Biochemistry Practice Exam 3, (Ch. 19, 20 , 21

Front 1

1. Which of the following terms are used to describe the tendency of a reaction to occur when the substrates and products of the reaction are at any concentration?

A. ΔG
B. ΔGo
C. ΔGo'
D. -TΔS
E. ΔH

Back 1

A

Front 2

2. For the enzyme reaction A+ B = C + D, Delta Go' = + 1 kcal/mol. This reaction will proceed spontaneously in a forward direction if:

A. The concentration of D is increased one-hundred fold
B. The concentration of C is increased one-hundred fold
C. The concentration of A is increased one-hundred fold
D. The concentration of B is lowered one-hundred fold
E. The concentration of both A and D are increased one-hundred fold

Back 2

C

Front 3

During muscle contraction:
Answer
a.
ATP binds to the actin-ATPase
b.
Low calcium concentration allows interaction of myosin and actin
c.
ATP hydrolysis causes necessary changes in conformation
d.
Binding of ATP to actin allows association of actin and myosin
e.
AMP is the product of ATP hydrolysis

Back 3

C

Front 4

Oxidative phosphorylation:
Answer
a.
Is anaerobic
b.
Requires AMP
c.
Requires the electron transport system
d.
Is not dependent upon development of a proton gradient
e.
Is independent of mitochondria

Back 4

C

Front 5

Patients with hyperthyroidism complain constantly of feeling hot and sweaty. All of the following are reasons EXCEPT:
Answer
a.
Thyroid hormone induces many proteins that catalyze the oxidation of fats, carbohydrates, and proteins
b.
Thyroid hormone stimulates the Na+,K+-ATPase
c.
Thyroid hormone increases the flux through most anabolic pathways
d.
All spontaneous reactions convert some free energy to heat
e.
Thyroid hormone causes the non-enzymatic hydrolysis of ATP

Back 5

E

Front 6

Which of the following is not a function of the citric acid cycle?
Answer
a.
Catabolism of carbon structures of some amino acids
b.
Catabolism of acetate groups from acetyl CoA
c.
The production of GTP
d.
The production of NADPH
e.
The production of carbon structures for the synthesis of some amino acids

Back 6

D

Front 7

In the citric acid cycle, a substrate level phosphorylation is catalyzed by:
Answer
a.
Citrate synthase
b.
Succinyl CoA synthetase
c.
Fumarase
d.
Isocitrate dehydrogenase
e.
Citrate lyase

Back 7

B

Front 8

In contrast to NADH, FAD(2H):
Answer
a.
Can donate electrons, but only two at a time, in a chemical reaction
b.
Has a low affinity for its apoenzyme
c.
Is very reactive in solution
d.
Is an excellent feedback inhibitor
e.
Is derived from a vitamin

Back 8

C

Front 9

The anaplerotic reaction that links glycolysis to the TCA cycle:
Answer
a.
Uses thiamin as a cofactor
b.
Is called phosphoenolpyruvate carboxykinase
c.
Produces oxaloacetate
d.
Is activated by malonyl CoA
e.
Is dependent upon vitamin B12

Back 9

C

Front 10

Which of the following two enzymes are thought to be the major control enzymes of the TCA cycle?
Answer
a.
Malate dehydrogenase and fumarase
b.
Succinate dehydrogenase and fumarase
c.
Succinyl CoA synthetase and succinate dehydrogenase
d.
Succinyl CoA synthetase and alpha-ketoglutarate dehydrogenase
e.
α-ketoglutarate dehydrogenase and isocitrate dehydrogenase

Back 10

E

Front 11

Wet beriberi results in low peripheral resistance and cardiomyopathy. Both of these symptoms are explained as follows:
Answer
a.
Thiamin pyrophosphate is a cofactor for pyruvate carboxylase
b.
Without thiamin, the TCA cycle produces too much ATP
c.
Thiamin is an important intermediate in the electron transport chain
d.
Without thiamin, energy cannot be adequately produced by muscle cells
e.
Thiamin permeabilizes membranes so no proton gradient can be established

Back 11

D

Front 12

The ATP synthase responsible for most of the ATP synthesis in the body is located:
Answer
a.
On the outer side of the outer mitochondria membrane
b.
On the inner side of the outer mitochondria membrane
c.
On the outer side of the inner mitochondria membrane
d.
On the inner side of the inner mitochondria membrane
e.
Free in the matrix of the mitochondria

