Biology Chapters 8-10

A pH of 2.0 demonstrates the peak activity for pepsin.

Based on the graph, what is the optimal pH for pepsin activity?

A pH of 8.0 demonstrates the peak activity for trypsin.

Based on the graph, what is the optimal pH for trypsin activity?

A substance that causes or quickens a chemical reaction; any agent that causes change

Catalyst

exergonic; endergonic

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _______ is to _______.

A non-spontaneous chemical reaction in which free energy is absorbed from the surrounding.

Endergonic reactions are (diagram)

The activation energy is changed by the presence of an enzyme in a reaction. An enzyme is a macromolecule that acts as a catalyst, a chemical agent that speeds up a reaction without being consumed by the reaction. An enzyme catalyzes a reaction by lowering the activation energy (EA) barrier, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures. An enzyme cannot change the ΔG for a reaction; it cannot make an endergonic reaction exergonic. Enzymes can only hasten reactions that would eventually occur anyway, but this function makes it possible for the cell to have a dynamic metabolism, routing chemicals smoothly through the cell's metabolic pathways. And because enzymes are very specific for the reactions they catalyze, they determine which chemical processes will be going on in the cell at any particular time.

Which of the following is changed by the presence of an enzyme in a reaction? The G value for the reactants The G value for the products The activation energy The sign of ΔG The magnitude of ΔG

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O

Which of the following metabolic processes can occur without a net influx of energy from some other process?

P4 binds E1 and deactivates it. Many enzymatic pathways are regulated by the feedback inhibition model described here. In fact, it is so common that another name for it is end-product inhibition.

Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?

The Calvin cycle of photosynthesis diagram

requires ATP and NADPH, can occur in both light and dark conditions, and generates glucose

The light reactions of photosynthesis use _____ and produce _____.

water ... NADPH NADPH is a reactant in the Calvin cycle.

Competitive inhibitors compete physically and structurally with the substrate for an enzyme's active site; they can be outcompeted by adding extra substrate. Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme's shape. Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate it permanently. Most medications are enzyme inhibitors of one kind or another.

1. A (n)______________ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate. 2. A (n)______________ inhibitor binds to a site on the enzyme that is not the active site. 3. Usually, a(n) _____________ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity. 4. The competitive inhibitor competes with the substrate for the ______________ on the enzyme .5. When the noncompetitive inhibitor is bonded to the enzyme, the shape of the ______________ is distorted. 6. Enzyme inhibitors disrupt normal interactions between an enzyme and its ______________. 1. competitive 2. noncompetitive 3. irreversible 4. active site 5. enzyme 6. substrate

Which of these equations best summarizes photosynthesis?

6 CO2 + 6 H2O → C6H12O6 + 6 O2 This is the equation that summarizes the reactions of photosynthesis.

In the net reaction for glycolysis, glucose (the electron donor) is oxidized to pyruvate. The electrons removed from glucose are transferred to the electron acceptor, NAD+, creating NADH.

6. The reduced form of the electron acceptor in glycolysis isNADH.

The reaction rate would decrease. Most reactions double in rate for each 10*C increase in temp.

Ammonia, NH3NH3, is used in numerous industrial processes, including the production of pharmaceuticals such as sulfonamide and antimalarials and vitamins such as the B vitamins. The equilibrium equation for the synthesis of ammonia (sometimes known as the Haber process) is N2(g)+3H2(g)⇌2NH3(g) The Haber process is typically carried out at a temperature of approximately 500∘C∘C. What would happen to the rate of the forward reaction if the temperature were lowered to 100∘C∘C?

pyruvate, ATP, and NADH ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis. In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?

ATP can be regenerated by the addition of a phosphate group to ADP. An organism at work uses ATP continuously, but ATP is a renewable resource that can be regenerated by the addition of phosphate to ADP. The free energy required to phosphorylate ADP comes from exergonic breakdown reactions (catabolism) in the cell. This shuttling of inorganic phosphate and energy is called the ATP cycle, and it couples the cell's energy-yielding (exergonic) processes to the energy-consuming (endergonic) ones. Cells do not store large amounts of either ATP or ADP. The hydrolysis of ATP is a reversible reaction. ATP is generated by the addition of a phosphate group to ADP, not the opposite.

