Exam 3 - Biochem

Under certain circumstances, glycolysis takes place in the absence of oxygen. When this happens, which of the following products may be produced? 1) lactate 2) ethanol 3) carbon dioxide 4) acetyl CoA

1,2 and 3 may be produced

Which of the following are products of glycolysis? 1) ATP 2) pyruvate 3) NAD+ 4) NADP+

1. ATP and 2. Pyruvate

NAD+ is: a. a reducer b. an oxider c. a peptide d. an enzyme

An oxidizer - meaning it accepts electrons

If you are only given the Vmax value of 25 Mol/sec that was calculated from the Lineweaver-Burk plot for an enzyme. is it possible to calculate the Km?

No - Km is equal to the [S] at 1/2 Vmax, would need to know the [S]

In glycolysis, which of the following molecules is needed first in the metabolism of glucose? a. ATP b. NADH c. FADH2 d. ADP

a. ATP - converted to ADP by hexokinase

Even though Hb is not an enzyme, many enzymatic concepts can apply. Based on your knowledge of how carbon monoxide interacts with hemoglobin, what kind of inhibitor does it behave most similar to? a. Competitive Inhibitor b. NonCompetitive Inhibitor c. UnCompetitive Inhibitor

a. Competitive Inhibitor- the more saturated the blood is with oxygen, the less carbon monoxide, competes with oxygen for binding

Select the THREE enzymes that catalyze reactions that are the most exergonic in glycolysis: a. hexokinase b. TIM c. GAP dehydrogenase d. pyruvate kinase e. phosphofructokinase f. enolase g. phosphoglucoisomerase h. phosphoglycerate mutase

a. Hexokinase, d. Pyruvate kinase, e. phosphofructokinase - all three steps where ATP is converted to ADP (energy released)

Select the enzymes that catalyze the production of ATP in glycolysis a. phosphoglycerate kinase b. TIM c. hexokinase d. enolase e. pyruvate kinase f. phosphoglucoisomerase g. phosphoglycerate mutase h. GAP dehydrogenase i. phosphofructokinase

a. Phosphoglycerate kinase, e. pyruvate kinase

Alternative splicing can result in two enzyme isoforms that can carry out the same reaction with different activities a. True b. False

a. True

Serine proteases are hydrolases a. True b. False

a. True - consider Chymotrypsin, a serine protease, transfers functional groups to H2O molecules

Enzymes can be regulated by phosphorylation a. True b. False

a. True - phosphorylation causes a conformational change in enzymes towards more active/ inactive forms

The initial reactions of the Pentose Phosphate pathway break down glucose ________. a. by oxidation b. by reduction c. by substrate level phosphorylation d. to prepare glucose for glycolysis

a. by oxidation - the first phase of the pentose phosphate pathway is the oxidative generation of NADPH

In serine protease enzymes, the pKa of serine sidechain OH is ___ by the catalytic triad, resulting in its being ___. a. decreased and deprotonated b. increased and protonated c. decreased and protonated d. increased and deprotonated

a. decreased and deprotonated, Ser is activated by imidazole on His forming an alkoxide ion - pKa lower than pH = deprotonated

NADH is formed: a. from the oxidation of Carbons of glucose b. from the reduction of Carbons of glucose c. from the H+ in metabolizing cells d. from CO2 releasing H as it forms bicarbonate

a. from the oxidation of Carbons of glucose - NAD+ is an oxidizer (accepts electrons)

What reaction does glucose-6-phosphatase catalyze? a. the conversion of glucose-6-phosphate to glucose b. the conversion of glucose-6-phosphate to fructose c. the conversion of glucose-6-phosphate to glucose-1-phosphate d. None of the listed responses is correct.

a. the conversion of glucose-6-phosphate to glucose in gluconeogenesis

If the Lineweaver-Burk plot crosses the X-axis at -0.2 for Enzyme A action on substrate M. Which X-intercept would be most likely for the Lineweaver-Burk plot of a competitive inhibitor of this reaction? a. -0.2 b. -0.1 c. -0.3 d. 0

b. -0.1 , with a competitive inhibitor, Km increases, and since X intercept = -1/Km, a larger denominator makes a smaller product - must be less but cannot be 0

