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XX. BioChemistry > EXAM 2 > Flashcards

EXAM 2 Flashcards

1
Q

Which of the following is correct about enzymes?
A. Most of them are RNA molecules, but a few are proteins
B. Most of them exhibit a lower degree of specificity than non-biologic catalysts
C. Most of them exhibit a lower catalytic power than non-biologic catalysts
D. Most of them act under mild conditions

A

D. Most of them act under mild conditions

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2
Q

The ratio of catalyzed rate/uncatalyzed rate is known as:
A. Catalytic activity
B. Rate enhancement
C. Enzyme efficiency
D. Catalytic power

A

B. Rate enhancement

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3
Q

Which of the following is incorrect about the enzyme chymotrypsin?
A. It catalyzes the addition of water across a double bond
B. It is known as a serine protease
C. Artificial substrates are used to monitor the reaction catalyzed by the enzyme
D. It is classified as a hydrolase

A

A. It catalyzes the addition of water across a double bond

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4
Q

The reaction below is catalyzed by:
A. Pyruvate carboxylase
B. Acetaldehyde decarboxylase
C. Pyruvate decarboxylase
D. None of these

A

C. Pyruvate decarboxylase

The name of the reaction is pyruvate carboxylase

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5
Q

The reaction shown below is catalyzed by a:
A. Hydrolase
B. Oxidoreductase C. Transferase
D. Isomerase

A

A. Hydrolase

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6
Q

Which of the following is correct about enzymes?
A. They increase the activation energy of a reaction
B. They do not alter a reaction’s free energy change
C. They affect a reaction’s free energy change
D. They do not have an effect on the activation energy of a reaction

A

B. They do not alter a reaction’s free energy change

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7
Q

Which of the following is correct about enzyme cofactors?
A. They are amino acids that are essential for enzyme activity
B. They can be metal ions or coenzymes
C. All of them are inorganic compounds
D. They are non-amino acid substances that
are not essential for enzyme activity

A

B. They can be metal ions or coenzymes

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8
Q

Which of the following catalytic mechanisms involves the use of a nucleophile?
A. Metal ion catalysis
B. Covalent catalysis
C. Acid catalysis
D. Base catalysis

A

B. Covalent catalysis

The nucleophile belongs to the enzyme and forms a covalent bond with the substrate

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9
Q

Which of the following amino acids cannot participate in acid-base catalysis?
A. Serine
B. Histidine
C. Tyrosine
D. Alanine

A

D. Alanine
nonpolar

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10
Q

Which of the following amino acids cannot participate in covalent catalysis?
A. Serine
B. Histidine
C. Tyrosine
D. Leucine

A

D. Leucine
nonpolar

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11
Q

Which of the following is incorrect about the mechanism below?
A. Serine acts as a nucleophile
B. Aspartate holds His in the proper orientation
C. Histidine acts as an acid
D. None; all are incorrect

A

C. Histidine acts as an acid

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12
Q

Which of the following is incorrect about the mechanism below?
A. Histidine acts as a base
B. Aspartate holds His in the proper orientation
C. The (-) charge of O is stabilized by the oxyanion hole
D. None; all are correct

A

A. Histidine acts as a base

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13
Q

A conformational change in an enzyme upon binding of a substrate is called:
A. Lock and key fit
B. Catalytic change
C. Induced fit
D. Substrate induction

A

C. Induced fit

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14
Q

Which of the following is incorrect about chymotrypsin, trypsin, and elastase?
A. They have similar amino acid sequences
B. They have similar tertiary structures
C. They have similar substrate specificity
D. They catalyze the same reaction
(i.e. hydrolysis of peptide bond)

A

C. They have similar substrate specificity

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15
Q

Which of the following is incorrect?
A. Proteases are synthesized in the form of inactive precursors called zymogens
B. Activation of zymogens requires the removal of peptides
C. Trypsin is the zymogen of trypsinogen
D. Chymotrypsinogen is the zymogen of chymotrypsin

