BIL255 Exam 2

Intermediate filaments are found in_________. nuclear lamina extracellular matrix intestinal lumen organelle membranes

nuclear lamina FEEDBACK: Intermediate filaments form a meshwork that consititutes the nuclear lamina to provide support to the nucleus.

Kinesin and dynamin transport organelles in_________. the same direction opposite direction the same direction depending on the microtubule composition none of the above

opposite direction FEEDBACK: Kinesin and dynamin transport organelles in opposite direction.

Microtubule growth dynamics are important to________. maintain a stable cytosolic environment precisely target organelles to the same location within the cytosol respond to changes that require rapid reorientation of the cell attach microtubules to desmosomes

respond to changes that require rapid reorientation of the cell FEEDBACK: Microtubule growth dynamics are important to respond to changes that require rapid reorientation of the cell.

If a reaction is energetically favorable (exergonic), then it must produce a(n) a) increase in entropy. b) decrease in heat. c) increase in activation energy. d) decrease in reaction time.

a) increase in entropy FEEDBACK: Reactions that are energetically favorable increase the entropy (or disorder) of the universe. This can be through either the release of free energy in different forms, or the release of energy as heat (energy in its most disordered form).

In an enzymatic reaction, a molecule gains an electron. This is known as a(n) ___________ reaction. a) reduction b) oxidation c) hydrogenation d) electronegative

a) reduction FEEDBACK: Gain of electrons by a molecule is called reduction; loss of electrons is called oxidation.

What is gluconeogenesis? a) the synthesis of glucose from pyruvate b) the mobilization of glucose from glycogen stores c) the production of glucose from starch d) the blockage of glycolysis at the first step

a) the synthesis of glucose from pyruvate

What is the value of ΔG at equilibrium? a) zero b) positive c) negative d) It depends on the concentration of substrates and products.

a) zero FEEDBACK: When equilibrium is reached, the forward and reverse reactions are equal, so there is no net change in the number of reactants and products. The reaction does not proceed forward or backward at this point and ΔG is equal to zero.

Microtubules extend from organizing centers in the cell. Which is an example of an organizing center? a. basal body of a cilium b. centromere of a chromosome c. nuclear periphery d. vesicle membrane

a. basal body of a cilium FEEDBACK: Microtubules grow from organizing centers that are found in different cell components. In the base of a cilium, a basal body acts as an organizing center for microtubules to grow into the cilia. Another example is the centrosomes from which the microtubules of mitotic spindle grow.

Microtubules are inherently unstable unless they are a. bound to GTP, which forms a cap at the plus end. b. stabilized by minus end attachment. c. bound to kinesin. d. assembled in the nucleus.

a. bound to GTP, which forms a cap at the plus end. FEEDBACK: Microtubules undergo dynamic growing and shrinking from their (+) ends to explore the cell. If the end is capped by GTP because it cannot hydrolyze to GDP fast enough, then microtubule is growing and doesn't retract.

The layered membrane organization in mitochondria and other tissues is a means to_________ to trap ions that would normally diffuse more rapidly. reduce the chemical gradient. increase the surface area to increase the efficiency of biological processes. to increase proton number during electron transfer.

increase the surface area to increase the efficiency of biological processes.

Epidermolysis bullosa simplex is a disease by which________. neurofilaments are mutated keratin filaments are mutated the vimentin structure is changed All of the above

keratin filaments are mutated FEEDBACK: Epidermolysis bullosa simplex is a disease by which the genes, Keratin 5 and Keratin 14 are mutated.

Which of the following represents the placement of microtubules in an epithelial cell? A B C none of these

B (spider looking one) FEEDBACK: Microtubules extend from organizing centers to locations throughout the cytoplasm and internally in the cell. Actin filaments are most concentrated in the cell cortex, whereas intermediate filaments are also located throughout the interior of the cell but are not nucleated from particular locations.

