Metabolism and Nutrition: Study Guide for Aerobic Glucose Catabolism

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Metabolism and Nutrition

Metabolism: Overview

Metabolism refers to the sum of all chemical reactions occurring within the body's cells. These reactions include both the breakdown of molecules (catabolism) and the building of molecules (anabolism).

Catabolism: The process of breaking down complex molecules into simpler ones. This releases energy and is considered exergonic.
Anabolism: The process of building complex molecules from simpler ones. This requires energy input and is considered endergonic.
Memory hook: CATabolism = a cat tearing things apart (breaking down). ANabolism = ADDING/Assembling (building up).

Nutrient Monomers Used for ATP Synthesis

Cells utilize three main classes of nutrient monomers to generate energy for ATP synthesis:

Carbohydrates: Monosaccharides (e.g., glucose)
Proteins: Amino acids
Lipids (fats): Fatty acids and glycerol

Coupling of Exergonic and Endergonic Reactions

Cells couple exergonic reactions (which release energy) with endergonic reactions (which require energy) to efficiently perform cellular work. The energy released from catabolic breakdown (exergonic) is used to drive anabolic processes or other cellular activities (endergonic).

Example: ATP hydrolysis (exergonic) powers muscle contraction (endergonic).

ATP Hydrolysis: Why It Is Highly Exergonic

ATP contains three phosphate groups linked by high-energy phosphoanhydride bonds. These bonds are unstable due to repulsion between closely packed negative charges. Hydrolysis of ATP (breaking a bond with water) relieves this repulsion and releases a large amount of energy.

Equation:

Oxidation and Reduction Reactions

Oxidation and reduction (redox) reactions are fundamental to metabolism:

Oxidation: Loss of electrons (often loss of hydrogen atoms)
Reduction: Gain of electrons (often gain of hydrogen atoms)
Memory hook: LEO the lion says GER — Lose Electrons = Oxidation, Gain Electrons = Reduction. These always occur together.

Electromotive Force

Electromotive force is the difference in potential energy between an electron in a higher-energy position and a lower-energy position. It drives electrons through the electron transport chain, releasing energy for ATP synthesis.

Electron Carriers in Metabolism

Electron carriers transport high-energy electrons during metabolic reactions:

Electron Carrier	Reduced Form	Location
NAD+ (Nicotinamide adenine dinucleotide)	NADH	Cytosol (glycolysis), Mitochondrial matrix (intermediate step, Krebs cycle)
FAD (Flavin adenine dinucleotide)	FADH2	Mitochondrial matrix (Krebs cycle)

ATP Generation: Substrate-Level vs. Oxidative Phosphorylation

ATP can be generated by two main methods:

Method	How it works	Where it occurs
Substrate-level phosphorylation	Phosphate group transferred directly from substrate to ADP	Glycolysis (cytosol), Citric Acid Cycle (mitochondrial matrix)
Oxidative phosphorylation	Energy from electrons in ETC used to pump H+, driving ATP synthase	Inner mitochondrial membrane (ETC)

Aerobic Glucose Catabolism: The Four Stages

Overview Table

Stage	Location	Input	ATP Yield (direct)
1. Glycolysis	Cytosol	1 Glucose	Net 2 ATP
2. Intermediate (Pyruvate) step	Mitochondrial matrix	2 Pyruvate	0 ATP
3. Citric Acid (Krebs) Cycle	Mitochondrial matrix	2 Acetyl-CoA	2 ATP
4. Electron Transport Chain	Inner mitochondrial membrane	NADH + FADH2	34 ATP

Additional info: Each NADH yields ~3 ATP, each FADH2 yields ~2 ATP via ETC.

Glycolysis

Glycolysis is the splitting of one 6-carbon glucose molecule into two 3-carbon pyruvate molecules in the cytosol. It is anaerobic and the first step in both aerobic and anaerobic pathways.

Yield (per 1 glucose)	Amount
ATP used (investment phase)	2 ATP
ATP produced (payoff phase)	4 ATP
NET ATP	2 ATP
NADH produced	2 NADH
Pyruvate produced	2 Pyruvate

Intermediate Step (Pyruvate Oxidation)

After glycolysis, pyruvate undergoes further processing:

Aerobic (O2 present): Pyruvate is converted to Acetyl-CoA, releasing CO2 and producing NADH.
Anaerobic (O2 absent): Pyruvate is converted to lactate (lactic acid fermentation), regenerating NAD+ for glycolysis. No additional ATP is produced.

Citric Acid (Krebs) Cycle

The Citric Acid Cycle occurs in the mitochondrial matrix. Acetyl-CoA combines with a 4-carbon molecule to form citrate, which is broken down through a series of reactions, releasing CO2 and transferring electrons to NADH and FADH2.

Yield (per 1 glucose = 2 Acetyl-CoA)	Amount
ATP (substrate-level)	2 ATP
NADH produced	6 NADH
FADH2 produced	2 FADH2
CO2 released	4 CO2

Electron Transport Chain and Oxidative Phosphorylation

The electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane. NADH and FADH2 donate electrons, which pass through the chain, releasing energy to pump H+ ions and create a gradient. H+ flows back through ATP synthase, driving ATP production. Oxygen is the final electron acceptor, forming water.

Equation:

Role of Oxygen in Glucose Catabolism

Oxygen is essential as the final electron acceptor in the ETC. Without oxygen, the ETC stops, NADH and FADH2 cannot be recycled, and ATP production from glucose is severely limited.

Overall Reaction of Aerobic Glucose Catabolism

The complete oxidation of one glucose molecule in the presence of oxygen yields water, carbon dioxide, ATP, and heat.

Equation:

ATP Yield from Aerobic Catabolism of One Glucose Molecule

Process	Direct ATP	Electron carriers produced	ATP from carriers via ETC	Subtotal
Glycolysis	2 ATP	2 NADH	2 × 3 = 6 ATP	8
Pyruvate oxidation (intermediate step)	—	2 NADH	2 × 3 = 6 ATP	6
Citric acid cycle	2 ATP	6 NADH + 2 FADH2	(6×3) + (2×2) = 22 ATP	24
TOTAL	4 ATP	10 NADH + 2 FADH2	34 ATP	38 ATP

Total: 38 ATP per glucose molecule.