Ch339L Final Study

Front 1

For each acetyl-CoA that is incorporated into a growing fatty acid, what energy inputs are required, assuming that the growing fatty
acid already contains at least 4 carbons?
A) 1 NADPH, 1 FADH2, 1 ATP
B) 2 NADPH, 1 ATP E) 2 NADPH, 2 ATP
C) 2 NADPH, 1 FADH2, 1 ATP
D) 1 NADPH, 1 FADH2, 2ATP
E) 2 NADPH, 2 ATP

Back 1

B) 2 NADPH, 1 ATP E) 2 NADPH, 2 ATP

Front 2

How are fatty acids longer than 16 carbons formed?
A) by elongation reactions catalyzed by enzymes on the endoplasmic reticulum
B) by one-carbon additions at the mitochondrial membrane
C) by elongation reactions catalyzed by enzymes in the peroxisomes
D) All of the above.
E) None of the above.

Back 2

A) by elongation reactions catalyzed by enzymes on the endoplasmic reticulum

Front 3

. If the bicarbonate used in malonyl-CoA synthesis were labeled with 14C in the biosynthesis of palmitate, where would the label be
found in the reaction products?
A) evenly distributed in palmitate B) C‒16 of palmitate C) C‒1 of palmitate D) CO2 E) none of the above

Back 3

D) CO2

Front 4

When comparing the energy in stored fat (triacylglycerols) versus the energy in stored glycogen, what must be taken into account to
determine the actual energy available per gram of metabolite?
A) fats are more highly oxidized than glycogen
B) fats are anhydrous while glycogen binds large amounts of water
C) fats are neutral while glycogen is highly charged
D) fats are attached to protein while glycogen is not
E) all of the above

Back 4

B) fats are anhydrous while glycogen binds large amounts of water

Front 5

What is the pH of a 1.5 x 10-9 solution of HCl?
A) ~6 B) ~7 C) ~8 D) ~9 E) none of the above

Back 5

B) ~7

Front 6

What is the committed step in fatty acid synthesis?
A) binding of the fatty acyl group to the acyl carrier protein D) the formation of acetoacetyl-ACP
B) synthesis of malonyl CoA E) None of the above.
C) transacylase reaction

Back 6

B) synthesis of malonyl CoA

Front 7

Which of the following lists the enzymes (in order) required to transport a molecule of acetyl-CoA from the mitochondrion to the
cytosol while returning the “acetyl-CoA acceptor” back to the mitochondrion?
A) citrate synthase, citrate lyase, pyruvate carboxylase
B) citrate synthase, citrate lyase, malate dehydrogenase, pyruvate carboxylase
C) citrate synthase, citrate lyase, malate dehydrogenase, pyruvate carboxylase, malic enzyme
D) citrate synthase, citrate lyase, malate dehydrogenase
E) citrate synthase, citrate lyase, malate dehydrogenase, malic enzyme

Back 7

8. D

Front 8

Which of the following mechanisms explains why fatty acid synthesis and breakdown do not compete with each other in the body?
A) Synthesis and breakdown take place in two separate compartments of the cell.
B) One process uses NADH/NAD+
and the other uses NADPH/NADP+
.
C) They are not attached to the same carrier molecule in the two processes.
D) All of these mechanisms are in operation.

Back 8

D

Front 9

The primary function of biotin in metabolism is:
A) to participate as a cofactor in the exchange of amino groups to other molecules
B) to inhibit acetyl-CoA carboxylase
C) to inhibit carnitine palmitoyltransferase
D) to participate as a cofactor in the addition of CO2 to other molecules.
E) all of these

Back 9

D

Front 10

The synthesis of 1 molecule of cholesterol requires _____ molecules of isopentenyl pyrophosphate, with each molecule of isopentenyl
pyrophosphate requiring _____ molecules of acetyl-CoA.
A) 4; 2 B) 5; 2 C) 6; 2 D) 5; 3 E) 6; 3