Glycogen phosphorylase and phosphoglucomutase do not require ATP. What is the net yield of ATP of glycolysis when glycogen is the source of glucose? a. 4 b. 3 c. 5 d. 1 e. 2

b. 3 - the initial ATP is not needed, thus the net is 3 instead of 2 ATPs when using Glycogen

Fructose metabolism in the liver follows the same pathway as in adipose tissue. a. True b. False

b. False - Fructose in adipose tissue is first converted to Fructose-6p, then Gap then pyruvate Fructose in the liver converts to DHAP then GAP

Kinase enzymes are a specific type of ligase a. True b. False

b. False - Kinase enzymes are transferases; specifically phosphotransferases that catalyze phosphorylation reactions

Enzymes catalyze reactions by: a. Raising the energies of the reactant and product closer to the transition state energy b. Lowering the transition state energy only c. Lowering the energies of the reactant, product and transition state because enzymes catalyze reversible reactions d. By raising the energy of the reactant to closer to the transition state energy for a higher exergonic reaction.

b. Lowering the transition state energy only - enzymes provide a reaction pathway where transition state has lower free energy, increasing reaction rate

Would you expect to find a catalytic triad at the active site of an aspartyl protease? a. Yes but there would be three asp residue in a row. b. No c. Yes but the serine would be mutated to an aspartate. d. Yes

b. No - unlike in catalytic triad where functional groups are activated, aspartyl proteases activate an H2O molecule to serve as the nucleophile

How would ethanol oxidation from heavy drinking affect glycolysis? a. No effect. b. Slow it down c. Speed it up

b. Slow it down, alcohol is converted to acetylaldehyde and creates NADH in the process, this leaves little NAD+ to be used in stage 2 of glycolysis

What is the primary role of fermentation? a. To produce NADH b. To produce NAD+ c. To produce CO2 d. To produce lactate e. To produce NADP+ f. To produce NADPH g. To produce ethanol h. To produce ethanol or lactate accompanied with CO2

b. To produce NAD+, pyruvate is reduced to lactate to regenerate NAD+

All kinases are transferases a. True b. False

b. True - all kinases couple ATP hydrolysis with addition of a phosphate to the substrate

Pick 2 best choices: Enzymes _____ a. catalyze a reaction in one direction b. catalyze reaction in both forward and reverse directions c. stabilize the transition state d. bind reactant tighter enabling faster reaction e. are always proteins

b. catalyze reaction in both forward and reverse directions c. stabilize the transition state

How would AMP affect the rate of PFK (and flux of glycolysis) a. decease b. increase c. no effect

b. increase - AMP (or adenine monophosphate) is a positive regulator of PFK - high AMP means the cells is starved for energy and glycolysis must run to replenish ATP

Adrenaline signals cells to produce more energy to fight or flee. Adrenaline activates an enzyme that controls the production of fructose 2,6-bisphosphate. What is the expected effect of adrenaline on 1) fructose 2,6-bisphosphate concentration and 2) gluconeogenesis? a. decrease, increase b. increase, decrease c. no effect, decrease d. no effect, no effect e. increase, increase f. increase, no effect g. decrease, decrease h.no effect, increase

b. increase, decrease - as the concentration of fructose 2,6-biphosphate increases, PFK-2 is activated which increases glycolysis and inhibits gluconeogenesis

Aspartyl protease is a(n): a. enzyme that has a serine with catalytic function to cleave proteins b. protein cutting enzyme that uses aspartate as its nucleophile c. protein-cutting enzyme that uses serine as its nucleophile to cut at aspartate sites d. enzyme that uses aspartate as a cofactor

b. protein cutting enzyme that uses aspartate as its nucleophile - Aspartyl signifies Asp is the nucleophile, proteases cleave proteins

If the Lineweaver-Burk plot crosses the X-axis at -0.2 mM-1 what is the Km (mM)? a. +0.2 b. -5 c. +5 d. -0.2

c. +5 , X intercept = -1/ Km

Enzyme A has the following Km values for substrates P (1 x 10-2 M) and Q (1 x 10-3 M). Which substrate binds tighter? a.Both bind equally. b.P c.Q d.Not enough information is given to answer the question.

c. Q - the lower the Km, the tighter an enzyme is bound

Hexokinase IV has a Km value that is substantially higher than the Km for other hexokinases. What is the significance of this fact? a. The higher Km reflects lower affinity for its substrate, and therefore this kinase is only operational when glucose levels are low. b. The higher Km reflects high affinity for its substrate, and therefore this kinase is only operational when glucose levels are high. c. The higher Km reflects lower affinity for its substrate, and therefore this kinase is only operational when glucose levels are high. d. The higher Km reflects higher affinity for its substrate, and therefore this kinase is only operational when glucose levels are low.

