Bio 203 Exam 2 Quizzes Reveiw

Stage two of photosynthesis (or the light-independent reactions) uses which input molecules to produce organic food molecules?

ATP, NADPH, CO2 (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)

What is the value of ΔG at equilibrium?

zero (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)

If the products of a reaction have more free energy than the reactants, then that reaction is...

not energetically favorable. (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.)

The first step of glycolysis uses one ATP molecule in order to...

phosphorylate glucose. (The first step of glycolysis is the phosphorylation of glucose to glucose-6-phosphate. This uses a phosphate from ATP hydrolysis.)

In addition to being converted to acetyl CoA for the citric acid cycle, pyruvate made during glycolysis can be used for

synthesis of alanine and fermentation. (Pyruvate is a substrate for various reactions in the cell. It can be used to synthesize the amino acid alanine in ethanol and lactic acid fermentation, to regenerate NAD+, to make acetyl CoA for use in the citric acid cycle, or for other uses.)

In the presence of high levels of ___________, the enzyme phosphofructokinase [PFK] is inhibited.

ATP (Phosphofructokinase is a glycolytic enzyme, catalyzing one of the irreversible steps of glycolysis, the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate. This enzyme's activity is shut down by feedback inhibition when there are high levels of ATP, because if ATP is abundant, further glycolysis becomes unnecessary.)

The first living things on Earth probably generated ATP by what mechanism?

fermentation (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.)

Protons are pumped across the mitochondrial inner membrane to accumulate in the

intermembrane space. (The electron-transport chain pumps electrons from the mitochondrial matrix into the intermembrane space. This produces a higher concentration of protons in the intermembrane space, which is used to power ATP synthase.)

Which of the following has the lowest electron affinity?

NADH dehydrogenase complex (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.)

Condensation reactions are energetically ___________ and hydrolysis reactions are energetically ___________.

unfavorable; favorable (Condensation reactions reduce the disorder in the universe and are energetically unfavorable. Hydrolysis reactions increase the disorder in the universe and are energetically favorable.)

The major products of the citric acid cycle are

CO2 and NADH. (The citric acid cycle produces carbon dioxide and activated carriers from the oxidation of acetyl CoA.)

Each molecule of acetyl-CoA entering the citric acid cycle produces two ___________ and four ___________.

CO2; activated carriers (Acetyl CoA is a two-carbon molecule. In the citric acid cycle those carbons are oxidized to two CO2 molecules. In the process of acetyl CoA oxidization, four activated carriers are converted to their reduced forms: 3 NADH and 1 FADH2.)

The citric acid cycle produces which activated carriers that transfer high-energy electrons to the electron-transport chain?

NADH and FADH2 (The citric acid cycle produces reduced forms of two activated carriers, NADH and FADH2. These electron carriers transfer a hydride ion, two electrons, and one proton to the electron-transport chain complexes.)

Glycogen synthetase enzyme, which forms glycogen from glucose, is activated by excess

glucose 6-phosphate. (The synthesis of glycogen, a form of stored glucose is produced by an enzyme glycogen synthetase. The activity of this enzyme is triggered by high levels of glucose 6-phosphate)

Living systems can generate and maintain order without violating the second law of thermodynamics because they generate

heat (Even though living systems produce ordered structures from smaller building blocks, this does not violate the second law of thermodynamics because they still create disorder by releasing energy in the form of heat. Heat is energy in its most disordered form.)

If a reaction is energetically favorable (exergonic), then it must produce a(n)

increase in entropy. (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).

The cytochrome complexes contain heme prosthetic groups, which have a higher redox potential than the iron-sulfur centers found in other electron-transport chain complexes like NADH dehydrogenase. Where in the electron-transport chain would the cytochrome complexes thus be located relative to iron-sulfur center complexes?

later in the chain (Iron-sulfur centers have a relatively low affinity for electrons and thus have a low redox potential. This propensity to give up electrons makes the transfer of electrons to a complex with a higher electron affinity energetically favorable. Thus, complexes containing chemical groups with higher electron affinities/high redox potential occur later in the electron-transport chain.)

Enzymes increase the speed of a chemical reaction because they...

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

The proton flow through the transmembrane H+ carrier of ATP synthase results in

mechanical rotation that is converted into the chemical-bond energy of ATP. (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.)

How is pyruvate imported across the inner membrane into the mitochondrial matrix for use in the citric acid cycle?

proton gradient-driven symport (Pyruvate is transported across the mitochondrial inner membrane using the proton gradient. The transport protein is a symporter, moving protons in the same direction as the pyruvate molecule)

In an enzymatic reaction, a molecule gains an electron. This is known as a(n) ___________ reaction.

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

Chlorophyll appears green because it ________ light.

reflects green light. (Chlorophyll absorbs light at different wavelengths in the blue and red regions of the spectrum. However, the molecule appears green because it reflects light in the green region of the spectrum.)

Gluconeogenesis requires a total of ___________ ATP and GTP molecules combined.

six (Gluconeogenesis, uses ATP and GTP to form glucose from pyruvate. In total, this process requires four molecules of ATP and two molecules of GTP for a total of six.)

Glycolysis alone captures approximately what percentage of the free energy available in a molecule of glucose?

10% (Glycolysis captures about 10% of the free energy available in a molecule of glucose, which is roughly comparable to the efficiency of a gasoline-powered engine.)

In the following condensation reaction, how does ATP power the formation of product A-B?

A phosphate is first transferred to reactant A−OH to form a high energy intermediate. (ATP powers the formation of energetically unfavorable bonds between two molecules by first breaking its own high-energy phosphoanhydride bond and transferring the phosphate to another molecule. This new phosphate linkage can then be broken to power the bond formation between molecules.)

