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BIOCHEM > Fourth 50 > Flashcards

Fourth 50 Flashcards

1
Q

An inhibitor that binds only to the ES complex and not free enzyme is known as a(n) __________ inhibitor.

irreversible

competitive

uncompetitive

mixed

A

uncompetitive

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2
Q

The Lineweaver–Burk plot shows data obtained for an enzyme in the absence and presence of a reversible inhibitor. Which type of inhibitor was used in the experiment?

competitive

uncompetitive

mixed

noncompetitive

A

noncompetitive

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3
Q

A Lineweaver–Burk plot displays parallel lines for an enzyme in the absence and presence of increasing amounts of an inhibitor. The inhibitor in this experiment

binds both the free enzyme and the ES complex.

is competitive.

alters the Km but not the vmax.

is uncompetitive.

A

is uncompetitive.

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4
Q

Which of the following statements are true?

ATCase is regulated by feedback inhibition.

CTP is an allosteric activator of ATCase.

ATP is an allosteric inhibitor of ATCase.

GTP is an allosteric inhibitor of ATCase.

A

ATCase is regulated by feedback inhibition.

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5
Q

What is the appropriate order of the following steps?
A. Glutamine binding to uridylyltransferase
B. Adenylation of glutamine synthetase
C. Deuridylation of glutamine synthetase adenylyltransferase

C, B, A

A, C, B

A, B, C

C, A, B

A

A, C, B

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6
Q

Glutamine synthetase is in the R state when Tyr397 is

deadenylated.

uridylated.

phosphorylated.

dephosphorylated.

A

deadenylated.

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7
Q

First messengers, but NOT second messengers

bind to a protein.

act as a transcription factor.

are located extracellularly.

are an allosteric effector.

A

are located extracellularly.

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8
Q

Estradiol is secreted by the ovaries, travels through the bloodstream, and interacts with estrogen receptors on breast epithelial cells. In this scenario estradiol is acting through which type of mechanism?

synacrine

paracrine

endocrine

autocrine

A

endocrine

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9
Q

What characteristic is true for both RTKs and GPCRs?

The receptor binds to intracellular proteins only when activated.

When activated, the receptor has enzymatic activity.

The receptor transmits ions.

The receptor undergoes a conformational change on activation.

A

The receptor undergoes a conformational change on activation.

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10
Q

Which of the following is a GTPase?

GB

Gy

Gsa

GBy

A

Gsa

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11
Q

The a subunit of trimeric G proteins can function to

regulate ion channels.

activate adenylate cyclase.

inhibit phospholipase A.

inhibit phosphodiesterase.

A

activate adenylate cyclase.

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12
Q

An estrogen-dependent breast cancer cell line is grown in a medium that contains estrogen. Cell proliferation is monitored over time. In a separate experiment, the cell line is grown in a medium that lacks estrogen but includes bisphenol A, a compound found in polycarbonate plastics. When monitored, cell proliferation is higher than in the presence of estrogen. A possible explanation of these results is that bisphenol A

inhibits the binding of estrogen to the estrogen receptor.

is an agonist of the estrogen receptor.

inhibits adenylate cyclase.

is toxic to the cell line.

A

is an agonist of the estrogen receptor.

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13
Q

Liver cells were monitored for changes in metabolic enzymatic activity after exposure to glucagon. The enzymes that showed changes in activity were then analyzed to assess if they had been covalently modified. Which of the following results were likely observed?

Enzymes that showed lower activity were not phosphorylated.

Enzymes that showed higher activity were methylated.

Enzymes that showed altered activity (higher or lower) were phosphorylated.

Enzymes that showed altered activity (higher or lower) were methylated.

A

Enzymes that showed altered activity (higher or lower) were phosphorylated.

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14
Q

If protein kinase A is activated in a liver cell in response to glucagon binding to the mc164-1.jpg2-adrenergic receptor, which of the following will result?

Glycogen synthesis will be turned on.

Glycogen degradation will be turned on.

Glucose synthesis will be turned off.

GLUT1 expression will be upregulated.

A

Glycogen degradation will be turned on.

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15
Q

Below is the molecular structure of a single bovine B-arrestin subunit. Two locations are indicated. What is most likely to interact with the protein at these locations?

