Prelim 1 Questions

Question 1

When the temperature falls, Bacillus subtilis can adapt its membrane fluidity by:

A. the enzymatic conversion of unsaturated to saturated fatty acid chains in membrane phospholipids
B. modification of DesR, which prevents expression of a lipid desaturase
C. expression of an uncoupler protein to increase cell temperature
D. catalyzing the conversion of cholesterol into deoxycholesterol
E. synthesizing an enzyme to increase levels of unsaturated fatty acid chains in membrane phospholipids

Answer 1

E. synthesizing an enzyme to increase levels of unsaturated fatty acid chains in membrane phospholipids

Question 2

What is TRUE about transporters that use an alternating access mechanism?

A. They can move substrates against a concentration gradient (from low to high) in the absence of an energy input
B. They function in import of solutes but not in export
C. They bind their substrate on one face of the membrane, and then the entire protein-substrate complex flips over to release substrate to the other side
D. Substrates pass through a hydrophobic channel that spans the membrane
E. They bind solute on one face of the membrane, and then the protein changes shape to allow release to the other side

Answer 2

E. They bind solute on one face of the membrane, and then the protein changes shape to allow release to the other side

Question 3

Plant cells maintain a proton-gradient across the cell membrane. Import of sucrose (a sugar) is mediated by a sucrose-proton symporter. Which treatment will most directly increase the rate of sucrose import?

A. increasing H⁺ concentration inside cells
B. adding an uncoupler to reduce PMF
C. decreasing extracellular pH
D. decreasing extracellular sucrose concentration

Answer 3

C. decreasing extracellular pH

Question 4

Biological membranes form a semipermeable barrier between the cell interior and the environment. In cells, specific transport proteins do NOT function to increase the movement of:

A. Water (H₂O)
B. CO₂
C. Glucose
D. bicarbonate (HCO₃⁻)
E. Sodium ion (Na⁺)

Answer 4

B. CO₂

Question 5

The sodium-potassium ATPase is considered an electrogenic pump because it:

A. transports equal numbers of Na⁺ and K⁺ ions in opposite directions
B. uses a Na⁺ gradient to power import of ATP
C. is an active transporter that generates a charge gradient
D. uses passive transport to exchange Na⁺ for K⁺
E. catalyzes redox reactions to generate an electrical gradient

Answer 5

C. is an active transporter that generates a charge gradient

Question 6

Phospholipids form a lipid bilayer membrane in water because

A. clustering of fatty acid tails (on phospholipids) allows favorable hydrophobic interactions
B. polar head groups form a hydrogen-bonded network with each other and water
C. the positively charged choline groups make ionic bonds with negatively charged phosphate
D. integral membrane proteins confer membrane integrity
E. cholesterol forms favorable interactions that hold the phospholipids together

Answer 6

A. clustering of fatty acid tails (on phospholipids) allows favorable hydrophobic interactions

Question 7

A plant is growing in your dorm room, and you turn out the lights. As a result, the plant will immediately stop the production of:

A. CO₂
B. O₂ and CO₂
C. O₂ and NADH
D. O₂
E. NADH and NADPH

Answer 7

D. O₂

Question 8

In muscle cells during exercise, glycolysis converts one glucose (C₆H₁₂O₆) into 2 pyruvate. When oxygen is depleted, what happens to most of the pyruvate?

A. it is oxidized by NADH to regenerate NAD⁺
B. it is reduced by NADH to lactate to regenerate NAD⁺
C. it reacts with pyruvate dehydrogenase to form acetyl-CoA and CO₂
D. it is decarboxylated to acetaldehyde and then reduced
E. it is reduced by NAD⁺ to lactate to regenerate NADH

Answer 8

B. it is reduced by NADH to lactate to regenerate NAD⁺

Question 9

A molecule that functions as an uncoupler is added to plant cells and collapses the proton gradients present across membranes in both the chloroplast (thylakoid membrane) and mitochondrion. The most immediate effect of this chemical uncoupler will be:

A. more rapid consumption of CO₂ and faster oxidation of NADH
B. an increase in the production of O₂
C. a reduction in ATP synthesis
D. a rapid decrease in the production of O₂
E. a reduction in the production of CO₂

Answer 9

C. a reduction in ATP synthesis

Question 10

Glycolysis is conventionally divided into an initial energy investment phase dependent on _______ and an energy payoff phase dependent upon ________, with a net yield of two ATPs per glucose.

