EXAM 1 Questions

If fructose labeled with 14C at C-1 were metabolized in the liver, the radioactive pyruvate formed (radioactive from 14C) from this fructose by the most direct path (path A- the F-6-P pathway and glycolysis) would be labeled at which of its carbons (#1, 2, and/or 3 of pyruvate)?

C-3

Which carbon or carbons of glucose, if metabolized via glycolysis and TCA cycle, would be converted to CO2 first?

C-3 and C-4 of GLC since both these the carboxyl group of 2 pyruvates, which then are converted to CO2 in the pyruvate dehydrogenase (PDH) reaction, which happens before TCA cycle.

The phosphorylation of glyceraldehyde-3-phosphate (G-3-P) to 1,3 bisphosphoglyceric acid (1,3 bis PGA) A. Requires 1 ATP B. Generates NAD+ C. Reduces G-3-P D. Is catalyzed by a kinase-type enzyme E. None of the above

E. None of the Above

Which of the following statements is a correct general statement about metabolism? A. All enzymatic reactions are physiologically irreversible. B. There is a net positive production of ATP in anabolic pathways. C. Catabolic pathways of diverse compounds converge into a few central metabolic pathways. D. Storage polymers are glucose, pyruvate and acetyl CoA. E. Anabolic pathways produce energy, typically ATP, in the synthesis of complex biomolecules.

Catabolic pathways of diverse compounds converge into a few central metabolic pathways.

Describe the two major biochemical roles for the TCA cycle.

One role is: The immediate products of the TCA cycle are NADH and FADH2 and GTP. The first two are re-oxidized by the ETC (electron transport chain), producing energy in the form of ATP. Other compounds in addition to carbohydrate are catabolized into acetyl CoA or TCA cycle compounds, so their catabolism can also produce ATP (these are fatty acids and amino acids). Role Two: TCA cycle metabolites/ intermediates are used as biosynthetic precursors for multiple essential compounds of the cell. That is why TCA cycle is called the CENTRAL WHEEL of METABOLISM

Oxidation of one mole of acetyl-CoA via one turn of the citric acid cycle results in net: A. production of one mole of citrate B. consumption of one mole of oxaloacetate C. production of 7 moles of ATP D. production of 2 moles of CO2 E. production of one mole of succinate

D. production of 2 moles of CO2

In addition to NADH, ______ and _______ are produced in one or more of the 10 steps in aerobic glycolysis, but the _____ produced must be returned by another process to the form used as a substrate in glycolysis for aerobic glycolytic flux to continue. A. ATP, lactate, NADH B. Pyruvate,ATP,pyruvate C. ATP,lactate,NAD+ D. Pyruvate, ATP, NADH E. No combination is correct

Pyruvate, ATP, NADH

Why is the amount of oxygen consumed so much greater than the amount of OAA or malate added?

OAA is regenerated after each turn, so the addition of OAA (or malate) will stimulate the oxidation of a much larger amount of acetyl-CoA (an input), which will produce much more NADH and FADH2.

How is ethanol catabolized in humans? What effect does this have on the NADH balance in the cell? What process oxidizes the ethanol produced? What is the evolutionary explanation for the presence of the ethanol catabolic pathway in humans?

