Unit 4: Metabolism I - Practice Quiz

1 What does the abbreviation ATP stand for?

2 Which of the following is an electron carrier that is reduced to ?

3 Energy is released when ATP is hydrolyzed to which molecule?

4 In which cellular compartment does glycolysis take place?

5 What is the final product of glycolysis?

6 What is the net yield of ATP from one molecule of glucose during glycolysis?

7 Which enzyme catalyzes the first committed and rate-limiting step of glycolysis by phosphorylating fructose-6-phosphate to fructose-1,6-bisphosphate using ATP?

8 In human muscle cells during intense exercise, pyruvate is converted into which product by fermentation?

9 What is the main purpose of fermentation in cells?

10 Alcoholic fermentation carried out by yeast produces ethanol and which gas?

11 Gluconeogenesis is the metabolic process that synthesizes which molecule?

12 In which organ does gluconeogenesis primarily occur?

13 Which of the following is a common precursor for gluconeogenesis?

14 Which important reducing molecule is produced by the pentose phosphate pathway?

15 The pentose phosphate pathway provides ribose-5-phosphate, which is a precursor for the synthesis of which molecules?

16 What sugar molecule serves as the starting substrate of the pentose phosphate pathway?

17 The breakdown of glycogen into glucose units is called what?

18 Which enzyme is chiefly responsible for cleaving glucose units from glycogen during its breakdown?

19 The process of forming glycogen from glucose is known as which of the following?

20 Which enzyme adds glucose units to a growing glycogen chain during glycogen synthesis?

21 During oxidation of one molecule of through the electron transport chain, approximately how many ATP are synthesized (using the conventional P/O ratio)?

22 Why is energetically 'worth' fewer ATP than in oxidative phosphorylation?

23 In glycolysis, which enzyme catalyzes the first committed and irreversible step that is subject to allosteric regulation?

24 What is the net ATP yield per molecule of glucose during glycolysis?

25 Which glycolytic step generates ?

26 What is the primary metabolic purpose of lactate fermentation in vigorously contracting muscle?

27 In alcoholic fermentation by yeast, which two products are formed from pyruvate?

28 Which enzyme allows gluconeogenesis to bypass the irreversible pyruvate kinase step of glycolysis by converting oxaloacetate to phosphoenolpyruvate?

29 Why can acetyl-CoA (from fatty acid oxidation) not be used for net glucose synthesis in humans?

30 How many ATP equivalents are required to synthesize one glucose molecule from two pyruvate molecules?

31 What are the two major biosynthetic products of the oxidative phase of the pentose phosphate pathway?

32 Which enzyme catalyzes the committed, rate-limiting step of the pentose phosphate pathway?

33 A deficiency in glucose-6-phosphate dehydrogenase makes red blood cells especially vulnerable to oxidative stress because they cannot adequately produce which molecule?

34 What is the primary product released when glycogen phosphorylase cleaves an -1,4 glycosidic bond in glycogen?

35 Why can only the liver, and not muscle, release free glucose into the blood from glycogen breakdown?

36 The debranching enzyme is required during glycogenolysis to handle which type of linkage?

37 Which activated sugar donor is used by glycogen synthase to add glucose units to a growing glycogen chain?

38 Which enzyme is responsible for creating the -1,6 branch points in glycogen?

39 How does insulin promote glycogen synthesis in response to high blood glucose?

40 Complete oxidation of one glucose molecule via glycolysis, the citric acid cycle, and oxidative phosphorylation yields approximately how many ATP (modern estimate)?

41 The standard free energy of hydrolysis of ATP is kJ/mol. In a cell where mM, mM, and mM, the actual of hydrolysis (at 310 K, kJ/mol) is closest to which value?

42 NADH and NADPH have nearly identical redox potentials, yet cells maintain a high ratio and a low ratio. What is the primary functional rationale?

43 In glycolysis, the reaction catalyzed by phosphoglycerate kinase and the reaction catalyzed by pyruvate kinase both produce ATP. Which statement correctly distinguishes them thermodynamically and mechanistically?

44 Arsenate () is a phosphate analog that can substitute for in the glyceraldehyde-3-phosphate dehydrogenase reaction. What is the net metabolic consequence when arsenate replaces phosphate at this step?

45 The phosphofructokinase-1 (PFK-1) reaction is a key control point. Fructose-2,6-bisphosphate () strongly activates PFK-1. Which combination of hormonal signal and enzyme state raises in liver?

46 During intense anaerobic exercise, lactate dehydrogenase regenerates . If this regeneration were blocked, glycolysis would stall specifically because:

47 Ethanol fermentation in yeast converts pyruvate to ethanol in two steps. Which pair of enzymes and cofactor is required, and what is the redox bookkeeping per glucose?

48 Gluconeogenesis from pyruvate requires bypassing the pyruvate kinase step. This bypass uses two reactions consuming high-energy phosphates. What is the total nucleoside triphosphate cost of converting one pyruvate to one PEP?

49 Why must oxaloacetate be shuttled out of the mitochondrion as malate (or aspartate) during gluconeogenesis in most tissues?

50 A patient with a deficiency in fructose-1,6-bisphosphatase presents with fasting hypoglycemia and lactic acidosis. Which explanation best accounts for the lactic acidosis?

51 A cell needs large amounts of NADPH but little ribose-5-phosphate. How does the pentose phosphate pathway accommodate this demand?

52 Transketolase transfers a two-carbon unit and requires a specific cofactor; transaldolase transfers a three-carbon unit and does not. Which cofactor does transketolase require, and what shared reaction feature explains why transaldolase needs no such cofactor?

53 Individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency are prone to hemolysis under oxidative stress. What is the mechanistic link between the enzyme defect and red cell lysis?

54 Glycogen phosphorylase cleaves -1,4 bonds but stops four residues from an -1,6 branch point. The debranching enzyme resolves this using two activities. What are they, and what is the product distribution near the branch?

55 Most glucose residues released from glycogen leave as glucose-1-phosphate, but a smaller fraction leaves as free glucose. Given a linear chain of many residues between branch points, roughly what fraction of released monomers is free glucose, and why?

56 Phosphorylase uses inorganic phosphate rather than water to cleave glycogen. What is the primary energetic advantage of this phosphorolysis over hydrolysis for the cell?

57 Glycogen synthase adds glucose from UDP-glucose to a growing chain. Considering the cost of making UDP-glucose and regenerating UTP, what is the true ATP-equivalent cost of incorporating one glucose-6-phosphate into glycogen?

58 Glycogen synthase can only extend existing chains and needs a primer. Which molecule provides the initial primer, and what is its distinctive feature?

59 Both glycogen synthase and glycogen phosphorylase are regulated by phosphorylation, but with opposite outcomes. Under high glucagon (liver, fasting), what are the activity states of the two enzymes and why is this coordinated?

60 Muscle uses the malate-aspartate and glycerol-3-phosphate shuttles to move cytosolic NADH reducing equivalents into mitochondria. Why does the glycerol-3-phosphate shuttle yield less ATP per cytosolic NADH than the malate-aspartate shuttle?