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Biochemistry > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

____ is the membrane protein that catalyzes the transition from ATP to cAMP.
G-protein
Insulin receptor
Protein kinase A
Phospholipase C
Adenylate cyclase

A

Adenylate cyclase

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2
Q

The inhibitor that binds only to the Enzyme-Substrate complex and lowers the Vmax and Km.
Allosteric
Non-competitive
Suicide
Uncompetitive
Competitive

A

Uncompetitive

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3
Q

True or False: Epinephrine stimulates glycogen synthesis

A

False

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4
Q

Some tumor cells become less sensitive to a range of drugs as they become resistant to only one drug because they:
Have more ATP-binding cassettes than other cells
Obtain the multidrug-resistance protein that transports different drugs from the cell.
Obtain the MDR ion channel that transports different drugs from the cell.
Obtain P-glycoprotein that transports different drugs inside the cell.
Have mutated the ATP-regulated chloride channel.

A

Obtain the multidrug-resistance protein that transports different drugs from the cell

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5
Q

Which of the following is true under the conditions: The enzyme concentration is 5 nM, the substrate concentration is 5 mM, and the Km is 5 uM.
The enzyme is saturated with substrate.
Most of the enzyme does not have substrate bond.
There is more enzyme than substrate.
None of the above.

A

The enzyme is saturated with substrate

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6
Q

Why does myoglobin not exhibit cooperativity?
It has high affinity to oxygen.
It has low affinity to oxygen.
It only has one subunit.
It is not an enzyme.

A

It only has one subunit

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7
Q

What should be the approximate length of a phospholipid molecule, considering the average thickness of membranes?
60 - 100 A.
10 A.
50 nm.
6 - 10 nm.
30 - 50 A.

A

30 - 50 A

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8
Q

The enzyme Hexokinase catalyzes the phosphorylation of 6-carbon sugars. The Km for hexokinase with glucose is 0.15 mM. The Km for hexokinase with fructose is 1.5 mM. Which substrate does hexokinase bind more strongly?
Fructose and glucose are both 6-carbon sugars, so hexokinase binds them equally strong.
Glucose.
Fructose.
There is not enough information provided.

A

Glucose

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9
Q

Enzymes that are activated by specific proteolytic cleavage are called ____.
Allosteric.
Zymogens.
Apoenzyme.
Heterozymes.
Isozymes.

A

Zymogens

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10
Q

What value of [S], as a fraction of Km is required to obtain 20% Vmax? [S] =
0.25 Km
0.2 Km
0.5 Km
0.75 Km
0.8 Km

A

0.25 Km

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11
Q

What can enzymes alter in reactions?
Reaction rate
Gibs free energy
Reaction equilibrium
Reaction rate
Substrate concentration
Equilibrium constant

A

Reaction rate

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12
Q

Which of the following is not correct concerning myoglobin?
The function of myoglobin is oxygen storage in muscle.
The iron of the heme group is in the Fe2+ oxidation state.
The globin chain contains an extensive alpha-helix structure.
The heme group is bound to the globin chain by 2 disulfide bonds to cysteine residues.

A

The heme group is bound to the globin chain by 2 disulfide bonds to cysteine residues.

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13
Q

Which of the following are NOT true of enzymes?
Enzymes use hydrophobic interactions in binding substrates.
All enzymes are proteins.
The catalytic activity of enzymes is often regulated.
Enzymes have great catalytic power.

A

All enzymes are proteins

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14
Q

Plasma membrane is selectively permeable, allowing certain molecules to cross the membrane, but not others. What are all the molecules that can cross plasma membrane through simple diffusion.
CO2.
Steroid hormones.
O2.
Amino acids.
K+.
Glucose.

A

CO2, steroid hormones, O2

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15
Q

Myglobin and the subunits of hemoglobin have:
Different primary structures, but very similar tertiary structures.
Very similar primary and tertiary structures.
Very different primary and tertiary structures.
No obvious structural relationship.
Very similar primary structures, but different tertiary structures.

A

Different primary structures, but very similar tertiary structures

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16
Q

G-protein coupled signaling always has these 3 components:
Nuclear receptor.
An effector enzyme in the plasma membrane.
7TM receptor.
Methylation of G-protein.
G-protein.
Receptor tyrosine kinase.
Internalization of the receptor.

A

Effector enzyme in the plasma membrane
7TM receptor
G-protein

17
Q

The mechanism by which insulin-signaling processes might be terminated includes
Protein dephosphorylation by phosphatases.
Change in temperature.
Degradation of insulin receptor.
Aggregation of all protein units.

A

Protein dephosphorylation by phosphatases

18
Q

What is unique about steroid receptor signaling?
It is the only system that does not use second messenger molecules.
It is the only signaling system that stimulates a change in gene expression.
It is the only system used for hormone signaling.
It is the only system that does not require phosphorylation
It is the only one of the signaling systems that has ligand receptors in the nucleus.

A

It is the only one of the signaling systems that has ligand receptors in the nucleus.