Cells use ATP constantly, but ATP is considered a renewable resource. What process makes this possible? ADP and ATP are stored in large amounts in a cell. ADP is generated by the addition of a phosphate group to ATP. The hydrolysis of ATP is an irreversible reaction. ATP can be regenerated by the addition of a phosphate group to ADP. None of the listed responses is correct. (diagram)

1. An enzyme is DENATURED when it loses its native conformation and its biological activity. 2. An enzyme is considered a CATALYST because it speeds up chemical reactions without being used up. 3. An enzyme is considered SPECIFIC because of its ability to recognize the shape of a particular molecule. 4. A COFACTOR, such as a vitamin, binds to an enzyme and plays a role in catalysis. 5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) COMPLEX. 6. A substrate binds to an enzyme at the ACTIVE SITE, where the reaction occurs. 7. In a catalyzed reaction a reactant is often called a SUBSTRATE. A substrate binds at an enzyme's active site; the enzyme typically recognizes the specific shape of its substrate. A cofactor, such as an inorganic ion or vitamin, may bind to the enzyme and assist in catalyzing the reaction. The reaction environment must be appropriate for catalysis to proceed. An enzyme will denature, or change its shape and lose its biological activity, at too high a temperature or at a pH outside the enzyme's optimal range.

Complete this vocabulary exercise relating to enzymes.

increase the rate of a reaction without being consumed by the reaction. This permits enzyme molecules to be used repeatedly.

Enzymes are described as catalysts, which means that they _____.

chloroplast structure diagram

Exciting chlorophyll: chlorophyll in thylakoids absorb light, which excites electrons to produce potential energy

A spontaneous chemical reaction in which there is a net release of free energy. (energy outward)

Exergonic reactions are

Net Input: ADP, NAD⁺, Glucose Net Output: ATP, NADH and Pyruvate not input or output: O₂, CO₂, coenzyme A and acetyl CoA In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no O2 uptake or CO2 release in glycolysis.

From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis.

Proteins. They work by reducing the energy of activation. Enzymes are proteins that behave as organic catalysts.

In general, enzymes are what kinds of molecules?

substrate-level phosphorylation A phosphate group is transferred from GTP to ADP.

In the citric acid cycle, ATP molecules are produced by _____.

As in glycolysis, the electrons removed from carbon-containing intermediates during acetyl CoA formation and the citric acid cycle are passed to the electron carrier NAD+, reducing it to NADH. The citric acid cycle also uses a second electron carrier, FAD (flavin adenine dinucleotide), the oxidized form, and FADH2, the reduced form.

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors. Drag the labels on the left to show the net redox reaction in acetyl CoA formation and the citric acid cycle. Note that two types of electron carriers are involved.

Region C

In which region is the enzyme saturated with substrate?

A catabolic pathway. Cellular respiration is a catabolic pathway.

The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____. See Concept 8.1 (Page)

Natural selection favors enzymatic activity of pepsin at a pH of 2.0 because 2.0 is the pH inside the stomach.

Using the figure to guide your response, select the best explanation for why natural selection might have resulted in the optimal pH for pepsin. (diagram)

The energy of activation must be overcome in order for a reaction to proceed.

What is the correct label for "A"? (diagram)

The entropy of the products is greater than the entropy of the reactants. A large molecule (glucose) has been converted into several smaller molecules (water and carbon dioxide); thus, the products have more disorder (greater entropy) than the reactants.

Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct? See Concept 8.2 (Page)

The γ-phosphate is the primary phosphate group on the ATP molecule that is hydrolyzed when energy is needed to drive anabolic reactions. Located the farthest from the ribose sugar, it has a higher energy than either the α- or β-phosphate.

Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme?

This process utilizes energy released by electron transport.

oxidative phosphorylation

one of the atoms sharing electrons is more electronegative than the other. When an atom is bonded to a more electronegative atom, the electrons of the bond are not shared equally and a polar covalent bond is formed. Such bonds vary in their polarity, depending on the relative electronegativity of the two atoms. Atoms that have similar (or the same) electronegativities will form a nonpolar covalent bond. For example, a C-H bond is nonpolar because C and H have similar electronegativities.

