Midterm II

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Molecular Biology of the Cell
Chapters 3, 8, 10-13, 16, 19
updated 3 months ago by Jonathan_Miranda
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1

During the elongation phase of protein synthesis

A) an initiator tRNA carrying methionine binds at P-site of the small ribosomal subunit.

B) translation initiation factors guide small ribosomal subunit to the mRNA and assist tRNA-ribosome in locating start site.

C) elongation factor EF-Tu provides opportunities for proofreading of the codon–anticodon match.

D) release factor binds and initiates the addition of water to the polypeptide.

C

2

Proteins are synthesized starting at the

A) 5’ end of the protein.

B) N-terminus of the protein.

C) 3’ end of the protein.

D) C-terminus of the protein.

B

3

Which of the following is NOT required for initiation of protein synthesis?

A) the mRNA start codon AUG

B) release factor binding at the aminoacyl-tRNA site

C) ATP

D) GTP

B

4

Proteins are

A) branched polymers of amino acids.

B) chains of amino acids held together by interactions between amino groups.

C) 3-dimensional structures made of 2 or more polypeptides.

D) unbranched polymers of amino acids.

D

5

a-helices are

A) a tertiary structure of proteins.

B) commonly found in fibroin, a silk protein.

C) a coiled amino acid polymer, with the R groups on the outside.

D) a quaternary structure of proteins in which 2 or more polypeptides are coiled together.

C

6

Secondary structures of proteins are stabilized by

A) covalent bonds between R groups of amino acids.

B) hydrogen bonds between amino acids polypeptide backbone.

C) ionic interactions between subunits.

D) peptide bonds between R groups of amino acids.

B

7

Peptide bonds are

A) ionic bonds between an amino group and a carboxyl group.

B) are flexible and destabilize secondary structure of polypeptides.

C) link amino acids in the primary structure of a polypeptide.

D) covalent bonds that link one peptide to another.

C

8

Which proteins have a quaternary structure?

A) NADH dehydrogenase and myoglobin

B) NADH dehydrogenase and hemoglobin

C) myoglobin and hemoglobin

D) All proteins have quaternary structure.

B

9

Sickle cell anemia is

A) due to multiple amino acid substitutions.

B) due to protein aggregation.

C) affects myoglobin.

D) due to a change in the amino acid sequence of both a- and b-subunits of hemoglobin.

B

10

Tertiary protein structure is stabilized by

A) only weak noncovalent interactions between R groups.

B) many covalent interactions and fewer weak noncovalent interactions.

C) many weak noncovalent interactions and fewer covalent interactions.

D) only covalent interactions between R groups.

C

11

Which of the following statements is FALSE?

A) The 3-dimensional structure of a protein dictates its function by determining its binding specificity for the molecules (ligands) that the protein interacts with.

B) Allosteric modulators are ligands that bind competitively to the protein active site.

C) Protein interactions with their ligands are specific and display molecular complementarity.

D) Changes in the amino acid sequence of a protein can decrease binding of a ligand.

B

12

Which of the following statements about enzymes is TRUE?

A) Catalysis of an energetically unfavorable reaction by an enzyme will enable that reaction to occur.

B) Enzymes decrease the activation energy of a reaction.=

C) An enzyme can be a polymer of monosaccharides.

D) Enzymes are permanently altered after catalyzing a reaction.

B

13

Which of the following is NOT a protein function?

A) converting the chemical energy stored in ATP into mechanical work

B) recognizing foreign particles in the body

C) transmitting signals

D) storing genetic information

D

14

Which of the following is NOT a molecular motor?

A) α-synuclein

B) myosin

C) dynein

D) kinesin

A

15

Enzymes

A) bind tightly to their substrates.

B) have only a single substrate and a single product.

C) have an active site where enzyme activity is regulated.

D) None is true.

D

16

Which of the following is NOT a way in which cells regulate enzyme activity?

A) allostery

B) phosphorylation/GTP binding

C) changing amino acid sequence of the protein

D) location of enzymes; co-locating enzymes that contribute to the same pathway

C

17

In the allosteric regulation of protein activity

A) binding of a regulatory molecule at the active site alters protein activity.

B) binding of a molecule at the regulatory site may increase or decrease protein activity.

C) binding of a co-enzyme increases protein activity.

D) binding of the substrate at an auxiliary site increases protein activity.

