Chapter 3 - Energy, Chemical Reactions, and Cellular Respiration - Problems

What did you learn? 2 Muscle contraction is an example of what form of energy?

Kinetic (Mechanical) Energy

10. Oxidative phosphorylation involves a. electrons transported in the electron transport chain and accepted by O2. b. ATP synthetase harnessing the energy in a proton gradient. c. coenzymes NADH and FADH2 giving up their electrons. d. all of the above.

d. all of the above.

What did you learn? 9 What is the relationship of enzymes and activation energy?

enzymes lower activation energy

8. All stages of cellular respiration are decreased in conditions of insufficient oxygen except a. glycolysis. b. the intermediate stage. c. the citric acid cycle. d. the electron transport system.

a. glycolysis.

3. All of the following increase enzymatic activity except a. an increase in temperature. b. an increase in pH. c. an increase in concentration of the substrate. d. an increase in concentration of the enzyme that catalyzes the reaction.

b. an increase in pH.

4. ATP inhibits phosphofructokinase by binding to an allosteric site in glycolysis. ATP is functioning as a a. competitive inhibitor. b. competitive activator. c. noncompetitive inhibitor. d. noncompetitive activator.

c. noncompetitive inhibitor.

WHat DID YOU Learn? 27 Pyruvate is converted to what molecule if there is insufficient oxygen? Explain why this occurs.

convert to lactate to generate NAD+ otherwise glycolysis is halted.

5. All of the following are accurate about enzymes except a. Enzymes are typically globular proteins with an active site. b. Enzymes decrease activation energy. c. Enzymes can be used over and over to catalyze a substrate to a product. d. Enzymes are versatile and can catalyze different types of chemical reactions.

d. Enzymes are versatile and can catalyze different types of chemical reactions

What did you learn? 3 Energy can neither be created nor destroyed. However, according to the first and second laws of thermodynamics, what can happen to it, and what is always generated?

- can be converted to other forms - heat is always generated

2. Oxidation-reduction can be best classified as a(n) reaction. a. exchange b. endergonic c. synthesis d. reversible

a. exchange

1. Energy in ATP is used to power skeletal muscle contraction. This is an example of what type of energy conversion? a. chemical energy to mechanical energy b. light energy to mechanical energy c. chemical energy to light energy d. electrical energy to chemical energy

a. chemical energy to mechanical energy

What did you learn? 5 For a biochemical reaction that involves simple chemical structures bonded together into a more complex molecule, choose the more accurate term in each pair that best describes this type of chemical reaction: (a) synthesis or decomposition reaction; (b) exergonic or endergonic reaction; (c) collective term for this type of reaction (catabolism or anabolism).

(a) synthesis; (b) endergonic reaction; (c) collective term for this type of reaction (anabolism).

WHAT DID YOU LEARN? 1 Both the movement of Na+ down its concentration gradient and the movement of an electron from a higher energy to a lower energy state are examples of (a) potential energy or (b) kinetic energy?

(b) kinetic energy?

What do you think? 3 What is the net energy transfer during glycolysis?

2 ATP + 2 NADH

15. Describe a metabolic pathway, and explain how it is controlled by negative feedback.

A metabolic pathway is formed by numerous enzymes. Each enzyme catalyzes one progressive change to its specific substrate molecule and then releases the product. In turn, the product of one enzyme becomes the substrate of the next enzyme. Metabolic pathways is regulated to prevent overproduction of an unneeded product and exhaustion of substrates that could be used elsewhere. This regulation occurs through the process of negative feedback. The product from a metabolic pathway acts as an allosteric inhibitor to turn off an enzyme early in the metabolic pathway, for example. As the product accumulates, it is more likely to become bound to the enzyme and inhibit the metabolic pathway, with progressively less and less product being formed. Over time, as the amount of product decreases, the amount of the allosteric inhibitor bound to the enzyme decreases, and activity of that enzymatic pathway increases once again. In this way, a steady state of product is produced. One specific mechanism for regulating enzymes is by either phosphorylation or dephosphorylation of the enzyme. Note that phosphorylation may turn on some enzymes but turn off other enzymes. Equally, dephosphorylation may cause opposite effects in activity by different types of enzymes.