A

C. Trypsin is the zymogen of trypsinogen

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16
Q

Which of the following is incorrect about an enzyme-catalyzed reaction?
A. Its progress can be expressed as the velocity of the disappearance of substrate
B. Its progress can be expressed as the velocity of the formation of product
C. Reaction velocity is usually expressed as change in [substrate] or [product] with time
D. None; all the other choices are correct

A

D. None; all the other choices are correct

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17
Q

Which of the following is correct about the velocity of an enzyme-catalyzed reaction?
A. The more enzyme present, the slower the reaction
B. The rate of the reaction does not change when changing the [enzyme]
C. The rate of the reaction will double if [enzyme] is doubled
D. None; all the other choices are incorrect

A

C. The rate of the reaction will double if [enzyme] is doubled

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18
Q

Which of the following is correct about the Michaelis-Menten plot?
A. The x-axis is reaction velocity B. The y-axis is [enzyme]
C. It has a hyperbolic shape
D. It has a sigmoidal shape

A

C. It has a hyperbolic shape

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19
Q

Which of the following is the correct value of the KM?
A. It is half of the Vmax
B. It is [substrate] at Vmax
C. It is [substrate] at half Vmax
D. It is half [enzyme]

A

C. It is [substrate] at half Vmax

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20
Q

Which of the following represents the “steady-state” assumption?
A. That [S] decreases linearly
B. That [ES] has a constant value
C. That [E] has a constant value
D. That [P] increases linearly

A

B. That [ES] has a constant value

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21
Q

Which of the following is incorrect about the “initial velocity” assumption?
A. Reaction is monitored for the first few minutes
B. Product is not allowed to accumulate
C. Reverse reaction of the second step is ignored
D. Reverse reaction of the first step is ignored

A

D. Reverse reaction of the first step is ignored

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22
Q

Which of the following is incorrect about the catalytic constant, kcat?
A. It is also known as the turnover number
B. It indicates how fast an enzyme operates
after it has bound its substrate
C. It corresponds to be the same as the rate
constant of forward reaction of 2nd step
D. None; all the other choices are correct

A

D. None; all the other choices are correct

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23
Q

Which of the following is incorrect about the Lineweaver-Burk plot?
A. The y-axis is the reciprocal of the velocity
B. The x-axis is the reciprocal of [E]
C. It has a linear shape
D. None; all the other choices are correct

A

B. The x-axis is the reciprocal of [E]

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24
Q

Which of the following enzyme- catalyzed reactions follow the Michaelis-Menten kinetics?
A. Reactions with multiple substrates and products
B. Reactions proceeding via multiple steps
C. Reactions catalyzed by allosteric enzymes
D. Reactions with a single substrate and product

A

D. Reactions with a single substrate and product

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25
Q

Which of the following is incorrect about allosteric enzymes?
A. They are monomeric enzymes
B. They exhibit cooperative behavior C. Their activity can be regulated
D. They are multimeric enzymes

A

A. They are monomeric enzymes

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26
Q

Which of the following is incorrect about a sigmoidal plot?
A. It shows the effect of cooperative substrate binding
B. It is a plot of the initial velocity versus [substrate]
C. It shows that the KM value is lower than in the hyperbolic plot
D. It describes the kinetics of allosteric enzymes

A

C. It shows that the KM value is lower than in the hyperbolic plot

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27
Q

Which of the following is incorrect about enzyme inhibitors?
A. Some bind reversibly
B. The so-called suicide inhibitors bind irreversibly
C. All inhibitors form a covalent bond with the enzyme
D. Some bind irreversibly

A

C. All inhibitors form a covalent bond with the enzyme

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28
Q

Which of the following is incorrect about the competitive inhibitors?
A. They are structurally similar to the substrate
B. They increase the affinity of the enzyme for the substrate
C. They increase KM
D. They do not affect Vmax