11. The fates of the two carbons of acetyl CoA are not the same. No 14C-CO2 is released after the first turn. The carbonyl C of acetyl CoA is converted to one of the carboxy groups of OAA after the first turn. Either carboxy group becomes labeled because succinate and fumarate are symmetrical molecules and the enzymes cannot distinguish between the two ends of the molecule (so, in a population of molecules that one analyzes, 14C will be found in half of the molecules at C1 of OAA, the other have with have it at C4 of OAA). In the second turn, all 14C is released as CO2 because both carboxy groups of OAA are the source of the carbon dioxide released in the second turn. For the methyl group, no 14C-CO2 is released in the first round for the reasons given above (the CO2 comes from the OAA in the first turn). But no 14C-CO2 is released in the second turn. Every subsequent turn would release half of the remaining label. 5 Practice Problem Set #3 for midterm 1 BIS103 11. Ethanol is oxidized to acetaldehyde catalyzed by alchohol dehydrogenase (ADH), then acetaldehyde is oxidized to acetate by aldehyde dehydrogenase. Both of the two previous reactions are oxidoreductases using NAD+ as the sink for the electrons from alcohol and acetaldehyde, respectively, and both reactions producing NADH. Then acetate converted into acetyl CoA. This acetyl CoA can be oxidized in the TCA cycle to provide energy. So, alcohol can provide energy. It is proposed that ADH was retained in mammals because fermenting fruits would contain some ethanol and some intestinal bacteria could produce ethanol. So, there would be a use for ADH.

Which of the following statements below about the metabolite above is most correct? *LOOK AT PICTURE FIRST* A. The disaccharide is a reducing sugar. B. The disaccharide is not a reducing sugar. C. This compound is not a sugar. D. The monosaccharides are linked by alpha1,6 glycosidic bonds. E. None of the statements are correct.

The disaccharide is a reducing sugar.

Four characteristic of coenzymes

They bind to enzymes . They provide a broader range of catalytic properties than provided by amino acid side groups on enzymes. They can be synthesized from water-soluble vitamins in humans. Some serve as electron carriers

For the following enzymes name the type of enzyme and write a balanced equation for the reaction they catalyze. a). Alcohol dehydrogenase b). Lactate dehydrogenase c). Phosphofructokinase-1

a) oxidoreductase, (see HB for reaction). b). oxidoreductaase (see HB for reaction) c). transferase (in glycolysis, see HB for reaction), a common term is kinase

Which of the following applies to a comparison of D-glucose and D-galactose? a) epimers and diastereomers b) enantiomers and epimers c) diasteriomers and enatiomers d) both are metabolites in aerobic glycolysis pathway e) all of the above

epimers and diastereomers *epimers*: different in one carbon

The following is most likely to be the first step in the catabolism of this disaccharide when present in the human diet (that is, eaten). *LOOK AT PICTURE FIRST* A. phosphorylation B. isomerization C. hydrolysis D. oxidation E. epimerization

hydrolysis

patient comes into the emergency room very inebriated. The patient claims that he/she only had 1/4th of an 8 oz. beer bottle to drink. You suspect this individual has an alteration in ethanol metabolism. Which change in enzyme activity relative to "normal" individuals has most likely occurred in this patient based on this information? A. reduced ADH activity B. increased ADH activity. C. increased GLC catabolism in the liver D. increased TCA cycle activity E. increased ALDH activity

reduced ADH activity

The first reaction catabolizing this compound after being taken up into liver cells is most likely to be: *LOOK AT PICTURE FIRST* A. phosphorylation B. isomerization C. hydrolysis D. oxidation E. epimerization

phosphorylation

Describe types of reactions catalyzed by oxidoreductases, isomerases, kinases, transferases and hydrolases.

*Oxidoreductases* catalyze oxidation-reduction reaction; *isomerases* catalyze intra-molecular rearrangements *hydrolases* catalyze the cleavage of a single bond in a molecule with the incorporation of water in the two products, *kinases* catalyze the transfer of a phosphoryl group from a nucleoside triphosphate (using ATP) and transferases catalyze transfer of one group to another molecule.