WHat DID YOU Learn? 15 What is a metabolic pathway? Explain the role of negative feedback in enzyme regulation.

A metabolic pathway is formed by numerous enzymes. Each enzyme catalyzes one progressive change to its specific substrate molecule and then releases the product. In turn, the product of one enzyme becomes the substrate of the next enzyme. Metabolic pathways is regulated to prevent overproduction of an unneeded product and exhaustion of substrates that could be used elsewhere. This regulation occurs through the process of negative feedback. The product from a metabolic pathway acts as an allosteric inhibitor to turn off an enzyme early in the metabolic pathway, for example. As the product accumulates, it is more likely to become bound to the enzyme and inhibit the metabolic pathway, with progressively less and less product being formed. Over time, as the amount of product decreases, the amount of the allosteric inhibitor bound to the enzyme decreases, and activity of that enzymatic pathway increases once again. In this way, a steady state of product is produced. One specific mechanism for regulating enzymes is by either phosphorylation or dephosphorylation of the enzyme. Note that phosphorylation may turn on some enzymes but turn off other enzymes. Equally, dephosphorylation may cause opposite effects in activity by different types of enzymes.

What did you learn? 6 What molecule is formed from exergonic reactions and used as the energy currency for endergonic reactions and other energy-requiring processes within the cell?

ATP

13. Explain ATP cycling.

ATP cycling is the continuous formation and breakdown of ATP. This cycling involves ATP formation (an endergonic reaction) and ATP splitting (an exergonic reaction). ATP is formed when energy is released in exergonic reactions using glucose or other fuel molecules from the foods we eat. These molecules undergo oxidation, and energy stored within their chemical bonds is transferred to ADP and Pi (free phosphate) to form ATP. In turn, ATP is then split into ADP and Pi, and the energy released is used for endergonic reactions, as well as other energy-requiring cellular processes. Thus, energy released in exergonic reactions in the body is coupled to endergonic reactions that require energy input so that endergonic reactions can proceed. A cell cannot stockpile ATP, so typically only a few seconds worth of ATP is present. Instead, the formation of ATP must occur continuously through the processes of breakdown of glucose (and other fuel molecules) to provide energy for endergonic reactions.

What do you think? 2 Given what you already know about isomers (see section 2.3a), what can you predict that an enzyme in the isomerase class would do?

Converts one isomer to another

12. Describe the different ways of classifying chemical reactions, and explain the category to which oxidation-reduction belongs.

Criteria for classifying chemical reactions: 1) change in chemical structure (synthesis, decomposition, exchange). 2) change in chemical energy (endergonic, exergonic). 3) reversible vs irreversible. Oxidation-reduction is an exchange reaction.

What did you learn? 13 How do changes in substrate concentration, temperature, and pH affect the reaction rate of enzyme-catalyzed chemical reactions?

Effect of Enzyme and Substrate Concentration The rate of a chemical reaction may be accelerated by either an increase in enzyme concentration or an increase in substrate concentration. An increase in substrate concentration, however, increases the rate of reaction only up to the point of saturation of the enzyme. Saturation occurs when so much substrate is present that all enzyme molecules are actively engaged in the chemical reaction, resulting in no further increase in reaction rate. Effect of Temperature Enzymes are proteins, and their three-dimensional shape is dependent upon environmental variables, including temperature and pH. Each enzyme has a specific environment in which it can most effectively participate in a chemical reaction. Human enzymes function efficiently at their optimal temperature, usually 37°C (98.6°F), which is the normal body temperature. Temperature increases in the body increase enzymatic activity; one advantage is that this enhances the body's ability to fight off infectious agents. More severe increases in temperature—meaning temperatures greater than 40°C (104°F) in humans—weaken the intramolecular bonds that hold an enzyme's protein structure in its three-dimensional shape. The protein subsequently denatures, permanently losing function. The greater the increase in temperature, the more likely this is to occur. Effect of pH Enzymes function most efficiently at their optimal pH. Optimal pH for most human enzymes is between pH 6 and 8, and changes in pH can affect the enzyme . An increase in H+ (which causes a decrease in pH) results in additional H+ binding to the enzyme. In contrast, a decrease in H+ (which causes an increase in pH) results in the release of H+ from an enzyme. In either case, the change in amount of H+ attached to the enzyme disrupts the electrostatic interactions that hold the enzyme protein in its shape. A significant disruption results in denaturation of the enzyme.

