Cellular Respiration and Metabolism: Study Notes for ANP College

Cellular Respiration and Metabolism

Overview of Cellular Respiration

Cellular respiration is the process by which cells convert glucose and other nutrients into energy (ATP), water, and carbon dioxide. This process is essential for maintaining cellular functions and supporting life.

• Cellular Respiration: The breakdown of glucose to produce ATP.

• ATP (Adenosine Triphosphate): The main energy currency of the cell.

• Stages: Glycolysis, Krebs Cycle (Citric Acid Cycle), Electron Transport Chain.

Glycolysis

Glycolysis is the first stage of cellular respiration, occurring in the cytoplasm. It breaks down glucose into pyruvate, producing a small amount of ATP and NADH.

• Location: Cytoplasm

• Reactants: Glucose

• Products: 2 Pyruvate, 2 ATP, 2 NADH

• Key Steps: Glucose is split into two 3-carbon molecules (pyruvate).

Krebs Cycle (Citric Acid Cycle)

The Krebs Cycle occurs in the mitochondria and further breaks down pyruvate, generating NADH, FADH2, and ATP.

• Location: Mitochondrial matrix

• Reactants: Acetyl-CoA (derived from pyruvate)

• Products: CO2, NADH, FADH2, ATP

• Key Steps: Acetyl-CoA enters the cycle, producing high-energy electron carriers.

Electron Transport Chain (ETC)

The Electron Transport Chain is the final stage, located in the inner mitochondrial membrane. It uses NADH and FADH2 to generate a large amount of ATP.

• Location: Inner mitochondrial membrane

• Reactants: NADH, FADH2, O2

• Products: ATP, H2O

• Key Steps: Electrons are transferred through protein complexes, creating a proton gradient that powers ATP synthesis.

Fermentation

Fermentation occurs when oxygen is not available. It allows glycolysis to continue by regenerating NAD+, producing lactic acid or ethanol.

• Types: Lactic acid fermentation (in muscles), Alcohol fermentation (in yeast)

• Products: Lactic acid or ethanol, CO2

• Purpose: Regenerate NAD+ for glycolysis

ATP Yield from Cellular Respiration

The total ATP yield from one molecule of glucose is approximately 36-38 ATP, depending on the cell type and conditions.

• Glycolysis: 2 ATP

• Krebs Cycle: 2 ATP

• Electron Transport Chain: 32-34 ATP

Metabolism: Anabolic and Catabolic Pathways

Metabolism refers to all chemical reactions in the body. It includes anabolic (building up) and catabolic (breaking down) pathways.

• Anabolism: Synthesis of complex molecules from simpler ones (e.g., protein synthesis).

• Catabolism: Breakdown of complex molecules into simpler ones (e.g., cellular respiration).

• Example: Glucose catabolism provides energy; amino acid anabolism builds proteins.

Enzymes in Metabolism

Enzymes are biological catalysts that speed up metabolic reactions without being consumed.

• Function: Lower activation energy for reactions.

• Specificity: Each enzyme acts on a specific substrate.

• Example: Hexokinase catalyzes the first step of glycolysis.

Summary Table: Cellular Respiration Stages

Stage	Location	Main Reactants	Main Products	ATP Yield
Glycolysis	Cytoplasm	Glucose	Pyruvate, NADH	2
Krebs Cycle	Mitochondrial matrix	Acetyl-CoA	CO2, NADH, FADH2	2
Electron Transport Chain	Inner mitochondrial membrane	NADH, FADH2, O2	ATP, H2O	32-34

Key Equations

• Overall Cellular Respiration Equation:

$\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP}$

• ATP Hydrolysis:

$\mathrm{ATP + H_2O \rightarrow ADP + P_i + \text{energy}}$

Regulation of Metabolism

Metabolic pathways are regulated by hormones, feedback mechanisms, and enzyme activity.

• Hormonal Regulation: Insulin promotes glucose uptake; glucagon stimulates glucose release.

• Feedback Inhibition: End products inhibit pathway enzymes to prevent overproduction.

Diagram: Metabolic Pathways and Regulation

The following image illustrates the flow of substrates and products in cellular respiration and the regulation of metabolic pathways.