Biochem Exam 2

Ketone bodies can be used as an alternative fuel source by the liver. True False

False

The ATP yield from NADH transported across the mitochondrial inner membrane by the glycerol phosphate shuttle is the same as if the malate/aspartate shuttle were used.

False

β-oxidation of unsaturated fatty acids yields the same amount of energy as saturated fatty acids with the same number of carbons. True False

False

How do FAs of different carbon lengths cross into the mitochondrial matrix for oxidation? 1) Small FAs of 10 carbons or fewer can freely diffuse through the membrane. 2) Large FAs are cleaved into two smaller units that are actively transported across the membrane. 3) A membrane-bound transferase catalyzes the conversion of long-chain FAs to FA-carnitine esters, which are transported across the membrane via a specific carrier. 4) The breakdown of large FAs starts outside the matrix, allowing for smaller particles to pass easily through the membrane.

Only statements 1 and 3 are correct.

Which of the following is NOT true of respiratory control?

Oxidative phosphorylation is regulated by allosteric mechanisms.

Which regulatory effects are results of internalized cholesterol? 1) It activates acyl-CoA:cholesterol acyltransferase. 2) It increases endogenous cholesterol synthesis. 3) It downregulates the production of LDL receptors. 4) It inhibits HMG-CoA reductase.

Statements 1, 3, and 4 are direct results of the internalization of cholesterol.

When the identical subunits of chicken liver fatty acid synthase are dissociated in vitro, all of the activities can be detected in the separated subunits except for the β-ketoacyl synthase reaction and the overall synthesis of palmitate. Explain these observations.

The acyl-ACP produced by one subunit undergoes the next round of reductive two-carbon addition on the other subunit.

Which of the following statements is FALSE? -The cholesterol ester content of HDL is generally less than that of chylomicrons. -Some fatty acids become complexed with serum albumin for transport in the blood to peripheral cells. - VLDL transports triacylglycerol synthesized in the liver to peripheral tissues. - Chylomicrons are lipoproteins that transport dietary fat from intestine to peripheral tissues. - LDL is the main form in which cholesterol is transported to tissues.

The cholesterol ester content of HDL is generally less than that of chylomicrons.

Compare these two values. -The energy yield from tripalmitin is larger than the energy yield from glucose. - The energy yield from tripalmitin is smaller than the energy yield from glucose. -These values are equal.

The energy yield from tripalmitin is larger than the energy yield from glucose.

If only chlorophyll a were involved in the light reactions, would blue light (wavelength about 490 nm) be effective in driving photosynthesis?

The graph indicates that chlorophyll a absorbs very little blue light, so we can predict that blue light would not be effective.

CoQ carries electrons from NADH-Coenzyme Q reductase and succinate dehydrogenase as well as other flavoproteins to CoQ:Cytochrome c oxidoreductase.

True

HMG-CoA reductase, the major control point of cholesterol biosynthesis is regulated by transcriptional and post-transcriptional mechanisms mediated by Insig proteins bound in the endoplasmic reticulum membrane. True False

True

Mono- and poly-unsaturated fatty acids are produced in the endoplasmic reticulum by desaturase enzymes. T/F

True

Oleic acid

oleate+25.5O2+120.5ADP+118.5Pi→18CO2+119.5ATP+AMP+135.5H2O

Palmitic acid

palmitate+23O2+108ADP+106Pi→16CO2+107ATP+AMP+122H2O

Proton-driven rotation of the c-ring of the F0 unit of the F1F0 ATP synthase is required for complete passage of protons from the intermembrane space to the matrix.

True

The liver is the central organ in animals for processing lipoproteins whether they are derived from the diet or from biosynthetic pathways. True False

True

Photosynthesis takes place in all higher plants and algae in chloroplasts. Which of the following statements accurately describe these organelles?1) In plants, they are located in mesophyll cells.2) They are semiautonomous in that they carry their own DNA and ribosomes.3) Unlike mitochondria, they have three membranes.4) The carbohydrates produced by this reaction are stored as cellulose.

1,2,3

Which of these equations best summarizes photosynthesis?

6 CO2 + 6 H2O → C6H12O6 + 6 O2

Which of the following compounds is NOT derived from cholesterol?

