Ch2: Metabolic Processes

Question 1

Which of the following statements about metabolism is FALSE?

a) Metabolism is the sum of all anabolic and catabolic processes.
b) Anabolism involves breaking down large molecules to release energy.
c) Catabolism involves breaking down compounds into smaller molecules to release energy.
d) Living organisms must continually capture, store, and use energy.

Answer 1

B

Question 2

What is activation energy?

Answer 2

The energy required to break a chemical bond.

Question 3

Inorganic molecules or metal ions required for enzyme activity by assisting in binding through transfer of electrons are called?

Answer 3

Cofactors

Question 4

Which type of enzyme inhibitor binds to another part of the enzyme (allosteric site) and changes the shape of the active site?

Answer 4

Noncompetitive inhibitor

Question 5

Where does anaerobic respiration (fermentation) primarily occur within the cell?

Answer 5

Cytosol

Question 6

What is the main purpose of glycolysis?

Answer 6

To make pyruvate

Question 7

A net yield of how many ATP molecules is produced during glycolysis per molecule of glucose?

Answer 7

2

Question 8

How many NADH molecules are produced during glycolysis per molecule of glucose?

Answer 8

2

Question 9

Where does the Krebs Cycle (including pre-Krebs) primarily occur within the cell?

Answer 9

Matrix of the mitochondria

Question 10

Before entering the Krebs cycle, pyruvate is converted into acetyl-CoA. This process involves the removal of carbon (decarboxylation) which forms/releases?

Answer 10

CO2

Question 11

Per glucose molecule, how many total NADH are produced from the Krebs cycle (including pre-Krebs)?

Answer 11

8

Question 12

Per glucose molecule, how many total FADH2 are produced from the Krebs cycle?

Answer 12

2

Question 13

The Electron Transport Chain (ETC) primarily occurs in which part of the mitochondria?

Answer 13

Inner mitochondrial membrane

Question 14

As electrons are transported across the ETC, H+ ions are pumped through the membrane, resulting in a buildup of H+ ions in which location?

a) Cytosol
b) Mitochondrial matrix
c) Intermembrane space
d) Outer mitochondrial membrane

Answer 14

C

Question 15

The diffusion of H+ ions back into the matrix through ATP Synthase is driven by what?

Answer 15

The concentration gradiet

Question 16

What is the theoretical maximum total ATP yield from one molecule of glucose undergoing complete aerobic cellular respiration?

Answer 16

38

Question 17

If the flow of electrons is blocked in the Electron Transport Chain, what happens to NADH and FADH2 molecules?

Answer 17

They won’t be oxidized, creating a buildup.

Question 18

In anaerobic conditions in animal tissue, which substance will be produced following glycolysis?

Answer 18

Lactic acid

Question 19

Explain why oxygen is essential for the Krebs Cycle to continue, even though it is not directly consumed within the cycle itself.

Answer 19

Oxygen is essential because it is the final electron acceptor in the Electron Transport Chain (ETC). If oxygen is absent, the ETC shuts down, causing a backlog of electrons. This prevents NADH and FADH2 from being oxidized back to NAD+ and FAD. Without NAD+ and FAD, which are generated in the ETC and used in the Krebs cycle to pick up electrons, the Krebs cycle cannot continue to run.

Question 20

Describe how an enzyme’s specific shape is critical to its function and how the “induced fit” model explains this interaction.

Answer 20

Enzymes have a specific and unique three-dimensional shape, particularly at their active site, that only fits a certain substrate. This specificity is crucial because if the active site’s shape doesn’t match the substrate’s, the enzyme cannot bind to the substance and catalyze the reaction. The “induced fit” model explains that while the initial binding between enzyme and substrate might be imperfect, both the enzyme and substrate change their shapes slightly to bind together more strongly and tightly, facilitating the reaction.

Question 21

Why can humans only survive off anaerobic cellular respiration for a short period of time, and why is it “uneffective in the long-run”?

Answer 21

Humans can survive off anaerobic cellular respiration (fermentation) for a short period because it produces a small amount of ATP (2 net ATP from glycolysis) without oxygen. However, it is ineffective in the long run because it does not produce an adequate number of ATP molecules to sustain the body’s energy demands. Aerobic respiration, which requires oxygen, yields significantly more ATP (up to 38 ATP per glucose), making it the primary and necessary pathway for long-term survival and high energy requirements.

Question 22

Describe the role of NAD+ and FAD as electron carriers in cellular respiration and where they pick up and release electrons.