B-ARK

GTP-boundG-a

dephosphorylated GPCR

phosphorylated GPCR

A

phosphorylated GPCR

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16
Q

Which of the following proteins contains an SH3 domain?

growth factor receptor-bound 2 (GRB2)

phosphoinositide-3 kinase (PI-3K)

SOS protein

RasGAP

A

growth factor receptor-bound 2 (GRB2)

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17
Q

On binding of an insulin molecule to the insulin receptor, a conformational change occurs that

increases the affinity of a second insulin binding site.

causes the dimerization of the receptor.

brings the L1 region of the mc167-1.jpg subunit closer to the membrane.

stimulates tyrosine autophosphorylation in the B subunits.

A

stimulates tyrosine autophosphorylation in the B subunits.

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18
Q

Caspases contain

phosphorylated tyrosines when activated.

death domains.

an active site cysteine residue.

SODD.

A

an active site cysteine residue.

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19
Q

Which protein is part of the TNF receptor–activated programmed cell death signaling pathway?

FADD

TRAF2

NFκB-inducing kinase

IKK

A

FADD

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20
Q

Place the following steps of the apoptotic pathway in their proper order.
A. CASP3 cleavage of cellular proteins
B. Cleavage of procaspase 8
C. Cleavage of procaspase 3
D. Assembly of DD and DED protein complexes

D, C, B, A

B C, A, D

D, B, C, A

D, C, A, B

A

D, B, C, A

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21
Q

Below shows the cell survival pathway promoted by TNF-a. A complex is indicated with a question mark. What is this complex?

inactive NFκB

active NFκB

active CASP3

NIK

A

active NFκB

22
Q

Which of the following acts as a transcription factor in the cell survival pathway activated by TNF-mc172-1.jpg?

p50:p65 complex

NIK:RIP complex

IκBa

IKK

A

p50:p65 complex

23
Q

Phosphorylation of which of the following is necessary for the increased expression of antiapoptotic genes?

RIP

TNF receptor

FADD

IKK

A

IKK

24
Q

Consider a mutation in procaspase 3 that changes Asp28 to an amino acid that is no longer a substrate for autocleavage. This mutant would

no longer be cleaved by caspase 8.

no longer obtain a quaternary structure.

be partially activated.

be fully activated.

A

be partially activated.

25
Q

This Zn2+-containing homodimer is part of

the glucocorticoid receptor.

PPARy-RXRma

TRADD.

the retinoic acid receptor.

A

the glucocorticoid receptor.

26
Q

The __________ domain functions as a protein–protein interaction module and is located in the cytoplasmic tail of TNF receptors.

death

SH2

SH3

RIP

A

death

27
Q

The result of TRADD proteins binding to TNF receptors is that

TRADD is phosphorylated.

an activated adaptor complex is formed.

downstream signaling proteins are inactivated.

TNF is degraded.

A

an activated adaptor complex is formed.

28
Q

Metabolism is best defined as a collection of

biochemical reactions that convert chemical energy into work.

biochemical reactions that convert mechanical energy into work.

enzymes that convert glucose into carbon dioxide.

enzymes that convert amino acids into proteins.

A

biochemical reactions that convert chemical energy into work.

29
Q

For the following reaction A→ B, if at equilibrium delta DG > 0, what can be said about the directionality of the reaction?

strongly favored in the forward direction

strongly favored in the reverse direction

strongly favored in both directions

Not enough information is given.

A

strongly favored in the reverse direction

30
Q

Which of the following pathways are found in both plants and animals?

photosynthesis and carbon fixation

urea cycle

nitrogen fixation

citrate cycle

A

citrate cycle

31
Q

Review the figure below. Shared intermediates are used so effectively in coupled reactions because they

allow products to diffuse through membrane to increase concentration gradient.

increase the value of mc181-2.jpg.

decrease the value of Q.

limit product diffusion and allow intermediates to channel from one enzyme to the next.

A

limit product diffusion and allow intermediates to channel from one enzyme to the next.

32
Q

Which of the following is an energy conversion pathway?

urea cycle

citrate cycle

nitrogen fixation and assimilation

fatty acid degradation and synthesis

A

citrate cycle

33
Q

A carbohydrate that reacts with oxidizing agents such as Cu+2 is called a(n) __________ sugar.

oxidizing

reducing

rentose

aldose

A

reducing

34
Q

Which of the following is NOT a reason why glycolysis is considered one of the core metabolic pathways in nature?

Glycolytic enzymes are hugely conserved among all living organisms.

It is a primary pathway for ATP generation under anaerobic conditions.

Metabolites of glycolysis are precursors for a large number of interdependent pathways.

It is a primary pathway for nitrogen generation.