A covalent bond is likely to be polar when

Is unchanged. Enzymes are not changed as a result of their participation in a reaction.

As a result of its involvement in a reaction, an enzyme _____.

ATP drives transport work inside a cell by phosphorylating a transport protein. Transport and mechanical work in the cell are also nearly always powered by the hydrolysis of ATP. In these cases, ATP hydrolysis leads to changes in a protein's shape and often its ability to bind to another molecule. Sometimes this occurs via a phosphorylated intermediate. ATP hydrolysis causes changes in the shapes and binding affinities of proteins. This can occur directly, by phosphorylation, for a membrane protein carrying out active transport of a solute or indirectly, via noncovalent binding of ATP and its hydrolytic products, as is the case for motor proteins that move vesicles (and other organelles) along cytoskeletal "tracks" in the cell. Mechanical work is driven by ATP binding to motor proteins. Chemical work is driven by ATP providing free energy to facilitate the formation of polymers from monomers. ATP adds a phosphate to a transport protein for this kind of work. A phosphate is not removed from the protein. ATP adds free energy to chemical reactions. It does not remove it.

How does ATP drive transport work inside a cell? By removing free energy from a chemical reaction By removing a phosphate from a transport protein By providing free energy to facilitate the formation of polymers from monomers By phosphorylating a transport protein By binding to motor proteins

oxygen is the final electron acceptor of cellular respiration.

What molecule is indicated by the letter D?

Water at the top of a dam has potential energy; water falling through a dam has kinetic energy. The moving water performs work by moving the blades of turbines in the dam to generate electricity.

Which of the following statements is true regarding potential energy and kinetic energy?

acetyl CoA Acetyl CoA is a reactant in the citric acid cycle.

Which of these enters the citric acid cycle?

It is stored in NADH and FADH2 The electrons obtained from the oxidation of glucose are temporarily stored in NADH and FADH2. The energy derived from the oxidation of NADH and FADH2 is used to drive the electron transport chain and chemiosmotic synthesis of ATP.

A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose? See Concept 9.4 (Page)

ATP inhibits ATP-producing pathways through feedback inhibition. When ATP allosterically inhibits an enzyme in an ATP-generating pathway, the result is feedback inhibition, a common mode of metabolic control. In feedback inhibition, a metabolic pathway is halted by the inhibitory binding of its end product to an enzyme that acts early in the pathway. Feedback inhibition thereby prevents the cell from making more product than is necessary and thus wasting chemical resources. Positive feedback is a type of feedback where the product facilitates, but does not inhibit, a process. ATP is an allosteric inhibitor, not a competitive inhibitor. Cooperativity is a mechanism that amplifies the response of enzymes to substrates. Denaturing is the breakdown in structure of an enzyme, not an inhibition process.

ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________. competitive inhibition denaturing feedback inhibition cooperativity positive feedback (diagram)

Releases; absorbs

An exergonic reaction __________ free energy, and an endergonic reaction __________ free energy. absorbs; absorbs absorbs; releases destroys; creates releases; absorbs releases; releases

Which of the following is a true statement? Anabolic pathways build molecules, require energy, and are endergonic. Catabolic pathways break down molecules, require energy, and are exergonic. Anabolic pathways break down molecules, require energy, and are endergonic. Catabolic pathways build molecules, release energy, and are exergonic.

Anabolic pathways build molecules, require energy, and are endergonic. If you had trouble with this question, review the following material: Catabolic pathways release energy by breaking down complex molecules to simpler compounds. These exergonic reactions proceed with a net release of free energy. Anabolic pathways, in contrast, are endergonic because they consume energy to build complex molecules from simpler ones.

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

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?

Increase the enzyme concentration. If an enzyme is saturated with substrate, and it is operating at optimum pH and optimum temperature, there is very little that can be done except to increase the enzyme concentration. Some enzymes can be activated further by allosteric activators, in which case one might add some activator to the reaction. But otherwise, increasing the enzyme concentration is the only option.

Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction?

This diagram of the citric acid cycle shows the carbon skeletons of each intermediate. The net result of this complex series of reactions is the complete oxidation of the two carbon atoms in the acetyl group of acetyl CoA to two molecules of CO2.