Answer 22

NAD+ and FAD are compounds that act as electron carriers in cellular respiration. They are able to pick up electrons from energy-rich compounds and then transfer these electrons to low-energy compounds. Specifically, NAD+ is reduced to NADH in glycolysis and during the conversion of pyruvate to acetyl-CoA and multiple steps within the Krebs cycle. FAD is reduced to FADH2 in the Krebs cycle during the oxidation of succinate to fumarate. These reduced forms (NADH and FADH2) then deliver their electrons to the Electron Transport Chain, where they become oxidized back to NAD+ and FAD, respectively, to be reused in earlier stages.

Question 23

Compare and contrast Aerobic and Anaerobic respiration in terms of oxygen requirement.

Question 24

Compare and contrast NADH and FADH2 in terms of where they enter the Electron Transport Chain and their resulting ATP yield.

Answer 24

NADH: Enters the first electron-carrying protein in the ETC. Each NADH ideally results in the pumping of 3 H+ ions and contributes to the production of about 3 ATP molecules.

FADH2: Is more electronegative than the first protein, so it enters the ETC at coenzyme Q, starting at ETC protein 2. Each FADH2 ideally results in the pumping of 2 H+ ions and contributes to the production of about 2 ATP molecules.

Contrast: NADH enters earlier and yields more ATP per molecule than FADH2. FADH2 enters later in the chain.

Compare: Both are electron carriers generated in earlier stages of cellular respiration (glycolysis, Krebs cycle) that donate electrons to the ETC to drive ATP synthesis.

Question 25

A person consumes a meal rich in glucose. Trace the path of this glucose molecule through the main stages of aerobic cellular respiration, specifying the primary input and output molecules for each major stage until the formation of waste products.

Question 26

Define "substrate" and "active site" in relation to enzymes. What is "induced fit"?

Answer 26

Substrate: The substance or reactant on which an enzyme acts. Each enzyme has a specific substrate. Active site: The region of an enzyme that binds to the substrate. Induced fit: The change in the shape of an enzyme's active site induced by the substrate, allowing for a strong, tight binding.

Question 27

List and briefly explain at least three factors that affect enzyme activity.

Answer 27

1.Temperature: High temperatures can denature proteins, slowing down or stopping enzyme activity. Most enzymes prefer normal body temperatures (around 37.5°C). 2.pH: Most enzymes prefer a neutral pH (6 to 8). Enzyme activity slows down when the pH value deviates from ideal conditions, and ionic salts can denature enzymes. 3.Cofactors and Coenzymes: These are non-protein molecules sometimes required for enzyme activity. Cofactors are inorganic molecules or metal ions assisting in binding, often by transferring electrons (e.g., iron in hemoglobin). Coenzymes are organic cofactors, usually derived from vitamins, that act as carriers in metabolic pathways. 4.Enzyme Inhibitors: Molecules that block or decrease enzyme activity.

Question 28

Differentiate between competitive and non-competitive enzyme inhibitors.

Answer 28

Competitive inhibitors: Chemicals that resemble the enzyme's substrate and compete with it for the active site. Non-competitive inhibitors: Chemicals that do not enter the active site but bind to another part of the enzyme (an allosteric site), changing its shape and active site.

Question 29

What are the two main types of cellular respiration based on oxygen requirement, and where do their primary stages occur?

Answer 29

Aerobic respiration: Needs oxygen and occurs mainly in the mitochondria (Krebs cycle and Electron Transport Chain). Anaerobic respiration (fermentation): Does NOT need oxygen and occurs in the cytosol (glycolysis).

Question 30

What are the net products of glycolysis from one glucose molecule?

Answer 30

For one glucose molecule, glycolysis produces a net yield of 2 ATP, 2 NADH, and 2 pyruvate molecules. Although 4 ATP are produced, 2 ATP are used at the beginning, resulting in a net gain of 2 ATP.

Question 31

For one glucose molecule, glycolysis produces a net yield of 2 ATP, 2 NADH, and 2 pyruvate molecules. Although 4 ATP are produced, 2 ATP are used at the beginning, resulting in a net gain of 2 ATP.

Answer 31

6 CO₂ (2 from pre-Krebs, 4 from Krebs) 8 NADH (2 from pre-Krebs, 6 from Krebs) 2 FADH₂ (from Krebs) 2 ATP (from Krebs)

Question 32

What is the theoretical maximum ATP yield from one glucose molecule during aerobic cellular respiration, and how is this breakdown distributed among the stages?

Answer 32

Glycolysis: Net 2 ATP + 2 NADH (worth 3 ATP each in ETC) = 8 ATP. Krebs Cycle (including pre-Krebs): 2 ATP + 8 NADH (worth 3 ATP each in ETC) + 2 FADH₂ (worth 2 ATP each in ETC) = 30 ATP. (2 direct ATP + 24 ATP from NADH + 4 ATP from FADH2).