Back 12

D

Front 13

If electrons were removed from α-ketoglutarate and you could watch them move down the electron transport system, the order of movement would be as follows:
Answer
a.
NADH, Complex I, CoQ, Complex III, Cytochrome C, Complex IV, H2O
b.
NADH, Complex I, Complex II, CoQ, Cytochrome C, Complex IV, H2O
c.
NADH, Complex II, CoQ, Cytochrome C, Complex III, Complex IV, H2O
d.
NADH, Complex I, CoQ, Complex II, Cytochrome C, Complex III, H2O
e.
NADH, Complex I, Complex II, Cytochrome C, Complex III, CoQ, Complex IV, H2O

Back 13

A

Front 14

Which of the following statements does NOT help explain the chemiosmotic theory?
Answer
a.
Protons move down a concentration gradient with negative free energy change
b.
ADP and Pi combine to form ATP, this reaction has a positive change in free energy
c.
The inner mitochondria membrane is impermeable to protons
d.
The only way protons can enter the mitochondria is through the ATP synthase with the concomitant synthesis of ATP
e.
The outside of the mitochondria is negative with respect to the matrix

Back 14

E

Front 15

A mitochondrion is producing ATP at a constant rate and, then, a chemical uncoupler is added. Compared to before the uncoupler was added:
Answer
a.
Less heat would be produced
b.
Less water would be produced
c.
More NADH would be oxidized
d.
More ATP would be produced
e.
The proton gradient across the membrane would be increased

Back 15

C

Front 16

Regarding Cora Nari, which of the following statements about her heart attack and subsequent treatment and effects are FALSE?
Answer
a.
Tissue plasminogen activator causes an increased production of plasmin
b.
Tissue plasminogen activator can be given following a heart attack to dissolve blood clots
c.
Because of its high energy demands, the normal heart relies on anaerobic respiration to meet its needs
d.
Nitroprusside can be given following a heart attack to dilate blood vessels
e.
Cardiac muscle cells, sperm cells, and other active cells have a relatively high number of mitochondria

Back 16

C

Front 17

The cleavage of the high-energy bond of ATP into ADP and Pi is an example of what type of reaction?
Answer
a.
Oxidation-reduction
b.
Phosphorylation
c.
Acetylation
d.
Hydrolysis
e.
Amination

Back 17

D

Front 18

Delta-G is negative, Delta-Go' is positive. Will the reaction occur spontaneously?
Answer
a.
Yes
b.
No
c.
Not enough information to determine the answer

Back 18

A

Front 19

Which of the following is NOT an example in which ATP is utilized in the body for work?
Answer
a.
Contraction of muscle
b.
Entry of water into cells through specific pores
c.
Phosphorylation of glucose by hexokinase
d.
Maintenance of the Na+ and K+ concentration gradients
e.
Formation of glycosidic bonds to make glycogen

Back 19

B

Front 20

Which of the following is NOT a step during muscle contraction?
Answer
a.
The terminal end of a myosin filament binds ATP
b.
Cleavage of ADP into AMP and Pi provides energy for mechanical work
c.
Thick myosin filaments bind thin actin filaments
d.
Presence of calcium enables myosin to bind actin
e.
ATP is cleaved by an ATPase located on the myosin filament

Back 20

B

Front 21

The phosphorylation of glucose to glucose-6-phosphate has a Delta Go'of +3.3 kcal/mol. So why does the reaction occur in almost every cell of our body?
Answer
a.
Glucose becomes unstable intracellularly
b.
Hexokinase is present
c.
ATP hydrolysis
d.
High concentration of glucose in the blood compared to cell
e.
This reaction is coupled to another that has a much higher positive Delta Go

Back 21

C

Front 22

Which of the following statements regarding electron-accepting coenzymes is INCORRECT?
Answer
a.
FAD accepts electrons as the hydrogen atom
b.
NADH is the reduced form of the coenzyme
c.
FAD(H2) is synthesized from the vitamin riboflavin
d.
The Delta Go' for the oxidation of NADH by the electron transport chain is negative
e.
The electrons donated to these coenzymes are subsequently removed by the enzymes of the TCA cycle

Back 22

E

Front 23

Which of the following statements regarding the TCA cycle is CORRECT?
Answer
a.
The rate-limiting step involves the enzyme malate dehydrogenase
b.
For each acetyl CoA entering the cycle, two molecules of CO2 are produced
c.
For each acetyl CoA entering the cycle, 24 high-energy phosphate bonds are produced
d.
The cycle will not function unless glutamate is present
e.
The TCA cycle occurs in the rough endoplasmic reticulum of virtually every cell in the body

Back 23

B

Front 24

Which of the following statements regarding the alpha-ketoglutarate dehydrogenase complex is INCORRECT?
Answer
a.
One of its coenzymes - lipoic acid - comes from the vitamin B-carotene
b.
It requires FAD as a coenzyme
c.
Carbon dioxide is produced by this complex
d.
One of its coenzymes - CoASH - comes from the vitamin pantothenate
e.
It catalyzes the reaction converting a-ketoglutarate into succinyl CoA