B

18

The first of 3 major steps in the breakdown of cellular fuel is

A) the Krebs cycle.

B) the production of acetyl CoA from sugars

C) the breakdown of macromolecules (like polysaccharides and fats) into monomeric subunits (like monosaccharides and fatty acids).

D) None is correct.

C

19

The advantage to the cell of the gradual oxidation of glucose during glycolysis and the Krebs cycle compared with oxidation to CO2 and H2O in a single step is

A) more free energy is released for a given amount of glucose oxidized

B) energy can be extracted in usable amounts.

C) less CO2 is produced for a given amount of glucose oxidized.

D) less O2 is required for a given amount of glucose oxidized.

B

20

Acetyl CoA

A) is oxidized to CO2 and NADH/FADH2 through the Krebs cycle.

B) is an electron carrier.

C) is a form of cellular energy because it has a phosphate group.

D) contains about 7.4 kcal/mol.

A

21

Oxidation-reduction reactions

A) are key to metabolism because they generate ATP by phosphorylating ADP

B) oxidize electrons.

C) occur together because electrons are conserved in a chemical reaction.

D) consume molecular oxygen.

C

22

Which of the following is NOT true of ATP?

A) ATP is a stable molecule; its hydrolysis is favored but does not occur spontaneously

B) ATP is energetically expensive to synthesize and is made only in mitochondria

C) ATP is often called the energy currency of the cell

D) ATP is similar to an adenine nucleotide

B

23

Glycolysis is a sequence of 10 metabolic reactions in which glucose is oxidized to generate

A) Pyruvate and NAD+.

B) Acetyl CoA and NADH.

C) Pyruvate and NADH.

D) Acetyl CoA and NAD+.

C

24

Which of the following are NOT products of the Krebs cycle?

A) NADH and FADH2

B) GTP

C) CO2

D) ATP

D

25

Which of the following is NOT an electron acceptor/carrier that participates in the mitochondrial electron transport chain?

A) cytochrome

B) ubiquinone

C) rhodopsin

D) iron-sulfur center

C

26

Which of the following statements about complex I of the electron transport chain is TRUE?

A) It receives electrons from NADH, passes them to ubiquinone, and all electrons that contribute to ATP synthesis must pass through it.

B) It receives electrons from FADH2, passes them to ubiquinone, and contains heme proteins.

C) It receives electrons from NADH, passes them to cytochrome c, and does not pump protons (H+).

D) It receives electrons from NADH, passes them to ubiquinone, and pumps protons (H+).

D

27

Which of the following statements about ATP synthase is TRUE?

A) It is a transmembrane protein and an enzyme.

B) It is the final electron acceptor in the electron transport chain.

C) Protons pass through it from the matrix into the cytosol.

D) It catalyzes a substrate-level phosphorylation.

A

28

Skunk cabbage and mammalian neonates can generate significant heat in their mitochondria

A) because both have thermogenin in their mitochondria.

B) because both have proteins in the inner mitochondrial membranes that uncouple proton (H+) flow from ATP synthesis.

C) because both have a futile loop that synthesizes ATP and then allows it to hydrolyze without capturing energy.

D) because both are inefficient.

B

29

ATP synthesis occurs

A) because a chemical potential (a difference in pH) is created across the outer mitochondrial membrane between cytoplasm and intramembrane space.

B) because an electrical potential (a difference in ionic charge) is created across the inner mitochondrial membrane between the intramembrane space and the matrix.

C) through osmosis.

D) when electrons are transferred from NADH/FADH2 to ADP so that a third phosphate group can be added

B

30

Photophosphorylation produces _________ and _________.

A) H2O; ADP

B) O2; NADH

C) O2; ATP

D) NADH; ATP

C

31

Which of the following statements about the carbon fixation cycle is FALSE?

A) In the initial reaction of the cycle rubisco catalyzes a carboxylation: CO2 and H2O are incorporated into 3-phosphoglycerate.

B) The cycle outputs glyceraldehyde 3-phosphate, which is either converted to starch and fat in the chloroplast stroma, or transported out of the chloroplast into the cytosol.

C) The cycle consumes numerous ATPs and requires the oxidation of FADH2 as a source of electrons.

D) The cycle is also known as the dark reactions of photosynthesis

C

32

Proteins must be sorted and transported from their site of synthesis to the intracellular compartment that is their site of function. Which of the following is NOT a mechanism for protein sorting?

