Exam 2 - multi

Question 1

An allosteric interaction between a ligand and a protein is one in which:

Select one:

a. binding of the ligand to the protein is covalent.
b. binding of a molecule to a binding site affects binding of additional molecules to the same site.
c. two different ligands can bind to the same binding site.
d. binding of a molecule to a binding site affects binding properties of another site on the protein.
e. multiple molecules of the same ligand can bind to the same binding site

Answer 1

d. binding of a molecule to a binding site affects binding properties of another site on the protein.

Question 2

An individual molecular structure within an antigen to which an individual antibody binds is as a(n):

Select one:

a. antigen.
b. epitope.
c. Fab region.
d. MHC site.
e. Fc region

Answer 2

b. epitope.

Question 3

Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship. In each case, the single intermediate is the ES complex.

Reaction coordinates
PICTURE

Select one:

a. The activation energy for the uncatalyzed reaction is given by #5 + #6 in (a) and by #7 + #4 in (b).
b. (a) describes a strict “lock and key” model, whereas (b) describes a transition-state complementarity model.
c. The activation energy for the catalyzed reaction is #5 in (a) and is #7 in (b).
d. The ES complex is given by #2 in (a) and #3 in (b).

Answer 3

b. (a) describes a strict “lock and key” model, whereas (b) describes a transition-state complementarity model.

Question 4

Enzymes are potent catalysts because they:

Select one:

a. lower the activation energy for the reactions they catalyze.
b. drive reactions to completion while other catalysts drive reactions to equilibrium.
c. are very specific and can prevent the conversion of products back to substrates.
d. are consumed in the reactions they catalyze.
e. increase the equilibrium constants for the reactions they catalyze.

Answer 4

a. lower the activation energy for the reactions they catalyze.

Question 5

From the abbreviated name of the compound Gal(Beta1 to 4)Glc, we know that:

Select one:

a. the glucose is in its pyranose form.
b. C-4 of glucose is joined to C-1 of galactose by a glycosidic bond.
c. the compound is a D-enantiomer.
d. the galactose residue is at the reducing end.
e. the glucose residue is the alpha anomer.

Answer 5

b. C-4 of glucose is joined to C-1 of galactose by a glycosidic bond.

Question 6

In DNA sequencing by the Sanger (dideoxy) method:

Select one:

a. specific enzymes are used to cut the newly synthesized DNA into small pieces, which are then separated by electrophoresis.
b. the template DNA strand is radioactive.
c. the role of the dideoxy CTP is to occasionally terminate enzymatic synthesis of DNA where Gs occur in the template strands.
d. the dideoxynucleotides must be present at high levels to obtain long stretches of DNA sequence.
e. radioactive dideoxy ATP is included in each of four reaction mixtures before enzymatic synthesis of complementary strands.

Answer 6

c. the role of the dideoxy CTP is to occasionally terminate enzymatic synthesis of DNA where Gs occur in the template strands.

Question 7

In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues:

Select one:

a. glutamine or arginine.
b. glycine, alanine, or aspartate.
c. tryptophan, aspartate, or cysteine.
d. aspartate or glutamate.
e. asparagine, serine, or threonine.

Answer 7

e. asparagine, serine, or threonine.

Question 8

In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:

Select one:

a. hyperbolic.
b. anabolic
c. linear with a positive slope.
d. random.
e. sigmoidal

Answer 8

a. hyperbolic.

Question 9

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as

Reaction

Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression:

Select one:

a. k1 ([Et] + [ES])[S].
b. k2 [ES].
c. k-1 [ES].
d. k1 ([Et] / [ES]).
e. k-1 [ES] + k2 [ES].

Answer 9

e. k-1 [ES] + k2 [ES].

Question 10

Monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies:

Select one:

a. are synthesized only in living organisms.
b. are produced by cells from the same organism that produced the antigen.
c. have only a single polypeptide chain that can recognize an antigen.
d. are synthesized in a population of identical or “cloned” cells.
e. are labeled with chemicals that can be visualized.

Answer 10

d. are synthesized in a population of identical or “cloned” cells.

