Cellular Respiration and Fermentation Quiz

Learning Objectives

• Cellular Respiration and Fermentation, Chapter 9, details energy release from food and redox reaction processes in cellular metabolism.
• It covers the major steps in cellular respiration (glycolysis, etc.) and the importance of NAD+/NADH.
• Electron transport down the ETC is coupled with ATP production via chemiosmosis.
• Students will compare fermentation types to cellular respiration (aerobic and anaerobic).

Obtaining Cellular Energy

• Cells require energy from external sources to perform work, including mechanical, chemical, and transport functions.
• Organisms obtain energy by ingesting other animals or performing photosynthesis.

Energy Flows and Chemicals Cycle

• Energy enters ecosystems as light and leaves as heat.
• Chemical elements are recycled in ecosystems, such as carbon and nitrogen cycles.

Energy Flows and Chemicals Cycle (continued)

• Photosynthesis converts light energy into organic molecules and oxygen, which, in turn, feeds cellular respiration.
• Cells use the stored chemical energy in organic molecules to produce ATP, which is critical for cellular work.

Catabolic Pathways

• Catabolic pathways release stored energy by breaking down complex molecules (fuel).
• Breaking down complex molecules releases electrons and these are central to respiration processes.
• Glucose is a common molecule broken down in respiration. Its chemical equation is: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + Energy (ATP + heat).

Different Catabolic Pathways to Produce ATP

• The breakdown of organic molecules is an exergonic process.
• These molecules are often called fuels.
• Fermentation is a partial sugar breakdown without oxygen. This is a pathway often used to produce wine, cheese, beer and bread, and extracts energy simply from glycolysis..

Different Catabolic Pathways to Produce ATP (continued)

• Aerobic respiration is a chemical process that uses organic molecules and oxygen to produce ATP.
• It is a common process in most eukaryotic cells and many prokaryotic cells.

Different Catabolic Pathways to Produce ATP (continued)

• Anaerobic respiration is similar to aerobic respiration, but uses compounds other than oxygen (e.g., NO₃- or SO₄2-).
• Cellular respiration is a broad term and often refers only to aerobic respiration since it is most common in cells.

In Cellular Respiration, Electrons are Transferred

• Electrons are transferred during chemical reactions in organic molecules.
• This releases energy, used to synthesize ATP.
• Chemical reactions moving electrons are called oxidation-reduction (redox) reactions.

Redox Reactions

• The electron donor is the reducing agent.
• The electron receptor is the oxidizing agent.
• Some redox reactions don't transfer electrons, but change electron sharing in covalent bonds instead.

The Steps of Cellular Respiration

• Glycolysis breaks down glucose to pyruvate.
• The citric acid cycle completes the breakdown of glucose.
• Oxidative phosphorylation accounts for most ATP synthesis (~90%).

Overview of Cellular Respiration

• Glycolysis occurs in the cytosol, breaking glucose into pyruvate and producing electrons via NADH.
• Pyruvate oxidation moves into the mitochondria, producing Acetyl CoA which enters the citric acid cycle, creating further electrons via NADH and FADH₂.
• Oxidative phosphorylation uses electron transport to create a proton gradient, providing energy to produce ATP by ATP synthase.

ATP Production via Phosphorylation

• Oxidative phosphorylation is primarily powered by redox reactions of the electron transport chain.
• It is responsible for ~90% of ATP production.
• Substrate-level phosphorylation occurs from enzyme transfer of phosphate to ADP, but produces a much smaller yield of ATP than oxidative phosphorylation.

Glycolysis:

• Glycolysis breaks down glucose into two pyruvate molecules.
• This occurs in the cytosol and does not need oxygen.
• The glycolysis process is in two phases, which involves both the breaking down and subsequent reorganisation of the original molecule.

2 Major Phases of Glycolysis:

• Energy investment phase: cells use 2 ATP to start the process
• Energy payoff phase: cell produces 4 ATP and 2 NADH + 2H+

Electron Transport Chain (ETC)

• The ETC is located in the inner membrane (cristae) of mitochondria.
• Most of the components are multi-protein complexes.
• The ETC moves electrons from NADH & FADH₂ to O₂ forming H₂O.

Electron Transport Chain (ETC) - continued

• Electrons lose energy as they move along the ETC and this energy is used to pump protons (H+) into the intermembrane compartment.
• This builds a proton concentration gradient.

Electron Transport Chain and Chemiosmosis

• The proton gradient produced by the ETC is used to power ATP synthase, which is also located in the inner membrane.
• H+ move from high to low concentrations across the membrane
• ATP is generated.

Chemiosmosis

• Chemiosmosis is the use of a proton (H+) gradient to drive cellular work.
• H⁺ ions move into binding sites on the rotor of ATP synthase.
• This spins and helps catalyze phosphorylation of ADP to ATP
• This helps produce ATP.

Oxidative Phosphorylation

• Oxidative phosphorylation is a process that produces ATP using the electron transport chain.

An Audit of ATP Production

• During cellular respiration, most energy flows from glucose to NADH/FADH₂ to the ETC, then to proton-motive force and finally ATP.
• Typically about 30-32 ATP per glucose molecule and the remaining energy is lost as heat.

An Audit of ATP Production (continued)

• ATP production depends on how electrons from cytosolic NADH cross the mitochondrial membrane.

Anaerobic Respiration

• Some prokaryotes use electron transport chains, but do not use oxygen as the final acceptor.
• This process typically produces less energy, and no water.

Fermentation

• Fermentation occurs in the absence of oxygen.
• Fermentation is coupled with glycolysis.
• It regenerates NAD⁺ so glycolysis can continue, producing a small amount of ATP.

Fermentation and Types of Fermentation

• Fermentation uses substrate-level phosphorylation to generate ATP.
• It includes reactions after glycolysis that regenerate NADH so glycolysis can continue.
• Two major types are alcohol and lactic acid fermentation

Alcohol Fermentation

• Pyruvate is converted to ethanol.
• CO2 is released.
• NAD⁺ is regenerated.

Lactic Acid Fermentation

• Pyruvate is converted to lactate to regenerate NAD⁺.
• No CO₂ is released.

Comparing Fermentation with Aerobic and Anaerobic Respiration

• All of these processes use glycolysis to oxidize glucose and harvest energy (chemical).
• NAD+ is the oxidizing agent that accepts electrons in glycolysis.
• Aerobic respiration produces greater ATP than fermentation or anaerobic respiration.

Glycolysis During Evolution

• Glycolysis is present in both prokaryotic and eukaryotic cells.
• It does not require membrane-bound organelles.
• It likely evolved before oxygen was common in the atmosphere.

Energy from Multiple Sources

• Catabolic pathways funnel electrons from various organic molecules (e.g., carbohydrates, proteins, fats) into cellular respiration.