Module 5: Practice Quizzes and Module Quiz (Ch 24, 25, 26, 27, 28)

Triacylglycerol catabolism can convert glycerol for use in energy production. How many net ATPs will glycerol metabolism directly generate (i.e., substrate level phosphorylation) via glycolysis?

1 Correct. One ATP is spent, and two are generated.

The degradation of an 18-carbon saturated fatty acid would be expected to yield how many NADH and FADH2 per fatty acid molecule?

8 Correct. Eight cycles of the β-oxidation pathway are required to degrade a fatty acid to acetyl-coenzyme A with one NADH and FADH2 being produced in each cycle. Note that eight cycles are required and not nine, because the last step of the eighth cycle yields two molecules of acetyl-CoA.

In skeletal muscle, the binding of _____ stabilizes phosphorylation b into the active form

AMP

The activity of glycogen phosphorylase b in muscle tissue is also controlled by allosteric means with _____ acting as a positive effector and _____ as a negative effector.

AMP; ATP Correct. The AMP is a signal that ATP needs to be made and that the phosphorylase enzyme should be activated. ATP signals that sufficient ATP is present and that there is no need to be degrading glycogen at the moment.

The function of the enzyme acyl CoA synthetase is:

ATP-dependent activation of fatty acids using CoA.

Which of the following occurs after a carbohydrate-rich meal?

Blood-glucose levels increase leading to glycogen storage in the liver.

The removal of glucose subunits from glycogen using phosphorylase has an advantage over using α-1,6-glucosidase in that

DIDN'T GET CORRECT> ANSWERS ARE NOT: phosphorylase can remove all the glucose subunits in a chain that extend from an α-1,6 linkage. phosphorylase requires no input of energy to remove the glucose subunit.

The first step of β oxidation is a(n) _____-linked oxidation of the fatty acyl chain.

FAD

For every added double bond in a fatty acid, there is a subsequent loss of one _____ during a fatty acid β-oxidation cycle.

FADH2 Correct. In saturated fatty acid β-oxidation, FADH2 is made after a double bond is introduced into the chain by acyl CoA dehydrogenase. If a double bond is present, this step is bypassed.

_____ is the committed step of the pentose phosphate pathway.

Glucose 6-phosphate dehydrogenase

_____ is the enzynme that catalyzes the hydrolysis of the ester linkage of the lactone resulting in the ring opening.

Lactonase

Ethanol consumption inhibits fatty acid oxidation because cellular _____ levels increase as the ethanol is metabolized.

NADH

The coenzyme required for fatty acid synthesis is _____.

NADPH

Isomers with multiple asymmetric centers differing in only one asymmetric center are _____.

NOT SURE

Although glutathione is considered a tripeptide, there is an unusual feature about its structure. What is it?

One of the peptide bonds involves the glutamic acid R-group. Correct. The γ-carboxyl group of glutamate forms an amide linkage with the amino group of cysteine.

The enzyme that begins the kinase cascade activating glycogen degradation is:

PKA

Glutathione combats _____ in the organism.

ROS

Why is the T state of glycogen phosphorylase less active?

The active site is partially blocked.

Which of the following is NOT true of acetoacetate and β-hydroxybutyrate?

They allosterically modify other enzymes. Correct. This statement does NOT describe ketone bodies. Allosteric modification of these substances is not seen.

The synthesis of glycogen requires an activated form of glucose. Activated glucose includes a linkage to:

UDP

_____ acts as a "high-energy handle" for biosynthetic reactions including glycogen synthesis.

UDP

Glycogen synthase adds glucose units to growing glycogen molecules using

UDP-glucose. Correct. UDP-glucose is the activated form of glucose that the glycogen synthase uses to add glucose units to growing glycogen molecules.

A mutation that renders glucose-6-phosphatase nonfunctional in the liver would result in

a buildup of lactate in the bloodstream. Correct. The buildup of glucose 6-phosphate leads to increased glycolysis, which subsequently leads to the buildup of lactate.

Acetoacetate spontaneously decarboxylates to form _____.

acetone

A biotin-deficient diet may lead to an increase of cytosolic _____.

acetyl CoA

The ability to generate 5-carbon sugars from 3- and 6-carbon precursors takes advantage of enzymes that can add molecules to existing

aldehyde groups. Correct. Aldolase and transketolase reactions add functional groups to existing aldehydes.

Linoleate (18:2 cis-Δ9, Δ12) cannot be synthesized in mammals. Linoleate is (18:2 cis-Δ9, Δ12) _____ fatty acid.

an essential

Prostaglandins and thromboxanes are synthesized from _____, a 20-carbon fatty acid.

arachidonate

Glycogen breakdown in the liver is triggered by a cAMP cascade upon the binding of _____ to its receptor.

both glucagon and epinephrine

Under conditions in which NADPH is NOT needed, how are five-carbon sugars, such as ribose-5-phosphate, generated?

by withdrawing 3-carbon units from the glycolytic pathway and converting them into 5-carbon sugars via the nonoxidative branch of the pentose phosphate pathway Correct. Glyceraldehyde-3-phosphate and dihydroxyacetone phosphate can serve as starting points for generation of 5-carbon sugars in a series of reactions involving transketolase and transaldolase.