c. The higher Km reflects lower affinity for its substrate, and therefore this kinase is only operational when glucose levels are high. If Km is high, this is less affinity for a substrate meaning there would have to be more substrate (glucose)

What enzyme catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate? a. glucose-6-phosphate isomerase b. fructose-1,6-bisphosphate aldolase c. phosphofructokinase d. The reaction is spontaneous and does not require an enzyme to catalyze the reaction

c. phosphofructokinase - in glycolysis stage 1

Which of the following enzymes is NOT part of gluconeogenesis? a. pyruvate carboxylase b. fructose-1,6-bisphosphatase c. phosphofructokinase d. phosphoenolpyruvate carboxykinase

c. phosphofructokinase, in glycolysis the three main enzymes are hexokinase, phosphofructokinase, and pyruvate kinase

NADH is the __ form of NAD+ a. acidic b. a separate molecule c. reduced d. oxidized e. protonated f. carboxylate g. basic

c. reduced- NADH is an electron donor (reducer)

Which would you expect have the tightest binding by the enzyme: a. substrate structure b. product structure c. transition state structure d. none of these

c. transition state structure

What is the net difference in ATP produced from glucose in glycolysis compared to fructose metabolism in the liver? a. -1 b. +2 c. +1 d. 0 e. -2

d. 0

In glycolysis there is a net yield of _ ATP. a. 4 b. 5 c. 1 d. 2 e. 3

d. 2

What is the product of the reaction of glycerol-3-phosphate catalyzed by glycerol phosphate dehydrogenase? a. Glycerol b. GAP c. Glycerate 2-phosphate d. DHAP

d. DHAP

Which of the following statements about metabolism are true? 1) Catabolism is the process in which complex substances are broken down, yielding a net output of energy. 2) Metabolism is an integrated system in which many of the same reactions participate in degradative (catabolic) and biosynthetic (anabolic) pathways. 3) Anabolism involves the synthesis of polymeric biomolecules and complex lipids from monomers such as fatty acids and nucleotides. 4) All organisms derive raw materials and energy from organic molecules, such as glucose. a. All four statements are correct. b. Only 1 and 2 are correct c. Only 1 and 3 are correct d. Only 1, 2, and 3 are correct

d. Only 1, 2, and 3 are correct

The best inhibitor: a. binds allosterically b. mimics the reactant structure c. mimics the product structure d. mimics the transition state structure

d. mimics the transition state structure

What is the primary reason for the pentose phosphate pathway? a. To produce CO2 b. To regenerate NADP+ c. To regenerate NAD+ d. To produce ribose 5-phosphate, which is needed to generate ATP e. It is the only way to synthesize GAP from glucose f. To produce NADPH g. To form NADH

f. To produce NADPH - NADPH is for anabolic (fat synthesis) occurring in adipose tissue

Select only the enzymes that are distinct to gluconeogenesis. a. pyruvate kinase b. GAPDH c. hexokinase d. enolase e. phosphoglucoisomerase f. pyruvate phosphatase g. PEPCK h. glucose 6-phosphatase i. fructose 1,6-bisphosphatase j. phosphoglycerate mutase

g. PEPCK, h. glucose 6-phosphatase, i. Fructose 1,6 biphosphatase

Select the enzyme that catalyzes reaction that produces NADH in glycolysis a. phosphoglycerate kinase b. TIM c. hexokinase d. enolase e. pyruvate kinase f. phosphoglucoisomerase g. phosphoglycerate mutase h. GAP dehydrogenase i. phosphofructokinase

h. GAP (glyceraldehyde 3-phosphate) dehydrogenase

What type of enzyme would catalyze the following reaction? a. hydrolysis b. ligase c. transferase d. lyase e. oxidoreductase f. isomerase

look at products: 1. Hydrolysis - transfer functional groups to H2O molecules 2. Lysase - addition/removal of groups to form double bonds/ rings 3. Oxidoreductase - oxidation reduction 4. Ligase - ligation/ joining of two substrates at expense of ATP 5. Isomerase - forms isomers 6. Transferase - transfer of various groups