Back 10

E

Front 11

The ultimate precursor of all the carbon atoms in steroids is
A) acetyl-CoA B) acyl-CoA C) succinyl-CoA D) isoprenyl-CoA E) malonyl-CoA

Back 11

A

Front 12

Which of the following lipoproteins distributes dietary lipids?
A) chylomicron D) low density lipoprotein
B) very low density lipoprotein E) high density lipoprotein
C) intermediate density lipoprotein

Back 12

A

Front 13

A) a prostaglandin G derivative B) a prostaglandin E derivative C) a leukotriene D) a thromboxane E) none of the
above

Back 13

C

Front 14

Acetylation of serine on prostaglandin synthase (COX enzymes) leads to the reduction of which lipid mediator.
A) Prostacyclin B) Thromboxane C) Prostaglandins D) All of the above E) None of the above

Back 14

D

Front 15

The biosynthesis of cardiolipin involves the reaction of phosphatidylglycerol with a molecule of ___________.
A) phosphatidylglycerol B) phosphatidylserine C) phosphatidylethanolamine D) glycerol E) a fatty acyl-CoA

Back 15

A

Front 16

You are studying the enzymes in the synthesis of cholesterol in the heart and liver. You have discovered that two different enzymes
LN1 and HN1 that use lanosterol as a substrate in different tissues. You carry out an in vitro assay to measure the reaction catalyzed
by LN1 or HN1 and add 250 µM lanosterol (LNS) to the reaction mixture containing equivalent amounts of enzymes LN1or HN1.
After 1 minute, which enzyme will have produced more product: LN1 or HN1?

Reaction Enzyme Km Vmax
LNS--> LGG LN1 750 µM 265 nM/sec
LNS--> LGG HN1 0.7 mM 250 nM/sec

A) LN1 B) HN1 C) they will be ~ equal

Back 16

C

Front 17

Which of the following citric acid cycle intermediates can be converted to aspartate via transamination?
A) succinate B) fumarate C) -ketoglutarate D) citrate E) oxaloacetate

Back 17

E

Front 18

A molecule that signals vasodilation is _____, which is synthesized from the precursor _____.
A) nitric oxide, arginine D) nitrous oxide, citrulline
B) nitrous oxide, arginine E) none of the above
C) nitric oxide, citrulline

Back 18

A

Front 19

Fumarate from the urea cycle is converted to malate and then to ______, which can be used for gluconeogenesis.
A) succinate B) pyruvate C) citrate D) oxaloacetate E) -ketoglutarate

Back 19

D

Front 20

When glutamate is oxidatively deaminated by glutamate dehydrogenase, the products include
A) NADH, -iminoglutarate, and NH3. D) NAD(P)H, H2O, and -ketoglutarate.
B) NAD(P)H + H+, NH4+, and -ketoglutarate.
E) none of the above.
C) NADH, glutamine, and NH3.

Back 20

B

Front 21

In what form(s) is/are ammonia made bioavailable?
A) glutamate B) glutamine C) asparagine D) carbamoyl phosphate E) all of the above

Back 21

E

Front 22

Production of enzymes for the urea cycle increase/decrease as the needs of the organism change. High levels of the urea cycle
enzymes are associated with both high-protein diets and with starvation. Why?
A) The increased need for carbamoyl phosphate to make purines
B) The increased need for disposal of nitrogen from the breakdown of amino acids to make glucose
C) The increased need for Ac-CoA to synthesize mevalonate for cholesterol synthesis
D) All of the above are correct
E) None of the above are correct

Back 22

B

Front 23

Transaminases must deaminate one amino acid and then add the amino group to another ketoacid during transamination. How do
these two parts of the processes differ?
A) The first reaction requires the formation of a Schiff base, but the second part does not.
B) The second reaction takes place in another active site on the enzyme.
C) The coenzyme requires activation by an external aldimine group for only the second reaction.
D) The second part of the reaction (adding an amino group) is the reverse of the first (deamination).
E) The first reaction proceeds through a classic first order mechanism, but the second reaction is a ping-pong mechanism.