A

B. They increase the affinity of the enzyme for the substrate

29
Q

Which of the following is incorrect about the non-competitive inhibitors?
A. They are structurally different than the substrate
B. They do not affect the affinity of the enzyme for the substrate
C. They do not affect KM
D. They do not affect Vmax

A

D. They do not affect Vmax

30
Q

Which of the following is incorrect about the transition state analogs?
A. They can be better inhibitors than substrate analogs
B. They are synthetic compounds
C. They are not as effective inhibitors as the substrate analogs
D. They resemble the proposed transition state for the reaction

A

C. They are not as effective inhibitors as the substrate analogs

31
Q

All of the following are mechanisms for regulating enzyme activity in the cell, except:
A. Allosteric feedback inhibition
B. Rate of enzyme synthesis at the gene level
C. Covalent modification like phosphorylation
D. Changes in pH

A

D. Changes in pH

32
Q

Which of the following type of fatty acid will have the lowest boiling point?
A. Saturated
B. Monounsaturated
C. Polyunsaturated

A

C. Polyunsaturated

33
Q

Which of the following is incorrect about the fatty acid shown below?
A. It is polysaturated
B. It is an omega 3
C. It is not monounsaturated
D. It is an omega 9
E. It is an omega 6

A

A. It is polysaturated

34
Q

Which of the following type of lipid is shown below?
A. Triacylglycerol
B. Glycerophospholipid
C. Sphingophospholipid
D. Wax
E. Steroid

A

A. Triacylglycerol

35
Q

Which of the following type of lipid is shown below?
A. Triacylglycerol
B. Glycerophospholipid
C. Sphingophospholipid
D. Wax
E. Steroid

A

B. Glycerophospholipid

36
Q

Which of the following type of lipid is shown below?
A. Triacylglycerol
B. Glycerophospholipid
C. Sphingophospholipid
D. Wax
E. Steroid

A

D. Wax

37
Q

Which of the following type of lipid is shown below?
A. Triacylglycerol
B. Glycerophospholipid
C. Sphingophospholipid
D. Wax
E. Steroid

A

C. Sphingophospholipid

38
Q

Which of the following type of lipid is shown below?
A. Triacylglycerol
B. Glycerophospholipid
C. Sphingophospholipid
D. Wax
E. Steroid

A

E. Steroid

39
Q

Which of the following is incorrect about the lipid shown below?
A. It’s called a fat
B. It’s liquid at room temperature
C. Most of its acyl chains are saturated
D. None; all the other choices are correct

A

B. It’s liquid at room temperature

40
Q

Which of the following is incorrect about signaling pathways?
A. A ligand carrying a signal binds specifically to the receptor
B. Ligand-receptor interaction triggers some kind of response inside the cell
C. Ligands carrying the signals are usually called hormones
D. The ligand always enters the cell

A

D. The ligand always enters the cell

41
Q

Which of the following is incorrect?
A. Receptor-ligand binding is described by a hyperbolic plot
B. Ligands bind to receptors with a characteristic affinity (Kd)
C. Kd is the [ligand] when half of the receptors have bound ligand
D. Kd is the [ligand] when all the receptors have bound ligand

A

D. Kd is the [ligand] when all the receptors have bound ligand

42
Q

A ligand that binds to a receptor and elicits a biological effect is known as a(n):
A. Agonist
B. Antagonist
C. Effector
D. Activator

A

A. Agonist

43
Q

Which of the following is incorrect about the G protein signaling pathways?
A. They involve the G protein-coupled receptors (GPCR)
B. Ligand binding to receptor activates the G protein
C. The G protein-coupled receptors are known as 7TM receptors
D. The G protein activates a kinase that catalyzes the formation of ATP

A

D. The G protein activates a kinase that catalyzes the formation of ATP

44
Q

Which of the following is incorrect?
A. Epinephrine (adrenaline) is a ligand of the G protein signaling pathway
B. The G protein cycle describes the activation/inactivation of the G protein
C. The G protein is composed of three subunits
D. A major target of activated G protein is ATP synthase