A. ATP, NAD⁺
B. ATP, substrate-level phosphorylation
C. active transport, kinases
D. glucose isomerization, oxidation of NADH
E. glucokinase, F₁F₀ ATPase

Answer 10

B. ATP, substrate-level phosphorylation

Question 11

Which of the following is a FALSE statement about electron transport chains?

A. electrons pass through a series of electron carriers in the membrane and, in the process, a proton gradient is generated across the membrane
B. electron transport chains are used in both aerobic and anaerobic respiration
C. NADH or FADH₂ can serve as electron donors
D. in plants, high energy electrons can be generated from a special pair of chlorophyll molecules using energy from light
E. in human mitochondria, nitrate can serve as an alternate electron acceptor when O₂ levels fall

Answer 11

E. in human mitochondria, nitrate can serve as an alternate electron acceptor when O₂ levels fall

Question 12

Halobacterium salinarum is a red-colored, halophilic (salt-loving) member of the Archaea that gets energy from light. This process depends on:

A. carotenoids and chlorophyll
B. a sodium ion gradient
C. rubisco
D. the oxygen-evolving complex
E. bacteriorhodopsin

Answer 12

E. bacteriorhodopsin

Question 13

In land plants, the generation of NADPH results most directly from:

A. high energy electrons from the reaction center of photosystem I
B. the activity of the F₁F₀ ATPase
C. donor energy transfer between accessory pigments and chlorophyll
D. cyclic photophosphorylation
E. the activity of Rubisco in the Calvin cycle

Answer 13

A. high energy electrons from the reaction center of photosystem I

Question 14

In land plants, photosystem II contains a ‘special pair’ of chlorophyll molecules (the P₆₈₀ reaction center) that become oxidized when excited by light energy to generate high energy electrons. The function of light harvesting complexes is to:

A. generate NADPH
B. generate O₂ to support respiration
C. allow absorption of more light energy
D. provide electrons to replace those lost by excitation of the reaction center

Answer 14

C. allow absorption of more light energy

Question 15

Threonine deaminase is the first enzyme in a five-step pathway to make the amino acid isoleucine. When isoleucine levels are high, isoleucine binds to threonine deaminase away from the active site to reduce its catalytic activity. This is an example of:

A. allosteric activation
B. negative cooperativity
C. competitive inhibition
D. allosteric inhibition
E. positive feedback

Answer 15

D. allosteric inhibition

Question 16

Which of the following steps in aerobic respiration produce carbon dioxide?

A. glycolysis from glucose to pyruvate
B. substrate-level phosphorylation
C. conversion of pyruvate to acetyl-CoA
D. ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
E. oxidation of NADH by the electron transport chain

Answer 16

C. conversion of pyruvate to acetyl-CoA

Question 17

The amino acids L-alanine (L-Ala) and D-alanine (D-Ala) are isomers and have the same free energy (G). In our food, nearly all Ala is the L-isomer, but Bacteria in our gut need D-Ala to make cell walls. What statement is TRUE about the reaction catalyzed by the enzyme Alanine Racemase?

A. The reaction L-Ala → D-Ala is spontaneous when L-Ala is in excess, so there is no need for alanine racemase
B. Alanine racemase uses NAD⁺ as a cofactor
C. At equilibrium, the concentration of D-Ala is much greater than L-Ala
D. Starting with high L-Ala (L-Ala&raquo_space; D-Ala), the reaction L-Ala → D-Ala is exergonic
E. Alanine racemase binds to L-Ala but not to D-Ala

Answer 17

D. Starting with high L-Ala (L-Ala&raquo_space; D-Ala), the reaction L-Ala → D-Ala is exergonic

Question 18

What is NOT a mechanism used by enzymes in a yeast cell growing on glucose by aerobic respiration?

