Cellular Respiration and Anaerobic Respiration

What is the most common fuel molecule used by cells?

Glucose (C₆H₁₂O₆)

What is the overall purpose of the glucose catabolism pathway?

To harvest energy from glucose in the form of ATP, NADH, and FADH₂ for use in cellular processes.

Write the balanced chemical equation for the metabolism (burning) of glucose, including free energy as a product.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~686 kcal/mol (ΔG°' = -686 kcal/mol)

What are the three main stages of aerobic catabolism (cellular respiration)?

1) Glycolysis

2) Krebs Cycle (Citric Acid Cycle)

3) Oxidative Phosphorylation (Electron Transport Chain + Chemiosmosis)

Define the terms oxidation and reduction in the context of electron transfer.

Oxidation: Loss of electrons (often with H⁺) Reduction: Gain of electrons (often with H⁺)

In the overall equation for glucose metabolism, which molecule is oxidized and which is reduced?

-Glucose is oxidized to CO₂

-Oxygen is reduced to H₂O

Explain the relationship between the loss or gain of electrons and the transfer of H⁺ in redox reactions.

-Electrons are often transferred with H⁺.

-Loss of electrons and H⁺ = Oxidation

-Gain of electrons and H⁺ = Reduction

Identify the key coenzyme (molecule) that acts as an electron carrier in cellular respiration redox reactions.

NAD⁺ (Nicotinamide adenine dinucleotide)

Describe the role of NAD⁺. What is its reduced form, and why is this reduced form considered an important energy intermediary in cells?

NAD⁺ is reduced to NADH by gaining electrons. NADH temporarily stores energy and donates electrons to the electron transport chain to help produce ATP.

During the oxidation of glucose, approximately what percentage of the potential free energy is conserved in the reduced coenzymes (NADH and FADH₂)?

About 40% of the energy is conserved in NADH and FADH₂; the rest is lost as heat.

What key substance determines whether the pyruvate molecule resulting from glycolysis proceeds into aerobic respiration or fermentation?

Oxygen (O₂)

Compare and contrast the final waste products and the net energy trapped (ATP per glucose) for cellular respiration (aerobic) and fermentation (anaerobic):

-Aerobic Respiration: CO₂ and H₂O; ~30-32 ATP

-Fermentation: Lactic acid or ethanol + CO₂; 2 ATP

Where does glycolysis take place within the cell?

Cytoplasm

In eukaryotic cells, where does the majority of aerobic respiration take place?

Mitochondria

What is the product of glycolysis?

2 Pyruvate molecules

What is the net yield per molecule of glucose from glycolysis in terms of ATP, NADH, and pyruvic acid?

-2 ATP (net)

-2 NADH

-2 Pyruvate

Where in the cell does the Krebs cycle (Citric Acid Cycle) occur?

Mitochondrial matrix

What is the general purpose of the Krebs cycle?

To oxidize acetyl-CoA to CO₂ and produce NADH and FADH₂ for the electron transport chain.

List the final yield per molecule of glucose from the Krebs cycle in terms of CO₂, NADH, FADH₂, and ATP (from GTP):

-4 CO₂

-6 NADH

-2 FADH₂

-2 ATP (from GTP)

Define oxidative phosphorylation

The production of ATP using energy from electrons transferred through the electron transport chain, coupled with chemiosmosis.

What two distinct stages comprise oxidative phosphorylation?

1) Electron Transport Chain (ETC)

2) Chemiosmosis

Where in the mitochondrion does the electron transport chain occur?

Inner mitochondrial membrane

Describe the flow of electrons in the electron transport chain, starting with the reduced coenzymes.

Electrons flow from NADH and FADH₂ through protein complexes in the ETC, finally reducing O₂ to form water.

What is the role of O₂ in the electron transport chain?

O₂ is the final electron acceptor and forms water by combining with electrons and H⁺.

During electron transport, what is the fate of the protons (H⁺) and where do they accumulate?

Protons are pumped into the intermembrane space, creating a proton gradient.

What is the potential energy stored in the H⁺ concentration gradient and charge difference called?

Proton-motive force

Explain the process of chemiosmosis and the function of ATP synthase.

Chemiosmosis is the movement of H⁺ through ATP synthase back into the mitochondrial matrix, driving the synthesis of ATP.

ATP synthase is described as a molecular motor. What are its two main parts and what is the function of each?

1) F₀ unit: Allows H⁺ to pass through the membrane

2) F₁ unit: Catalyzes the formation of ATP

What is the total theoretical maximum number of ATP molecules generated per molecule of glucose during aerobic respiration?

30-32 ATP

What general type of catabolic pathway do organisms use to generate ATP when oxygen (O₂) is scarce or absent?

Fermentation

In which three situations would a cell or organism rely on anaerobic respiration (fermentation)?

-Low oxygen environments

-Sudden high energy demand (e.g., sprinting)

-Microbial life in anaerobic habitats

What are the two best-known forms of fermentation, and what are their primary waste products?

1) Lactic Acid Fermentation: Lactic acid

2) Alcoholic Fermentation: Ethanol and CO₂

What is the final net yield of ATP per molecule of glucose from glycolysis followed by fermentation?

2 ATP

What is the specific goal of the fermentation stage (e.g., lactic acid fermentation) following glycolysis?

To regenerate NAD⁺ so that glycolysis can continue.

In lactic acid fermentation, which molecule acts as the final electron acceptor, and what does it become?

Pyruvate is the final electron acceptor and becomes lactic acid

Write the summary equation for the reactions and products of lactic acid fermentation:

C₆H₁₂O₆ → 2 C₃H₆O₃ + 2 ATP (Glucose → 2 Lactic Acid + 2 ATP)

What is the phosphagen energy system, and why is it used during short-term, intense activities?

A system that uses creatine phosphate to rapidly regenerate ATP during short bursts of high-intensity activity.

Describe the reaction that the phosphagen system uses to quickly produce ATP in muscle tissue:

Creatine phosphate + ADP → Creatine + ATP

Rank the three main ATP production mechanisms (phosphagen use, anaerobic glycolysis, aerobic catabolism) from fastest peak rate to slowest peak rate:

1) Phosphagen system (fastest)

2) Anaerobic glycolysis

3) Aerobic catabolism (slowest)

In terms of ATP yield (total possible ATP), which mechanism provides the largest amount and which provides the smallest amount?

-Largest: Aerobic respiration (~30-32 ATP)

-Smallest: Phosphagen system (limited, short-term)