BCH Exam 2

In bacteria and plants, there is an alternative route to replenish oxaloacetate and regulate flux through the citric acid cycle. How is oxaloacetate replenishment different in plants and bacteria?

-An alternative route leads directly from phosphoenolpyruvate to oxaloacetate. -The reaction is catalyzed by phosphoenolpyruvate carboxylase (PEP). -The reaction requires neither an energy cofactor nor biotin.

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors. __________ is reduced to __________.

1) FAD 2) FADH2

A dehydrogenase is an oxidoreductase that... a) catalyzes the oxidation of a substrate by transferring oxygen from O2 to the substrate. b) catalyzes substrate oxidations, which involve the loss of hydrogen. Typically, the substrate loses a hydride ion and a proton. c) catalyzes the transfer of a hydrogen atom from the substrate to an oxygen molecule. d) catalyzes the oxidation of a substrate by hydrogen peroxide.

b) catalyzes substrate oxidations, which involve the loss of hydrogen. Typically, the substrate loses a hydride ion and a proton

Arrange the sequence of events that occur in complex I in their proper order. 1. Fe+2 is oxidized to Fe+3 while Coenzyme Q is reduced to CoQH2 2. NADH is oxidized to NAD+ while FMN is reduced to FMNH2. 3. FMNH2 is oxidized while Fe+3 is reduced to Fe+2 4. Reduced CoQH2 is released. a) 2, 1, 3, 4 b) 3, 2, 1, 4 c) 2, 3, 1, 4 d) 2, 3, 4, 1

c) 2, 3, 1, 4

Which of the following statements about complex II are true? 1.The complex draws electrons from succinate derived from fatty acid oxidation. 2.The electrons flow toward Coenzyme Q, just as they do in complex I. 3.The electrons pass from FADH2to Fe+3 to cytochrome b to Coenzyme Q. 4.Unlike complex I, the transfer of electrons to Coenzyme Q does not involve the pumping of protons. a)3 and 4 b) All answers are correct. c) 2, 3, and 4 d) 2 and 4

c) 2, 3, and 4

Plants, algae, and Cyanobacteria use water as reductant in photosynthesis. Green sulfur bacteria use which compound as reductant? a) Green sulfur bacteria can use different reductants. b) H2 c) H2S d) SO3 ^2-

c) H2S

Cytochrome c, an essential protein of the electron transport chain, is located in the mitochondria. Please identify its specific location. a) Matrix b) Outer membrane c) Intermembrane space d) Inner membrane

c) Intermembrane space

Arsenic compounds inhibit respiration by covalently modifying which cofactor? a) Flavin adenine dinucleotide (FAD) b) NAD+ c) Lipoamide groups d) Thiamine pyrophosphate

c) Lipoamide groups

All of the enzymes of the citric acid cycle are located in the ________. a) Cytoplasm b) Inner cell membrane c) Mitochondrion d) Golgi complex

c) Mitochondrion

Which term describes ATP production resulting from the capture of light energy by chlorophyll? a) Oxidative phosphorylation b) Dephosphorylation c) Photophosphorylation d) Substrate-level phosphorylation

c) Photophosphorylation

According to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis? a) Temperature gradient b) Osmotic gradient c) Proton gradient d) Electrons

c) Proton gradient

Which of the following particles can pass through the ATP synthase channel? a) ATP b) ADP c) Protons d) Inorganic phosphate

c) Protons

The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean a lower rate of O2 production. In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions. But is the inverse true as well? Do the light reactions depend on the Calvin cycle? Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50 % ( because the stomata closed to conserve water ) . Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.) a) The rate of O2 production would remain the same because the light reactions are independent of the Calvin cycle. b) The rate of O2 production would remain the same because the light intensity did not change. c) The rate of O2 production would decrease because the rate of ADP and NADP production by the Calvin cycle would decrease. d) The rate of O2 production would decrease because the rate of G3P production by the Calvin cycle would decrease.

c) The rate of O2 production would decrease because the rate of ADP and NADP production by the Calvin cycle would decrease.