Intermediate filaments are polarized. True False

False FEEDBACK: Intermediate filaments contain a C and N-terminus on both sides and therefore are not considered to have a polar orientation.

ATP synthase harnesses protons from the electron transport chain to make ATP. True False

True

Mitochondria and Chloroplasts make energy by generating a proton gradient that drives the formation of ATP True False

True

Why do cells use enzymes to harvest energy from food molecules rather than by direct oxidation? a) Enzymes transfer energy from food to carrier molecules in small steps. b) Enzymes release all the energy from food molecules in a single efficient step. c) Direct oxidation cannot release all the energy from food molecules. d) Direct oxidation is energetically unfavorable.

a) Enzymes transfer energy from food to carrier molecules in small steps.

(Q009) Which of the following has the lowest electron affinity? a) NADH dehydrogenase complex b) oxygen c) cytochrome c reductase complex d) cytochrome c oxidase complex

a) NADH dehydrogenase complex FEEDBACK: The passage of electrons along the complexes of the electron-transport chain is energetically favorable because electrons are passed from a complex that has a lower electron affinity to one with a higher electron affinity. Thus, the complex with the lowest affinity is the first complex, NADH dehydrogenase complex.

Why is the oxidation of NADPH energetically favorable? a) The oxidized form of NADPH is more stable than the reduced form. b) NADPH is the form of the molecule that can gain two high-energy electrons. c) The biosynthetic reactions that are coupled to NADPH oxidation are energetically favorable. d) Oxidation of NADPH breaks a high-energy phosphoanhydride bond.

a) The oxidized form of NADPH is more stable than the reduced form. FEEDBACK: NADPH carries two high-energy electrons. Losing these electrons in an oxidation reaction is energetically favorable because the oxidized form, NADP+, is more stable than the reduced form (NADPH).

Reactions that build larger molecules in the cell are called ___________; reactions that break down molecules into smaller ones are called ___________. a) anabolic; catabolic b) catabolic; anabolic c) anabolic; metabolic d) metabolic; anabolic

a) anabolic; catabolic FEEDBACK: Metabolism is the sum total reactions in a cell, which are of two types. Catabolic reactions are the reactions where cells break down the large molecules in foodstuffs into their constituent building blocks. Anabolic reactions are biosynthetic—they build larger molecules from smaller building blocks.

(Q020) In oxidative phosphorylation in mitochondria, high-energy electrons are transferred to the electron-transport chain from activated carriers like NADH. Stage 1 of photosynthesis also uses an electron-transport chain to pump protons and make ATP. In this case, where do the high-energy electrons come from? a. chlorophyll b. NADPH c. FADH2 d. ADP

a. chlorophyll FEEDBACK: The first stage of photosynthesis produces ATP and NADPH using an electron-transport chain, proton pumping, and ATP synthesis just as in oxidative phosphorylation. However, the high-energy electrons come from the chlorophyll special pair that has captured energy from sunlight and transfers it via electron carrier to the electron-transport chain.

Which of the following actin-binding proteins promote filopodia formation? a. formins b. formins and profilin c. thymosin and profilin d. thymosin and ARPs

a. formins FEEDBACK: The formation of actin filaments is regulated by many proteins in the cell. The polymerization of actin is inhibited by the binding of thymosin and profilin to actin monomers. On the other hand, the polymerization of actin is promoted by ARPs and formins.

At the leading edge of a cell, ARP proteins help form new branches on actin filaments to push the leading edge forward using the force of the polymerization, as shown in the figure below. What type of structure is being formed? a. lamellipodium b. filopodium c. actopodium d. All of the above

a. lamellipodium FEEDBACK: ARPs promote the formation of a web consisting of branched actin filaments, called a lamellopodium, at the cell's leading edge to promote migration.

The products generated in the citric acid cycle are a) pyruvate and ATP. b) CO2, FADH2, GTP, and NADH. c) H2O and ATP. d) NADH and ATP.

b) CO2, FADH2, GTP, and NADH.

