Deck 16: Lipid Metabolism

Question 1

Which enzyme catalyzes the modification of a fatty acid, so that it can be transported into the mitochondria for oxidation?

A) acyl-CoA dehydrogenase
B) acetyl-CoA carboxylase
C) fatty acyl-CoA synthetase
D) carnitine acyltransferase I

Answer 1

carnitine acyltransferase I

Question 2

What is the key enzyme involved in priming fatty acids for degradation?

A) acetyl-CoA carboxylase
B) fatty acyl-CoA synthetase
C) carnitine acyltransferase I
D) fatty acyl hydrolase

Answer 2

fatty acyl-CoA synthetase

Question 3

In order for a fatty acyl-CoA to be moved into the mitochondria for $\beta$ -oxidation, it must be

A) transported by the carnitine-acylcarnitine translocase.
B) activated by ATP.
C) reduced by NADH and FADH₂.
D) hydrolyzed into acetyl-coA fragments.

Answer 3

transported by the carnitine-acylcarnitine translocase.

Question 4

Why is the fatty acid oxidation pathway also referred to as the $\beta$ -oxidation pathway?

A) The carbon adjacent to the fatty acyl-CoA reacts with oxygen.
B) The pathway utilizes NAD⁺ and FAD as cofactors.
C) A carbon atom that is two carbons away from the carboxylic acid end of the fatty acid chain is oxidized.
D) The resulting products are referred to as $\beta$ -bodies.

Question 5

About more ATPs can be obtained from one 16:0 fatty acid than from one glucose molecule.

A) 32
B) 106
C) 2
D) 75

Question 6

What enzyme class catalyzes the following reaction?

A) ligase
B) hydratase
C) transferase
D) oxidoreductase

Question 7

How many high-energy FADH₂ and NADH molecules, respectively, are made from each pass through the $\beta$ -oxidation pathway?

A) 1 FADH₂; 2 NADH
B) 1 FADH₂; 0 NADH
C) 0 FADH₂; 2 NADH
D) 1 FADH₂; 1 NADH

Question 8

How many total NADH + FADH₂s are made in the $\beta$ -oxidation pathway from the breakdown of the following fatty acid to all acetyl-CoAs?

A) 6
B) 8
C) 4
D) 2

Question 9

How many ATPs are obtained from the complete $\beta$ -oxidation of one mole of stearoyl-CoA (18Cs) compared with three molecules of glucose (3 * 6C = 18Cs)?

A) 106 versus 32
B) 100 versus 100
C) 36 versus 90
D) 120 versus 90

Question 10

Which molecule is used to transport fatty-acyl groups into the mitochondria?

A) CoA-SH
B) ATP
C) biotin
D) carnitine

Question 11

Carnitine is

A) used for transporting fatty acids into the cell.
B) attached to the growing fatty acid chain in fatty acid synthesis.
C) attached to fatty acid groups that are moved into the mitochondria for degradation.
D) attached to acetyl groups to activate them for addition to the growing fatty acid chain in fatty acid synthesis.

Question 12

Which cofactor is utilized in the following fatty acid oxidation reaction?

A) ATP
B) NAD⁺
C) FAD
D) NADP⁺

Question 13

The complete $\beta$ -oxidation of 1 mole of palmitic acid (16:0) yields moles of ATP after TCA cycle and oxidative phosphorylation processes.

A) 8
B) 32
C) 106
D) 156

Question 14

Which of the following is NOT an intermediate in the $\beta$ -oxidation of a fatty acid?

A)
B)
C)
D)

Question 15

How many passes through the fatty acid oxidation pathway are required to degrade palmitic acid?

A) 1
B) 7
C) 8
D) 16

Question 16

What precursors are required for the breakdown of palmitate?

A) 14 ATP and 14 NADH
B) ATP and CoA
C) acetyl-CoA
D) NADH and FADH₂

Question 17

What enzyme class catalyzes the following reaction? (Note that there may be some missing reactants and products.)

