BIOL 1406 EXAM 3 (CH 8-10)

Which of the following correctly states the relationship between anabolic and catabolic pathways?

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description?

Organisms acquire energy from and lose energy to their surroundings.

Which of the following states the relevance of the first law of thermodynamics to biology?

Energy can be freely transformed among different forms as long as the total energy is conserved.

According to the second law of thermodynamics, which of the following is true?

The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists.

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously?

Energy input into the organism must be occurring to drive the decrease in entropy.

Which part of the equation ΔG = ΔH – TΔS tells you if a process is spontaneous?

ΔG

An exergonic (spontaneous) reaction is a chemical reaction that __________.

releases energy when proceeding in the forward direction

Which of the following reactions would be endergonic?

glucose + fructose → sucrose

Which of the following determines the sign of ΔG for a reaction?

The free energy of the reactants and the free energy of the products

Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend(s) to keep these pathways away from equilibrium?

The continuous removal of the products of a pathway to be used in other reactions

An input of free energy from outside the pathway

The free energy derived from the hydrolysis of ATP can be used to perform many kinds of cellular work. Which of the following is an example of the cellular work involved in the production of electrochemical gradients?

Proton movement against a gradient of protons

In general, the hydrolysis of ATP drives cellular work by __________.

releasing free energy that can be coupled to other reactions

Which of the following best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways?

The hydrolysis of ATP

A chemical reaction is designated as exergonic rather than endergonic when __________.

the potential energy of the products is less than the potential energy of the reactants

Which of the following is changed by the presence of an enzyme in a reaction?

The activation energy

What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction?

Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction.

How do enzymes lower activation energy?

By locally concentrating the reactants

Which of the following statements about enzymes is/are true?

Enzymes speed up the rate of the reaction without changing the DG for the reaction.

Which of the following statements about enzyme function is correct?

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.

Which of the following statements about enzymes is incorrect?

An enzyme is consumed during the reaction it catalyzes.

Which of the following statements about the active site of an enzyme is correct?

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.

What is meant by the "induced fit" of an enzyme?

The enzyme changes its shape slightly as the substrate binds to it.

Which of the following statements correctly describe(s) the role or roles of heat in biological reactions?

Heat from the environment is necessary for substrates to get over the activation energy barrier.

The kinetic energy of the substrates is increased as the amount of heat in the system is increased.

Enzyme activity is affected by pH because __________.

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

Which of these statements about enzyme inhibitors is true?

The action of competitive inhibitors may be reversible or irreversible.

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule outside the active site is an example of __________.

allosteric activation

Which of the following statements about allosteric proteins is/are true?

1. They are acted on by inhibitors.

2. They exist in active and inactive conformations.

3. They are sensitive to environmental conditions.

The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs?

The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.

A molecule becomes more oxidized when it __________.

loses an electron

In the overall process of glycolysis and cellular respiration, __________ is oxidized and __________ is reduced.

glucose; oxygen

Most of the ATP produced in cellular respiration comes from which of the following processes?

Oxidative phosphorylation

Which of the following is a correct description of the events of cellular respiration in proper sequence?

Oxidation of glucose to pyruvate; oxidation of pyruvate; citric acid cycle; oxidative phosphorylation

Oxygen gas (O₂) is one of the strongest oxidizing agents known. The explanation for this is that __________.

the oxygen atom is very electronegative

The function of cellular respiration is to __________.

extract usable energy from glucose

During the reaction C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O, which compound is reduced as a result of the reaction?

Oxygen

A small amount of ATP is made in glycolysis by which of the following processes?

Transfer of a phosphate group from a fragment of glucose to ADP by substrate-level phosphorylation

Where do the reactions of glycolysis occur in a eukaryotic cell?

The cytosol

Which of the following processes generates most of the NADH that delivers electrons to the electron transport chain?

The citric acid cycle

In preparing pyruvate to enter the citric acid cycle, which of the following steps occurs?

Pyruvate is oxidized, and a molecule of carbon dioxide is removed. The electrons removed in this process are used to reduce NAD⁺ to NADH.

Why is the citric acid cycle called a "cycle"?

The four-carbon acid that accepts the acetyl CoA in the first step of the cycle is regenerated by the last step of the cycle.

In the citric acid cycle, for each pyruvate that enters the cycle, one ATP, three NADH, and one FADH₂ are produced. For each glucose molecule that enters glycolysis, how many ATP, NADH, and FADH₂ are produced in the citric acid cycle?

Two ATP, six NADH, two FADH₂

Where do the reactions of the citric acid cycle occur in eukaryotic cells?

The matrix of the mitochondrion

How many molecules of ATP are gained by substrate-level phosphorylation from the complete breakdown of a single molecule of glucose in the presence of oxygen?

4

Which of the following represents the major energy-related accomplishment of the citric acid cycle, even though it is not the only energy-related accomplishment?

Formation of NADH and FADH₂

After completion of the citric acid cycle, most of the usable energy from the original glucose molecule is in the form of __________.

NADH

Which of the following events accompanies the conversion of pyruvate to acetyl CoA before the citric acid cycle?

Release of CO₂ and synthesis of NADH

The energy given up by electrons as they move through the electron transport chain is used in which of the following processes?

Pumping H⁺ across a membrane

Energy for synthesizing ATP is obtained by ATP synthase directly from which of the following processes?

The flow of H⁺ across the inner mitochondrial membrane through the ATP synthase enzyme

Most of the electrons removed from glucose by cellular respiration are used for which of the following processes?

Reducing NAD+ to NADH in glycolysis and the citric acid cycle AND producing a proton gradient for ATP synthesis in the mitochondria.