A

D. A major target of activated G protein is ATP synthase

45
Q

The second messenger in the G protein signaling pathway is:
A. GDP
B. Cyclic AMP
C. ATP
D. GTP
E. Cyclic GMP

A

B. Cyclic AMP

46
Q

Which of the following is incorrect?
A. Protein kinase A (PKA) is activated by the second messenger
B. Inactive protein kinase A (PKA) is a tetramer
C. Protein kinase A (PKA) has catalytic subunits
D. Protein kinase A (PKA) has regulatory subunits
E. None; all the other choices are correct

A

E. None; all the other choices are correct

47
Q

Phosphorylations catalyzed by protein kinase A (PKA) can be reversed by:
A. Phospholipases
B. Protein phosphatases
C. Proteases
D. Protein phosphorylases

A

B. Protein phosphatases

48
Q

What is the correct classification of fructose?
A. Aldohexose
B. Aldopentose
C. Ketohexose
D. Ketopentose

A

C. Ketohexose

49
Q

What type of linkage is found in the disaccharide below?
A. α-(1,4)
B. β -(1,4)
C. α-(1,6)
D. β -(1,6)

A

C. α-(1,6)

50
Q

Which of the following is incorrect about carbohydrates?
A. They have the molecular formula (CH2O)n
B. They are called sugars or saccharides
C. Some are poly-hydroxylated aldehydes
D. Some are poly-hydroxylated ketones
E. Their names end in -ase

A

E. Their names end in -ase

51
Q

Which of the following is incorrect about carbohydrates?
A. They have the molecular formula (CH2O)n
B. They are called sugars or saccharides
C. Some are poly-hydroxylated aldehydes
D. Some are poly-hydroxylated ketones
E. Their names end in -ase

A

E. Their names end in -ase

52
Q

Which of the following is not a monosaccharide derivative?
A. Fructose-6-phosphate B. Glucosamine
C. Galactose
D. Glucose-1-phosphate E. 2-Deoxyribose

A

C. Galactose

53
Q

A monosaccharide with 5 C atoms and an aldehyde functional group is classified as a(n):
A. Pentaldose
B. Ketopentose
C. Aldopentose
D. Aldohexose
E. Pentaldolase

A

C. Aldopentose

54
Q

The D enantiomer of glucose has the –OH group of:
A. C #5 (i.e. chiral C farthest to C=O group) is pointing to the left side
B. C #5 (i.e. chiral C farthest to C=O group) is pointing to the right side
C. C #2 (i.e. chiral C closest to C=O group) is pointing to the right side
D. C #2 (i.e. chiral C closest to C=O group) is pointing to the left side

A

B. C #5 (i.e. chiral C farthest to C=O group) is pointing to the right side

55
Q

Which of the following is incorrect?
A. The cyclization of a monosaccharide generates the alpha and beta anomers
B. The cyclization of a monosaccharide involves an attack of a –OH group to the C of a C=O group
C. The alpha and beta anomers can interconvert
D. Haworth projections are used to show the cyclic forms of monosaccharides
E. The alpha anomer has the –OH attached to C #1 pointing up

A

E. The alpha anomer has the –OH attached to C #1 pointing up

56
Q

Which of the following is incorrect for a monosaccharide if its anomeric C is not linked to another molecule?
A. It can be oxidized
B. It can reduce Cu(II) to Cu(I)
C. It is called a reducing sugar
D. None; all the other choices are correct

A

D. None; all the other choices are correct

57
Q

What is the correct classification of fructose?
A. Aldohexose
B. Aldopentose
C. Ketohexose
D. Ketopentose

A

C. Ketohexose

58
Q

What type of linkage is found in the disaccharide below?
A. α-(1,4)
B. β -(1,4)
C. α-(1,6)
D. β -(1,6)