A. Enzymes lower the activation energy required to convert substrates to products
B. ATP hydrolysis is used to help drive otherwise unfavorable reactions
C. Pyruvate is decarboxylated to acetaldehyde and then reduced to ethanol
D. ATP is generated by substrate-level phosphorylation
E. Some enzymes use cofactors like NAD⁺ or FAD in redox reactions

Answer 18

C. Pyruvate is decarboxylated to acetaldehyde and then reduced to ethanol

Question 19

Which of the following statements about a healthy human gut microbiota is FALSE? The gut microbiota…

A. help prevent colonization by pathogens
B. synthesize enzymes to degrade cellulose fibers in plant material
C. can synthesize vitamins
D. help to maintain intestinal barrier function
E. contains many hundreds of different types of bacteria

Answer 19

B. synthesize enzymes to degrade cellulose fibers in plant material

Question 20

In cyanobacteria, O₂ can inactivate ______ by reaction with ______, and also act as a competitive inhibitor of ________.

A. rubisco, metal centers, nitrogenase
B. nitrogenase, metal centers, rubisco
C. the oxygen-evolving complex, manganese,
D. leghemoglobin
leghemoglobin, heme, rubisco
E. nitrogenase, heme, cytochrome-c oxidase

Answer 20

B. nitrogenase, metal centers, rubisco

Question 21

Some plants express leghemoglobin to lower the local concentration of O₂ gas. This benefits the plant because:

A. it provides a more favorable environment for symbiotic Rhizobium species
B. it reduces the levels of reactive oxygen species that damage chloroplasts
C. it stores O₂ for later use by mitochondria
D. it functions as a carbon-concentration mechanism
E. it increases the efficiency of CO₂ fixation by rubisco

Answer 21

A. it provides a more favorable environment for symbiotic Rhizobium species

Question 22

The insect respiratory system is distinct from mammals because:

A. insects directly aerate their tissues using fine tubules (tracheoles)
B. myoglobin stores O₂ for later use in insects
C. circulating hemoglobin in insects has positive cooperativity in O₂-binding
D. a one-way flow of air prevents mixing of new and stale air in insects
E. counter-current exchange increases the efficiency of gas exchange in insects

Answer 22

A. insects directly aerate their tissues using fine tubules (tracheoles)

Question 23

Which of the following is a FALSE statement about nitrogen fixation?

A. fixation of N₂ into ammonium requires energy from ATP
B. nitrogen fixation is only observed inside some bacterial and archaeal cells
C. nitrogen fixation in some cyanobacteria occurs in specialized cells (heterocysts)
D. plant cells produce nitrogenase enzyme in response to Nod factors
E. fixation of N₂ into ammonium in the rhizosphere can benefit plant growth

Answer 23

D. plant cells produce nitrogenase enzyme in response to Nod factors

Question 24

The enzyme carbonic anhydrase (CA) catalyzes the reversible reaction:

CO₂ + H₂O ↔ H₂CO₃

Which reaction or process does NOT benefit from CA activity?

A. Use of CO₂ as a substrate for Rubisco in the Calvin cycle
B. Efficient release of CO₂ into the alveoli during mammalian respiration
C. Conversion of CO₂ from respiring tissues into carbonic acid and then bicarbonate for transport to the lungs
D. Reduction of water concentration inside cells exposed to hypertonic solutions

Answer 24

D. Reduction of water concentration inside cells exposed to hypertonic solutions

Question 25

Complete the statement: In pregnant women, there is a 30% increase in the allosteric regulator 2,3-bisphosphoglycerate (2,3-BPG) which ________, and the fetus expresses fetal hemoglobin which ___________.

A. reduces the positive cooperativity of O₂ binding; binds 2,3-BPG as an allosteric activator
B. decreases O₂ affinity for maternal hemoglobin; is much less sensitive to 2,3-BPG
C. acts as a competitive inhibitor of O₂-binding to the heme; binds heme more tightly
D. travels into the fetus to increase oxygen binding; is activated by 2,3-BPG
E. has a high affinity for maternal hemoglobin; binds O₂ with negative cooperativity

Answer 25

B. decreases O₂ affinity for maternal hemoglobin; is much less sensitive to 2,3-BPG