpers Illustrated Biochemistry 31st ed. Chapter 17: Glycolysis & the Oxidation of Pyruvate,Page 163

Answer 98

A

d. Undergo Mitosis

Glycine gives off one of its carbon to purines which is essential in DNA and RNA synthesis.

Reference: Doc Jan’s Video Lecture Protein Metabolism Part 3

Answer 99

A

a. Isocitrate dehydrogenase.

Reference: Doc VH’s lecture

Answer 100

A

d. Oxidized glutathione.

Oxidized Glutathione accumulates because of G6PD deficiency. The pentose phosphate pathway in RBCs maintains glutathione in a reduced state. Glucose-6-phosphate dehydrogenase (G6PD) is required to catalyze nicotinamide adenine dinucleotide phosphate (NADP) to its reduced form (NADPH).

In patients with G6PD Deficiency, during oxidative stress ther is a build-up of NADP, and NADPH levels are too low to maintain glutathione in a reduced state.

As a result of lowered levels of reduced glutathione, there is a build-up of oxidants, which damages hemoglobin as well as enzymes. The affected RBCs are ultimately removed from circulation by the spleen causing anemia.

Reference: Doc VH’s lecture

Answer 101

A

a. Proline

Proline synthesis and catabolism is via the pathway of ornithine and glutamate, the latter two amino acids serve as its immediate precursors as well as metabolites. Ornithine is one of the intermediates for urea cycle, and glutamate is metabolically connected to tricarboxylic acid (TCA) cycle, the major cycle for energy production.

It is hypothesized that the significantly increased rates of net nitrogen loss and energy “production”, as the consequence of the accelerated activities of both the urea and TCA cycles in burn injury “drain” both ornithine and glutamate, thus depleting tissues of the availability of proline. Hence, the de novo synthesis of proline is likely to be affected by the reduced availability of its major precursors: glutamate and ornithine.

This hypothesis is supported by 1) tissue and circulating glutamine content are reduced in stressed conditions; 2) ornithine disposal via oxidation is significantly increased after burn injury(2). Therefore, the availability of proline is likely to be limiting after burn injury for the synthesis of proteins. On the other hand, proline requirement is significantly increased in burn patients due to the high demand for tissue repair and wound healing. As a result, providing an adequate proportion of its precursors, glutamine / glutamate and / or as performed proline, is of importance to maintain the appropriate supply and balance of amino acids for protein and other synthetic functions after burn injury.

References: https://clinicaltrials.gov/ct2/show/NCT00216983

Answer 102

A

d. 30 to 32

Reference: Doc VH’s lecture video

Answer 103

A

d. 3 to 5 ATP molecules

The number of ATP molecules derived from each NADH molecule generated via glycolysis depends on the shuttle that transports the NADH (or more accurately, the reducing equivalents it carries) from the mitochondria across the inner mitochondrial membrane into the mitochondrial matrix (recall that glycolysis occurs in the cytoplasm). If the malate-aspartate shuttle is used, 2.5 molecules of ATP per NADH will be generated because NADH is the cofactor accepting the reducing equivalents in the matrix side. On the other hand, if the glycerophosphate pathway is used, only 1.5 molecules of ATP per NADH will be generated since the receiving cofactor in the matrix side is FAD.

Reference: Doc VH’s lecture video

Answer 104

A

b. Glutamine

References: Garcia-Bermudez, J., Williams, R., Guarecuco, R., & Birsoy, K. (2020). Targeting extracellular nutrient dependencies of cancer cells. Molecular Metabolism, 33, 67-82. doi: 10.1016/j.molmet.2019.11.011

Answer 105

A

d. NADH and FADH2

The electron carriers produced (NADH and FADH2) cannot provide energy to cellular processes directly. Instead, the processes of the electron transport chain and oxidative phosphorylation will use the energy from these molecules to activate the enzyme complex ATP synthase, which produces ATP. The role of NADH and FADH2 is to donate electrons to the electron transport chain. They both donate electrons by providing an hydrogen molecule to the oxygen molecule to create water during the electron transport chain. NADH is a product of both the glycolysis and Kreb cycle. FADH2 is only produced in Krebs cycle.