Drag the labels from the left (which represent numbers of carbon atoms) onto the diagram to identify the number of carbon atoms in each intermediate in acetyl CoA formation and the citric acid cycle. Labels may be used more than once. (diagram)

Glycolysis - Cytosol Acetyl CoA - Mitochondrial matrix Citric acid cycle - Mitochondrial matrix Oxidative phosphorylation - inner mitochondrial membrane Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2 produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.

Each of the four stages of cellular respiration occurs in a specific location inside or outside the mitochondria. These locations permit precise regulation and partitioning of cellular resources to optimize the utilization of cellular energy. (diagram)

The covalent bonds of a sugar molecule: potential energy. Bonds are a form of potential energy because the energy arises from the relative positions of the atoms that form the bond.

Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy? See Concept 8.1 (Page)

Net Input: NADH, ADP, O₂ Net Output: NAD⁺, ATP, and Water Not Input or Output: Pyruvate, Glucose, Acetyl CoA, Coenzyme A and CO₂. In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.

From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation.

The woman climbing the ladder to the diving platform is releasing chemical energy from the food she ate for lunch and using some of that energy to perform the work of climbing. The kinetic energy of muscle movement is thus being transformed into potential energy due to her increasing height above the water. The man diving is converting his potential energy to kinetic energy, which is then transferred to the water as he enters it, resulting in splashing, noise, and increased movement of water molecules. A small amount of energy is lost as heat due to friction.

How is energy converted from one form to another?

Both electron transport and ATP synthesis would stop. Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation. In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)

Net Input: NAD⁺, coenzyme A, pyruvate Net Output: NADH, acetyl CoA, CO₂ Not input or output: O₂, ADP, glucose and ATP In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.

In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation.

to function as the final electron acceptor in the electron transport chain The only place that O2 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor. Oxygen's high affinity for electrons ensures its success in this role. Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.

In mitochondrial electron transport, what is the direct role of O2?

Net Input: Acetyl CoA, NAD⁺, ADP Net Output: Coenzyme A, CO₂, NADH, ATP Not Input or Output: Pyruvate, Glucose, O₂ In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced.

In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA. Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.

In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction. Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct. More ATP is produced per CO2 released in cyclic processes than in linear processes. It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA. Redox reactions that simultaneously produce CO2 and NADH occur only in cyclic processes. Cyclic processes, such as the citric acid cycle, require a different mechanism of ATP synthesis than linear processes, such as glycolysis.

In region C of the graph, the reaction rate is independent of substrate concentration.

Look at the graph of reaction rate versus substrate concentration for an enzyme. In which region does the reaction rate remain constant?

Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor. (diagram) Electrons derived from the oxidation of FADH2 enter the electron transport chain at Complex II, farther down the chain than electrons from NADH (which enter at Complex I). This results in fewer H+ ions being pumped across the membrane for FADH2 compared to NADH, as this diagram shows. Thus, more ATP can be produced per NADH than FADH2.

NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2?

(From lowest to highest) Uncatalyzed Reaction, Reaction catalyzed by enzyme A, Reaction catalyzed by enzyme B. Enzymes lower the activation energy of a chemical reaction. This means that a catalyzed reaction is more likely to proceed than an uncatalyzed reaction, and it forms products more rapidly than an uncatalyzed reaction.

Rank these by reaction rate, as measured by the rate of product formation per unit time, from lowest reaction rate to highest reaction rate. To rank items as equivalent, overlap them.

Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three). This molecule fuels many different endergonic (energy-requiring) enzymatic processes in biological organisms. ATP molecules diffuse or are transported to the place where the energy is needed and deliver chemical energy from the breaking of their phosphate bonds.

Select the highest energy form of adenosine from the following images.

Correct: -One of the substrates is a molecule derived from the breakdown of glucose -An enzyme is required in order for the reaction to occur -A bond must be broken between an organic molecule and phosphate before ATP can form. Incorrect: -The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions. -The enyzmes involved in ATP synthesis must be attached to a membrane to produce ATP. In substrate-level phosphorylation, an enzyme transfers a phosphate group from one molecule (an intermediate in the breakdown of glucose to pyruvate) to ADP to form ATP. This is very different from the mechanism of ATP synthesis that takes place in oxidative phosphorylation.