In the citric acid cycle, ATP molecules are produced by __________. a) photosynthesis b) oxidative phosphorylation c) substrate-level phosphorylation d) cellular respiration e) photophosphorylation

c) substrate-level phosphorylation

oxidative phosphorylation

the culmination of energy yielding metabolism in aerobic organisms; involves the reduction of O2 to H2O with electrons donated by NADH and FADH2

transamination pairs

1) glutamate + oxaloacetate ⇌ α-ketoglutarate + aspartate 2) α-ketoglutarate + aspartate ⇌ glutamate + oxaloacetate

Both pathways use simple two-carbon organic molecules (such as __________) as common intermediates. These intermediates can then enter the___________, where they are further __________ to generate carbon dioxide and __________ electron carriers, along with small amounts of ATP. The electrons on these carriers are finally sent through the __________ to create a proton (H+) gradient. Release of this proton gradient results in the generation of ____________.

1. acetyl-CoA 2. citric acid cycle 3. oxidized 4. reduced 5. electron transport chain 6. ATP

Metabolism can be bisected into two subcategories: catabolism and anabolism. __________ takes complex organic molecules and breaks them down into simpler molecules; this is often accompanied by the __________ of energy. ___________ builds up biomolecules from simpler substances; this is often accompanied by the ____________ of energy.

1. catabolism 2. release 3. anabolism 4. consumption

What is the equation for photosynthesis?

6CO2 + 6H2O ------> C6H12O6 + 6O2

What is a Coenzyme?

A coenzyme is a non proteinaceous group that binds or interacts with an enzyme, or rather apoenzyme, to activate it. When a cofactor binds tightly to an enzyme, it is termed as a prosthetic group. When loosely bound to an enzyme, the cofactor is called a coenzyme. Coenzymes are groups that are a part of an enzyme catalyzed reaction.

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors. Pyruvate is oxidized to __________.

Co2

True false? The region of ATP synthase that catalyzes the production of ATP from ADP and inorganic phosphate spans the chloroplast membrane.

False

True or false? The chemiosmotic hypothesis states that the synthesis of ATP generates a proton gradient that leads to electron flow through an electron transport chain.

False

In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.

Function of CoA

Its structure is such that it reacts with carboxylic acids and forms thio-esters. When it forms these bonds, CoA is referred to as an acyl group carrier. This ability of the CoA helps in transfer of fatty acids from the cytoplasm to the mitochondria for its oxidation. Pyruvate is converted to acetyl CoA in the last step of glycolysis, after which it enters the citric acid cycle. This acetyl CoA is necessary for the conversion of oxaloacetate to citrate, which is the first step of the cycle in aerobic cellular respiration. Thus it assists citrate synthase and transfers the acetyl group to the oxaloacetate to form citrate.

CoA structure

Its structure is synthesized in a step by step process: +Vitamin B5 gets phosphorylated to form 4'- phosphopantothenate, by the enzyme pantothenate kinase +A cysteine molecule is added to the 4'-phosphopantothenate and the new molecule formed is 4'- phospho- N-pantothenoylcysteine. +This reaction is catalyzed by phosphopantothenoylcysteine synthetase. +The molecule is then decarboylated to form 4'- phosphopantetheine, catalyzed by the enzyme phosphopantothenoylcysteine decarboylase. +The molecule is then subjected to adenylation that forms dephospho-CoA. +Dephospho-CoA is then phosphorylated with ATP to form CoA. This reaction is catalyzed by dephosphocoenzyme A kinase.

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors. NAD+ is reduced to __________.

NADH

After analyzing the role of oxaloacetate in the first step of the citric acid cycle and formation reactions of ketone bodies above, your research group proposed several possible mechanisms for increased ketone bodies levels when oxaloacetate is depleted. Based on the information about ketone body synthesis, predict which possibility is the most reasonable.

Oxaloacetate is unavailable to react with acetyl-CoA, resulting in acetyl-CoA being converted into acetoacetate, one of the ketone bodies.

Identify the reactants and products of the citrate synthase reaction in Step 1 of the citric acid cycle.

REACTANTS ---acetyl CoA ---oxaloacetate PRODUCTS ---CoA-SH ---citrate ---heat

The standard free energy for the regeneration of oxaloacetate, unlike that for the other steps in the citric acid cycle, is significantly positive: ΔG∘=29.7 kJ/mol. Thus the malate dehydrogenase reaction needs help in proceeding to the right. What drives the reaction catalyzed by malate dehydrogenase to proceed to the right?

The next reaction in the cycle is highly exergonic and drives it to the right by keeping oxaloacetate levels exceedingly low.