Indicate the general type of reaction in which each co-enzyme is typically involved. lipoic acid NAD+ CoA FAD TPP

*lipoic acid* oxidation to thioester, bound acyl unit carrier *NAD+* oxidation/reduction reactions- hydride transfer *CoA* mobile carrier of acyl units (acetyl is 2C acyl group) *FAD* oxidation/reduction reactions-2H carrier, transfer *TPP* decarboxylation of alpha keto acids and carrier of "activated" aldehyde group (not required to know)

Which of the standard free energy changes below best represents the value for the transfer of a phosphoryl group from PEP to ADP? A. +32 kJ/mol B. -32 kJ/mol C. -93 kJ/mol D. +93 kJ/mol E. -3.2 kJ/mol

-32 kJ/mol

The compound differs from GLC:

1 Carbon

The aerobic oxidation starting with 1 mole of 3-PGA (3-phosphoglycerate) in humans to 3 mol CO2 yields a net of X mol ATP. Calculate X. A. 32 moles of ATP B. 31 moles of ATP C. 13.5 moles of ATP D. 18.5 moles of ATP E. 12.5 moles of ATP

13.5 moles of ATP

he aerobic oxidation starting with 1 mole of GLC in humans to 6 CO2 yields a net of:

32 moles of ATP

Which of the following correctly describes the TCA cycle in mammals? A. Oxygen is required to re-oxidize reduced electron carriers produced in TCA cycle B. Equal molar amounts of OAA (oxaloacetate) are required along with acetyl CoA as input into the TCA cycle during GLC oxidation to 6 x CO2. C. The yield of ATP is 12.5 ATP/acetyl CoA from one turn of the TCA cycle and ETC. D. Pyruvate reduction to lactate is required for TCA cycle flux E. TCA cycle's sole purpose is for ATP synthesis from oxidation of carbon to CO2.

A. Oxygen is required to re-oxidize reduced electron carriers produced in TCA cycle Explain Why the Others are Wrong

Based on reactions we have studied so far, decarboxylation of alpha keto acids requires which of the following co-enzyme? A. TPP, thiamine pyrophosphate. B. NAD, nicotinamide dinucleotide C. FAD, Flavin adenine dinucleotide D. Coenzyme A E. Lipoic acid

A. TPP, thiamine pyrophosphate.

A patient has been diagnosed with a rare disease with a mutation in Aldehyde dehydrogenase (ALDH), preventing the enzyme from functioning. Which of the following would you most likely observe after ethanol consumption compared with before ethanol consumption by this patient? A. Increased rate of catabolism of pyruvate B. Decreased glucose levels in the liver and bloodstream C. An increase in acetaldehyde levels in the liver and bloodstream D. An increase in acetic acid levels in the liver and bloodstream E. Reduction of acetyl-CoA in the liver

An increase in acetaldehyde levels in the liver and bloodstream

The importance of glycogen in the liver stems from its primary role in the body to A. provide building blocks for new cells B. provide blood glucose between meals. C. Buffer the pH of the cell D. Keep BIS103 students busy E. Provide precursors for TCA cycle

B. provide blood glucose between meals.

33. This compound can be catabolized by humans to CO2 to produce ATP because: A. it is a sugar, and all sugars automatically can be catabolized for energy in humans. B. while catabolism of this sugar requires specific enzymes that are not in glycolysis, these specific additional enzymes are present in human cells to catalyze the conversions required to convert this sugar into one of the metabolites of glycolysis. C. it is closely related to glucose. D. oxidation of the carbons in this sugar to that of GLC is energetically favorable. E. the DGo' of catabolism to 6 x CO2 is positive.

B. while catabolism of this sugar requires specific enzymes that are not in glycolysis, these specific additional enzymes are present in human cells to catalyze the conversions required to convert this sugar into one of the metabolites of glycolysis

Glucose labeled with 14C in C-3 and C-4 is completely converted to acetyl-CoA via glycolysis and the pyruvate dehydrogenase complex. What percentage of the acetyl-CoA molecules formed will be labeled with 14C, and in which position of the acetyl moiety will the 14C label be found? A. 100% of the acetyl-CoA will be labeled at C-1 (carboxyl). B. 50% of the acetyl-CoA will be labeled, all at C-2 (methyl) C. No label will be found in the acetyl-CoA molecules D. 100% of the acetyl-CoA will be labeled at C-2 E. Not enough information is given to solve this problem