Sort the statements into the appropriate bin depending on whether or not they correctly describe some aspect of substrate-level phosphorylation in glycolysis.

The compound is a competitive inhibitor. A competitive inhibitor slows down the enzyme by competing with the substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.

The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation? See Concept 8.4 (Page)

Pyruvate molecules are transported from the cytosol into mito but doesnt enter the citric acid cycle as pyruvate. A chemical reaction occurs that removes a carbon atom thru carbon dioxide. CoA joins w 2 fragment NADH to for Acetyl-CoA. One molecule of Acetyl-CoA enters the cycle. the 2 carbon fragment attaches to 4 carbon molecule of oxaloacetate in the first reaction--forms citrate. Two carbon atoms are released one at a time in CO2. Produces 2 ATP, 3 NADH, and 1 FADH2 per cycle.

The citric acid cycle video

Exergonic reactions drive endergonic reactions. Based on their free-energy changes, chemical reactions can be classified as either exergonic ("energy outward") or endergonic ("energy inward"). An exergonic reaction proceeds with a net release of free energy. An endergonic reaction absorbs free energy from its surroundings. A key feature in the way cells manage their energy resources in order to do this work is energy coupling, the use of an exergonic process to drive an endergonic one. ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work. Catabolic reactions typically drive anabolic reactions. Exergonic reactions drive endergonic reactions. If chemical reactions in cells are at equilibrium, the cell is dead. Endergonic and exergonic reactions often occur together.

The primary manner in which cells manage their energy resources in order to do work is called energy coupling. Which of the following statements accurately defines energy coupling?

Glucose and oxygen Photosynthesis produces glucose and releases oxygen into the atmosphere.

What molecules belong in space A and B?

carbon dioxide and water Carbon dioxide and water are by-products of cellular respiration.

What molecules belong in spaces E and F?

Substrate. This is the name given to the reactants in an enzymatically catalyzed reaction.

What name is given to the reactants in an enzymatically catalyzed reaction?

mitochondrion Mitochondria are the sites of cellular respiration.

What organelle is indicated by the letter C?

Glycolysis Glycolysis occurs in the cytosol. Video notes: Cellular respiration stage 1: cytosol (glycolysis--c=glucose breaks down to 2 of Pyruvate. A small amount created ATP but Electrons carried via NADH stage 2: Citric acid cycle Stage 3: Oxidative phosphorylation

What process occurs in Box A? (diagram)

Photosynthesis. Chloroplasts are the sites of photosynthesis. Video notes: photosynthesis needs carbon dioxide(from the air) and water(damp soil by plants roots. Chloroplast uses energy from the sun to convert the two into sugars like glucose, releases oxygen back into the envt. Animals use mitochondria for cellular respiration and the cycle continues

What process occurs in structure H? (diagram)

the citric acid cycle The citric acid cycle transfers electrons to NADH and FADH2.

What process occurs within Box B?

Hydrolysis. Hydrolysis involves breaking bonds with the addition of water.

What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?

Both forward and reverse rates increase. The Haber process can be cheaply catalyzed using porous iron. A much more effective catalyst for the Haber process is osmium; however, it is very expensive and toxic.

What will happen to the rates of the forward and reverse reactions when a catalyst is added?

The reaction rate would decrease. As the concentration of nitrogen decreases, collisions between nitrogen and hydrogen are less likely to occur.

What would happen to the rate of the forward reaction if the concentration of nitrogen were decreased?

Remains the same: proton pumping rate, electron transport rate, rate of oxygen uptake Decreases (or goes to zero): Rate of ATP synthesis, size of the proton gradient Gramicidin causes membranes to become very leaky to protons, so that a proton gradient cannot be maintained and ATP synthesis stops. However, the leakiness of the membrane has no effect on the ability of electron transport to pump protons. Thus, the rates of proton pumping, electron transport, and oxygen uptake remain unchanged.

When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the rates of electron transport, proton pumping, and ATP synthesis in oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration.) Sort the labels into the correct bin according to the effect that gramicidin would have on each process.