A) lyase
B) hydrolase
C) transferase
D) dehydrogenase

Question 18

Why is less ATP obtained from the average carbon in a sugar molecule than from a carbon in a fat molecule?

A) The sugar carbons require more water weight during cellular storage.
B) The carbons in fatty acids are a more reduced form of carbon than those in sugars.
C) The sugar carbons yield more NADH than ATP.
D) The sugar carbons are derived from CO₂.

Question 19

What is the cellular location of the fatty acid oxidation pathway?

A) cytoplasm
B) peroxisome
C) mitochondrial matrix
D) smooth endoplasmic reticulum

Question 20

Which enzyme is responsible for assembly of palmitate from activated acetyl-CoA fragments?

A) acyl-CoA dehydrogenase
B) acetyl-CoA carboxylase
C) fatty acyl-CoA synthetase
D) fatty acid synthase

Question 21

How many more enzymes does the oxidation of a polyunsaturated fat such as linoleoyl-CoA (18:2) require than the oxidation of stearoyl-CoA (18:0)?

A) 0
B) 1
C) 2
D) 3

Question 22

Which is found in the ketone body pathway?

A) succinyl-CoA.
B) propionyl-CoA.
C) dihydroxyacetone phosphate.
D) hydroxybutyrate.

Question 23

What extra enzyme types are often required in the degradation of polyunsaturated fats by the $\beta$ -oxidation pathway?

A) reductase and isomerase
B) hydrolase and isomerase
C) oxidoreductase and reductase
D) synthase and isomerase

Question 24

The following fatty acid __________ be metabolized by _.

A) will; being run through the $\beta$ -oxidation pathway until the double bond is isomerized for the pathway to continue
B) will not; not being recognized by $\beta$ -oxidation pathway enzymes
C) will not; entering the pathway as normal but eventually inhibiting the enzymes
D) will; being run through the $\beta$ -oxidation pathway as normal

Question 25

Which of the following do $\beta$ -oxidation and fatty acid synthesis have in common?

A) the presence of an oxidized fatty acyl $\beta$ -carbon with a hydroxyl or carbonyl group as a pathway intermediate
B) their cellular location
C) their use of NADH
D) the number of enzymes involved in the pathways

Question 26

What is the primary difference in the oxidation of stearic acid (18:0) and oleic acid (18:1)?

A) Stearic acid requires one more pass through the fatty acid oxidation pathway.
B) Oleic acid will yield one less FADH₂ product molecule.
C) Oleic acid cannot be fully metabolized.
D) Stearic acid yields less ATP.

Question 27

How many more passes through $\beta$ -oxidation does the saturated fat stearic acid (18:0) require, compared with the monounsaturated fat oleic acid (18:1)?

A) 0
B) 1
C) 2
D) 17

Question 28

Which of the following are ketone bodies?

A) "acetyl-CoA, hydroxymethylglutaryl-CoA"
B) " $\beta$ -ketoacyl-ACP, hydroxymethylglutaryl-CoA"
C) "methylmalonyl-CoA, acetyl-CoA"
D) "hydroxybutyrate, acetoacetate"

Question 29

What molecule is the odd chain fatty acid product propionyl-CoA converted into?

A) butyryl-CoA
B) succinyl-CoA
C) citrate
D) palmitate

Question 30

What enzyme catalyzes the following reaction in the first step of fatty acid synthesis?

A) fatty acyl-CoA synthetase
B) acetyl-CoA carboxylase
C) fatty acid synthase
D) fatty acyl-CoA dehydrogenase

Question 31

A difference between FA synthesis and $\beta$ -oxidation is that FA synthesis , whereas $\beta$ -oxidation _.

A) reactions use ATP; reactions directly yield ATP
B) occurs in the mitochondria; takes place in the cytoplasm
C) uses NADH; uses NADPH
D) uses acyl-ACP; uses acyl-CoA

Question 32

The synthesis of fatty acids requires which cofactor?

