Biochemistry MD21 Page 1

The Reason answer after completing the MCQ of Biochemistry

1. b. Fructose

Reason: Fructose cannot be transport using passive diffusion and can only be transport by using protein carriers, but it

doesnt need energy which is why it is absorbed by facilitated transport.

2. a. alpha-amylase

Reason: alpha-amylase can breakdown polysaccharides such as starch, dextrins.etc.

3. c. Thiamine

Reason: Thiamine or vitamin-B is needed for the efficiency of glucose metabolism which can aid in a much easier

absorption for glucose in intestine.

4. d. Chloride ions

Reason: They are not found in the salivary amylase which is why it is needed as activator for the breakdown of

polysaccharides.

5. b. Thyroid hormones

Reason: Thyroid hormones are responsible for increasing the metabolism of carbohydrates.

6. d. NAD+

Reason: NAD+ is an essential cofactor for converting UDP-Glucose to UDP-glucuronic acid. The Enzyme for converting

is UDP-glucose 6-hydrogenase.

7. b. Pyruvate

Reason: It is the somnol leftover product of glycolysis.

8. c. Pyruvate carboxylase (Pyruvate Kinase)

Reason: Pyruvate carboxylase is not needed for the conversion of lactic acid to glucose but its function is to convert PA to

OAA in pyruvate acid formation.

9. d. Muscle phosphorylase

Reason: MacArdles disease involved in muscles weakening which is why it is related to muscle phosphorylase enzyme

because the deficiency of this enzyme can leads to muscle failure or weakening.

10. b. Brain

Reason: brain cells (neuron cells) uses almost twice the energy than normal cells and as stated normal resting state our

other cells such as muscles or bones are not working as much as our brain does which means our brain is sending signals

here and there in order keep our body functioning. That is why our brain uses the most energy while our body is in a

normal resting state.

11. e. Glucose-6-PO4

Reason: Glucose-6-PO4 is the key enzyme for activating the enzyme glycogen synthase.

12. b. Acetyl-CoA

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Reason: Pyruvate carboxylase needs ATP, carbon dioxide, biotin and Acetyl-CoA to function or activate. However,

Acetyl-CoA also act as its modifier (regulating).

13. b. Malonate

Reason: Malonate is one of the two inhibitors of succinate dehydrogenase enzyme. (the other one is Oxaloacetate)

14. d. Citric acid cycle

Reason: Catabolic role is to breakdown carbohydrates, lipids and proteins into water, carbon dioxide and glucose.

Whereas, anabolic role is to synthesize other substances. Citric acid cycle is considered both of them in nature. It forms

both CO2 and H2O then giving off energy like catabolic role and formation of non-essential amino acid, FA synthesis,

cholesterol, and steroid synthesis like anabolic role.

15. d. Thiamine deficiency

Reason: Transketolase activity can be delayed due to the lack of carbohydrate metabolism which is why thiamine

deficiency can also affect its activity.

16. d. Decrease gluconeogenesis

Reason: Gluconeogenesis is the process of producing glucose which means diabetes wont be affecting by the decreasing

of it.

17. b. 6-phosphogluconate

Reason: it is the leftover from the process of breaking down of 6-phospho gluconolactone by Glucondactone hydrolase

enzyme.

18. b. Glucose-6-phosphatase

Reason: Von Gierkes disease is also called as glycogen storage disease type I which is mainly caused by the deficiency

of glucose-6-phosphate enzyme. Due to the fact that this enzyme is much needed for glycogen synthesis. When glycogen

cannot be formed, there is no way to store energy as glycogen causing this type of disease known as glycogen storage

disease.

19. c. Muscle

Reason: it can only store glycogen unlike liver which can do both the storing and processing.

20. d. UTP

Reason: this enzyme also known as UDP-glucose is essential for glycogenesis because it is need to convert glucose-1-

phosphate to UTP-glucose in the 4th step of glycogenesis.

21. c. Fructose-1,6-bi-P

Reason: Aldolase is an enzyme in aldol reaction which aldol means any type of fructose bi phosphate. That is why c.