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. Metabolism as a whole manages the material and energy resources of the cell. Some metabolic pathways release energy by breaking down complex molecules to simpler compounds. These degradative processes are called catabolic pathways, or breakdown pathways. A major pathway of catabolism is cellular respiration, in which the sugar glucose and other organic fuels are broken down in the presence of oxygen to carbon dioxide and water. Energy that was stored in the organic molecules becomes available to do the work of the cell, such as ciliary beating or membrane transport. Anabolic pathways, in contrast, consume energy to build complicated molecules from simpler ones; they are sometimes called biosynthetic pathways. Examples of anabolism are the synthesis of an amino acid from simpler molecules and the synthesis of a protein from amino acids. Catabolic and anabolic pathways are the "downhill" and "uphill" avenues of the metabolic landscape. Energy released from the downhill reactions of catabolic pathways can be stored and then used to drive the uphill reactions of anabolic pathways.

Which of the following correctly states the relationship between anabolic and catabolic pathways? The flow of energy between catabolic and anabolic pathways is reversible. Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways. Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

It represents the first stage in the chemical oxidation of glucose by a cell. Catabolism of glucose begins with glycolysis.

Which of the following describes the process of glycolysis? See Concept 9.2 (Page) Glycolysis produces 30 ATP from each molecule of glucose. It converts one glucose molecule to two molecules of pyruvate and carbon dioxide. It requires ATP and NADH. It represents the first stage in the chemical oxidation of glucose by a cell. Glycolysis occurs in the mitochondria.

The active site can provide heat from the environment that raises the energy content of the substrate. An enzyme cannot extract heat from the environment to speed a reaction. It can only lower the activation energy barrier so that more substrates have the energy to react.

Which of the following is NOT a way in which an enzyme can speed up the reaction that catalyzes?

The formation of a covalent bond between two amino acids. Chemical reactions involve the making and breaking of chemical bonds, leading to changes in the composition of matter. Ice melting changes the state of water rather than the composition of water, and hydrogen bonds do not change the composition of the molecules involved. Chemical reactions cannot create or destroy atoms but can only rearrange (redistribute) the electrons among them.

Which of the following is a chemical reaction?

ATP is a molecule that acts as an intermediary to store chemical energy for cellular work. If you had trouble with this question, review the following material: ATP is a renewable resource that can be regenerated by the addition of inorganic phosphate (Pi) to ADP. Energy released by catabolism in the cell is used to phosphorylate ADP, regenerating ATP. Chemical energy stored in ATP drives most cellular work.

Which of the following is the most correct interpretation of the figure? Pi acts as a shuttle molecule to move energy from ATP to ADP. Energy from catabolism can be used directly for performing cellular work. ADP + PiPi are a set of molecules that store energy for catabolism. ATP is a molecule that acts as an intermediary to store chemical energy for cellular work.

The reaction proceeds with a net release of free energy. Chemical reactions are classified based on their free-energy changes. An exergonic reaction proceeds with a net release of free energy, whereas an endergonic reaction is one that absorbs free energy from its surroundings. If a chemical process is exergonic (downhill), releasing energy in one direction, then the reverse process must be endergonic (uphill), using energy.

Which of the following is true for all exergonic reactions? A net input of energy from the surroundings is required for the reactions to proceed. The reaction proceeds with a net release of free energy. The reaction goes only in a forward direction: All reactants will be converted to products. The products have more total energy than the reactants.

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

Which of the following is true regarding metabolic pathways? Metabolic pathways are not important to a cell's ability to function. Each reaction in the pathway is catalyzed by the same enzyme. Metabolic pathways consist of only anabolic pathways. Metabolic pathways consist of a single chemical reaction. Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme.

This reaction would be endergonic: Glucose + fructose → sucrose. An endergonic reaction is one that absorbs free energy from its surroundings. Because this kind of reaction essentially stores free energy in molecules (G increases), ΔG is positive. Such reactions are nonspontaneous, and the magnitude of ΔG in the equation ΔG = ΔH - TΔS is the quantity of energy required to drive the reaction. Combining glucose and fructose to produce sucrose is an example of an energy storing endergonic reaction with the product more complex (lower entropy) than the reactants (glucose and fructose).