α-tocopherol

Identify and briefly discuss each mechanism ensuring against simultaneous fatty acid synthesis and oxidation in the same cell.

-Malonyl-CoA, a key intermediate in fatty acid synthesis, inhibits carnitine acyltransferase I, thereby blocking the entry of fatty acyl units into the mitochondrion for oxidation. -Fatty acyl-CoAs, the substrates for fatty acid oxidation, inhibit fatty acid synthesis by interfering with the polymerization of acetyl-CoA carboxylase - Hormonal effects on adipocytes: insulin promotes fatty acid synthesis by several mechanisms, while glucagon promotes fat breakdown and fatty acid oxidation.

Glucagon secretion causes inhibition of intracellular acetyl-CoA carboxylase activity by several mechanisms. Name all you can think of.

- Glucagon promotes triacylglycerol breakdown, yielding increased levels of fatty acids, which could prevent polymerization and activation of acetyl-CoA carboxylase -Glucagon activates phosphorylation of pyruvate dehydrogenase, which inhibits the formation of acetyl-CoA, the substrate for the enzyme.

Which step in lipid metabolism would you expect to be affected by 3,4-dihydroxybutyl-1-phosphonic acid (shown here)? Explain your answer.

-The esterification of glycerol-3-phosphate with fatty acyl-CoA, catalyzed by glycerophosphate acyltransferase. -This is a nonhydrolyzable analog of glycerol-3-phosphate, so it is acylated without difficulty to give the phosphonate analog of diacylglycerol.

Which of the following statements about photosynthesis are true?1) This process describes the catabolism of carbohydrates to CO2.2) For plants, water is the ultimate reducing agent in this process.3) The process releases oxygen as a byproduct.4) The energy required for this transformation comes in the form of light.

2,3,4

In some instances, the levels of LDL cholesterol exceed the ability of the body to maintain homeostasis, and as a result, the excess material accumulates into fatty deposits that harden into plaques. Arrange in the correct order the sequence of events that leads to this condition, known as atherosclerosis: 1) The plaques harden, blocking the flow of blood in major arteries. 2) White blood cells become engorged with fatty deposits. 3) Excess LDL cholesterol accumulates in the interior of arterial walls. 4) Macrophages are drawn to this site.

3-4-2-1

Arrange the order of events in the fatty acid (FA) metabolism pathway in the correct order: 1) The modified FA is transported across the inner membrane of the mitochondrion. 2) Dehydration occurs to generate an α,β-unsaturated FA. 3) The free FA is converted to acetyl CoA ester. 4) Thiolytic cleavage occurs, releasing a molecule of acetyl CoA and a new FA with two fewer carbon atoms. 5) The FA CoA ester is converted to its carnitine ester. 6) Hydration occurs to yield a β-hydroxy ester. 7) The FA CoA ester is regenerated.

3-5-1-7-2-6-4

The β-oxidation of odd-numbered FAs presents a small problem in that once most of the oxidation has occurred, the last component is propionyl-CoA rather than acetyl CoA. This has one more carbon and as such cannot be utilized any further. Outline the events that control the metabolism of this unit in their proper order: 1) Methylmalonyl-CoA epimerase converts S-methylmalonyl-CoA to R-methylmalonyl-CoA. 2) Methylmalonyl-CoA mutase demethylates R-methylmalonyl-CoA to succinyl-CoA. 3) Propionyl-CoA carboxylase catalyzes the addition of CO2 to propionyl-CoA. 4) The odd-carbon FA is metabolized to propionyl-CoA.

4-3-1-2

Approximately what wavelength of light is best absorbed by chlorophyll a, the pigment that participates directly in the light reactions?

435

Which wavelength of light is best absorbed by chlorophyll b?

455

Using Figure 16.9 on page 515 in the text, arrange the order of events for the internalization of LDL particles into cells: 1) A combination of cholesterol and apolipoprotein binds to LDL receptors and becomes internalized as endocytotic vesicles. 2) The environment of the endosome becomes acidic, which causes the LDL to dissociate from its receptor; additionally, the endosome fuses with a lysosome. 3) Several endocytotic vesicles fuse to form an endosome. 4) The LDL particle is degraded by the lysosome. 5) LDL receptors migrate to the cell surface and cluster in clathrin-coated pits.