18. Describe how oxygen becomes part of water during cellular respiration.

Electrons are transferred from coenzymes to O2. The coenzyme, either NADH or FADH2, releases hydrogen (e- and H+) and it is oxidized. The released electrons are passed through the electron transport chain to O2, which serves as the final electron acceptor. O2 combines with 4 e- + 4 H+ to produce two molecules of H2O. Thus, oxygen is a reactant in cellular respiration, and it becomes part of the water that is produced. Notice that the oxygen you breathe is converted to water within the mitochondria of your cells.

What did you learn 14 How are enzymes regulated through competitive and noncompetitive inhibitors?

Enzyme Control An enzyme continues to facilitate the conversion of its substrate(s) to product as long as ample substrate is present and environmental conditions are close to normal. However, uncontrolled enzymes would result in depleted substrate levels and concentration of products that exceeds what is needed. Thus, enzymes must be temporarily "turned off" to prevent overproduction. Control of enzymes occurs through inhibitors that are substances that bind to an enzyme and turn it off, thus preventing it from catalyzing the reaction. Later, the release of the inhibitor from the enzyme allows it to function and continue catalyzing the reaction. This switching occurs in different ways, depending upon whether the inhibitor is competitive or noncompetitive. Competitive inhibitors A competitive inhibitor resembles the substrate and binds to the active site of the enzyme. Consequently, the substrate and the regulatory compound compete with each other for occupation of the enzyme's active site. The amount of substrate relative to the amount of competitive inhibitor determines the degree of inhibition. The greater the concentration of the substrate, the less likely the competitive inhibitor will occupy the enzyme's active site. In contrast, if substrate concentration decreases, the competitive inhibitor is more likely to occupy the enzyme's active site, and lower amounts of product are formed. Noncompetitive inhibitors Noncompetitive inhibitors do not resemble the substrate. They inhibit an enzyme by binding to a site on the enzyme other than the active site, a site termed the allosteric site. Binding of a noncompetitive inhibitor to the allosteric site induces a conformational change in the enzyme with an accompanying change in the shape of the enzyme's active site. Noncompetitive inhibitors are also called allosteric inhibitors because they bind to the allosteric site. This type of inhibition is not influenced by the concentration of substrate.

What did you learn? 11 What is the mechanism of enzyme action, including the role of cofactors?

Examples of enzymatic activity are diagrammed in figure 3.10. We show both an example of a decomposition reaction involving the enzyme lactase and a synthesis reaction involving the enzyme glycogen synthetase. In both cases, the enzyme facilitates the reaction as follows: 1. The substrate enters the active site of the enzyme, and the enzyme temporarily binds with the substrate to form an enzyme-substrate complex. 2. Entry of the substrate into the active site induces the conformation (structure) of the enzyme to change slightly, resulting in an even closer fit between substrate and enzyme. This response is referred to as the induced-fit model of enzyme function. The interaction is analogous to giving someone a hug. 3. Stress on chemical bonds in the substrate molecule is caused by the change in enzyme shape. Consequently, this stress lowers Ea, and the bonds in the substrates are more easily broken, permitting new chemical bonds to be formed. 4. The newly formed molecule, now called the product, is released from the enzyme. The enzyme is then free to repeat the process again and again with other substrates. • Enzymes often require cofactors that are "helper" ions or molecules to ensure that a reaction occurs. A cofactor is a nonprotein structure that may be either an inorganic or organic substance (see section 2.7a) associated with a particular enzyme or enzymatic reaction. • Inorganic cofactors are attached to the enzyme and are required for their normal function. For example, zinc ion is bound to carbonic anhydrase enzyme; without zinc, carbonic anhydrase is unable to function. In addition, many vitamins (e.g., B6 and B12), derivatives of vitamins, or modified nucleotides such as NAD+ may serve as organic cofactors. • Organic cofactors are not at- tached to enzymes and have specific functions in assisting enzymes. For example, the NAD+ coenzyme accepts hydrogen during chemical reac- tions to become NADH. Organic cofactors are more specifically referred to as coenzymes in some sources, and this term is also used in this text.