Which of the following is a reason why ATP hydrolysis has a negative ΔG0? a) ATP has a high concentration in cells. b) The removal of the phosphate is energetically favorable. c) The reverse reaction is extremely fast. d) The products have more free energy than the reactants.

b) The removal of the phosphate is energetically favorable. FEEDBACK: The products of the ATP hydrolysis reaction—ADP and free phosphate—are more stable and have a lower free energy. Release of free phosphate is energetically favorable because it relieves the repulsion of the negative charges of the neighboring phosphate groups and the aqueous environment to make hydrogen bonds with the phosphate.

What is the role of activated carriers in cells? a) They are enzymes that catalyze biosynthetic reactions and make them feasible at the temperature of a cell. b) They capture energy from energy releasing reactions and transfer it to other reactions. c) They are enzymes that catalyze the reactions that break down foodstuffs for energy generation in the cell. d) They carry energy from anabolic reactions for use in catabolic reactions.

b) They capture energy from energy releasing reactions and transfer it to other reactions. FEEDBACK: Activated carriers collect electrons from oxidation of molecules in catabolic reactions and transfer them to anabolic reactions that require electrons for the reduction of molecules.

Why is sunlight the ultimate source of energy for nearly all living things on Earth? a) because the Earth makes a full rotation on it's axis, which provides light once a day b) because photosynthetic organisms produce food molecules using light energy c) because animals obtain heat energy from the sun, which keeps them alive d) because all animals must consume plants for obtaining energy

b) because photosynthetic organisms produce food molecules using light energy FEEDBACK: Organic molecules for energy are obtained by animals through their diet, by consuming either plants or animals that eat plants. Plants produce organic molecules using energy from the sun, thus the source of energy from food molecules in plants is ultimately from the sun.

The food molecule whose breakdown generates most of the energy for a majority of animal cells is a) sucrose. b) glucose. c) fat. d) protein.

b) glucose

What is the fermentation product produced in an anaerobic muscle cell? a) ethanol b) lactic acid c) 1 ATP d) 1 ADP

b) lactic acid

Enzymes increase the speed of a chemical reaction because they a) increase the temperature to provide the necessary boost of energy. b) lower the activation energy needed to start the reaction. c) make the reaction more energetically favorable. d) make the reaction spontaneous.

b) lower the activation energy needed to start the reaction. FEEDBACK: Enzymes work by lowering the threshold energy input, called the activation energy, needed to start a reaction.

(Q019) Shown is a chloroplast with labeled structures. The photosynthetic machinery is found in which of the compartments shown? a) stroma b) thylakoid membrane c) inner membrane d) outer membrane

b) thylakoid membrane FEEDBACK: Chloroplasts have a double-membrane layer, with the outer membrane being highly permeable to molecules. There is a third membrane inside the stroma of the chloroplast, called the thylakoid membrane, where the photosynthetic machinery is located.

What is the function of a kinase? a) to oxidize a molecule b) to add a phosphate group to a molecule c) to rearrange the bonds into an isomeric form d) to shift a chemical group from one position to another in a molecule

b) to add a phosphate group to a molecule

The end of the microtubule that has /alpha-tubulin exposed is the a. (+) end. b. (-) end. c. Both (+) and (-) ends. d. Neither end has /alpha-tubulin exposed.

b. (-) end FEEDBACK: The protofilaments that form the microtubule are assembled such that the /beta-tubulin end of the dimer is always exposed on the (+) end and /alpha-tubulin on the (-) end.

The end of the microtubule that has alpha-tubulin exposed is the a. (+) end. b. (-) end. c. Both (+) and (-) ends. d. Neither end has /alpha-tubulin exposed.

b. (-) end. FEEDBACK: The protofilaments that form the microtubule are assembled such that the /beta-tubulin end of the dimer is always exposed on the (+) end and /alpha-tubulin on the (-) end.