5-1-3-2-4

The overall net synthesis of palmitate starting from acetyl CoA requires:

8 acetyl-CoA, 7 ATP and 14 NADPH and 7 H+.

Which of the following statements about oxidative phosphorylation by ATP synthase is FALSE?

A proton gradient alone without a corresponding energy input is not sufficient to drive the synthesis of ATP.

Free fatty acids are released from the adipocyte after mobilization of fat stores by: -adipose triglyceride lipase. - hormone sensitive lipase. -monoacylglycerol lipase. - lipoprotein lipase. -A, B, and C.

A, B, and C.

Mammals cannot undergo net synthesis of carbohydrate from acetyl-CoA, but the carbons of acetyl-CoA can be incorporated into glucose and amino acids. Present pathways by which this could come about.

Acetyl−CoA⟶(citricacidcycle)oxaloacetate⟶PEP(carboxykinase)PEP⟶(gluconeogenesis)glucose

Which of the following statements regarding the β-oxidation of FA is NOT correct? -Acyl-CoA dehydrogenase catalyzes the synthesis of a cis α,β-unsaturated CoA thioester. - 3-L-hydroxyacyl-CoA dehydrogenase catalyzes the oxidation of the 3-hydroxyacetyl CoA ester to the corresponding 3-ketone. -Enoyl-CoA hydratase catalyzes the hydration of the α,β-unsaturated CoA thioester to a β-hydroxy CoA thioester. -Thiolase catalyzes the thiolytic cleavage of a 3-ketoacyl CoA ester to release acetyl CoA and a new FA with two fewer carbons.

Acyl-CoA dehydrogenase catalyzes the synthesis of a cis α,β-unsaturated CoA thioester.

Complete Constants | Periodic Table In the early days of "mitochondriology", P/OP/O ratios were determined from measurements of volume of O2O2 taken up by respiring mitochondria and chemical assays for disappearance of inorganic phosphate. Now, however, it is possible to measure P/OP/O ratios simply with a recording oxygen electrode.

Add ADPADP in limiting amount and measure O2O2 uptake. The ratio of μ�mol ADPADP consumed to μ�atom oxygen taken up is identical to the P/OP/O ratio.

Normally, DCMUDCMU blocks O2O2 evolution, but addition of ferricyanide to chloroplasts allows O2O2 evolution in the presence of DCMUDCMU. Explain.

Addition of ferricyanide as an electron donor allows a Hill reaction.

What kinds of experiments could test your proposed explanation?

Addition of radiolabeled PS to an enzyme system would not label PE, because phosphatidylserine decarboxylase would act only on PS generated by phosphatidylserine synthase.

Which of the following statements about β-oxidation of fatty acids is CORRECT? - Fatty acids of any length are oxidized by exactly the same enzymes. - All fatty acids must be activated to acyl-CoAs before entering the pathway. - Thiolytic cleavage releases acetyl-CoA and a free fatty acid in the final step of the cycle. - Both dehydrogenation reactions produce a C=C double bond. - Both dehydrogenation reactions use FAD as the electron acceptor.

All fatty acids must be activated to acyl-CoAs before entering the pathway.

Insulin stimulates fatty acid synthesis by which of the following mechanisms? -Stimulation of dephosphorylation of pyruvate dehydrogenase -Activation of citrate lyase -Dephosphorylation of acetyl-CoA carboxylase -Stimulation of a glucose transport across the plasma membrane -All of the above

All of the above

One pathway that appears to relate elevated cholesterol levels to atherosclerosis involves the oxidation of LDL. Which of the following are consequences of this process? -Oxidized LDL products induce an immune response that includes recruitment of monocytes and T lymphocytes. - Though the mechanism by which this occurs is not completely understood, this oxidation includes the peroxidation of fatty acids, the hydroxylation of cholesterol, and the oxidation of amino acids. -The presence of scavenger receptors on macrophages allows unlimited cholesterol uptake, leading to its conversion to foam cells. - All of the listed responses are consequences of this process.

All of the listed responses are consequences of this process.

Which of the following enzymes are required for the oxidation of unsaturated FA? -acyl-CoA dehydrogenase -enoyl-CoA isomerase -2,4-Dienoyl-CoA reductase -All of the listed responses are correct.