WHat DID YOU Learn? 28 Why is oxygen required to burn fatty acids?

Fatty acids are broken down through beta-oxidation in the mitochondria to generate acetyl-CoA (then citric acid cycle) + NADH + FADH2 (then electron transport chain). It is named as such because the beta carbon of the fatty acid undergoes oxidation to a carbonyl group. Beta-oxidation is primarily facilitated by the mitochondrial trifunctional protein, an enzyme complex associated with the inner mitochondrial membrane, although some fatty acids are oxidized in peroxisomes. Oxygen is required to regenerate NAD+ and FAD.

What did you learn? 12 Explain how enzymes are generally named.

The name of a given enzyme is generally based upon the name of the substrate or product involved in the chemical reaction, sometimes the name of the subclass, and the suffix -ase, added to the final word of the name.

WHat DID YOU Learn? 18 What are the four stages of cellular respiration for glucose oxidation, and identify the cellular location in which each occurs?

Glucose oxidation occurs within cells and is a step-by-step enzymatic breakdown of glucose with the accompanying release of energy to synthesize ATP. If oxygen is available, glucose is completely broken down and carbon dioxide and water are formed. Here we describe several significant features of glucose oxidation. Glucose has the chemical formula C6H12O6. It is an energy-rich molecule because of its many C-C, C-H, and C-O chemical bonds. When enzymes com- pletely disassemble glucose, the net chemical reaction for the process is C6H12O6 + 6 O2 → 6 CO2 + 6 H2O Four Stages of Cellular Respiration We separate the processes of glucose oxidation into four stages: glycolysis, intermediate stage, citric acid cycle, and the electron transport system. Glycolysis occurs in the cytosol and does not require oxygen; thus, glycolysis can occur either in the presence of oxygen or in the absence of oxygen. The other three stages occur in the mitochondria and require oxygen to proceed..

19. Identify the source of carbon in carbon dioxide.

Glucose.

20. Based on what you know about glycolysis and aerobic cellular respiration, explain the advantage in terms of ATP production of a healthy respiratory and cardiovascular system.

Healthy respiratory and cardiovascular system => adequate oxygen available for cellular respiration => efficient at energy formation as opposed to heavy dependence on glycolysis due to insufficient oxygen.

Can You Synthesize What You've Learned? 1. Tiffany had returned to her college dorm and was having difficulty breathing. She knew she was having an asthma attack. What changes in her energy level are predicted?

Lower energy levels due to diminished capacity to generate ATP.

14. Describe the structure and mechanism of enzymes.

Most enzymes are globular proteins that varied sizes. The amino acids in the protein chain form a unique three-dimensional molecular structure with a region called the active site. The active site accommodates the substrate(s) of a reaction to temporarily form an enzyme-substrate complex . The specificity in the shape of the active site permits only a single substrate, or type of substrate, to bind to the active site, and thus the enzyme is capable of catalyzing only one specific reaction. Mechanism of enzyme action: 1) The substrate enters the active site of the enzyme, and the enzyme temporarily binds with the substrate to form an enzyme-substrate complex. 2) Entry of the substrate into the active site induces the conformation (structure) of the enzyme to change slightly, resulting in an even closer fit between substrate and enzyme. This response is referred to as the induced-fit model of enzyme function. 3) Stress on chemical bonds in the substrate molecule is caused by the change in enzyme shape. Consequently, this stress lowers Ea, and the bonds in the substrates are more easily broken, permitting new chemical bonds to be formed. 4) The newly formed molecule, now called the product, is released from the enzyme. The enzyme is then free to repeat the process again and again with other substrates.

What did you learn? 10 What is the active site of an enzyme and how does it relate to a substrate?

Most enzymes are globular proteins, where its chain of amino acids form a unique three-dimensional molecular structure with a region called the active site. The active site accommodates the substrate(s) of a reaction to temporarily form an enzyme-substrate complex. The specificity in the shape of the active site permits only a single substrate, or type of substrate, to bind to the active site, and thus the enzyme is capable of catalyzing only one specific reaction.