19
Q

Mark all the correct statements about the different type of enzyme inhibition:
Competitive inhibitors are often similar in chemical structure to the substrates of the inhibited enzyme.
Uncompetitive inhibition on the enzyme cannot be overcome by adding large amounts of substrate.
Competitive inhibition occurs when a substrate competes with an enzyme for binding to an inhibitor protein.
Competitive inhibition occurs when the substrate and the inhibitor compete for the same active site on the enzyme.
Noncompetitive inhibitors often bind to the enzyme irreversibly.

A

Competitive inhibitors are often similar in chemical structure to the substrates of the inhibited enzyme.
Competitive inhibition occurs when the substrate and the inhibitor compete for the same active site on the enzyme.
Uncompetitive inhibition on the enzyme cannot be overcome by adding large amounts of substrate.

20
Q

How can a reaction be described if it is exergonic?
Spontaneous
At equilibrium
With a positive free energy change
Required cofactor
Oxidation-reduction

A

Spontaneous

21
Q

True or False: Kcat varies with substrate concentration

A

False

22
Q

What type(s) of inhibition can be reserved?
All of the above
Competitive
Uncompetitive
Noncompetitive
None of the above

A

All of the above

23
Q

The structure of normal adult hemoglobin can be described as:
Tetramer composed of 2 alpha2 and 2 beta2 dimers.
Tetramer composed of 2 alpha2 and 2 gamma2 dimers.
Tetramer composed of 2 alpha beta dimers.
Tetramer composed of 4 myoglobin molecules.

A

Tetramer composed of 2 alpha2 and 2 beta2 dimers

24
Q

To what atom does oxygen bind in hemoglobin?
Fe2+
Fe3+
Mg2+
Ca2+
H+

A

Fe2+

25
Q

When the substrate concentration is much greater than Km, the rate of the reaction is almost equal to:
Vmax.
[S] + Km.
Vmax/2.
(Vmax/Km)[S].
Vmax.
Kcat.

A

Vmax.

26
Q

Which statement about membranes is true?
Most plasma membranes contain more than 70% proteins.
Cholesterol is common in plant cell plasma membranes.
The plasma membranes of all cell types within a particular organism have basically the same lipid and protein composition.
Cholesterol is common in bacterial plasma membranes.
Cholesterol is common in human cell plasma membranes.

A

Cholesterol is common in human cell plasma membanes.

27
Q

When activated, the insulin receptor results in the mobilization of ____ to the cell surface.
Glucose transporters.
cAMP.
G-proteins.
Phospholipids.
More insulin receptors.

A

Glucose transporters

28
Q

Which component of membranes provides their impermeability to polar molecules and ions?
Integral proteins.
Peripheral proteins.
Hydrophobic tails of phospholipids.
Hydrophilic heads of phospholipids.
Cholesterol.

A

Hydrophobic tails of phospholipids

29
Q

Which of the following is true?
Enzymes force reactions to proceed in only one direction.
Enzymes alter the equilibrium of the reaction.
Enzymes alter the standard free energy of the reaction.
All of the above.
None of the above.

A

None of the above

30
Q

In competitive inhibition, and inhibitor:
Binds covalently to the enzyme.
Binds only to the ES complex.
Binds reversibly at the active site.
Lowers the characteristic Vmax of the enzyme.
Binds at several different sites on an enzyme.

A

Binds reversibly at the active site

31
Q

What type of transport can proceed against a concentration gradient?
Passive transport.
Simple diffusion.
Facilitated diffusion.
Lateral diffusion.
Active transport.

A

Active transport

32
Q

What is the molecular basis for the (general) dependence of enzymatic activity on hydrogen ion concentration?
Brownian motion
Ionizable groups
Metal ions
Special cofactors
Disulfide bonds

A

Ionizable groups

33
Q

Alcohol dehydrogenase belongs to what class of enzyme?
Isomerases.
Oxydoreductases.
Transferases.
Ligases.
Hydrolases.

A

Oxydoreductases

34
Q

From the list below, the most fluid would be a bilayer made of lipids with:
Polyunsaturated 18-carbon fatty acids.
Polyunsaturated 16-carbon fatty acids.
One double bond in 18-carbon fatty acids.
Saturated 16-carbon fatty acids.
Saturated 18-carbon fatty acids.

A

Polyunsaturated 16-carbon fatty acids

35
Q

During the early stages of an enzyme purification protocol, when cells have been lysed by cytosolic components have not been separated, the reaction velocity versus substrate concentration is sigmoidal. As you continue to purify the enzyme, the curve shifts to the right. Explain your results.
This is an allosteric enzyme, but you must use a Lineweaver-Burk plot to determine Km and Vmax correctly.
This is an enzyme that displays Michaelis-Menten kinetics, but you must use a Lineweaver-Burk plot to determine Km and Vmax correctly.
This is an allosteric enzyme, and during purification you purify away one of the substrates.
This is an allosteric enzyme, and during purification you purify away a heterotrophic activator.
This is an enzyme that displays Michaelic-Menten kinetics, and you purify away a homotrophic inhibitor.

A

This is an allosteric enzyme, and during purification you purify away a heterotrophic activator.

36
Q

Name the enzyme that transfers a phosphoryl group between 2 compounds:
Phospholipase
Protein phosphotase
Ligase
Protein kinase
ATPase

A

Protein kinase

Biochemistry (18 decks)

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