All of the listed responses are correct.

Which of the following are key discoveries of the experiments conducted by Brown and Goldstein? 1) Cholesterol is taken into cells through the action of a specific receptor. 2) The receptor for the LDL particle recognizes B-100 apolipoprotein. 3) The entire receptor complex, unlike hormones involved in signaling pathways, enters the cell via endocytosis. 4) Familial hypercholesterolemia patients have defective or deficient LDL receptors.

All of the listed statements are true.

The antibiotic valinomycin is an ionophore that forms a specific complex with potassium ion. Because the complex is lipophilic and can diffuse into the membrane, valinomycin brings about the transport of K+K+ through the inner membrane. Valinomycin acts by decreasing the ΔψΔ� (membrane potential) component of the pmf, without a direct effect on the pHpH gradient. Another antibiotic, nigericin, acts as a K+/H+K+/H+ antiporter; it carries H+H+ in one direction, coupled with the reverse transport of K+K+. Thus, nigericin dissipates the pHpH component of the pmf, with little effect on ΔψΔ� .

Because the electrical component (Δψ)(Δ�) makes a greater contribution to the proton motive force than the pHpH gradient (ΔpH)(ΔpH), valinomycin would be expected to be a more effective uncoupler than nigericin.

Years ago there was interest in using uncouplers such as dinitrophenol as weight control agents. Presumably, fat could be oxidized without concomitant ATPATP synthesis for re-formation of fat or carbohydrate.

Because the energy not used for ATPATP was dissipated as heat, and the subjects developed uncontrollable fevers.

Explain why a deficiency of steroid 21-hydroxylase leads to excessive production of sex steroids (androgens and estrogens).

By shutting down the pathway leading to aldosterone, this deficiency increases the supply of progesterone available for conversion to sex steroids.

Cells from FH individuals exhibited high levels of reductase activity, regardless of the presence or absence of LDL in the culture medium.

Cells from FH individuals were deficient in their ability to take up cholesterol from the culture medium.

When cultured in the presence of LDL, normal cells showed low activity of HMG−CoA reductase. After removal of lipopoteins, including LDL, HMG−CoA reductase activities increased some 50- to 100-fold in normal cells (panel a). This high level of enzyme activity was rapidly suppressed upon addition of LDL back to normal cells (panel b).

Cholesterol is normally transported into the cell, where it regulates its own synthesis by suppressing the activity of HMG−CoA reductase, the rate-limiting enzyme.

Part complete Which of the following is NOT an electron acceptor in the mitochondrial respiratory chain

CoQH2

When pure reduced cytochrome c is added to carefully prepared mitochondria along with ADPADP, PiPi, antimycin AA, and oxygen, the cytochrome c becomes oxidized, and ATPATP is formed, with a P/OP/O ratio approaching 1.0.

Cytc⟶CuA⟶hemea⟶hemea3−CuB⟶O To block oxidation of endogenous substrates and to inhibit reverse electron flow (i.e., to prevent electrons flowing back up the respiratory chain). Because ATPATP is formed, with a P/OP/O ratio of ~1.0, complex IV must be a coupling site (i.e., a site of proton pumping).

Part complete Which of the following statements is FALSE?

Cytochrome c and coenzyme Q are both soluble electron carriers that are loosely attached to the outside of the inner mitochondrial membrane.

The Light Reaction letters:

E,B,A,C, A and C,

All of the cytochromes in the mitochondrial respiratory chain contain the same heme moiety as found in hemoglobin.

False

Elongation of fatty acids from palmitate occurs only in the mitochondrion. True False

False

Excess cholesterol is metabolically degraded in the liver T/F

False

If mevalonate labeled with 14C in the carboxyl carbon were administered to rats, which carbons of cholesterol would become labeled?

NONE

Would you expect DCMUDCMU to interfere with cyclic photophosphorylation?

No. Plastoquinones are not involved in this process.

How could she tell whether photosystem I, II, or both are involved?

Observe the oxidation state of plastoquinones and plastocyanin using illumination at both 700 and 680 nmnm. If only p700 is involved, these will be oxidized. If only p680, they will be reduced. If both are involved, simultaneous illumination at the two wavelengths will give enhanced oxidation of the donor.