The glycerol produced during the lipolysis of triglycerides

can be used as either a source of energy or for gluconeogenesis. Correct. Phosphorylation and oxidation of glycerol produces glyceraldehyde-3-phosphate that can be degraded via the glycolytic pathway and citric acid cycle to generate ATP or be converted to glucose via gluconeogenesis.

Which biosynthetic pathway requires NADPH?

cholesterol fatty acid nucleotide *All of the answers are correct.

Acetyl CoA is transferred from the mitochondria to the cytoplasm in the form of _____.

citrate

Acetyl groups to be used for fatty acid biosynthesis are transferred across the mitochondrial membrane in what form?

citrate

Which of the following is a regulator of acetyl CoA carboxylase?

citrate glucagon insulin *All of the above

Which of the following is the MAIN regulatory factor for the pentose phosphate pathway?

concentration of NADP+

The synthesis of fatty acids takes place in the _____ of the cell.

cytoplasm *Cytosol will be labeled as incorrect.

In general, phosphorylated forms of glycogen synthase lead to _____ levels of glycogen.

decreased

Possible fates for the glucose 6-phosphate produced during glycogen breakdown include:

entering glycolysis. entering the pentose phosphate pathway. formation of glucose through the action of glucose 6-phosphatase. *All of the above

During the degradation of unsaturated fatty acids, the double bonds must be reduced. The reductant for this process is

fatty acid degradation through the citric acid cycle does not lead to a net increase in oxaloacetate. Correct. Two carbons enter the cycle in the form of acetyl-coenzyme A and two carbons are lost as CO2. So there is no net increase in oxaloacetate

NADPH is required by the liver and adipose for synthesis of _____.

fatty acids

Which of the following CANNOT be used as an energy source by the brain?

fatty acids Correct. Most fatty acids are bound to albumin in the blood plasma and not capable of crossing the blood-brain barrier. Although some short-chain fatty acids may cross this barrier in infants, they are in general not used as a source of fuel by the adult brain.

The hydrolysis catalyzed by α-1,6-glucosidase releases a(n) ________ molecule.

free glucose

Glycogen breakdown can be regulated hormonally when _____ is secreted from the _____.

glucagon; pancreas Correct.

In the liver, glycogen synthesis and degradation are regulated to maintain levels of _____ in blood.

glucose

The glycogen phosphorylase enzyme carries out a phosphorolysis reaction resulting in the formation of

glucose-1-phosphate. Correct. The phosphorolysis reaction removes glucose units from glycogen in the form of glucose-1-phosphate. G-1-p is subsequently converted into glucose-6-phosphate by phosphoglucomutase.

There is a high _____-to-insulin ratio in diabetes.

glycogen

The key enzyme in glycogen degradation is:

glycogen phosphorylase.

The reaction catalyzed by _____ transfers UDP-glucose to the hydroxyl of an existing glycogen core.

glycogen synthase

During a period of exercise, which of the following enzymes will dominate?

glycogen synthase b Correct. This is the inactive form of the enzyme that will turn glucose into glycogen.

In order for regulation of glycogen metabolism to function, there must also be a means to reverse the regulatory effects of the various kinases. Reversal of kinase activation is accomplished by protein phosphatase 1, an enzyme which

hydrolyzes the phosphate from the modified enzyme. Correct. The phosphatase enzyme uses water to hydrolyze the phosphate from the phosphorylated enzymes.

Which of the following is NOT carried out by mammalian fatty acid synthase?

incorporation of double bonds

Fatty acids are activated by attachment to coenzyme A at the outer mitochondrial membrane, but the resulting fatty acyl-coenzyme A is not degraded until it reaches the mitochondrial matrix. The fatty acyl-coenzyme A

is transferred to another molecule that is involved in transport of the fatty acid into the mitochondrial matrix. Correct. Fatty acids are transferred from coenzyme A to carnitine, which transports them across the inner mitochondrial membrane and then transfers them back to coenzyme A.

Type 2 diabetes is MOST commonly diagnosed _____ and involves _____.

later in life; insulin resistance

Glycogen phosphorylase exists in two forms: phosphorylase b, which is _____, and phosphorylase a, which is _____.

less active; more active Correct.

Which of the following is an essential fatty acid?

linoleate

Enzymes that digest the triacylglycerols into free fatty acids and monoacylglycerol are called:

lipases

Untreated, chronic ketone body production will ___________ blood pH levels.

lower

A deficiency of glucose 6-phosphate dehydrogenase confers resistance to:

malaria

Activation of acetyl CoA results in the production of _____.

malonyl CoA

The committed step of fatty acid synthesis is the formation of _____.

malonyl CoA

In eukaryotes, the degradation of fatty acids occurs in the

mitochondrial matrix

Fatty acid biosynthesis depends on the presence of CO2 (or HCO3-) to generate malonyl-coenzyme A from acetyl-coenzyme A. If a culture of cells is grown in the presence of 14C-labeled bicarbonate, which carbons of the newly synthesized fatty acids would be expected to be radiolabeled?

none of the carbons Correct. The labeled carbon in malonyl-coenzyme A is released as CO2 in the subsequent step and is not incorporated into the newly synthesized fatty acid.