Back 23

D

Front 24

25. The glutamine synthetase reaction functions as:
A) a metabolic entry point for fixed nitrogen D) A and B
B) a mechanism to trap excess ammonia E) A, B, and C
C) a source for accessible amino groups

Back 24

E

Front 25

What is the role of CTP in the synthesis of a phospholipid? What are the products of the reaction and how does that affect the
metabolic fate and/or energy expenditures?

Back 25

In the de novo synthesis, the CTP is used to activate the phosphatidate to form CDP-diacylglycerol and pyrophosphate. The reaction
is driven by the subsequent hydrolysis of the PPi to 2 Pi. The activated diacylglycerol can then react with another alcohol, such as
inositol, and CMP is released. The hydrolysis to CMP and subsequent hydrolysis of PPi drives the reaction forward as the hydrolysis
of PPi is irreversible. It takes the function equivalent of 2 ATP to regenerate the CTP.

Front 26

. Describe the math for fatty acid synthesis where C2 + C3 = C4?

Back 26

This is the activation and condensation of malonyl CoA and Acetyl CoA. The loss of a CO2 groups in the condensation results in a
new four carbon acyl chain

Front 27

Citrate is a high energy signal molecule that in inhibits glycolysis and regulates acyl CoA carboxylase (ACC) allosterically. How is
this important? What other method(s) is/are used to regulate ACC?

Back 27

High concentrations of citrate signal that there is plentiful energy/carbons that may be synthesized into fatty acids for storage by
activating ACC, the first/committed step in FA synthesis, which synthesizes malonyl CoA from the carboxylation of acetyl CoA.
Citrate is transported from mitochondria to cytoplasm and converted by citrate lyase to acetyl CoA for FA synthesis. Thus it makes
metabolic sense for citrate concentrations to allosterically regulate the first step of FA synthsis. Phosphorylation/dephosphorylation
of ACC is regulated hormones and also transcription regulation occurs to limit expression.

Front 28

NADPH reducing equivalents important for the biosynthesis of fatty acids. Name two sources of NADPH and any additional
metabolic roles, if any, of the source.

Back 28

One NADPH molecule is produce by the fatty acid synthetic pathway as it is transferred into the cytosol. The additional reducing
equivalents come from the pentose phosphate pathway, one of the main products of the pathway. The pentose phosphate pathway
provides the reducing power for fatty acid synthesis, but it also provides 5 carbon sugars for nucleotide biosynthesis and a salvage
pathway for the carbons if ribose is not required, but NADPH is.

Front 29

What are gangliosides? How do they differ from other membrane lipids? How are gangliosides synthesized? Why is their degradation
an issue in some genetic disorders? What tissue is affected?

Back 29

Gangliosides are spingolipids that are modified with one or more carbohydrates.

They differ in the backbone used for synthesis palmitoyl CoA and serine, rather than a glycerol backbone. These structures have
oligosaccharides attached to the ceramide moiety. The structures are synthesized in a stepwise manner. First a glucose or galactose residue is attached to the C-1 hydroxyl of ceramide
from the activated UDP-sugar. Then activated sugar residues (UDP-glucose, UDP-galactose, UDP-N-acetylgalactosamine, and a
CMP derivative of N-acetylneuraminate) are added to form the oligosaccharide units. These complex carbohydrate moities need to be removed in order for the lysosome to metabolize the ganglioside. A series of hydrolytic enzymes remove the various carbohydrate modifications. A genetic defect, such as Tay-Sachs where a hexoamidase is absent or inactive leads to the build of a degradation intermediate. This intermediate build up in lysome causes damage to cells.

Front 30

The following molecule is a competitive inhibitor of what enzyme and pathway? What family of drugs is it in? What is the
substrate? Circle the part of the molecule that is the part that mimics the substrate. Would you expect that this inhibitor would
increase or decrease the KM of the enzyme and how does it change the alter the activity of the enzyme?