A) FADH₂
B) NADH
C) thiamine pyrophosphate (TPP)
D) NADPH

Question 33

Ketone bodies are

A) transported to the liver for degradation.
B) an alternate storage form of glucose.
C) used as a fuel source by muscle cells as well as brain cells.
D) polymerized to form fatty acids.

Question 34

The $\beta$ -oxidation of mono- and polyunsaturated fatty acids

A) requires an extra cycle through the pathway.
B) involves the reduction of the double bonds and then the continuation of $\beta$ -oxidation.
C) yields succinyl-CoA.
D) involves isomerization and in some cases reduction of the double bonds before the continuation of $\beta$ -oxidation.

Question 35

What cofactor, common to carboxylase enzymes, is used by acetyl-CoA carboxylase?

A) NADPH
B) FAD
C) biotin
D) pyridoxal phosphate

Question 36

How do we deal with the double bonds during the degradation of unsaturated fatty acids?

A) Convert the three-carbon propionyl-CoA to succinyl-CoA and feed it into the TCA cycle.
B) Converge them with the TCA cycle to produce acetyl-CoAs.
C) Isomerize the position of the double bonds to converge them with the $\beta$ -oxidation pathway.
D) Reduce them to single bonds and feed the saturated fatty acid into the $\beta$ -oxidation pathway.

Question 37

How many more enzymes does the oxidation of oleoyl-CoA (18:1) require than the oxidation of stearoyl-CoA (18:0)?

A) 0
B) 1
C) 2
D) 3

Question 38

How many acetyl-CoAs per ketone body are delivered to cells in need of energy?

A) 1
B) 2
C) 3
D) 4

Question 39

The same four reactions that are central to the $\beta$ oxidation pathway are also present in the fatty acid synthesis pathway, except they are reversed. What is a key difference between the four reactions in these two pathways?

A) One set of reactions synthesizes an ATP, whereas the other set uses an ATP.
B) One set occurs in the muscle, whereas the second pathway occurs in the liver.
C) One pathway adds three carbon atoms at a time, whereas the other removes two carbons.
D) Four enzymes are used in one, whereas one enzyme is used in the other.

Question 40

Both the synthesis and $\beta$ -oxidation of saturated fatty acids

A) require FAD.
B) require NADPH.
C) occur in the cytosol.
D) involve acetyl-CoA.

Question 41

The synthesis of palmitic acid

A) occurs in mitochondria.
B) involves the acyl carrier protein (ACP).
C) uses FAD and NADP⁺.
D) requires ATP.

Question 42

The regulation of Acetyl-CoA carboxylase is

A) activated by glucagon.
B) activated by acyl-CoA binding.
C) stimulated by citrate.
D) inactivated by insulin.

Question 43

Which is true of the acyl carrier protein (ACP)?

A) It transports the fatty acid chain during oxidation and synthesis.
B) It directs the growing fatty acid chain from one enzyme active site to another in the fatty acid synthesis pathway.
C) It requires ATP for proper function.
D) It catalyzes the delivery of fatty acyl chains from the mitochondria to the cytosol.

Question 44

The rate-limiting reaction is catalyzed by in the synthesis of saturated fatty acids in the .

A) fatty acid synthase; cytosol
B) fatty acid synthase; mitochondrion
C) acetyl-CoA carboxylase; cytosol
D) citrate synthase; mitochondrion

Question 45

Membrane phospholipids are synthesized in which cellular location?

A) cytoplasm
B) mitochondrial intermembrane space
C) mitochondrial matrix
D) smooth endoplasmic reticulum

Question 46

How are double bonds added to fatty acid chains in humans?

A) The smooth endoplasmic reticulum is involved in elongating and unsaturating fatty acids.
B) FAD is used as an oxidant to create the double bonds in the smooth endoplasmic reticulum.
C) Unsaturated fatty acids are not made by humans and are therefore essential fats.
D) Fatty acid desaturase enzymes use O₂ and NADH to add double bonds to fatty acids.

Question 47

What class of enzyme is the human desaturase enzyme?