WHat DID YOU Learn? 16 What two processes involve phosphate and are commonly used to regulate enzymes in a metabolic pathway or a multienzyme complex?

One specific mechanism for regulating enzymes is by either phosphorylation or dephosphorylation of the enzyme. Note that phosphorylation may turn on some enzymes but turn off other enzymes. Equally, dephosphorylation may cause opposite effects in activity by different types of enzymes.

Can You Synthesize What You've Learned? 3. What occurs to the amount of product formed in a metabolic pathway if inhibition does not occur?

Product accumulates until thermodynamic is reached.

WHat DID YOU Learn? 20 What are the two general fates of pyruvate, and what is the criterion that determines its fate?

Pyruvate is the final product of glycolysis. If sufficient oxygen is available, pyruvate enters a mitochondrion to complete its aerobic breakdown yielding carbon dioxide and water. In contrast, if sufficient oxygen is not available, pyruvate is converted to lactate.

17. In general terms, explain the fate of pyruvate if there is (a) sufficient oxygen, and (b) insufficient oxygen.

Pyruvate is the final product of glycolysis. If sufficient oxygen is available, pyruvate enters a mitochondrion to complete its aerobic breakdown yielding carbon dioxide and water. In contrast, if sufficient oxygen is not available, pyruvate is converted to lactate. Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD+. It converts pyruvate, the final product of glycolysis, to lactate when oxygen is absent or in short supply, and it performs the reverse reaction during the Cori cycle in the liver. At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. It also catalyzes the dehydrogenation of 2-Hydroxybutyrate, but it is a much poorer substrate than lactate.

16. Summarize glycolysis, including where it occurs in a cell, if it requires oxygen, the substrate and final product, and the formation of energy containing molecules (i.e., ATP, NADH, FADH2).

Summarize glycolysis: - Net Chemical Reaction: C6H12O6 → 2 x pyruvate + 2 ATP + 2 NADH - Location: Cytosol - Oxygen Requirements: Not dependent on oxygen. - Formation of Energy Containing molecules: Glycolysis is regulated through negative feedback like many metabolic pathways. ATP acts as an allosteric inhibitor to "turn off" phosphofructokinase. Pyruvate is the final product of glycolysis. If sufficient oxygen is available, pyruvate enters a mitochondrion to complete its aerobic breakdown yielding carbon dioxide and water. In contrast, if sufficient oxygen is not available, pyruvate is converted to lactate.

WHat DID YOU Learn? 22 Summarize the metabolic pathway of the citric acid cycle—where it occurs, if the process requires oxygen, the net chemical reaction, and the net energy transfer.

The citric acid cycle (also known as the Krebs cycle) is a cyclic metabolic pathway that occurs through the activity of nine enzymes located within the matrix of mitochondria and requires oxygen. During the citric acid cycle, the acetyl CoA produced in the intermediate stage is converted to two CO2 molecules and a CoA molecule is released. Energy is transferred to form one ATP molecule, three NADH molecules, and 1 FADH2 molecule during one "turn" of the citric acid cycle. Acetyl CoA ===> 2 CO2 + 1 CoA The net transfer of energy produced in this cycle is used to form: 1 ATP + 3 NADH + 1 FADH2 This enzymatic pathway is called a "cycle" because oxaloacetic acid is involved in the first step and is regenerated in the last step.

WHat DO YOU tHInK? 4 Why is the enzymatic pathway of the citric acid cycle considered to be a "cycle"?

The citric acid cycle (also known as the Krebs cycle) is a cyclic metabolic pathway that occurs through the activity of nine enzymes located within the matrix of mitochondria and requires oxygen. During the citric acid cycle, the acetyl CoA produced in the intermediate stage is converted to two CO2 molecules and a CoA molecule is released. Energy is transferred to form one ATP molecule, three NADH molecules, and 1 FADH2 molecule during one "turn" of the citric acid cycle. Acetyl CoA ===> 2 CO2 + 1 CoA The net transfer of energy produced in this cycle is used to form: 1 ATP + 3 NADH + 1 FADH2 This enzymatic pathway is called a "cycle" because oxaloacetic acid is involved in the first step and is regenerated in the last step.