Question 11

Of the 20 standard amino acids, only glycine is not optically active. Its optical activity ceased when it was subjected to low pH. Gaining optical activity for this amino acid can be achieved by:

Select one:

a. increasing the pH
b. decreasing the pH
c. Hydrogenation of this amino acid
d. neutralization of the low pH by addition of sodium hydroxide
e. Methylation of this amino acid

Answer 11

e. Methylation of this amino acid

Question 12

The alkaline hydrolysis of RNA does not produce:

Select one:

a. 2’- AMP.
b. 3’,5’-cAMP.
c. 3’-UMP.
d. 2’,3’-cGMP.
e. 2’-CMP.

Answer 12

b. 3’,5’-cAMP.

Question 13

The DNA oligonucleotide abbreviated pATCGAC:

Select one:

a. violates Chargaff’s rules.
b. has an A at its 3’ end.
c. has 7 phosphate groups.
d. has a hydroxyl at its 3’ end.
e. has a phosphate on its 3’ end.

Answer 13

d. has a hydroxyl at its 3’ end.

Question 14

The interactions of ligands with proteins:

Select one:

a. are relatively rare in biological systems.
b. are usually transient.
c. usually result in the inactivation of the proteins.
d. are relatively nonspecific.
e. are usually irreversible.

Answer 14

b. are usually transient.

Question 15

The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA:

Select one:

a. are susceptible to alkaline hydrolysis.
b. are uncharged at neutral pH.
c. always link A with T and G with C.
d. join the 3’ hydroxyl of one nucleotide to the 5’ hydroxyl of the next.
e. form between the planar rings of adjacent bases.

Answer 15

d. join the 3’ hydroxyl of one nucleotide to the 5’ hydroxyl of the next.

Question 16

The reference compound for naming D and L isomers of sugars is:

Select one:

a. ribose.
b. glyceraldehyde.
c. sucrose.
d. glucose.
e. fructose.

Answer 16

b. glyceraldehyde.

Question 17

Vmax for an enzyme-catalyzed reaction:

Select one:

a. generally increases when pH increases.
b. increases in the presence of a competitive inhibitor.
c. is twice the rate observed when the concentration of substrate is equal to the Km.
d. is unchanged in the presence of an uncompetitive inhibitor.
e. is limited only by the amount of substrate supplied.

Answer 17

c. is twice the rate observed when the concentration of substrate is equal to the Km.

Question 18

When two carbohydrates are epimers:

Select one:

a. they differ in length by one carbon.
b. one is a pyranose, the other a furanose.
c. they rotate plane-polarized light in the same direction.
d. one is an aldose, the other a ketose.
e. they differ only in the configuration around one carbon atom.

Answer 18

e. they differ only in the configuration around one carbon atom.

Question 19

Which of following is an anomeric pair?

Select one:

a. Alpha-D-glucose and Beta-L-glucose
b. D-glucose and D-fructose
c. D-glucose and L-glucose
d. D-glucose and L-fructose
e. Alpha-D-glucose and Beta-D-glucose

Answer 19

e. Alpha-D-glucose and Beta-D-glucose

Question 20

Which of the following deoxyoligonucleotides will hybridize with a DNA containing the sequence (5’)AGACTGGTC(3’)?

Select one:

a. (5’)CTCATTGAG(3’)
b. (5’)GAGTCAACT(3’)
c. (5’)GACCAGTCT(3’)
d. (5’)TCTGGATCT(3’)
e. (5’)TCTGACCAG(3’)

Answer 20

c. (5’)GACCAGTCT(3’)

Question 21

Which of the following is a heteropolysaccharide?

Select one:

a. Chitin
b. Starch
c. Glycogen
d. Cellulose
e. Hyaluronate

Answer 21

e. Hyaluronate

Question 22

Which of the following is a palindromic sequence?

Select one:
a. GAATCC
CTTAGG
b. CCTTCC
GCAAGG
c. GTATCC
CATAGG
d. AGGTCC
TCCAGG
e. GGATCC
CCTAGG

Answer 22

e. GGATCC

CCTAGG

Question 23

Which of the following is not a reducing sugar?

Select one:

a. Ribose
b. Glyceraldehyde
c. Sucrose
d. Glucose
e. Fructose

Answer 23

c. Sucrose

Question 24

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?