A) gated passage through specialized pores

B) transmembrane insertion by virtue of a signal sequence

C) post-translational transport by virtue of protein unfolding

D) transport inside vesicles with specialized docking proteins

C

33

Transport through nuclear pores

A) is unidirectional from the nucleus to the cytosol.

B) requires a nuclear signal sequence, a receptor, and GTP.

C) occurs in the unfolded conformation so protein can be threaded through the elaborate structure of the nuclear pore.

D) requires nuclear signal sequences that are amino acid sequences at the C-terminal end of the protein.

B

34

Which of the following statements about nuclear signal sequences is FALSE?

A) nuclear localization signal (NLS) signals import of cytoplasmic proteins to the nucleus

B) nucleus export signal (NES) signals export of protein from the nucleus

C) an NLS or NES can be a continuous linear sequence at the end of a protein or a patch of the 3D structure composed of amino acids from different parts of the primary structure

D) None is false.

D

35

Mitochondrial proteins

A) are synthesized inside the mitochondria, because it has its own genome.

B) are synthesized in the cytosol and transported into mitochondria in a folded state.

C) pass easily through the outer mitochondrial membrane, which is a very porous membrane that allows most molecules to pass through.

D) are transported unfolded by a process that requires ATP and chaperones.

D

36

Which of the following statements about transport of proteins to the endoplasmic reticulum (ER) is FALSE?

A) It always occurs while the protein is being synthesized (co-translationally) by special ribosomes capable of docking on the ER.

B) An N-terminal sequence of amino acids (the ER signal sequence) directs the protein into the ER.

C) During co-translational transport, a signal recognition particle (SRP) docks the ribosome on the SRP receptor.

D) During co-translational transport, the SRP is displaced as the ribosome transfers to the translocation channel and the growing protein is extruded into the ER lumen.

A

37

Transport of proteins into mitochondria

A) requires expenditure of ATP at the inner and outer mitochondrial membranes.

B) requires expenditure of GTP at the inner and outer mitochondrial membranes.

C) requires expenditure of GTP only at the inner mitochondrial membrane.

D) requires expenditure of ATP only at the inner mitochondrial membrane.

A

38

Which of the following is NOT a function of cell membranes?

A) maintain distinct compartments with distinct chemistry

B) sense changes in the environment through membrane receptors

C) regulate movement of materials across the membrane

D) restrict cell size and movement

D

39

In addition to being fluid and impermeable to water-soluble solutes, cell membranes are

A) stable and uniform

B) stable and asymmetrical

C) stable and rigid

D) rigid and asymmetricaL

B

40

Membrane lipids include:

A) phospholipids, sphingolipids, and cholesterol

B) phospholipids, glycoproteins, and cholesterol

C) phosphates, sphingolipids, and cholesterol

D) phospholipids, glycolipids, and sterols

A

41

Phospholipids spontaneously form bilayer membranes and vesicles in solution because

A) their hydrophobic fatty acid tails associate.

B) they are lipids.

C) their hydrophilic head groups associate.

D) Phospholipids do not spontaneously form bilayer membranes and vesicles in solution.

A

42

Where, in a eukaryotic cell, does most new membrane synthesis take place?

A) in the Golgi complex

B) in the endoplasmic reticulum (ER)

C) in the plasma membrane

D) in the mitochondria

B

43

Which of the following statements about membrane fluidity is FALSE?

A) Increasing the proportion of fatty acids with unsaturated hydrocarbon tails in a lipid bilayer increases membrane fluidity.

B) Decreasing temperature would decrease membrane fluidity if plants and animals did not remodel their membranes to maintain fluidity.

C) Increasing the proportion of cholesterol in membranes decreases membrane stiffness.

D) Increasing the proportion of fatty acids with shorter hydrocarbon tails increases membrane fluidity.

C

44

Lipid rafts are

A) collections of proteins on the outer surface of the plasma membrane, associated with the membrane through non-covalent interactions.

B) regions within the plasma membrane where lipid density is high and protein density is low.

C) regions within the plasma membrane where cholesterol and protein density is high.

D) regions of the plasma membrane that are stiffened by high density of long-tailed phospholipids.

C

45

Which of the following is NOT a possible function of membrane proteins?

A) act as a receptor

B) provide catalysis as an enzyme

C) act as an anchor

D) convert the chemical energy stored in ATP into membr

D