During aerobic respiration, molecular oxygen (O₂) is used for which of the following purposes?

At the end of the electron transport chain to accept electrons and form H₂O

Which of the following substances is/are involved in oxidative phosphorylation?

1. ADP

2. Oxygen

3. ATP

Which of the following best describes the electron transport chain?

Electrons are passed from one carrier to another, releasing a little energy at each step.

Which of the following is the source of the energy that produces the chemiosmotic gradient in mitochondria?

Movement of electrons down the electron transport chain

In eukaryotic cells, the components of the electron transport chain are located in or on __________.

the inner membrane of the mitochondrion

Fermentation is essentially glycolysis plus an extra step in which pyruvate is reduced to form lactate or alcohol and carbon dioxide. This last step __________.

enables the cell to recycle the reduced NADH to oxidized NAD⁺

In glycolysis in the absence of oxygen, cells need a way to regenerate which compound?

NAD⁺

Muscle tissues make lactate from pyruvate to do which of the following?

Regenerate NAD⁺

In brewing beer, maltose (a disaccharide of glucose) is __________.

the substrate for alcoholic fermentation

Of the listed metabolic pathways, which is the only pathway found in all organisms?

Glycolysis

When protein molecules are used as fuel for cellular respiration, __________ are produced as waste.

amino groups

In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.

carbon dioxide

How does carbon dioxide enter the leaf?

Through the stomata

In a rosebush, chlorophyll is located in __________.

thylakoids, which are in chloroplasts in the mesophyll cells of a leaf

Chlorophyll molecules are in which part of the chloroplast?

Thylakoid membranes

In photosynthesis, what is the fate of the oxygen atoms present in CO₂? They end up __________.

in sugar molecules and in water

Molecular oxygen is produced during __________.

linear electron flow during the light reactions

The Calvin cycle occurs in the __________.

stroma

What is the role of NADP⁺ in photosynthesis?

It forms NADPH to be used in the Calvin cycle.

A photon of which of these colors would carry the most energy?

Blue

The most important role of pigments in photosynthesis is to __________.

capture light energy

What is the range of wavelengths of light that are absorbed by the pigments in the thylakoid membranes?

Violet-blue and red

When chloroplast pigments absorb light, __________.

the pigments’ electrons become excited

What structure is formed by the reaction center, light-harvesting complexes, and primary electron acceptors that cluster in the thylakoid membrane?

The photosystem

Where do the electrons entering photosystem II come from?

Water

During photosynthesis in chloroplasts, O₂ is produced from __________ via a series of reactions associated with __________.

H₂O; photosystem II

Which of the following is cycled in the cyclic variation of the light reactions?

Electrons

Both mitochondria and chloroplasts __________.

use chemiosmosis to produce ATP

You could distinguish a thylakoid membrane from an inner mitochondrial membrane because the thylakoid membrane would __________.

have photosynthetic pigments

The light reactions of photosynthesis generate high-energy electrons, which end up in __________ through linear electron flow. The light reactions also produce __________ and __________.

NADPH; ATP; oxygen

The energy used to produce ATP in the light reactions of photosynthesis comes from __________.

movement of H⁺ through a membrane

What is the role of NADP⁺ in photosynthesis?

It is reduced and then carries electrons to the Calvin cycle.

Of the following, which occurs during the Calvin cycle?

CO₂ is reduced.

Which of the following occurs during the Calvin cycle?

ATP is hydrolyzed, and NADPH is oxidized.

Rubisco is __________.

the enzyme in plants that captures CO₂ to begin the Calvin cycle

In the Calvin cycle, CO₂ is combined with __________.

a five-carbon compound to form an unstable six-carbon compound, which decomposes into two three-carbon compounds

Glyceraldehyde-3-phosphate (G3P) is produced in the stroma of chloroplasts. Which of the following statements is most accurate regarding this compound?

1. It is a three-carbon sugar.

2. For every three molecules of CO₂ reduced in the Calvin cycle, six molecules of G3P are formed but only one of these molecules exits the cycle to be used by the plant cell.

3. For every three molecules of CO₂, six molecules of G3P are formed but five molecules must be recycled to regenerate three molecules of RuBP

4. It is produced from glucose during glycolysis.

Which of the following statements correctly describes the relationship between the light reactions and the Calvin cycle?

The light reactions produce ATP and NADPH, both of which are used in the Calvin cycle.

Why are C₄ plants more suited to hot climates than C₃ plants?

Unlike C₃ plants, they keep fixing carbon dioxide even when the concentration of carbon dioxide in the leaf is low.

How does ATP drive mechanical work inside a cell?

By binding to motor proteins

Which of the following is true regarding metabolic pathways?

Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme.

Cells use ATP constantly, but ATP is considered a renewable resource. What process makes this possible?

ATP can be regenerated by the addition of a phosphate group to ADP.

Which of the following statements is correct regarding ATP?

The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups.

At low pH, a particular enzyme catalyzes a reaction at a high rate. At neutral pH, the enzyme is completely inactive. What statement best explains the difference in how pH affects the function of this enzyme?

The enzyme is adapted for low pH but is denatured at neutral pH, leaving it nonfunctional.

An exergonic reaction __________ free energy, and an endergonic reaction __________ free energy.

releases; absorbs

ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________.

feedback inhibition

As ATP begins to build up in a cell, metabolism slows down. How does this happen?

ATP acts as an allosteric inhibitor to many of the enzymes involved in metabolism, thus slowing their function.

What best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis that may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

Which of the following statements is correct regarding competitive and noncompetitive enzyme inhibitors?

Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site.

Which of the following statements correctly describes cofactors and coenzymes?

Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.