Select one:

a. It is normally found associated with the hemoglobin extracted from red blood cells.
b. It binds at a distance from the heme groups of hemoglobin.
c. It increases the affinity of hemoglobin for oxygen.
d. It is an allosteric modulator.
e. It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.

Answer 24

c. It increases the affinity of hemoglobin for oxygen.

Question 25

Which of the following is not true of all naturally occurring DNA?

Select one:

a. Deoxyribose units are connected by 3’,5’-phosphodiester bonds.
b. The ratio A+T/G+C is constant for all natural DNAs.
c. The two complementary strands are antiparallel.
d. The amount of A always equals the amount of T.
e. Two hydrogen bonds form between A and T.

Answer 25

b. The ratio A+T/G+C is constant for all natural DNAs.

Question 26

Which of the following pairs is interconverted in the process of mutarotation?

Select one:

a. Alpha-D-glucose and Beta-D-glucose
b. D-glucose and D-galactose
c. D-glucose and D-glucosamine
d. D-glucose and D-fructose
e. D-glucose and L-glucose

Answer 26

a. Alpha-D-glucose and Beta-D-glucose

Question 27

Which of the following parts of the IgG molecule are not involved in binding to an antigen?

Select one:

a. Fab
b. Fc
c. Variable domain
d. Light chain
e. Heavy chain

Answer 27

b. Fc

Question 28

Which of the following polysaccharides cannot be digested by mammalian salivary, gastric, or pancreatic enzymes?

Select one:

a. Amylose
b. starch
c. amylopectin
d. cellulose
e. Glycogen

Answer 28

d. cellulose

Question 29

Which of the following statements about cysteine is correct?

Select one:

a. Cysteine can form a peptide linkage with other two cysteines.
b. Cysteine is formed by the oxidation of the carboxylic acid group on cysteine.
c. Cysteine is an example of a nonstandard amino acid
d. Cysteine forms when the CH2-SH R group is oxidized to form a CH2-S-S-CH2- disulfide bridge between two cysteines.

Answer 29

a. Cysteine can form a peptide linkage with other two cysteines.

Question 30

Which of the following statements about protein-ligand binding is correct?

Select one:

a. The larger the Ka (association constant), the weaker the affinity.
b. The larger the Ka, the smaller the Kd (dissociation constant).
c. The Ka is independent of such conditions as salt concentration and pH.
d. The larger the Ka, the faster the binding.
e. The Ka is equal to the concentration of ligand when all of the binding sites are occupied.

Answer 30

b. The larger the Ka, the smaller the Kd (dissociation constant).

Question 31

Which of the following statements about starch and glycogen is false?

Select one:

a. Both starch and glycogen are stored intracellularly as insoluble granules.
b. Both serve primarily as structural elements in cell walls.
c. Glycogen is more extensively branched than starch.
d. Amylose is unbranched; amylopectin and glycogen contain many (alpha 1 to 6) branches.
e. Both are homopolymers of glucose.

Answer 31

b. Both serve primarily as structural elements in cell walls.

Question 32

Which of these statements about enzyme-catalyzed reactions is false?

Select one:

a. If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor.
b. The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax.
c. At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration.
d. The rate of a reaction decreases steadily with time as substrate is depleted.
e. The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction.

Answer 32

e. The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction.

Question 33

Which one of the following is true of the pentoses found in nucleic acids?

Select one:

a. The bond that joins nitrogenous bases to pentoses is an O-glycosidic bond.
b. The pentoses are always in the beta-furanose forms.
c. C-5 and C-1 of the pentose are joined to phosphate groups.
d. The straight-chain and ring forms undergo constant interconversion.
e. C-5 of the pentose is joined to a nitrogenous base, and C-1 to a phosphate group.

Answer 33

b. The pentoses are always in the beta-furanose forms.

Question 34

Which one of the following statements is true of enzyme catalysts?

Select one:

a. They lower the activation energy for the conversion of substrate to product.
b. They increase the equilibrium constant for a reaction, thus favoring product formation.
c. To be effective they must be present at the same concentration as their substrates.
d. They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates.
e. They bind to substrates, but are never covalently attached to substrate or product.

Answer 34

a. They lower the activation energy for the conversion of substrate to product.