Why do cells use enzymes to harvest energy from food molecules rather than by direct oxidation?

Enzymes transfer energy from food to carrier molecules in small steps. (Direct oxidation is the release of all the energy in glucose to CO2 and H2O in a single combustion step. This would lead to a massive release of energy as heat. Instead, cells use enzymes to harvest this energy in small steps for transfer to carrier molecules that carry energy in usable "packets.")

The food molecule whose breakdown generates most of the energy for a majority of animal cells is

Glucose (Glucose is the main energy source for animal cells, though other sources can be effectively used.)

What is the fermentation product produced in an anaerobic muscle cell?

Lactic acid (Muscle cells use a fermentation pathway that produces lactic acid. No ATP is generated in this process, it merely exists to recycle NADH back to NAD+ so that glycolysis can continue.)

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?

Superoxide radicals are formed as an intermediate, and are dangerous to the cell. (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.)

Which of the following is a reason why ATP hydrolysis has a negative ΔG0?

The removal of the phosphate is energetically favorable. (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.)

How do the high-energy electrons of activated carriers contribute to forming the high-energy phosphate bonds of ATP?

They are used by the electron-transport chain to make a proton gradient. (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.)

What is the role of activated carriers in cells?

They capture energy from energy releasing reactions and transfer it to other reactions. (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.)

Fatty acids can be used to produce energy by conversion to ___________ in the ___________ of the cell.

acetyl CoA; mitochondria (Fatty acids are broken down to acetyl CoA in the mitochondria. This acetyl CoA can then enter the citric acid cycle to produce energy.)

Reactions that build larger molecules in the cell are called ___________; reactions that break down molecules into smaller ones are called ___________.

anabolic; catabolic (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.)

Why is CO2 an end product of cellular respiration?

because it is the most stable form of carbon in our atmosphere (Cellular respiration is the breakdown of carbon-containing molecules through oxidation to release energy. Because the most energetically stable form of carbon in the presence of oxygen is carbon dioxide, this is the final end product of respiration.)

Why is sunlight the ultimate source of energy for nearly all living things on Earth?

because photosynthetic organisms produce food molecules using light energy (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.)

Why is the presence of oxygen required for the citric acid cycle to operate?

because the NADH passes its electrons to oxygen in the electron transport chain to renew NAD+ (In the absence of oxygen, the citric acid cycle cannot operate. Oxygen is the electron acceptor in the electron transport chain; it recycles NADH back to NAD+, which is used for the reactions of the citric acid cycle.)

What is gluconeogenesis?

the synthesis of glucose from pyruvate (Gluconeogenesis is the reversal of glycolysis—the synthesis of glucose from pyruvate. This process allows glucose to be remade if it becomes scarce.)

Shown is a chloroplast with labeled structures. The photosynthetic machinery is found in which of the compartments shown?

thylakoid membrane (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?

to add a phosphate group to a molecule (Kinase is the general term for an enzyme that adds phosphate groups to molecules, including to small molecules or other proteins. They are very specific to the molecule they phosphorylate. Hexokinase, for instance, phosphorylates the 6-carbon sugar glucose.)

Glycolysis produces ___________ net ATP molecules, whereas the complete oxidation of glucose to water and carbon dioxide produces ___________ ATP molecules.

two; thirty (Glycolysis uses two ATP molecules and produces four, yielding a net of two ATP molecules produced in the process. Complete oxidation of glucose to carbon dioxide by citric acid cycle and oxidative phosphorylation produces about thirty molecules of ATP.)

During glycolysis, the number of ATP consumed (per glucose molecule) is ___________, while the number produced is ___________.

two;four (In glycolysis, two molecules of ATP are consumed in the first half of the glycolysis pathway. In the second half, four molecules of ATP are formed.)

Which of the following is a mobile electron carrier in the electron-transport chain?

ubiquinone (The electron-transport chain is composed of three integral membrane complexes: NADH dehydrogenase complex, cytochrome c reductase complex, and cytochrome c oxidase complex, with two mobile carriers, ubiquinone and cytochrome c.)

If cells were undergoing glycolysis but could not carry out fermentation, what products would build up in the cytosol?

NADH and pyruvate (Glycolysis produces pyruvate, ATP, and NADH. Fermentation converts pyruvate to ethanol or lactic acid and recycles NADH back to NAD+, so in the absence of this process, the products of glycolysis NADH and pyruvate would accumulate)

Shown is the structure of a mitochondrion with different compartments labeled. Which of the numbers represents the most permeable membrane of the mitochondrion?

outer membrane (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.)

The low redox potential of NADH means that it has a...

tendency to give up electrons. (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.)

The number of ATP molecules that could be synthesized from the energy released by the transfer of two electrons from NADH to molecular oxygen is ___. (Hint: how many ATP are produced from NADH in the mitochondria?)

2.5 (When two electrons are transferred from NADH along the electron-transport chain, they are ultimately passed to molecular oxygen, a free-energy change of 219.2 kJ/mole. The free-energy change needed for forming a phosphate bond in ATP is 54 kJ/mole; thus about four ATP molecules can be formed from this, at 100% efficiency, but in reality, the process operates at around 50% efficiency.)

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?

chlorophyll (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.)

What purpose does NADPH serve in biosynthetic reactions like the one pictured below?

donating electrons for a reduction reaction (NADPH is a carrier of electrons that are used in reduction reactions often used in biosynthesis of molecules. In the process, NADPH donates electrons, and itself becomes oxidized to NADP+.)

What is the role of oxygen in the electron transport chain?

electron acceptor (Oxygen is the final electron acceptor in the electron transport chain; it captures the electrons that were transferred from activated carriers. In the process of accepting electrons, oxygen also accepts hydrogen ions and so is reduced to H2O.)