Reference: Molnar, C., & Gair, J. (2015). Concepts of Biology - 1st Canadian Edition. Bccampus. Retrieved from https://opentextbc.ca/biology/

Answer 106

A

a. Aldose reductase

Diabetic cataract results from osmolysis due to sorbitol accumulation.

The rise of glucose concentration in insulin insensitive tissues (peripheral nerves, renal glomeruli, seminal vesicles, and lens) increases the activity of the sorbitol pathway, which is responsible for the conversion of glucose to fructose. Glucose is reduced to sorbitol by aldose reductase, which cannot diffuse through cell membranes and remains trapped inside the cell. The accumulation of sorbitol inside the cell causes strong osmotic influx of water, resulting in swelling of the cell.

Reference: Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st ed., pp. 190-191). New York: Mcgraw-Hill Education.

Answer 107

A

c. The high Km and high Vmax of glucokinase

Glucokinase has high Km (low affinity) and high Vmax, while hexokinase has low Km (high affinity) and low Vmax.

Source: Doc Van Haute’s Video lecture - Carbohydrate Metabolism

Answer 108

A

a. The rate-limiting step of gluconeogenesis is affected, resulting in a patient’s hypoglycemia

With biotin deficiency as a result of ingesting an excessive amount of raw egg whites, the activity of the gluconeogenic enzyme pyruvate carboxylase, which is biotin-dependent, is impaired. As a result, oxaloacetate is not produced from pyruvate. Besides gluconeogenesis not proceeding as it is supposed to, replenishment of oxaloacetate needed for the Krebs cycle is likewise impaired (pyruvate carboxylase catalyzes the main anaplerotic reaction). Since a protein-only diet is another condition that makes gluconeogenesis favorable besides fasting/starvation, his raw egg white-only diet contributed to his condition (and may have worsened it since he cannot utilize the protein he ingested anyway on account of pyruvate carboxylase being inactive in light of his biotin deficiency). The pyruvate carboxylase step, however, is NOT the rate-limiting step of gluconeogenesis; the PEPCK step is.

Reference: Dr. VH’ Lecture on Carbohydrate Metabolism: Gluconeogenesis

Answer 109

A

d. Arginine

Arginine is another important amino acid because it stimulates T lymphocytes, augments natural killer cell performance, and accelerates nitric oxide synthesis, which improves resistance to infection

Source: Clark, A., Imran, J., Madni, T., & Wolf, S. E. (2017). Nutrition and metabolism in burn patients. Burns & Trauma, 5. doi:10.1186/s41038-017-0076-x

Answer 110

A

b. decreased GABA

GABA is an inhibitory neurotransmitter. It requires Glutamate for its synthesis. Since the patient has been diagnosed of liver cirrhosis due to long-term alcoholism, glutamate in the CNS is then sequestered to form glutamine to clear out ammonia. The decreases in GABA formation will then lead to seizures.

Reference: Doc Jan’s video lecture on Protein Breakdown, Nitrogen Turnover, and Urea Cycle

Answer 111

A

a. Phosphoglycerate from Glycolysis.

Oxidation of the α-hydroxyl group of the glycolytic intermediate 3-phosphoglycerate, catalyzed by 3-phosphoglycerate
dehydrogenase, converts it to 3-phosphohydroxypyruvate.
Transamination and subsequent dephosphorylation then form
serine (Figure 27-7).

Following conversion of methionine to homocysteine, homocysteine and serine form cystathionine, whose hydrolysis forms cysteine and homoserine (Figure 27-11).

Reference: Harper’s Illustrated Biochemistry 29th ed.