C. No label will be found in the acetyl-CoA molecules

Which of the conversions below is catalyzed by PFK-1? A. fructose + ATP --> fructose-6-P + ADP B. fructose + ATP--> fructose-1-P + ADP C. fructose-6-P+ATP --> fructose-1,6-bisP+ADP D. fructose-6-P + H2O--> fructose + Pi

C. fructose-6-P+ATP --> fructose-1,6-bisP+ADP

Consider the fate of pyruvate labeled with 14C in either carbon 1 (carboxyl group), carbon 2 (carbonyl), or 3 (methyl). Predict the fate of each labeled carbon as pyruvate is converted to acetyl CoA by PDH and is a substrate for the first reaction of the TCA and then after one turn of the TCA cycle as occurred.

C1: all released as CO2 by PDH. C2, C3: retained in OAA after one turn.

Based on reactions we have studied so far, acylation requires which of the following co-enzyme? A. TPP, thiamine pyrophosphate. B. NAD, nicotinamide dinucleotide C. FAD, Flavin adenine dinucleotide D. Coenzyme A E. none of the above

Coenzyme A

In glycolysis, fructose-1,6-bisphosphate is converted into two products with a standard free-energy change (DGo(not)) of +23.8 kJ/mol. Under what conditions encountered in a normal cell will the free-energy change (DG) be negative, enabling the reaction to proceed spontaneously from fructose-1,6-bisphosphate into two products? A. Under standard conditions, enough energy is released to allow flux in the reaction to the right. B. The reaction will not go to the right spontaneously under any conditions because the DGo' is positive. C. The driving force of this reaction in the pathway is supplied by a coupled exergonic reaction, the hydrolysis of ATP. D. The reaction may proceed to the right when appropriate concentrations of fructose-1,6-bisphosphate and the products are present in the cell. E. None of the explanations in A-D are correct.

D. The reaction may proceed to the right when appropriate concentrations of fructose-1,6-bisphosphate and the products are present in the cell.

Which of the following coenzymes is a two hydrogen carrier?

FAD, Flavin adenine dinucleotide

3. For each reaction of the TCA cycle operating in the direction of oxidation to carbon dioxide, determine which of the following below describes the type of reaction catalyzed (not all need to be used and two can describe a single TCA cycle step): condensation, carbon-carbon bond formation, dehydration, hydration, decarboxylation, oxidation/reduction, substrate level phosphorylation, isomerization, phosphorylation.

For an exam, you don't have to know the enzyme names. citrate synthase: condensation aconitase: isomerization isocitrate dehydrogenase: oxidation/reduction and decarboxylation alpha-ketoglutarate dehydrogenase: oxidation/reduction and decarboxylation succinyl CoA synthase: phosphorylation succinate dehydrogenase: oxidation/reduction fumarase: hydration malate dehydrogenase: oxidation/reduction

This disaccharide consists of the following monosaccharides: *LOOK AT PICTURE FIRST* A. galactose (GAL) and GLC B. GAL and GAL C. GLC and GLC D. fructose and GLC E. GAL and fructose

GLC and GLC

A patient has reduced activity in one of the metabolic enzymes listed below. Liver glycogen structure is normal. A drop in liver glycogen between meals also occurs normally. However, this patient has an abnormally low level of blood glucose between meals, but normal uptake of GLC from the blood after a meal. Based on what we have studied so far in class, this patient is most likely to have reduced activity of which of the following enzymes:: A. muscle glycogen phosphorylase. B. liver lactate dehydrogenase (LDH) C. GLC-6-P phosphohydrolase (GLC-6-P phosphatase) D. digestive starch hydrolase activity E. liver glycogen phosphorylase

GLC-6-P phosphohydrolase (GLC-6-P phosphatase)

15-6 The Vmax of the glycogen phosphorylase from skeletal muscle is much greater than the Vmax of the same enzyme from liver tissue. What is the physiological function of glycogen phosphorylase in skeletal muscle? In liver enzyme? Why does the Vmax of the muscle enzyme need to be greater than that of the liver enzyme?