During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization? a) Glucose utilization would increase a lot. b) Glucose utilization would increase a little. c) Glucose utilization would remain the same. d) Glucose utilization would decrease a little. e) Glucose utilization would decrease a lot.

a) Glucose utilization would increase a lot.

The 2 oxygen atoms that form the O2 in the photosynthesis reaction come from which molecule? a) H2O b) ATP c) CO2 d) 1 oxygen from H20 and 1 oxygen from CO2

a) H2O

Why was the muscle cells and its extracts the best choice for Krebs, Johnson and Szent-Györgyi to elucidate the cyclic nature of the citric acid cycle? a) In muscle the cycle intermediates are used almost exclusively for energy metabolism by the cycle and not for other reactions. b) The reactions of the cycle in muscle cells are more highly regulated, and therefore easier to study, than in other tissues. c) Muscle cells can more easily uptake oxygen than other cells, so monitoring the consumption of oxygen is easier for these cells. d) Muscle cells have an unusually high concentration of the starting material, pyruvate.

a) In muscle the cycle intermediates are used almost exclusively for energy metabolism by the cycle and not for other reactions.

Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. Which of these statements is the correct explanation for this observation? a) In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. b) ATP is needed to convert pyruvate to acetyl CoA. Without oxygen, no ATP can be made in oxidative phosphorylation. c) Oxygen is required to convert glucose to pyruvate in glycolysis. Without oxygen, no pyruvate can be made. d) Oxygen is an input to acetyl CoA formation.

a) In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration.

Coenzyme Q carries electrons between which stages of the electron-transport chain? Select all that apply. a) complex II and complex III b) complex I and complex II c) complex I and complex III d) complex III and complex IV

a) complex II and complex III c) complex I and complex III

The _________ pathway involves both catabolic and anabolic processes.

amphibolic

A(n) __________ process is the process in which complex biomolecules are built up from simpler ones.

anabolic

A(n) __________ process is the process that replenishes the stores of citric acid cycle intermediates.

anaplerotic

Which of the following stages describe the three stages of respiration? 1. electron transport and oxidative phosphorylation 2. the preparation of pyruvate 3. the oxidation of acetyl-CoA to two molecules of CO2 4. the conversion of pyruvate to acetyl-CoA a) 3 and 4 b) 1, 3, 4 c) 1 and 2 d) 1, 2, 3

b) 1, 3, 4

Which coenzyme is used for the decarboxylation of α-keto acids? a) Flavin adenine dinucleotide (FAD) b) Thiamine pyrophosphate (TPP) c) Coenzyme A (CoA) d) Lipoamide

b) Thiamine pyrophosphate (TPP)

Which of these is NOT a product of the citric acid cycle? a) ATP b) acetyl CoA c) FADH2 d) CO2 e) NADH + H+

b) acetyl CoA

A(n) __________ process is the process by which complex molecules are broken down into simpler ones.

catabolic

Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production? a) ATP levels would fall at first, increasing the inhibition of PFK and increasing the rate of ATP production. b) ATP levels would rise at first, increasing the inhibition of PFK and increasing the rate of ATP production. c) ATP levels would rise at first, decreasing the inhibition of PFK and increasing the rate of ATP production. d) ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

d) ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

Chloroplast membrane vesicles are equilibrated in a simple solution of pH 5. The solution is then adjusted to pH 8. Which of the following conclusions can be drawn from these experimental conditions? a) ATP will be produced because the proton gradient favors proton movement through the ATP synthase channels. b) The change in the solution's pH results in a gradient across the chloroplast membranes such that there is a lower concentration of protons inside the vesicles and a higher concentration outside. c) Protons will not diffuse toward the outside of the vesicles. d) ATP will not be produced because there is no ADP and inorganic phosphate in the solution.

d) ATP will not be produced because there is no ADP and inorganic phosphate in the solution.

Which of these enters the citric acid cycle? a) G3P b) pyruvate c) NADH + H+ d) acetyl CoA e) glucose

d) acetyl CoA

Which part of cellular metabolism of eukaryotic cells takes place in the cytosol? a) citric acid cycle b) amino acid oxidation c) fatty acid β-oxidation d) glycolysis

d) glycolysis

What enzyme catalyzes the reversible, biotin-dependent carboxylation of pyruvate to give oxaloacetate in animals?

pyruvate carboxylase

Where does the Calvin cycle occur?

stroma