A

It is a primary pathway for nitrogen generation.

35
Q

In which of the following metabolic conversions is ATP “consumed” during glycolysis?

1,3-Bisphosphoglycerate –> 3-phosphoglycerate

glucose –> glucose-6-phosphate

2-Phosphoglycerate –> 3-phosphoglycerate

glucose-6-phosphate –> fructose-6-phosphate

A

glucose –> glucose-6-phosphate

36
Q

How does phosphoglycerate kinase make glycolysis energy neutral at this step?

It uses ATP to produce 3-phosphoglycerate.

It produces 2 ATP along with 3-phosphoglycerate.

It results in a reaction at equilibrium.

It results in a reaction is endergonic.

A

It produces 2 ATP along with 3-phosphoglycerate.

37
Q

What advantage is there to phosphoglycerate kinase having an open and closed configuration?

It allows water to be trapped in the active site along with the substrate.

It forces covalent binding of the substrate to the enzyme active site.

The induced-fit mechanism maximizes accessibility of active site without sacrificing hydrophobic environment.

Changing of the configuration of the enzyme makes the reaction exergonic.

A

The induced-fit mechanism maximizes accessibility of active site without sacrificing hydrophobic environment.

38
Q

Using the table below, explain why glycolysis is an overall favorable reaction pathway.

Overall the pathway is delta G > 0.

Overall the pathway is delta G = 0.

Overall the pathway is delta G < 0.

Overall the pathway is delta G < 1.

A

Overall the pathway is delta G = 0.

39
Q

In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (delta G) of 23.8 kJ/mol. Under what conditions (encountered in erythrocytes) will the free-energy change (delta G) be negative, enabling the reaction to proceed to products?

The free-energy change will be negative if the concentrations of the two products are high relative to that of fructose 1,6-bisphosphate.

The reaction will not go to the right spontaneously under any conditions because the delta G is positive.

Under standard conditions, enough energy is released to drive the reaction to the right.

The free-energy change will be negative when there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.

A

The free-energy change will be negative when there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.

40
Q

Where in the body is glucokinase found?

small intestine

liver

heart

thyroid

A

liver

41
Q

If blood glucose levels are elevated, what does glucokinase do in response?

inhibits glycolysis

stimulates the production of more hexokinase

stimulates the release of insulin

inhibits production of 2,3-BPG

A

stimulates the release of insulin

42
Q

The rate limiting step can be defined as a level of enzyme activity that can be regulated to be __________ even when substrate levels are __________.

high; high

low; high

high; low

low; low

A

low; high

43
Q

In the presence of high concentrations of ADP and F6P, how does the equilibrium shift between the T state and R state of PFK-1? High concentrations of ADP and F6P

shift equilibrium to the R state.

shift equilibrium to the T state.

do not bind to PFK.

cancel each other out and have no effect.

A

shift equilibrium to the R state.

44
Q

Galactosemia is deficiency in which enzyme?

galactokinase

galactose-1-P uridyltransferase

UDP-galactose 4-epimerase

phosphoglucomutase

A

galactose-1-P uridyltransferase

45
Q

What would the effect be of a lack of lactate dehydrogenase?

buildup of glucose

buildup of CO2

deficiency of ATP

deficiency of pyruvate

A

deficiency of ATP

46
Q

When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase, the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate. Which one of the following statements is MOST correct, when applied to the reaction below (R = 8.315 J/mol·K and T = 298 K)?

Glucose 6-phosphate ↔ fructose 6-phosphate

delta G is +1.7 kJ/mol.

delta G is –1.7 kJ/mol.

delta G is zero.

It is not possible to calculate mc196-4.jpg

A

delta G is +1.7 kJ/mol.

47
Q

During glycolysis, the steps between glucose and formation of glyceraldehyde-3-phosphate

consume 2 ATP and 2 NADH.

consume 2 ATP.

produce 2 ADP and 2 NADH.

produce 2 ATP and 2 NADH.

A

consume 2 ATP.

48
Q

In two turns of the citrate cycle, how many electrons are transferred from the citrate cycle intermediates to NAD+ and FAD?

4

8

12

16

A

16

49
Q

The primary function of the citrate cycle is to oxidize

glucose.

pyruvate.

acetyl-CoA.

citrate.

A

acetyl-CoA.

50
Q

Which of the following is a reactant in the net reaction of the citrate cycle?

CO2

H2O

GTP

CoA

A

H2O

BIOCHEM (7 decks)

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