WHat DID YOU Learn? 21 Explain the enzymatic reaction involving pyruvate dehydrogenase in the intermediate stage—where it occurs, if the process requires oxygen, the net chemical reaction, and the net energy transfer.

The intermediate stage is an aerobic process that occur within mitochondria. The intermediate stage is the "link" between the multistep metabolic processes of glycolysis with the multistep metabolic processes that occur in the citric acid cycle. The intermediate stage is catalyzed by a multienzyme complex called pyruvate dehydrogenase. During the intermediate stage, pyruvate dehydrogenase brings together pyruvate and a molecule of coenzyme A (CoA) that is already present within the matrix to form acetyl CoA (a two-carbon molecule with CoA attached). Concurrently, a carboxyl group, consisting of one carbon atom and two oxygen atoms, is released from the pyruvate as carbon dioxide: pyruvate => Acetyl CoA + CO2 Termed as decarboxylation. Energy is released during decarboxylation as two hydrogen atoms (two electrons plus two hydrogen ions) are transferred to the coenzyme NAD+ to form NADH (and H+) during this process. Note that the intermediate stage must occur twice for the complete digestion of the original glucose molecule: 2 pyruvate = 2 NADH per glucose molecule. The acetyl CoA then enters the third stage of glucose oxidation, termed the citric acid cycle.

WHat DID YOU Learn? 25 What are the three primary steps that take place in the electron transport system?

The processes of the electron transport system are organized into three major steps: 1) Electrons are transferred from coenzymes to O2. The coenzyme, either NADH or FADH2, releases hydrogen (e- and H+) and it is oxidized. The released electrons are passed through the electron transport chain to O2, which serves as the final electron acceptor. O2 combines with 4 e- + 4 H+ to producetwo molecules of H2O. Thus, oxygen is a reactant in cellular respiration, and it becomes part of the water that is produced. Notice that the oxygen you breathe is converted to water within the mitochondria of your cells! 2) Proton gradient is established. As electrons are "falling" and passed through the electron transport chain, their kinetic energy is harnessed by H+ pumps to move H+ from the mitochondrial matrix into the outer compartment, maintaining a proton gradient. 3) Proton gradient is harnessed to form ATP. H+ moves down its concentration gradient as it is transported across the inner membrane by ATP synthetase. It moves from the outer compartment into the matrix. (Note that H+ moves back into the area of the mitochondrion from which it was just pumped.) This process is analogous to water falling over a dam and turning a water wheel. The kinetic energy of the falling H+ is harnessed by ATP synthetase to form a new bond between ADP and Pi, producing an ATP. This process of forming ATP is referred to as oxidative phosphorylation because it involves oxygen as the final electron acceptor, and ATP is formed from the phosphorylation of ADP. This process is distinguished from substrate-level phosphorylation, which forms ATP from energy directly released from a substrate, as occurs in specific steps of glycolysis and the citric acid cycle.

WHat DID YOU Learn? 24 What is the importance of NADH and FADH2 in energy transfer?

The role of NADH and FADH2 is to donate electrons to the electron transport chain. They both donate electrons by providing an hydrogen molecule to the oxygen molecule to create water during the electron transport chain. NADH is a product of both the glycolysis and Kreb cycles. FADH2 is only produced in Krebs cycle. Hydrogen molecules are necessary to the synthesis of ATP. ATP synthase molecules uses hydrogen molecules to create ATP from ADP. The process of creating ATP from ADP is called "oxidative phosphorlyation". During the electron transport chain, NADH become NAD+ and the H get transported across the membrane. As a result, electrons reduced from NAD+ are used in the transport chain. Similar thing happens to FADH2 as well. FADH2 becomes FAD+ and the H's are transported across the membrane. These hydrogens that were released by NAD+ and FAD+ are used by ATP synthase enzyme to make ATP by pulling hydrogen molecules back across the membrane.