Answer 112

A

b. Muscle glycogen phosphorylase
The symptoms described suggest a diagnosis of McArdle disease, a type V glycogen storage disorder caused by a lack of muscle glycogen phosphorylase (or myophosphorylase). This enzyme breaks down muscle glycogen by removing the a-1,4 glucosyl units from the outer branches of glycogen. In healthy individuals, the glucose-1-phosphate liberated by the phosphorylase is converted to glucose-6-phosphate and oxidized to pyruvate via glycolysis. Muscle pyruvate can be converted to lactate and released into the blood but most of it crosses into the mitochondria where it is used to generate ATP by oxidative phosphorylation.
As a consequence of the myophosphorylase deficiency, patients with McArdle disease are unable to obtain energy from muscle glycogen stores. The abnormal accumulation of glycogen in muscle tissue leads to painful cramps and myoglobinuria during strenuous exercise, with no increase in lactic acid in the blood as would normally be seen.
Reference: Principles of Biochemistry, 7th Edition by Albert Lehninger

Answer 113

A

c. Alkaline phosphatase

Elevations of ALP are of most diagnostic significance in the evaluation of hepatobiliary and bone disorders. In hepatobiliary disorders, elevations are more predominant in obstructive conditions than in hepatocellular disorders.

In biliary tract obstruction, ALP levels range from 3 to 10 times the ULN. Increases are primarily a result of increased synthesis of the enzyme induced by cholestasis.

Reference: Clinical Chemistry Principles, Techniques, and Correlations, 7th Edition by Bishop et al.

Answer 114

A

b. d (Succinyl-CoA)

Catabolism of branched chain amino acids (Leucine, Isoleucine, and Valine) is a multistep process catalyzed by the branched chain ketoacid dehydrogenase complex. The final product of Valine is propionyl CoA, which is then converted to succinyl CoA, which enters the Kreb’s cycle.

Reference: Doc Jan Monzon’s lecture and PPT- Protein and Amino Acid Metabolism
Rodwell, V. W., Bender, D. A., Botham, K. M., Kennelly, P. J., & Weil, P. A. (2018). Harper’s illustrated biochemistry (31st ed., p.281). New York: Mcgraw-Hill Education.

Answer 115

A

b. 20

Reference: Harper’s Illustrated Biochemistry 29th ed.

Answer 116

A

b. GAP to 1,3-BPG

In the Glycolysis, only GAP requires NAD+ to become 1,3-BPG.

Reference: Dr. Van Haute’s Lecture on Carbohydrate Metabolism: Glycolysis

Answer 117

A

a. Liver and muscles.

Branched Chain Amino Acids (BCAA) Valine and isoleucine are stored in the liver and significant on the skeletal muscles. Recent studies revealed that these BCAA are administered for treatment of advanced liver disease. Valine and Isoleucine form a significant of the flux between liver and muscles.

Reference: Doc Jan’s video lecture

Answer 118

A

b. Aspartate

Aspartate is converted into oxaloacetate by a reaction catalyzed by the enzyme aspartate aminotransferase, which transfers an amino group from aspartate to 2-oxoglutarate to produce glutamate and oxaloacetate.

Source: Doc Jan’s PPT on Metabolism of Proteins and Amino Acids Part 1

Answer 119

A

d. 2 NAD+ molecules

2 NAD+ - used at the 6th step of glycolysis yielding 2 NADH
2 ATP molecules - 1 ATP is used at the 1st and 3rd step while 2 ATPs are produced at the 7th and 10th step, yielding 2 ATP molecules
2 pyruvate - produced at the 10th step of glycolysis

Reference: Doc VH’s lecture video - Carbohydrate Metabolism (Glycolysis)

Answer 120

A

c. glycosaminoglycans

Glycosaminoglycans (GAGs) are made up of disaccharide repeating units. This disaccharide unit is composed of an amino sugar (hexosamine) and a uronic acid.

Reference: Doc VH’s lecture on Alternative Metabolic Pathways

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