Which of the following reactions would be endergonic?

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output. An enzyme catalyzes a reaction by lowering the activation energy (EA) barrier, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures. An enzyme cannot change the ΔG for a reaction; it cannot make an endergonic reaction exergonic. Enzymes can only hasten reactions that would eventually occur anyway, but this function makes it possible for the cell to have a dynamic metabolism, routing chemicals smoothly through the cell's metabolic pathways. And because enzymes are very specific for the reactions they catalyze, they determine which chemical processes will be going on in the cell at any particular time. Most metabolic reactions are reversible, and an enzyme can catalyze either the forward or the reverse reaction, depending on which direction has a negative ΔG. This in turn depends mainly on the relative concentrations of reactants and products. The net effect is always in the direction of equilibrium, a term that describes a state of maximum stability.

Which of the following statements about enzyme function is correct? Enzymes can change the equilibrium point of reactions, but they cannot speed up reactions because they cannot change the net energy output. Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output. Enzymes can greatly speed up reactions, but they cannot change the activation energy because they cannot change the net energy output. Enzymes can greatly speed up reactions, but they cannot change the net energy output because they cannot change the activation energy.

A reaction that is at equilibrium is not capable of doing any work. The ΔG for a reaction at equilibrium is zero, which means that there is no free energy available to do any work.

Which of the following statements about equilibrium of chemical reactions is correct? See Concept 8.2 (Page)

The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule. A key feature in the way cells manage their energy resources to do this work is energy coupling, the use of an exergonic process to drive an endergonic one. ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work. Read about energy coupling.

Which of the following statements about the role of ATP in cell metabolism is true?

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

Which of the following statements is correct regarding ATP? ATP molecules do not release free energy when hydrolyzed. The energy in an ATP molecule is released from the ribose group. The energy in an ATP molecule is released from the adenine group. ATP cannot transfer energy to other molecules. The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups.

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 is correct regarding competitive and noncompetitive enzyme inhibitors? Only competitive inhibitors affect enzyme function. Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site. Neither type of inhibitor affects enzyme function. Inhibitors always bind irreversibly to an enzyme. Competitive inhibitors do not bind directly to the active site of an enzyme while noncompetitive inhibitors do.

The enzyme has an allosteric regulatory site. The allosteric site is distinct from the active site, and does not affect the substrate specificity of the enzyme.

Which of the following would be unlikely to contribute to the substrate specificity of an enzyme? See Concept 8.4 (Page)

increasing the concentration of ammonia. The concentration of NH3 affects how quickly N2 and H2 can be made.

Which of the following would increase the rate of the reverse reaction?

acetyl CoA Acetyl CoA enters the citric acid cycle.

Which of these is NOT a product of the citric acid cycle?

WHAT YOU NEED TO KNOW The action of inhibitors may be reversible or irreversible is true. Certain chemicals selectively inhibit the action of specific enzymes, and we have learned a lot about enzyme function by studying the effects of these molecules. If the inhibitor attaches to the enzyme by covalent bonds, inhibition is usually irreversible. Many enzyme inhibitors, however, bind to the enzyme by weak interactions, in which case inhibition is reversible. Some reversible inhibitors resemble the normal substrate molecule and compete for admission into the active site. These mimics, called competitive inhibitors, reduce the productivity of enzymes by blocking substrates from entering active sites. This kind of inhibition can be overcome by increasing the concentration of substrate so that as active sites become available, more substrate molecules than inhibitor molecules are around to gain entry to the sites. In contrast, noncompetitive inhibitors do not directly compete with the substrate to bind to the enzyme at the active site. Instead, they impede enzymatic reactions by binding to another part of the enzyme. This interaction causes the enzyme molecule to change its shape in such a way that the active site becomes less effective at catalyzing the conversion of substrate to product.

Which of these statements about enzyme inhibitors is true? Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory. A competitive inhibitor binds to the enzyme at a place that is separate from the active site. A noncompetitive inhibitor does not change the shape of the active site. The action of inhibitors may be reversible or irreversible. When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.

Add more substrate; it will outcompete the inhibitor and increase the reaction rate. Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because the known enzyme's shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor's shape and structure should be.

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again?