Question 33

The primary reason ATP and NADPH are considered short-term energy molecules in plants, necessitating the Calvin cycle, is because: a) They are quickly consumed by photorespiration. b) Their chemical bonds are highly unstable and break down within minutes. c) They cannot be transported efficiently out of the thylakoid membrane. d) They spontaneously convert into ADP and NADP+ if not immediately used.

Answer 33

A

Question 34

Which of the following statements about C4 plants is INCORRECT? a) They are found in hot climates. b) They spatially separate carbon fixation from the Calvin cycle. c) They are less energy efficient than C3 plants due to additional steps. d) They have stomata that primarily open at night to conserve water.

Answer 34

d

Question 35

How do guard cells control the opening and closing of stomata, involving K+ ions and water movement?

Answer 35

Guard cells control the opening and closing of stomata. For opening, K+ ions are actively transported into the guard cell vacuoles, which increases solute concentration and decreases water concentration, making the cells hypotonic. Through osmosis, water moves into the cells, causing them to swell and become turgid, thus creating a gap between them. For closing, K+ pumps are deactivated, leading to K+ ions diffusing out of the guard cells, making them hypertonic. Water then moves out, causing the cells to become flaccid and the gap to close.

Question 36

Where specifically do the light reactions occur within the chloroplast?

Answer 36

Thylakoid

Question 37

Where does the Calvin cycle (dark reactions) take place within the chloroplast?

Answer 37

Stroma

Question 38

Why can't the Calvin cycle occur at night, even though it doesn't directly require light?

Answer 38

it cannot occur at night because it depends on ATP and NADPH, which are produced during the light reactions.

Question 39

How do enzymes reduce the activation energy of a reaction?

Answer 39

Enzymes are biological catalysts, mostly proteins, that speed up chemical reactions in living organisms without being consumed. They achieve this by lowering the activation energy, which is the energy required to break a chemical bond. Each enzyme has a specific active site that binds to a particular substrate. When the enzyme and substrate bind, they undergo an "induced fit," where their shapes change slightly to allow for a strong, tight binding. Although the sources do not detail the exact molecular mechanisms of how this binding directly lowers activation energy (e.g., by orienting reactants, straining bonds, or stabilizing the transition state), they consistently state that this is the function by which enzymes accelerate reactions.

Question 40

Compare the role of ATP synthase in cell respiration and photosynthesis.

Answer 40

In Cellular Respiration: ATP synthase is located in the inner mitochondrial membrane. Its role is to pump H+ ions from the intermembrane space back into the mitochondrial matrix, down their concentration gradient. This movement of H+ ions through ATP synthase serves as a cofactor for the phosphorylation of ADP into ATP, leading to ATP production. The H+ ion gradient itself is generated by the electron transport chain (ETC), which pumps H+ ions into the intermembrane space. In Photosynthesis: ATP synthase is located in the thylakoid membrane within the chloroplasts. Here, it pumps H+ ions from the lumen (the space inside the thylakoid) to the stroma (the fluid-filled space outside the thylakoid). This pumping action cofactors the phosphorylation of ADP into ATP. A high concentration of H+ ions in the lumen, creating a steeper gradient, is important for this process, allowing them to diffuse out and make ATP. The H+ ion gradient is primarily generated during the electron transport phase of the light reactions, where electrons from water are transported and H+ ions are produced and pumped into the lumen.

Question 41

Explain why photorespiration is a problem in warmer climates, compared to cooler climates.

Answer 41

Photorespiration occurs when the enzyme RUBISCO, which is responsible for carbon fixation in the Calvin cycle, binds with oxygen (O2) instead of carbon dioxide (CO2). This is a significant disadvantage for C3 plants, especially in warmer or dry climates. In warm and dry conditions, C3 plants tend to close their stomata to conserve water and prevent excessive water loss. While this helps with water retention, it also limits the intake of CO2. As CO2 is continuously used up in photosynthesis and O2 is produced, the internal CO2 concentration within the leaf decreases, while the O2 concentration increases. When CO2 levels are low and O2 levels are high, RUBISCO is more likely to bind to O2, initiating photorespiration instead of carbon fixation. This process is problematic because it consumes energy and releases CO2 without producing ATP or NADPH, making it an inefficient and wasteful pathway for the plant. In cooler, more humid climates, C3 plants can keep their stomata open more often, allowing for a steady supply of CO2 and reducing the likelihood of photorespiration.