Biochem Exam 1, 2, 3 multiple choice.

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1

The three-dimensional structure of macromolecules is formed and maintained primarily through
noncovalent interactions. Which one of the following is not considered a noncovalent interaction?

A) carbon-carbon bonds
B) hydrogen bonds
C) hydrophobic interactions
D) ionic interactions
E) van der Waals interactions

A) carbon-carbon bonds and peptide bongs

2

Which one of the following is not among the four most abundant elements in living organisms?

A) Carbon
B) Hydrogen
C) Nitrogen
D) Oxygen
E) Phosphorus

E) Phosphorus

3

Phosphoric acid is tribasic, with pKa's of 2.14, 6.86, and 12.4. The ionic form that predominates at pH 3.2 is:

A) H3PO4.
B) H2PO4-.
C) HPO42-.
D) PO43-.
E) none of the above.

B) H2PO4-.

4

Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________.

A) alanine; is a simple methyl group
B) glycine; is a hydrogen atom
C) glycine; is unbranched
D) lysine; contains only nitrogen
E) proline; forms a covalent bond with the amino group

B) glycine; is a hydrogen atom

5

The peptide alanylglutamylglycylalanylleucine has:

A) a disulfide bridge.
B) five peptide bonds.
C) four peptide bonds.
D) no free carboxyl group.
E) two free amino groups.

C) four peptide bonds.

6

Roughly how many amino acids are there in one turn of an alpha-helix?

A) 1
B) 2.8
C) 3.6
D) 4.2
E) 10

C) 3.6

7

A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-. The sequence is most probably part of a(n):

A) antiparallel B sheet.
B) parallel B sheet.
C) a helix.
D) a sheet.
E) B turn.

E) B turn.

8

The three-dimensional conformation of a protein may be strongly influenced by amino acid residues that are very far apart in sequence. This relationship is in contrast to secondary structure, where the amino acid residues are:

A) always side by side.
B) generally near each other in sequence.
C) invariably restricted to about 7 of the 20 standard amino acids.
D) often on different polypeptide strands.
E) usually near the polypeptide chain's amino terminus or carboxyl terminus.

B) generally near each other in sequence.

9

When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by:

A) one O atom and one amino acid atom.
B) one O2 molecule and one amino acid atom.
C) one O2 molecule and one heme atom.
D) two O atoms.
E) two O2 molecules.

B) one O2 molecule and one amino acid atom.

10

In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by:

A) Fe2+ binding.
B) heme binding.
C) oxygen binding.
D) subunit association.
E) subunit dissociation.

C) oxygen binding.

11

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

A) It binds at a distance from the heme groups of hemoglobin.
B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.
C) It increases the affinity of hemoglobin for oxygen.
D) It is an allosteric modulator.
E) It is normally found associated with the hemoglobin extracted from red blood cells.

C) It increases the affinity of hemoglobin for oxygen.

12

The role of an enzyme in an enzyme-catalyzed reaction is to:

A) bind a transition state intermediate, such that it cannot be converted back to substrate.
B) ensure that all of the substrate is converted to product.
C) ensure that the product is more stable than the substrate.
D) increase the rate at which substrate is converted into product.
E) make the free-energy change for the reaction more favorable.

D) increase the rate at which substrate is converted into product.

13

A biochemist is attempting to separate a DNA-binding protein (protein X) from other proteins in a solution. Only three other proteins (A, B, and C) are present. The proteins have the following properties:
pI(isoelectric Size Bind to
point) Mr DNA?
------------------------------------------
protein A 7.4 82,000 yes
protein B 3.8 21,500 yes
protein C 7.9 23,000 no
protein X 7.8 22,000 yes
------------------------------------------

What type of protein separation techniques might she use to separate
(a) protein X from protein A?
(b) protein X from protein B?
(c) protein X from protein C?

(a) size-exclusion (gel filtration) chromatography to separate on the basis of size;

(b) ion-exchange chromatography or isoelectric focusing to separate on the basis of charge;

(c) specific affinity chromatography, using immobilized DNA.

14

Which of these is a general feature of the lipid bilayer in all biological membranes?

A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer.
B) Individual lipid molecules in one face (monolayer) of the bilayer readily diffuse (flip-flop) to the other monolayer.
C) Polar, but uncharged, compounds readily diffuse across the bilayer.
D) The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules.
E) The polar head groups face inward toward the inside of the bilayer.

A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer.