In muscle, phosphorylase breaks down glycogen, releasing GLC-1-P, which undergoes isomerization to be GLC-6-P. This enters glycolysis to provide ATP for muscle contraction. During strenuous exercise, there is a high demand for glucose for glycolysis. In the liver, phosphorylase breaks down glycogen, releasing GLC-1-P, which undergoes isomerization to be GLC-6-P. In this case, a phosphatase present in the cell cleaves off the phosphate group, producing free GLC. This GLC can leave the cell if the concentration is lower in the blood. This occurs in response to a slow decline in blood GLC, which occurs relatively slowly. In the muscle, ATP requirements could becomehigh, so the flux of GLC production must be high. That is why it is more important that the Vmax of the muscle enzyme be higher.

14C-Labeled glyceraldehyde-3-phosphate was added to a yeast extract. After a short time, fructose-1,6-bisphosphate labeled with 14C at C-3 and C-4 was isolated. What was the location of the 14C in the starting glyceraldehyde-3-phosphate? Where did the second 14C label in fructose-1,6-bisphosphate come from? Explain.

In respect to G3P it will be carbon 1. The Carbon we are talking about comes from fructose-1,6-bisphosphate -DHAP will be Carbon 3 of F-1,6-bisP -G3P will be Carbon 4 of F-1,6-bisP

Which of the two following deficiencies might be more severe for an individual? Lacking the ability to phosphorylate fructose? Or lacking the ability to cleave F-1-P? Why?

Lacking the ability to cleave F-1-P has more severe consequences.ATP will be consumed due to the cell's ability to phosphorylate fructose.But F-1-P cannot be further catabolized, so, ATP is consumed but not regenerated (as in glycolysis). Also, F-1-P will accumulate and not leave the cell, if it increases in concentration, it can start to bind to other enzymes and affect other enzymes activities. The inability to phosphorylate fructosejust means the cell can't utilize this sugar, it can leave the cell more easily in the unphosphorylated form. It won't accumulate in cells.

Based on reactions we have studied so far, oxidation of alcohols to ketones typically requires which of the following co-enzyme?

NAD, nicotinamide dinucleotide

For the reaction shown below, which co-enzyme or combination of coenzymes are required for the reaction to proceed from left to right? (required coenzymes may not be shown even if they are changed by the reaction) A. NADH B. TPP, CoA, NAD , FAD, lipoic acid C. TPP D. CoA E. none

NADH

You add [3-14C] pyruvate (labeled only in the methyl position with an unstable isotope of carbon) to isolated mitochondria. After one turn of the TCA cycle, what is the location of 14C - in OAA?

One turn (also called a round; "turn" and "round" are equivalent) of the cycle would produce OAA with the 14C equally distributed between C-2 and C-3. 50% of the molecules would have 14C at position 2 and 50% of the molecules would have 14C at position 3. No single molecule would have label at both positions. If following one molecule through one turn, then it could be at either position with equal probability. This is because succinate and fumarate are completely symmetrical molecules. Enyzmes cannot discriminate between the two middle carbons, so oxygen is added to either "internal" carbon. If one of these is different by virtue of an 14-C isotope, then there would be a mixture of malates and OAAs, with 1⁄2 with oxygen bonded to 14- C carbon and 1⁄2 to 12-C carbon.

Why does the addition of OAA or malate stimulate oxygen consumption?

Oxygen consumption is a direct measure of the activity of the Electron Transport Chain which re-oxidizes reduced electron carriers (NADH and FADH2), most of which are produced in the TCA cycle and consumes oxygen (reduced to water- see after first midterm). Since TCA cycle intermediates can also be used as biosynthetic precursors, they can become depleted in the minced pigeon-breast muscle as they are converted into other compounds. So, addition of either OAA or malate will increase the levels of OAA, which is one substrate for the first reaction of TCA, thus increasing the rate of TCA cycle reactions and increasing oxygen consumption.