Back 24

A

Front 25

Which enzyme complex in the TCA cycle requires the cofactors thiamine pyrophosphate, lipoic acid, CoA, FAD and NAD+?
Answer
a.
Citrate synthase
b.
a-ketoglutarate dehydrogenase
c.
Succiny-CoA synthetase (succinate thiokinase)
d.
Malate dehydrogenase
e.
Fumarase

Back 25

B

Front 26

Which of the following statements about the coenzyme FAD is INCORRECT?
Answer
a.
It accepts single electrons
b.
The TCA cycle enzyme that transfers electrons to FAD is found in the inner mitochondrial membrane
c.
It is very reactive in solution
d.
It remains tightly bound to the holoenzyme
e.
FADH2 is an important allosteric inhibitor of the TCA cycle

Back 26

E

Front 27

Which of the following statements about the TCA cycle is CORRECT?
Answer
a.
Citrate is frequently used for gluconeogenesis in the liver
b.
The production of oxaloacetate by pyruvate carboxylase is one of several anaplerotic reactions for the TCA cycle
c.
Succinyl CoA is used to create a neurotransmitter in the brain
d.
Pyruvate dehydrogenase helps convert pyruvate into malate
e.
Pyruvate carboxylase is only found in RBCs

Back 27

B

Front 28

Which of the following statements regarding the pyruvate dehydrogenase complex is INCORRECT?
Answer
a.
When the complex is phosphorylated, it is inactive
b.
Binding of pyruvate to the enzyme complex decreases the activity of the kinase
c.
High [ADP] stimulates the conversion of pyruvate to acetyl CoA
d.
The phosphatase which activates the complex is itself inhibited by Ca2+
e.
The kinase associated with the pyruvate dehydrogenase complex is an enzyme that adds phosphate groups

Back 28

D

Front 29

Which of the following statements regarding Complex II is INCORRECT?
Answer
a.
This is one means by which the TCA cycle is linked to the electron-transport chain
b.
Succinate dehydrogenase is embedded in the inner mitochondrial membrane
c.
Neither the single- or 2-electron forms of FAD dissociate from the enzyme
d.
Complex II transfers its electrons directly to cytochrome c
e.
The transfer of electrons from FAD(2H) to the electron-transport chain results in the synthesis of approximately 1.5 ATPs

Back 29

D

Front 30

Which of the following are in the correct sequence?
Answer
a.
Cytochrome Q; NADH dehydrogenase; Cytochrome c; Cytochrome oxidase
b.
Complex I; Cytochrome c; Complex II; Cytochrome oxidase
c.
NADH dehydrogenase; Cytochrome b-c1; Cytochrome c; Cytochrome oxidase
d.
Succinate dehydrogenase; Coenzyme Q; Cytochrome oxidase; Cytochrome c
e.
Complex I; Complex II; Coenzyme Q; Cytochrome oxidase

Back 30

C

Front 31

All of the following can act as "uncouplers" EXCEPT:
Answer
a.
Brown adipose tissue
b.
Proton ionophores
c.
Thermogenin (in infants)
d.
Thyroid hormone
e.
Cyanide

Back 31

E

Front 32

A patient suffers a heart attack due to the blockage of an artery. The heart cells downstream from the blockage will receive less oxygen which will in turn cause
Answer
a.
[ATP] to increase
b.
[ADP] to decrease
c.
An increase in electron flow through the electron transport chain
d.
[NADH] to increase
e.
Anaerobic glycolysis to decrease

Back 32

D

Front 33

A patient has hyperthyroidism. Compared to normal, you would expect that the electron transport chain would
Answer
a.
increase electron flow (flux) through the chain
b.
decrease the oxidation of NADH
c.
decrease the production of water
d.
decrease the pumping of protons across the membrane
e.
increase its efficiency in terms of ATP production per NADH oxidized

Back 33

A

Front 34

Assume standard biological conditions and that all the enzymes are present to catalyze the reactions. Given the following data:

Glucose + Pi = glucose-6-P + H2O, ΔGo′ = +3.3 kcal/mol
ATP + H2O = Pi + ADP, ΔGo′ = -7.0 kcal/mole

Calculate the ΔGo′ for the following reaction and determine whether the reaction is spontaneous

Glucose + ATP --> Glucose-6-P + ADP
Answer
a.
–10.3 kcal/mol and spontaneous
b.
+10.3 kcal/mol and not spontaneous
c.
–3.7 kcal/mol and not spontaneous
d.
+3.7 kcal/mol and not spontaneous
e.
–3.7 kcal/mol and spontaneous

Back 34

E