(Q023) The first living things on Earth probably generated ATP by what mechanism? a. carbon fixation b. fermentation c. photosynthesis d. oxidative phosphorylation

b. fermentation FEEDBACK: Sophisticated processes like oxidative phosphorylation likely took time to evolve. The earliest cells are thought to have produced energy by breaking down organic molecules through fermentation processes.

Which of the following motor proteins has one head domain, moves along actin toward the plus end, and is found in all cell types? a. cytoplasmic dynein b. myosin-I c. myosin-II d. kinesin

b. myosin-I FEEDBACK: Myosins are the motor proteins that move along actin filaments; both myosins, I and II, move toward the plus end. Myosin-I has a single head domain and is found in all cell types, whereas myosin-II is found in muscle cells and has two head domains.

(Q005) Shown is the structure of a mitochondrion with different compartments labeled. Which of the numbers represents the most permeable membrane of the mitochondrion? a) 1 b) 2 c) 3 d) 4

c) 3 FEEDBACK: The mitochondrion has a smooth outer membrane that contains large porin proteins that allow for the passage of all molecules up to a certain size. The inner membrane is highly folded and contains the enzymes of the electron-transport chain.

(Q017) Cytochrome c oxidase catalyzes the reaction that reduces molecular oxygen (two oxygen atoms) to two water molecules. The electrons are added sequentially, and during the process cytochrome c oxidase must bind the oxygen tightly in the active site. Why? a) Oxygen will bind to the electron-transport chain and reverse the pumping of protons. b) If the oxygen escapes, it will bubble out as a gas and escape quickly. c) Superoxide radicals are formed as an intermediate, and are dangerous to the cell. d) The escaped oxygen will form carbon monoxide and kill the cell.

c) Superoxide radicals are formed as an intermediate, and are dangerous to the cell. FEEDBACK: The formation of two water molecules from the reduction of molecular oxygen is carried out by the addition of four electrons from the electron-transport chain, catalyzed in the active site of cytochrome c oxidase. Once one electron is added, the oxygen forms a superoxide radical that is dangerously reactive and can damage cell components.

(Q007) How do the high-energy electrons of activated carriers contribute to forming the high-energy phosphate bonds of ATP? a) They are pumped across the membrane to form an electron gradient. b) They are transferred directly to ADP to form ATP. c) They are used by the electron-transport chain to make a proton gradient. d) They are passed to ATP synthase to power ATP synthesis

c) They are used by the electron-transport chain to make a proton gradient. FEEDBACK: Activated carriers transfer their high-energy electrons to the electron-transport chain to form a proton gradient across the mitochondrial inner membrane. The proton gradient is then used to power ATP synthesis as they flow down their electrochemical gradient through ATP synthase.

(Q012) The proton flow through the transmembrane H+ carrier of ATP synthase results in a) bending of the carrier and stalk to produce mechanical force. b) moving ADP and Pi across the membrane into the enzyme active site. c) mechanical rotation that is converted into the chemical-bond energy of ATP. d) binding of the proton to ADP to enhance formation of the phosphate bond.

c) mechanical rotation that is converted into the chemical-bond energy of ATP. FEEDBACK: ATP synthase has a carrier subunit, a stalk, and a head. Movement of the protons through the carrier causes rotation of the carrier and stalk, which leads to conformational changes in the head, which drives formation of ATP.

If the products of a reaction have more free energy than the reactants, then that reaction is a) spontaneous. b) energetically favorable. c) not energetically favorable. d) physically impossible.

c) not energetically favorable. FEEDBACK: Reactions that have products with LESS free energy than the reactants will release free energy and create more disorder in the system. These will proceed spontaneously and are energetically favorable. However, when products of a reaction have MORE free energy than the reactants, there is no release of energy, and the reaction is not energetically favorable.

