Cellular Respiration, Energy, and Metabolism: Study Notes for Anatomy & Physiology

Energy and Thermodynamics

Basic Concepts of Energy

Energy is the capacity to do work or cause change. In biological systems, energy is essential for cellular processes and life functions.

• Kinetic Energy: The energy of motion. Example: Movement of molecules.

• Potential Energy: Stored energy due to position or structure. Example: Chemical bonds in glucose.

• Free Energy (G): The portion of a system's energy that can perform work at constant temperature and pressure.

• Lost Energy: Energy that is not available to do work, often released as heat.

First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe; some energy is lost as heat.

Catabolism and Anabolism

Metabolic Pathways

Metabolism includes all chemical reactions in a cell, divided into two main types:

• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy. Example: Cellular respiration.

• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy. Example: Protein synthesis.

Adenosine Triphosphate (ATP)

Role of ATP in Cells

ATP is the primary energy carrier in cells. It stores energy in its high-energy phosphate bonds.

• Structure: Adenine base, ribose sugar, and three phosphate groups.

• Function: Provides energy for cellular work by hydrolyzing to ADP and inorganic phosphate.

Enzyme Function and Regulation

Activation Energy and Enzyme Action

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy (Ea).

• Activation Energy (Ea): The minimum energy required to start a chemical reaction.

• Enzyme Regulation: Enzymes can be regulated by inhibitors, activators, and environmental conditions.

• Substrate: The reactant on which an enzyme acts.

• Active Site: The region of the enzyme where the substrate binds and the reaction occurs.

Example: Hexokinase catalyzes the phosphorylation of glucose in glycolysis.

Redox Reactions and Electron Carriers

Key Terms and Electron Carriers

Redox reactions involve the transfer of electrons between molecules, crucial for energy production in cells.

• Cellular Respiration: The process by which cells extract energy from organic molecules.

• Aerobic Respiration: Respiration that requires oxygen.

• Anaerobic Respiration: Respiration without oxygen.

• Fermentation: Energy production in the absence of oxygen, producing less ATP than respiration.

• Oxidative Phosphorylation: ATP synthesis powered by electron transport chain (ETC).

• Electron Carrier: Molecules that transport electrons during cellular respiration.

Important Electron Carriers:

• NAD+/NADH: Nicotinamide adenine dinucleotide; accepts and donates electrons.

• FAD/FADH2: Flavin adenine dinucleotide; another electron carrier.

Identifying Electron Carriers: NAD+ and FAD are oxidized forms; NADH and FADH2 are reduced forms (carry electrons and energy).

Aerobic Cellular Respiration

Purpose and Overview

Aerobic cellular respiration converts glucose and oxygen into ATP, carbon dioxide, and water, providing energy for cellular activities.

• Purpose: To produce ATP for cellular work.

• Major Steps: Glycolysis, Pyruvate Oxidation, Citric Acid Cycle, Electron Transport Chain (ETC), and Oxidative Phosphorylation.

Pathways and ATP Production

The main pathways of aerobic respiration and their cellular locations:

• Glycolysis: Occurs in cytoplasm; breaks down glucose into pyruvate.

• Pyruvate Oxidation: Converts pyruvate to acetyl-CoA in mitochondria.

• Citric Acid Cycle (Krebs Cycle): Completes glucose breakdown; produces NADH and FADH2.

• Electron Transport Chain (ETC): Series of proteins in mitochondrial membrane; transfers electrons to oxygen.

• Oxidative Phosphorylation: ATP synthesis via ATP synthase, powered by proton gradient.

Step Producing Most ATP: Oxidative phosphorylation in the ETC.

Electron Transport Chain and ATP Synthase

The ETC and ATP synthase are crucial for the final stage of aerobic respiration.

• ETC: Transfers electrons from NADH and FADH2 to oxygen, creating a proton gradient.

• ATP Synthase: Enzyme that uses the proton gradient to synthesize ATP from ADP and inorganic phosphate.

Site of Oxidative Phosphorylation: Inner mitochondrial membrane.

Final Electron Acceptor: Oxygen (O2).

Comparison of Aerobic Respiration and Fermentation

Conditions and Outcomes

Aerobic respiration and fermentation are two pathways for energy production, differing in oxygen requirement and ATP yield.

Process	Oxygen Required?	ATP Yield	End Products
Aerobic Respiration	Yes	~30-32 ATP per glucose	CO2 and H2O
Fermentation	No	2 ATP per glucose	Lactic acid (animals) or ethanol and CO2 (yeast)

Note: Anaerobic respiration is distinct from fermentation; it uses an electron transport chain with a final electron acceptor other than oxygen.

Key Equations

Cellular Respiration Equation

The overall chemical equation for aerobic cellular respiration:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

ATP Synthesis via Chemiosmosis

ATP is synthesized as protons flow through ATP synthase:

$\text{ADP} + \text{P}_i \rightarrow \text{ATP}$

Additional info: The above notes expand on brief points from the original file, providing definitions, examples, and context for each concept relevant to Anatomy & Physiology students.