9. In glycolysis, ATP are formed, and if sufficient oxygen is present, ATP are formed. a. 2, 2 b. 36, 38 c. 2, 30 d. 10, 30

a. 2, 2

6. Glucose is converted to pyruvate in which stage of cellular respiration? a. glycolysis b. intermediate stage c. citric acid cycle d. electron transport system

a. glycolysis

Can You Apply What You've Learned? 3. Another challenge to a patient with impaired respiratory func- tion is the buildup of CO2 in the blood. What would you pre- dict given the following enzymatic reaction that occurs in the blood? H O + CO H CO H+ + HCO - a. increased production of H2O b. increased production of H+ (with an accompanying decrease in pH) c. decreased production of H+ (with an accompanying increase in pH) d. All of the above.

b. increased production of H+ (with an accompanying decrease in pH)

Can You Apply What You've Learned? 1. Albinism (achromia) is a genetic condition in which an individual cannot synthesize melanin from tyrosine (an amino acid), a brown pigment of the hair, skin, and eyes. These individuals lack a. specific fatty acids. b. a protein that contains tyrosine. c. an enzyme that converts tyrosine to melanin. d. cofactors that convert tyrosine to melanin.

c. an enzyme that converts tyrosine to melanin.

Can You Apply What You've Learned? 5. Brown adipose tissue contains cells that allow H+ to fall down the concentration gradient in the electron transport chain without producing ATP. Instead, all of the kinetic energy is converted to heat. If scientists could increase the amount of brown adipose tissue in our bodies, then a. our body temperature would be cooler. b. these cells would be more efficient at producing ATP. c. we could eat more and not gain weight. d. we would be able to run faster.

c. we could eat more and not gain weight.

Can You Apply What You've Learned? 4. You would expect decreased production of ATP in all of the following individuals except a. an individual with impaired ability to transport oxygen in the blood, such as a person with anemia. b. an individual with severe asthma. c. an individual in congestive heart failure. d. an athlete.

d. an athlete.

7. NAD+ and FAD are examples of a. enzymes. b. high-energy organic molecules that are digested in cellular respiration. c. allosteric inhibitors. d. coenzymes.

d. coenzymes.

Can You Apply What You've Learned? 2. If an individual has impaired respiratory function, such as occurs with emphysema, you would expect all of the following except a. production of additional lactate. b. an impaired ability to make ATP. c. low energy levels and complaints of being tired. d. increased aerobic cellular respiration.

d. increased aerobic cellular respiration.

What did you learn? 8 Explain the effect a fever would have on chemical reaction rates within the body. What is the risk to protein structure with a high fever?

fever would increase reaction rates all throughout the body. At a high enough body temperature, proteins begin to denature.

What did you learn? 4 What are the differences between reactants and products in a chemical equation?

in a chemical reaction, reactants are depleted while products are formed

What did you learn? 7 Explain what occurs when the equilibrium is disturbed in reversible reactions by changes in reactants and products.

inc reactants, more prod formed until equilibrium is reached. inc products, more reactants formed until equilibrium is reached.

WHat DID YOU Learn? 26 How many net ATP molecules are generated through glycolysis (i.e., without participation of mitochondria)? How many net ATP molecules are formed through the combined processes that occur in the cytosol and those that occur within mitochondria?

see table

WHat DID YOU Learn? 23 What energy molecules are produced from the chemical breakdown of glucose during each of the three steps of cellular respiration?

see talbe

WHat DID YOU Learn? 19 Describe glycolysis—where it occurs, if the process requires oxygen (i.e., is aerobic), the net chemical reaction, and the net energy transfer.

• Glycolysis does not require oxygen. • Ten enzymes within the cytosol of a cell participate in the metabolic pathway of glycolysis. • Glucose is broken down in this pathway into two pyruvate molecules with an accompanying energy transfer to form a net production of 2 ATP molecules and 2 NADH molecules. Glycolysis is a metabolic process that occurs in the cytosol without the requirement of oxygen. Glucose is the initial substrate and pyruvate is the final product. The net transfer of energy is used in the formation of 2 ATP and 2 NADH molecules. Formation of ATP. Two ATP molecules are invested early in glycolysis (steps 1 and 3). Four ATP molecules are formed during glycolysis (steps 7 and 10, which occur twice per the original glucose molecule). Thus, there is a net of 2 ATP molecules formed during glycolysis (2 ATP invested, 4 ATP formed). Formation of NADH. Two NADH molecules are formed from glucose breakdown during glycolysis (step 6, which occurs twice per the original glucose molecule).