Cellular Respiration and Energy Metabolism

Cellular Respiration — Definition?

The process by which cells break down glucose using oxygen to produce ATP, carbon dioxide, water, and heat.

Cellular Respiration — Overall Chemical Equation?

Glucose + Oxygen → Carbon dioxide + Water + ATP + Heat
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~30–32 ATP

Cellular Respiration — Main Cellular Locations?

• Cytoplasm (glycolysis)

• Mitochondria (pyruvate oxidation, Krebs cycle, electron transport chain)

ATP (Adenosine Triphosphate) — Function?

The universal energy currency of the cell that directly powers cellular processes such as metabolism, movement, growth, and cell division.

ATP — Structure?

A nucleotide composed of:

• Adenine

• Ribose sugar

• Three phosphate groups

ATP Hydrolysis — Function?

Breakdown of ATP into ADP + phosphate releases energy used for cellular work.

Redox Reaction — Definition?

A chemical reaction involving transfer of electrons between molecules.

Oxidation — Definition?

Loss of electrons.

Reduction — Definition?

Gain of electrons.

NAD⁺ (Nicotinamide Adenine Dinucleotide) — Function?

Electron carrier that accepts electrons and hydrogen during cellular respiration, becoming NADH.

FAD (Flavin Adenine Dinucleotide) — Function?

Electron carrier that accepts electrons and hydrogen to form FADH₂ during cellular respiration.

NADH — Function?

Carries high-energy electrons to the electron transport chain to help generate ATP.

FADH₂ — Function?

Transfers high-energy electrons to the electron transport chain but produces slightly less ATP than NADH.

Substrate-Level Phosphorylation — Definition?

Direct formation of ATP by transferring a phosphate group from a phosphorylated substrate to ADP.

Oxidative Phosphorylation — Definition?

ATP production using energy released from electron transport and the proton gradient in mitochondria.

Cellular Respiration — Four Major Stages?

1. Glycolysis

2. Pyruvate oxidation

3. Krebs (Citric Acid) cycle

4. Electron transport chain

Glycolysis — Definition?

The first stage of cellular respiration that breaks glucose into two pyruvate molecules.

Glycolysis — Location?

Cytoplasm.

Glycolysis — Oxygen Requirement?

Does not require oxygen.

Glycolysis — ATP Investment Phase?

2 ATP are used to activate glucose.

Glycolysis — Net Products per Glucose?

• 2 Pyruvate

• 2 ATP (net)

• 2 NADH

Pyruvate Oxidation — Function?

Converts pyruvate into acetyl-CoA before entering the Krebs cycle.

Pyruvate Oxidation — Location?

Mitochondrial matrix.

Pyruvate Oxidation — Products per Glucose?

• 2 Acetyl-CoA

• 2 NADH

• 2 CO₂

Krebs Cycle (Citric Acid Cycle) — Definition?

A series of reactions that oxidize acetyl-CoA to generate electron carriers and ATP.

Krebs Cycle — Location?

Mitochondrial matrix.

Krebs Cycle — Main Function?

Harvest high-energy electrons for the electron transport chain.

Krebs Cycle — Products per Glucose?

• 4 CO₂

• 6 NADH

• 2 FADH₂

• 2 ATP

Electron Transport Chain (ETC) — Definition?

A series of protein complexes in the mitochondrial inner membrane that transfer electrons to produce ATP.

Electron Transport Chain — Location?

Inner mitochondrial membrane.

Electron Transport Chain — Primary Electron Donors?

• NADH

• FADH₂

Electron Transport Chain — Final Electron Acceptor?

Oxygen.

Oxygen — Role in Cellular Respiration?

Accepts electrons at the end of the ETC and combines with hydrogen to form water.

Chemiosmosis — Definition?

The movement of hydrogen ions across a membrane down their electrochemical gradient to generate ATP.

ATP Synthase — Function?

Uses the proton gradient created by the ETC to produce ATP

Total ATP Yield per Glucose — Maximum?

Approximately 30–32 ATP.

ATP Yield from NADH — Amount?

~2.5 ATP

ATP Yield from FADH₂ — Amount?

~1.5 ATP.

Aerobic Respiration — Definition?

ATP production using oxygen as the final electron acceptor.

Anaerobic Respiration — Definition?

ATP production without oxygen.

Anaerobic Respiration — ATP Yield?

Only 2 ATP per glucose (from glycolysis).

Lactic Acid Fermentation — Function?

Regenerates NAD⁺ so glycolysis can continue when oxygen is absent.

Energy Metabolism — Definition?

The combined processes of energy storage and energy production from nutrients.

Metabolism — Definition?

All chemical reactions occurring within a cell or organism.

Anabolism — Definition?

Energy-requiring reactions that build complex molecules.

Catabolism — Definition?

Energy-releasing reactions that break down molecules.

Primary Energy Source for Cells?

Glucose

Major Nutrients Used for ATP Production?

• Carbohydrates

• Lipids

• Proteins

Glycogenesis — Definition?

Formation of glycogen from glucose.

Gluconeogenesis — Definition?

Production of glucose from non-carbohydrate sources.

Triglycerides — Function?

Primary long-term energy storage molecules.

Lipolysis — Definition?

Breakdown of triglycerides into fatty acids and glycerol.

Beta-Oxidation — Definition?

Process where fatty acids are converted into acetyl-CoA for ATP production.

Ketone Bodies — Definition?

Alternative energy molecules produced from excess acetyl-CoA during prolonged fasting.

Major Ketone Bodies?

• Acetoacetate

• β-hydroxybutyrate

• Acetone

Deamination — Definition?

Removal of the amino group from amino acids.

Fate of Amino Acid Carbon Skeletons?

• Cellular respiration

• Gluconeogenesis

• Lipid synthesis