Back 30

this is a statin (atorvastatin or Lipitor) that inhibits HMG-CoA reductase, the rate limiting step in cholesterol biosynthesis. The
substrate is HMG-CoA and the product is mevalonate. This would increase the Km by occupying the active site and competing with
the substrate requiring more substrate to reach V max.

Front 31

What are the steps in LDL uptake into cells? What is (are) the consequence(s) of the inability to uptake LDL into cells?

Back 31

The LDL contains apolipoprotein B-100, which binds to an LDL receptor on the cell surface in a region known as a clathrin coated pit.
The complex is internalized by endocytosis, and the vesicles formed fuse with lysozomes inside the cell. The cholesterol esters are
hydrolyzed, and free cholesterol made available for cellular use. The LDL protein is hydrolyzed to free amino acids, and the receptor
is transported back to the cell surface and reused. The inability either from a genetic lack of receptors or mutation to dock LDL results in a high concentration of circulating LDL which
leads to inflammation, plaque formation and ultimately atherosclerosis.

Front 32

Incorporation of ammonium ions into urea for excretion removes the toxic ions from the bloodstream. Elevated blood ammonium
ion concentrations result in coma and eventual death. Increased ammonium concentration may shift the equilibrium of the glutamate
dehydrogenase reaction. What is the biochemical explanation of the toxicity of ammonium ion? Be sure to write out (words are
fine) the equation for the glutamate dehydrogenase reaction and indicate key metabolites and their relationship to other metabolic
pathways, as well as why this particular reaction may contribute to eventual death.

Back 32

glutamate + H2O + NAD+
<------> -ketoglutarate + NH4
+
+ NADH + H+


The increased ammonium ion concentration would shift the equilibrium to form glutamate. Eventually the -ketoglutarate would be
depleted causing the citric acid cycle to cease to function, ultimately leading to the loss of electron carriers and ATP synthase would
also cease to function leading to a lack of ATP and death would result from a lack of ATP.

Front 33

Glutamine synthetase in E. coli has several ways in which it is regulated. Describe the 3 different methods of regulation.

Back 33

1. Glutamine synthetase (GS) has feed back (allosteric) regulation by CTP, histidine,tryptophan, AMP, carbamoyl phosphate or
glucoseamine--these all require glutamine for their synthesis. This regulation is cumulative, in that each of these products inhibits the
enzyme a small amount. All must be present to completely inhibit the enzyme
2. Covalent modification of the enzyme by adenylation by adenyl transferase which inactivtes GS. AT is a bifunctional enzyme and
also can de-adenylate GS when a protein regulator PII of GS is uridylylated. When PII is not modified it is an activator of the adenyl
transferase. See also Fig. 20.8. 3. GS expression is also regulated at the level of transcription by PII.

Front 34

Outline the steps of the urea cycle. Indicate where in the cell these reactions are taking place and what tissue does it take place?
Indicate the points that intermediates may interact with other metabolic pathways. At which step/enzyme is the urea cycle regulated?
What is the regulator and from what is it derived? Why is this regulation so important?

Back 34

The urea cycle takes place in the liver. The enzymes and the reactions catalyzed are: 1) Carbamoyl phosphate synthetase catalyzes
the formation of carbamoyl phosphate (mitochondria). 2) Ornithine transcarbamoylase catalyzes the formation of citrulline from
ornithine and carbamoyl phosphate (mitochondria). 3) Argininosuccinate synthetase catalyzes the formation of argininosuccinate
from citrulline and aspartate (cytoplasm) . 4) Argininosuccinase converts argininosuccinate to arginine and eliminates fumarate
(cytoplasm). 5) Arginase catalyzes the generation of ornithine from arginine, with the elimination of urea (cytoplasm).

N-acetylglutamate (NAG) is an activator for carbamyl phosphate synthetase. It is synthesized from Ac-CoA and glutamate by
N-acetylglutamate synthase. Without this activator, the urea cycle stops and ammonia builds up and becomes toxic.