Fructose-1,6-bi-phosphate is the correct answer. It is the substrate for aldolase enzyme.

22. d. Vasopressin

Reason: Vasopressin has two primary function, to constrict blood vessels and retain water in our body.

23. a. NADP+

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Reason: Dehydrogenases function in HMP shunt is to produce NADPH by reduction reaction. It transfer 1 H-

atom to NADP+ to form NADPH. Generally HMP shunt is the process for creating NADPH and pentoses (5-

carbon sugars).

24. d. Enolase

Reason: Flouride is a competitor of the enolases substrate 2-PG. It replaces the substrate which can slow down

the enolases activity.

25. c. They facilitate transfer of hydrolytic products of TG to intestinal mucosal cell.

Reason: micelles can only transport monoglycerides and fatty acids for passive diffusion in small intestine.

Which is why c. is the correct answer because hydrolytic prodcuts of TG are monoglycerides and fatty acids

26. b. Fatty acids and two monoacylglycerol

Reason: b. Fatty acids and 2 monoacylglyercols are the products of TG hydrolysis. Stated above, the product of

hydrolysis of TGs are fatty acids and monoglycerdies (monoacylglyerols)

27. e. concentration of bile salts in gastric juice

Reason: the concentration only affecting the speed of lipid metabolism which means if there are higher bile salt

concentration, it will help the lipase to break down lipid more efficiently and faster.

28. b. enterokinase

Reason: enterokinase is responsible for activating the trypsinogen into trypsin (active form of trypsinogen)

which is why it is the enzyme which can also delay the gastric emptying rate also.

29. c. By soap formation

Reason: Calcium controls the breakdown of lipid by converting them into soaps (ca-soaps) which is insoluble

preventing the further process of lipase action.

30. b. extramitochondrial de novo fatty acids synthesis

Reason: NADPH acts as cofactor by serving needed electrons of H-. It is made by HMP shunt or pentose

phosphate cycle.

31. b. formation of mevalonate from HMG-CoA (3-hydroxy-3-methylglutaryl Coenzyme A)

Reason: It is called the committed step because it is irreversible in the process. It is the second step in

cholesterol synthesis which convert HMG-CoA by adding 1 electron from NADPH forming melanovate in the

process with the product of Melanovate + NADP+.

32. b. HMP shunt

Reason: because HMP shunt process produces NADPH and pentoses which is much needed for supplying the

reducing equivalents in fatty acid biosynthesis.

32. c. Red blood cells

Reason: They do not have mitochondria for using ketone bodies as energy.

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33. e. liver

Reason: Since ketone bodies are made up from fatty acids breakdown, this can be inferred that it is produced

inside liver mitochondria because fatty acids breaks down by enzyme in liver. (Lipase is the enzyme that breaks

down fatty acids into Acetyl-CoA)

34. e. Biotin

Reason: Acetyl-CoA carboxylase is a biotin dependent enzyme which is needed to convert acetyl-CoA to

malonyl-CoA. Which is why Biotin is the correct answer.

35. c. Involved in FA synthesis

Reason: FA synthesis only involved with Acetyl-CoA and Malonyl-CoA.

36. d. LDL

Reason: when a person did a 12 hour fasting, your LDL will not be affected by what you have consumed

making it measurable by a blood test. Cholesterol blood test is used for testing HDL and LDL (only with 9 12

hours fasting).

37. b. they are formed in kidneys

Reason: Ketone bodies are formed in livers because it is made from fatty acids which is stored and processes in

liver using enzymes (lipase).

38. b. Mitochondrial content higher than white adipose tissue

Reason: It is brown because it has a higher content of (iron-containing) mitochondria than white adipose cell.

Brown adipose cell has more capillaries because it needs more oxygen than most tissue.

39. d. increased fat utilization.

Reason: Ketone are made from breakdown of fatty acids and fatty acids are made from the breakdown of fats

which means when there are more usage of ketone bodies (ketosis) more fats are needed to breakdown for

formation of fatty acids; thus, formation of ketone bodies needed.