15

The fluidity of the lipid side chains in the interior of a bilayer is generally increased by:

A) a decrease in temperature.
B) an increase in fatty acyl chain length.
C) an increase in the number of double bonds in fatty acids.
D) an increase in the percentage of phosphatidyl ethanolamine
E) the binding of water to the fatty acyl side chains.

C) an increase in the number of double bonds in fatty acids.

16

Facilitated diffusion through a biological membrane is:

A) driven by a difference of solute concentration.
B) driven by ATP.
C) endergonic.
D) generally irreversible.
E) not specific with respect to the substrate

A) driven by a difference of solute concentration.

17

Which of the following is not involved in the specificity of signal transduction?

A) Interactions between receptor and signal molecules
B) Location of receptor molecules
C) Structure of receptor molecules
D) Structure of signal molecules
E) Transmembrane transport of signal molecules by receptor molecules

E) Transmembrane transport of signal molecules by receptor molecules

18

What would be true for the signaling system in an animal cell that lacks the ability to produce GTP?

a. It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
b. It could activate only the epinephrine system
c. It would be able to carry out reception and transduction, but would not be able to respond to a signal
d. Only A and C are true
e. A,B, and C are true

d. A and C are true

19

Affinity chromatography is a method that can be used to purify cell-surface receptors, while they retain their hormone-binding ability. A ligand (hormone) for a receptor of interest is chemically linked to polystyrene beads. A solubilized preparation of membrane proteins is passed over a column containing these beads. Only the receptor binds to the beads.

When an excess of the ligand (hormone) is poured through the column after the receptor binding step, what do you expect will occur?

A) The ligand will attach to those beads that have the receptor and remain on the column.
B) The ligand will cause the receptor to be displaced from the beads and eluted out.
C) The ligand will attach to the bead instead of the receptor.
D) The ligand will cause the bead to lose its affinity by changing shape.
E) The reaction will cause a pH change due to electron transfer.

The ligand will cause the receptor to be displaced from the beads and eluted out.

20

Affinity chromatography is a method that can be used to purify cell-surface receptors, while they retain their hormone-binding ability. A ligand (hormone) for a receptor of interest is chemically linked to polystyrene beads. A solubilized preparation of membrane proteins is passed over a column containing these beads. Only the receptor binds to the beads.

This method of affinity chromatography would be expected to collect which of the following?

A) molecules of the hormone
B) molecules of purified receptor
C) G proteins
D) assorted membrane proteins
E) hormone-receptor complexes

B) molecules of purified receptor

21

An inhibitor of phosphodiesterase activity would have which of the following effects?

a. block the response of epinephrine
b. decrease the amount of cAMP in the cytoplasm
c. block the activation of G proteins in response to epinephrine binding to its receptor
d. prolong the effect epinephrine by maintaining elevated cAMP levels in the cytoplasm
e. block the activation of protein kinase A

d. prolong the effect epinephrine by maintaining elevated cAMP levels in the cytoplasm

22

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who hasrecently consumed coffee would have increased levels of:

A) phosphorylated proteins.
B) GTP.
C) cAMP.
D) adenylyl cyclase.
E) activated G proteins.

C) cAMP.

23

Starch and glycogen are both polymers of:

A) fructose.
B) glucose1-phosphate.
C) sucrose.
D) alpha-D-glucose.
E) beta-D-glucose.

D) alpha-D-glucose.

24

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

A) Amylose is unbranched; amylopectin and glycogen contain many (alpha1--> 6) branches.
B) Both are homopolymers of glucose.
C) Both serve primarily as structural elements in cell walls.
D) Both starch and glycogen are stored intracellularly as insoluble granules.
E) Glycogen is more extensively branched than starch.

C) Both serve primarily as structural elements in cell walls.

25

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

A) asparagine, serine, or threonine.
B) aspartate or glutamate.
C) glutamine or arginine.
D) glycine, alanine, or aspartate.
E) tryptophan, aspartate, or cysteine.

A) asparagine, serine, or threonine.

26

Which one of the following statements about gluconeogenesis is false?

A) For starting materials, it can use carbon skeletons derived from certain amino acids.
B) It consists entirely of the reactions of glycolysis, operating in the reverse direction.
C) It employs the enzyme glucose 6-phosphatase.
D) It is one of the ways that mammals maintain normal blood glucose levels between meals.
E) It requires metabolic energy (ATP or GTP).

B) It consists entirely of the reactions of glycolysis, operating in the reverse direction.

27

6. Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial
preparation that is oxidizing pyruvate as a substrate, which of the following compounds would you expect to
decrease in concentration?

A) Citrate
B) Fumarate
C) Isocitrate
D) Pyruvate
E) Succinate

B) Fumarate