A

C. α-(1,6)

59
Q

Which of the following is incorrect about carbohydrates?
A. They have the molecular formula (CH2O)n
B. They are called sugars or saccharides
C. Some are poly-hydroxylated aldehydes
D. Some are poly-hydroxylated ketones
E. Their names end in -ase

A

E. Their names end in -ase

60
Q

Which of the following is not a monosaccharide derivative?
A. Fructose-6-phosphate B. Glucosamine
C. Galactose
D. Glucose-1-phosphate E. 2-Deoxyribose

A

C. Galactose (forms lactose)

61
Q

A monosaccharide with 5 C atoms and an aldehyde functional group is classified as a(n):
A. Pentaldose
B. Ketopentose
C. Aldopentose
D. Aldohexose
E. Pentaldolase

A

C. Aldopentose

62
Q

The D enantiomer of glucose has the –OH group of:
A. C #5 (i.e. chiral C farthest to C=O group) is pointing to the left side
B. C #5 (i.e. chiral C farthest to C=O group) is pointing to the right side
C. C #2 (i.e. chiral C closest to C=O group) is pointing to the right side
D. C #2 (i.e. chiral C closest to C=O group) is pointing to the left side

A

B. C #5 (i.e. chiral C farthest to C=O group) is pointing to the right side

63
Q

Which of the following is incorrect?
A. The cyclization of a monosaccharide generates the alpha and beta anomers
B. The cyclization of a monosaccharide involves an attack of a –OH group to the C of a C=O group
C. The alpha and beta anomers can inter-convert
D. Haworth projections are used to show the cyclic forms of monosaccharides
E. The alpha anomer has the –OH attached to C #1 pointing up

A

E. The alpha anomer has the –OH attached to C #1 pointing up (should be down - cellulose is B(1->4) pointing up)

64
Q

Which of the following is incorrect for a monosaccharide if its anomeric C is not linked to another molecule?
A. It can be oxidized
B. It can reduce Cu(II) to Cu(I)
C. It is called a reducing sugar
D. None; all the other choices are correct

A

D. None; all the other choices are correct

65
Q

Which of the following is incorrect for a monosaccharide if its anomeric C is not linked to another molecule?
A. It can be oxidized
B. It can reduce Cu(II) to Cu(I)
C. It is called a reducing sugar
D. None; all the other choices are correct

A

D. None; all the other choices are correct

66
Q

Which of the following is incorrect?
A. Starch is a polymer of glucose
B. Starch provides structural support to plants
C. Glycogen is a storage form of glucose in animals
D. The unbranched form of starch
(amylose) has only alpha (1,4) glycosidic bonds
E. The branched form of starch
(amylopectin) has alpha (1,6) glycosidic bonds at the branching points

A

B. Starch provides structural support to plants

67
Q

Which of the following is incorrect about cellulose?
A. It is a polymer of glucose
B. Its residues are linked by alpha (1,4) glycosidic bonds
C. It is unbranched
D. It plays a structural role in plants E. It can form many intra- and inter
-chain H-bonds

A

B. Its residues are linked by alpha (1,4) glycosidic bonds

68
Q

Which of the following is incorrect about glycoproteins?
A. They are proteins that have attached carbohydrates (usually oligosaccharides)
B. The carbohydrate chains can be attached to the N atom in the side chain of Asn
C. The carbohydrate chains can be attached to the O atom in the side chain of Ser
D. The carbohydrate chains can be attached to the S atom in the side chain of Met

A

D. The carbohydrate chains can be attached to the S atom in the side chain of Met

69
Q

Which of the following is incorrect?
A. Proteoglycans are very large linear polysaccharides attached to proteins
B. Peptidoglycans are polysaccharide chains cross-linked with peptides
C. Peptidoglycans are found in bacterial walls
D. Proteoglycans are not found in bacterial walls
E. None; all the other choices are correct

A

E. None; all the other choices are correct

XX. BioChemistry (15 decks)

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