In addition to making NADPH, the pentose phosphate pathway generates key molecules for the synthesis of

nucleotides. Correct. Nucleotides, particularly RNA, use ribose as the sugar molecule that makes the nucleotide subunit.

The NADPH used in the reductive steps of fatty acid biosynthesis comes from

one NADPH being generated per citrate leaving the mitochondria AND the degradation of glucose via the pentose phosphate pathway exclusively. Correct. Answer a (citrate leaving the mitochondria) provides some of the NADPH needed for fatty acid biosynthesis with the remainder coming from answer b (degradation of glucose via the pentose phosphate pathway).

The fact that liver tissue contains glucose-6-phosphatase while muscle tissue does not is physiologically important because

one of the major functions of the liver is to maintain the blood glucose level. Correct. The hydrolysis of the phosphate group to yield free glucose in the liver is important in maintaining the blood glucose level.

The first phase of the pentose phosphate pathway involves the _____ generation of _____.

oxidative; NADPH

Fatty acids are the building blocks of:

phospholipids and glycolipids.

The activity of glycogen phosphorylase is controlled by a modification catalyzed by the enzyme phosphorylase kinase. What is the nature of this modification?

phosphorylation—transfer of a phosphate from ATP to the phosphorylase enzyme Correct. Kinases transfer phosphate groups from nucleotide triphosphates to an acceptor molecule, in this case the phosphorylase enzyme.

β oxidation of odd-numbered fatty acids produces acetyl CoA and _____.

propionyl CoA Note: Avoid using "-" in any names, such as propionyl-CoA as these will be counted wrong.

Acetyl CoA carboxylase is a key regulator of fatty acid metabolism. The enzyme is subject to:

regulation by glucagon. control via reversible phosphorylation. control via allosteric regulation. *All of the above

he major use of NADPH generated by the pentose phosphate pathway is

serving as a reductant in biosynthetic pathways. Correct. The NADPH generated in the pentose phosphate pathway serves as a reductant in a variety of biosynthetic pathways.

Unsaturated fatty acids obtain their unsaturated state in:

the endoplasmic reticulum.

The attachment of glucose to UDP (glucose-1-phosphate + UTP ↔ UDP-glucose + pyrophosphate) is a readily reversible reaction. What provides the driving force in favor of the synthesis of UDP-glucose?

the energy from the subsequent hydrolysis of the pyrophosphate Correct. This is the case for many biosynthetic reactions where hydrolysis of pyrophosphate provides the driving force.

The major site(s) of glycogen storage is/are:

the liver and skeletal muscle

Which of the following is NOT a difference in the pathways by which fatty acids are degraded and synthesized?

the presence or absence of a double bond Correct. The presence or absence of a double bond is not a difference between fatty acid synthesis and degradation. A double bond is generated in both degradation and biosynthetic pathways.

Glucose-6-phosphate can be utilized by either the glycolytic or the pentose phosphate pathway. What is the major factor regulating how the use of glucose-6-phosphate is distributed between these two pathways?

the relative levels of NADP+ and NADPH Correct. The glucose-6-phosphate dehydrogenase enzyme needs NADP+ as a substrate and is competitively inhibited by NADPH.

The cleavage of triglycerides into glycerol and fatty acids is performed by lipases. The signaling process initiating the activation of lipases is

the same as that which signals the cell to break down glycogen. Correct. The same steps and signals (up to protein kinase A) are involved in activation of both processes. Epinephrine and glucagon are the triggers in both processes, for example.

Glycogen breakdown and synthesis are said to be reciprocally regulated. This means that

the same effectors affect both processes but in opposite directions. Correct. Identical effectors work in oppositive directions. Epinephrine, for example, signals to turn glycogen breakdown on and glycogen degradation off.

The binding of signal molecules such as epinephrine or glucagon to receptors on the cell surface triggers a cascade of events leading to the activation of glycogen phosphorylase. Which of the following is NOT involved in this post-binding cascade?

transport of the epinephrine or glucagon into the cell Correct. Epinephrine and glucagon trigger the cascade but are not involved in the cascade post-binding. Both of these signal molecules produce their effects without being transported into the cell.

The enzyme transketolase transfers a(n) _____-carbon fragment from a ketose to an aldose. Write the number out as a word.

two

The glycogen molecule has two types of linkages between the glucose molecules of which it is comprised. Of these, the _____ linkage is broken by the glycogen phosphorylase enzyme and the _____ linkage is not.

α-1,4; α-1,6 Correct. Glycogen phosphorylase uses phosphate to cleave the α-1,4 linkage, not the α-1,6 linkage.