Choose a pathway whereby some of the carbon from a fatty acid with an odd-numbered carbon chain could undergo a net conversion to carbohydrate.

Propionyl−CoA⟶methylmalonyl−CoA⟶SUCCINYL−CoA⟶oxaloacetate⟶PEP⟶glucose

An action spectrum plots the rate of photosynthesis at various wavelengths of visible light, and it shows that blue light with a wavelength of about 490 nm is effective in driving photosynthesis. Based on this information and the absorption spectra shown at left, what role may chlorophyll b and carotenoids play in photosynthesis?

These pigments are able to absorb more wavelengths of light (and thus more energy) than chlorophyll a alone can absorb. As part of light-harvesting complexes in photosystems, they broaden the range of light that can be used in the light reactions.

You obtain the pigments called carotenoids in your diet when you eat carrots. Why do carotenoids appear yellow and orange?

They absorb blue/green light and reflect yellow and red wavelengths of light.

Discuss the metabolic rationale for phosphorylation of acetyl-CoA carboxylase by AMP-activated protein kinase (AMPK) and cyclic AMP-dependent protein kinase (PKA)

This could be a way for a cell to INHIBIT fatty acid synthesis under conditions where substrates are needed for oxidation.

If you were to determine the P/OP/O ratio for oxidation of α�-ketoglutarate, you would probably include some malonate in your reaction system.

To block succinate dehydrogenase and measure phosphorylation resulting only from the α�-ketoglutarate dehydrogenase reaction.

Clathrin is a self-associating protein, which is able to form cage-like structures, which facilitate receptor-mediated endocytosis. True False

True

Because PS must be present in the membrane to serve as an intermediate, how might you explain its failure to accumulate to a significant extent?

Under certain conditions PS could never accumulate, because, once formed by phosphatidylserine synthase, it would immediately be converted to PE by phosphatidylserine decarboxylase.

Which of the following is NOT involved in the enzymatic inactivation of reactive oxygen species?

Vit C

The shuttle system for transfer of acetyl-CoA generated in the mitochondrial matrix to the cytosol includes: - citrate from the citric acid cycle. -the production of NADPH by malic enzyme. -citrate lyase in the cytosol. -ATP hydrolysis. -all of the above.

all of the above.

Which of the following statements about photosynthesis is FALSE? The dark reactions use the NADPH and ATP formed in the light reactions in reductive synthesis of carbohydrate from CO2 and water.In plants much of the carbohydrate formed is stored as sucrose.The light reactions occur within or on the thylakoid membranes.The dark reactions occur in the stroma of the chloroplast.The light reactions oxidise water to oxygen, reducing NADP+ to NADPH in the process

carbs are stored as sucrose

What is the most likely site of inhibition by 2-bromopalmitoyl-CoA?

carnitine palmitoyltransferase I

Choose a balanced equation for the synthesis of sn-1-stearoyl-2-oleoylglycerophosphorylserine, starting with glycerol, the fatty acids involved, and serine.

glycerol+stearicacid+oleicacid+3ATP+CTP+serine→sn−1−stearoyl−2−oleylglycerophosphorylserine+ADP+2AMP+3PPi+CMP

Linoleic acid

linoleate+25.5O2+118ADP+116Pi→18CO2+117ATP+AMP+135.5H2O

What would you expect to happen to levels of mevalonate in human plasma if an individual were to go from a meat-containing diet to a vegetarian diet?

mevalonate levels increase

Stearic acid

stearate+26O2+122ADP+120Pi→18CO2+121ATP+AMP+138H2O

In animal cells the mitochondrial electron transport chain is responsible for reoxidizing most of the NADH produced by oxidative pathways regardless of the cellular compartment in which it was produced.

t

The light reactions of photosynthesis use _____ and produce _____.

water, NADPH

Indicate the probable flow of electrons in this system.

β−hydroxybutyrate⟶NADH⟶complexI⟶CoQ⟶complexIII⟶cytochromec 2 mol Because NADHNADH cannot freely enter the mitochondrion. To block cytochrome oxidase, so that electrons exit the chain at cytochrome c. β−hydroxybutyrate+2cytcox+2ADP+2Pi+4H+⟶acetoacetate+2cytcred+2ATP+2H2O