(Q021) Stage two of photosynthesis (or the light-independent reactions) uses which input molecules to produce organic food molecules? a. O2, NADH, ADP b. amino acids, sugars, fatty acids c. ATP, NADPH, CO2 d. H2O, light, chlorophyll

c. ATP, NADPH, CO2 FEEDBACK: The light-independent reactions take the ATP and the NADPH produced in the light reactions and produce organic molecules from the carbon in CO2. This is called carbon fixation and produces sugars, amino acids, and fatty acids.

Shown below is a diagram of a centrosome and associated microtubules. What is the identity of the structure in red, indicated by the black dashed arrow? a. centriole b. microtubule c. gamma-tubulin ring complex d. kinesin molecule

c. gamma-tubulin ring complex FEEDBACK: Centrosomes are sites from which microtubules are nucleated in cells. They contain a pair of centrioles in the center, surrounded by a matrix of proteins. The proteins contain /gamma-tubulin ring complexes that act as nucleation sites from which new microtubules are assembled.

A ___________ is a long structure found in abundance in the cytoplasm of a single skeletal muscle fiber, and is composed of many bundles of actin and myosin filaments that are arranged in repeating units. a. sarcomere b. contractile ring c. myofibril d. thick filament

c. myofibril FEEDBACK: Myofibrils are large, long structures that make up the bulk of the cytoplasm of a skeletal muscle cell. Myofibrils are made up of numerous end-to-end sarcomere units of overlapping myosin and actin bundles.

Microtubules are made up of 13 ___________ that are linear chains of ___________. a. tubulin dimers; protofilaments b. tubulin rings; microfilaments c. protofilaments; tubulin dimers d. microfilaments; tubulin rings

c. protofilaments; tubulin dimers FEEDBACK: Dimers of tubulin stack into long protofilaments. Microtubules are made up of thirteen of these protofilaments, side by side, to form a tube.

The binding of ATP causes a conformational change in myosin that a. moves the myosin head one step forward on the actin filament. b. move the actin filament in a force-generating "power stroke." c. releases the myosin head from the actin filament. d. attaches the myosin head to the actin filament.

c. releases the myosin head from the actin filament. FEEDBACK: In the myosin ATPase cycle, the binding of ATP leads to the release of myosin from interaction with the actin filament. It is the subsequent release of the ATP hydrolysis products—inorganic phosphate and ADP—that lead to the binding of myosin to the actin filament and the power stroke, respectively.

In terms of structure, if cytoplasmic intermediate filaments are described as ropes, microtubules are described as_____ a. string. b. wood. c. tubes. d. glass.

c. tubes

(Q014) The low redox potential of NADH means that it has a a) low free energy. b) very stable bond. c) high electron affinity. d) tendency to give up electrons.

d) tendency to give up electrons. FEEDBACK: Molecules with a low redox potential are more likely to give up their electrons, and thus have a low affinity for electrons. This means that the electrons are in a "high energy bond" and the bond is easy to break, making NAD+ and FAD good candidates for carrying and delivering electrons to the electron-transport chain, the members of which have higher redox potentials.

What is the relationship between ΔG and ΔG0? a) ΔG0 is the free-energy change at standard temperature. b) ΔG0 is the free-energy change at standard pressure. c) ΔG0 is the free-energy change at standard concentrations. d) ΔG0 is the free-energy change at standard temperature and concentrations.

d) ΔG0 is the free-energy change at standard temperature and concentrations. FEEDBACK: The value of the free-energy change of a reaction, ΔG, is dependent upon the concentration of reactants and products, as well as the temperature of the system. ΔG0 is the standard free-energy change at standard temperature and concentrations to allow comparison of different reactions.

Intermediate filaments connect to other cells through_______. desmosomes loose meshwork attachments at the cell membrane growth and retraction to maintain a dynamic cell response extracellular matrix proteins

desmosomes FEEDBACK: Intermediate filaments connect to other cells through desmosomes to adjacent cells.

What is the goal of a membrane-based proton gradient? to generate energy in form of ATP to reduce the elctronegativity of atoms inside the electron transport chain to pump ATP across membranes to synthesize GTP

to generate energy in form of ATP