40. d. Lipoprotein Lipase

Reason: Triglycerides are broken down by LPL because they cannot be absorbed by the Duodenum causing

pancreas to release LPL (enzyme) to break triglycerides to free fatty acids (di or mono-glycerides) for

absorption.

41. a. Lysine

Reason: When lysine undergo 4 steps of bio-synthesis starting from N-trimethyllysine. It undergo hydroxylase

(changing to 3-hydroxy-N-trimethyllysine) then adolase (to 4-N-trimethylaminobutyraldehyde) dehydrogenase

(to Gamma-butryobetaine) and dioxygenase (L-carnitine).

42. d. 7-Dehydrocholesterol

Reason: It is one of the other common pathway of forming cholesterol by vitamin D in skin.

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43. c. Citrate lyase

Reason: Its function is to create Acetyl-CoA which is a very essential substance for FA synthesis.

44. b. Phosphatidic acid

Reason: Phosphatidic acid is the backbone of the TG and lecithin.

45. d. HMG-CoA reductase

Reason: It is the rate controlling enzyme of the metabolism which is why it can limit the rate in cholesterol

biosynthesis.

46. c. Cholecystokinin

Reason: Because there are only tryspinogen, chymotryspinogen, elastase, carboxypeptidase, pancreatic lipase,

nucleases and amylase. Fluid in GI tract.

47. a. Pepsin

Reason: Pepsin is a type of enzyme which digests proteins such as those in meat, eggs, seeds or dairy products.

48. b. Zinc

Reason: Cant find

49. d. Meat

Reason: Out of the 5 choices, only meat has collagens

50. c. Enterokinase

Reason: It removes peptide bond of trypsinogen (lysine). When the N-termnal peptide is removed, a slight

arrangement of the folded protein occurs forming a new N-terminal replacing the old one resulting in a more

conformational rearrangement.

51. c. Most of the digested proteins are absorbed in the intestine in the form of poly- (merl ot kernh ot

deng ey ke te)

Reason: Due to the breakdown process of proteins in the intestine.

52. d. Ca2+

Reason: Because milk contains Calcium.

53. c. a + c true

(a. enterokinase converts tryspinogen to trypsin)

(c. Trypsin activates procarboxypeptidase A and proclastase.)

Reason: Intestinal proteolysis is the process of breaking down proteins into shorter parts and into smaller

components. In the process, pancreatic juice is released. The enzymes in pancreatic juice becomes activated by

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other enzymes. Example: Trypsinogen transformed to trypsin. Then they start to activates others and start the

break down processes of proteins.

54. b. Acidic amino acid

Reason: It is needed for pepsin to break down large fragments of undigested materials (proteins).

55. b. Passive diffusion

Reason: It naturally move from a higher concentration to a lower concentration as a passive diffusion because it

doesnt need specific type of chemicals for transportation.

56. a. Phenyl alanine and tyrosine

Reason: Chymotrypsin hydrolyzes amino acid which have tryptophan, tyrosine and phenylalanine). This type of

amino acid fits into the hydrophobic pocket of the enzyme. This enzyme activated by trypsin.

57. c. Glutamate dehydrogenase

Reason: This enzyme is required for the urea synthesis as it converts glutamate to alpha-ketoglutarate and

ammonia, or the other way around. It helps regulate the amount of toxicity in our body.

58. d. Ammonia and aspartic acid

Reason: Since urea has the formula of CH4N2O we can know that there are 2 nitrogen atoms. According to the

urea cycle, one nitrogen atom is from ammonia and the other one is from the formation of aspartic acid from

fumaric acid in the cycle.

59. c. Fumarate

Reason: In the urea cycle, the fumarate was formed in the first reaction for breaking down or transform the

ammonia, bicarbonate and 2 moles of ATP to produce carbomoyl phosphate. After 2nd

and 3rd

reactions in urea

cycle, famarate and arginine were formed.