Sucrose could be cleaved by either Pi or water to produce fructose and GLC-1-P or fructose and glucose, respectively. Would either of these reactions offer an advantage over the other in the preparation of hexoses for entry in glycolysis?

Sucrose cleavage using Pi to produce a phosphorylated compound would keep it in the cell and produce GLC-6-P without using an ATP. Thus, the ATP yield would be higher. GLC-1-P would have to be isomerized to GLC-6-P.

Co-enzymes that help remove carboxylic groups.

TPP, CoA, NAD, FAD, lipoic acid

Organisms grow without oxygen can't use oxygen as the sink for electrons. Do they have a TCA cycle? Do they have reactions of the TCA cycle?

These organisms need most of the reactions to synthesize essential biochemical precursors. The reactions together don't operate as a cycle.

*HELP NOT SURE* 15-3 One way to study glycolysis in intact cells in whole tissues or organs is to artificially circulate blood through an isolated intact heart and measure the concentration of glucose before and after the blood passes through the heart. If the circulating blood is deoxygenated, heart muscle consumes glucose at a steady rate. When oxygen is added to the blood, the rate of glucose consumption drops dramatically, then continues at the new, lower rate. Why?

The yield of ATP/per glucose metabolized is greater in the presence of oxygen. The total amount of glucose consumes drops, because the needed amount of ATP is obtained from less glucose in the presence of oxygen compared to the absence of oxygen. Glucose consumption reaches a new steady state based on energy yield from the oxidation of the carbons all the way to carbon dioxide.

Suppose you discovered a mutant yeast whose glycolytic pathway was shorter because of the presence of a new enzyme catalyzing the reaction [Glyceraldehyde-3-phosphate] +[ H2O] + [NAD+]--> [3-phosphoglycerate] + [NADH] +[ H+] Although this mutant enzyme shortens glycolysis by one step, how would it affect anaerobic ATP production? Aerobic ATP production?

You essentially start the electrolytic pathway at G3P which means you *lose* the *2 ATPs*. But you still have the G3P which goes on to make 30 ATPs roughly.

If 32P labeled inorganic phosphate were introduced to erythrocytes undergoing glycolysis, would you expect to detect 32P in glycolytic intermediates? Which reaction (s) is (are) responsible?

Yes, likely first 1,3bisPGA, since Piis directly incorporated. Nextin ATP as the substrate level phosphorylations occur. Then in all other phosphorylated intermediates as they are produced from AT(32P) + GLC.

*HELP NOT SURE* 14-13 The oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, catalyzed by glyceraldehyde-3-phosphate dehydrogenase, proceeds with an unfavorable equilibrium constant (K'eq = 0.08; DGo' = + 6.3 kJ/mol). Despite this unfavorable equilibrium, the flow through this point in the pathway proceeds smoothly. How does the cell overcome the unfavorable equilibrium?

[G-3-P] to [1,3 bisPGA] [1,3 bisPGA] to [3-PGA] is such a favorable reaction that it overcomes the [G-3-P] to [1,3 bisPGA] *The reaction 1,3bisPGA to 3PGA is very energetically favorable and removes the 1,3bisPGA so that DG of the glyceraldehyde-3-phosphate dehydrogenase reaction is negative.*

Which of the terms below is a property of DHAP (dihydroxyacetone-P)? a) aldose b) triose c) carboxylic acid d) hexose e) all of the above

b) Triose (has three carbons) a) Aldose its a ketose c) No carboxylic group d) has three Carbons

Why will either malate or OAA produce the same effect?

malate is converted into OAA. Since it's a cycle, all intermediates will be converted to OAA, which is the substrate for the first reaction. Addition of any of the intermediates will stimulate the cycle.

The reaction shown below is likely catalyzed by the enzyme ________________. Glyceraldehyde + ATP---> glyceraldehyde-3-phosphate + ADP A. triose phosphate isomerase B. triosedehydrogenase C. triosephosphatase D. triose kinase E. triose mutase

triose kinase