A) isomerase
B) oxidoreductase
C) ATPase
D) transferase

Question 48

What are the different roles played the acyl carrier protein (ACP) and the ketoacyl synthase (KS) domain during fatty acid synthesis?

A) The ACP carries the growing fatty acid chain more than the KS domain.
B) The KS domain holds the growing fatty acid chain, whereas the ACP delivers two carbon fragments.
C) The KS domain associates with the fatty acid synthase enzyme, whereas the ACP does not.
D) The ACP delivers two carbon fragments one at a time, whereas the KS domain passes them on to the fatty acid.

Question 49

What enzyme catalyzes the following fatty acid synthesis reaction?

A) fatty acid synthase
B) fatty acyl-CoA synthetase
C) fatty acyl-CoA dehydrogenase
D) acetyl-CoA carboxylase

Question 50

Which fatty acid can be synthesized from scratch in humans by desaturase enzymes?

A)20:4, $\Delta$ 5,8,11,14
B) 18:2, $\Delta$ ^9,13
C) 20:2, $\Delta$ ^6,9
D) 16:2, $\Delta$ ^9,11

Question 51

Which enzyme activates acetyl-CoA so that it can be added to the growing fatty acid chain during the synthesis of palmitate?

A) acetyl-CoA carboxylase
B) fatty acyl-CoA synthase
C) acyl-CoA dehydrogenase
D) fatty acid synthase

Question 52

The introduction of ^{1 4}CO₂ into a cell actively synthesizing fatty acids results in ^{1 4}C labeled

A) malonyl-CoA.
B) acetyl-CoA.
C) acyl-CoA.
D) palmitate.

Question 53

Which correctly describes the synthesis of phosphatidylethanolamine?

A) Activated ethanolamine is added to a phosphatidic acid precursor.
B) Phosphatidylserine is decarboxylated.
C) Diacylglycerol is activated by CTP.
D) Triacylglycerol is phosphorylated with ATP.

Question 54

Which group is responsible for activating phosphatidic acid for the synthesis of phospholipids?

A) CoA
B) ATP
C) CO₂
D) CTP

Question 55

In triacylglycerol synthesis, from where is the glycerol backbone derived?

A) fatty acyl-CoA
B) pyruvate
C) dihydroxyacetone phosphate
D) acetyl-CoA

Question 56

The acetyl-CoA for fatty acid synthesis comes from the

A) breakdown of fats.
B) TCA cycle.
C) mitochondria via the citrate shuttle.
D) breakdown of cytoplasmic pyruvate.

Question 57

The synthesis of both triacylglycerols and membrane phospholipids occurs from which immediate precursor?

A) phosphatidic acid
B) glycerol
C) phosphatidylserine
D) diacylglycerol

Question 58

For every two carbons that are added to a growing fatty acid chain in the fatty acid synthesis pathway, __________ ATPs and __________ NADPHs are required.

A) 0; 1
B) 1; 2
C) 2; 1
D) 0; 2

Question 59

The NADPH required by the fatty acid synthesis pathway comes from the

A) pentose phosphate pathway and the shuttle of citrate from the mitochondria.
B) mitochondria.
C) breakdown of glucose.
D) TCA cycle and the shuttle of citrate from the mitochondria.

Question 60

Which of the following stimulate fatty acid synthesis when their concentrations are high?

A) citrate and insulin
B) glucagon and citrate
C) insulin and acyl-CoA
D) citrate, insulin, and palmitoyl-CoA

Question 61

Draw the overall balanced reaction for the breakdown of palmitic acid (16:0) to give all acetyl-CoA products. Please include all cofactors involved in the process.

Question 62

All of the following are metabolic fates of cholesterol EXCEPT

A) the majority of cholesterol is catabolized to bile salts.
B) cholesterol may be present in membranes.
C) cholesterol is a precursor for nucleotides.
D) steroids are derived from cholesterol.

Question 63

LDLs are referred to as "bad cholesterol" because

A) they are the blood serum particle with the highest concentration of cholesterol.
B) they contain cholesterol that is not as easily degraded.
C) their cholesterol has no specific cellular purpose other than to form plaques.
D) LDL levels surge after meals high in fat.

Question 64

During the conversion of VLDL to IDL, the

A) IDL becomes increasingly enriched in cholesterol.
B) core of IDL becomes increasingly enriched in TAGs.
C) LDL intermediate is formed.
D) IDL becomes depleted in protein.

Question 65

Starting from the 6C fatty acyl-CoA molecule shown below, draw the reactants and products, including all cofactors used for one round of the $\beta$ -oxidation pathway and list the enzyme
types involved in each step.

Question 66

By what process are LDL particles removed selectively from the blood serum?

A) through targeted digestion by serum lipases
B) by receptor-mediated endocytosis
C) They are replenished with triacylglycerols and never removed.
D) They form atherosclerotic plaques.

Question 67

Which enzyme catalyzes the rate-limiting step of cholesterol synthesis?

A) cholesterol synthase
B) HMG-CoA reductase
C) thiolase
D) HMG-CoA synthase

Question 68

Start with the following molecule. (A) Write the balanced equation for the products formed from its complete oxidation in the $\beta$ -oxidation pathway and (B) show how many ATPs would
be obtained from the complete metabolism of those products.

Question 69

The uptake of LDLs by cells is triggered by the

A) absorption of the LDL triacylglycerol and phospholipid core.
B) hydrolysis of LDL phospholipids by phospholipase enzymes.
C) binding of the apoB-100 lipoprotein on LDL to the LDL receptor.
D) formation of cholesterol plaques.

Question 70

The sterol regulatory element (SRE) is a(n) and the sterol regulatory element binding protein (SREBP) is a(n) _.

A) allosteric activator; enzyme
B) transport activator; transport protein
C) receptor; hormone
D) DNA promoter; transcription activator

Question 71

Cholesterol biosynthesis and cholesterol uptake is stimulated by

A) the binding of SREs to cholesterol uptake genes.
B) the binding of SREBPs to SREs and activating the transcription of cholesterol synthesizing genes.
C) increased levels of cholesterol binding to the SREBPs.
D) the uptake of LDLs through the LDL receptor.

Question 72

The smallest precursor molecule cholesterol is derived from

A) squalene.
B) isoprene.
C) arachidonic acid.
D) acetyl-CoA.

Question 73

Which of the following causes inhibition of fatty acid synthesis?

A) increased insulin
B) increased AMP-activated protein kinase (AMPK)
C) decreased cytoplasmic acyl-CoA
D) increased cytoplasmic acetyl-CoA

Question 74

All of the following genes are activated by the interaction of the SREBP with the SRE, EXCEPT for

A) HMG-CoA reductase.
B) LDL receptor.
C) HMG-CoA synthase.
D) cholesterol esterase.

Question 75

Which lipid is thought to give rise to the plaques that can clog arteries?

A) HDL
B) LDL
C) VLDL
D) chylomicrons

Question 76

The final formation of cholesterol from squalene involves

A) condensation with HMG-CoA and mevalonate.
B) more than 19 reactions including cyclization and oxidation.
C) oxidation and the addition of acyl-CoA.
D) dimerization and oxidation of squalene.

Question 77

Which one of the following lipoproteins functions to transport cholesterol from the peripheral tissues to the liver?

A) VLDL
B) LDL
C) HDL
D) chylomicron

Question 78

As in glycolysis and the degradation of glucose, the degradation of fatty acids also requires an initial investment of ATP energy. State the reaction or reactions where ATP energy is needed before fatty acids can be oxidized.

Question 79

What enzyme is activated by HDL to release cholesterol from the cell membranes of peripheral tissues?

A) phosphatidylcholine esterase
B) HDL apolipase
C) cholesterol esterase
D) lecithin-cholesterol acyltransferase

Question 80

Diagram the process by which the palmitoyl-CoA molecule moves from the cytosol into the mitochondria for degradation.