Energy and Cellular Metabolism: Structured Study Notes for ANP College Students

Introduction to Physiology

Definition and Scope

Physiology is the study of the normal functioning of living organisms and their component parts, including all chemical and physical processes. It seeks to understand both the 'why' (function) and the 'how' (mechanism) of biological phenomena.

• Function: Explains why a process occurs (its purpose).

• Mechanism: Describes how a process occurs (the steps involved).

Feedback Loops

Feedback loops are essential for maintaining homeostasis.

• Negative Feedback: Stabilizes variables and is homeostatic.

• Positive Feedback: Reinforces changes and is not homeostatic.

• Feedforward Control: Allows the body to anticipate changes.

Molecular Interactions

Elements and Biomolecules

Three elements make up 90% of the human body: Oxygen, Carbon, and Hydrogen. The four major groups of biomolecules are:

• Lipids: Fats and oils, hydrophobic, composed of a glycerol backbone and 1-3 fatty acids.

• Carbohydrates: Sugars, hydrophilic, includes monosaccharides (fructose, glucose, galactose) and disaccharides (sucrose, maltose, lactose).

• Proteins: Chains of amino acids with four structural levels.

• Nucleotides: Store and transmit genetic information, participate in energy transfer (e.g., ATP, ADP, cyclic AMP).

Protein Structure

Proteins have four levels of structure:

• Primary: Sequence of amino acids.

• Secondary: Hydrogen bonds create folding (α-helix, β-sheets).

• Tertiary: 3D shape formed by joining secondary structures.

• Quaternary: Multiple tertiary structures combine.

pH and Acidity

pH measures the concentration of hydrogen ions ([H+]) in a solution.

• High [H+]: Low pH (acidic).

• Low [H+]: High pH (basic).

• Bases: Bind free H+ and release hydroxide ions (OH-), forming water.

Compartmentation: Cells and Tissues

Body Cavities

The three major body cavities are:

• Cranial

• Thoracic

• Abdominopelvic

Cellular Structures

• Ribosomes: Not organelles (lack membrane), function as inclusions, synthesize proteins.

• Motor Proteins: Create movement along cytoskeletal fibers using ATP.

Energy and Cellular Metabolism

Energy in Biological Systems

All living organisms require energy. Plants (autotrophs) trap radiant energy from the sun and store it in chemical bonds. Animals (heterotrophs) ingest plants or other animals to obtain energy.

Trophic Levels and Energy Transfer

Energy transfer in food webs is inefficient:

• Primary Producers: Plants convert sunlight to chemical energy at ~1% efficiency.

• Energy Transfer: Only ~10% of energy is transferred to the next trophic level; ~90% is lost as heat.

Energy Storage and Use

Animals extract energy from biomolecules via respiration, consuming oxygen and producing carbon dioxide and water. Excess energy is stored in glycogen and lipids.

Types of Work

Energy is used for:

• Chemical Work: Making and breaking chemical bonds.

• Transport Work: Moving ions and molecules, creating concentration gradients.

• Mechanical Work: Moving organelles, changing cell shape, muscle contraction.

Potential vs. Kinetic Energy

• Potential Energy: Stored in concentration gradients and chemical bonds.

• Kinetic Energy: Energy of motion.

Thermodynamics

• First Law: Conservation of energy; total energy in a closed system is constant.

• Second Law: Natural processes increase entropy (disorder); the human body is an open system requiring energy input to maintain order.

Chemical Reactions

Bioenergetics

Bioenergetics studies energy flow through biological systems. Chemical reactions transfer or use energy stored in reactant molecules.

• Reactants: Starting materials.

• Products: End materials.

• Reaction Rate: Speed of reaction.

• Free Energy: Potential energy in chemical bonds.

Types of Chemical Reactions

• Decomposition: Large molecules broken into smaller ones ($AB \rightarrow A + B$).

• Synthesis: Small molecules combined to form larger ones ($A + B \rightarrow AB$).

• Exchange: Functional groups exchanged between molecules ($AB + C \rightarrow A + BC$).

Activation Energy

Activation energy is the initial input required to start a chemical reaction.

Exergonic and Endergonic Reactions

• Exergonic: Release energy; products have lower free energy than reactants.

• Endergonic: Store energy; products have higher free energy than reactants.

Coupled Reactions

Exergonic and endergonic reactions are often coupled, allowing energy released from one to drive another.

Enzymes

Role of Enzymes

Enzymes are globular proteins that lower the activation energy of reactions, increasing reaction rates.

Enzyme Structure and Function

Enzymes have a unique 3D structure with an active site that temporarily forms an enzyme-substrate complex.

Enzyme Regulation

Enzymes can be activated, inactivated, or modulated by allosteric activators, which bind away from the active site and induce conformational changes.

Classification and Naming

Enzymes are named based on their substrate or function, often ending in '-ase' (e.g., glucokinase adds a phosphate group to glucose).

Types of Enzymatic Reactions

• Oxidation-Reduction: Electron transfer between molecules.

• Hydrolysis-Dehydration: Addition or removal of water.

• Addition-Subtraction-Exchange: Functional groups added, removed, or exchanged.

• Ligation: Joining two molecules using ATP.

Metabolism

Overview

Metabolism encompasses all chemical reactions in an organism, including energy extraction and molecule synthesis or breakdown.

• Catabolism: Energy-releasing breakdown.

• Anabolism: Energy-utilizing synthesis.

• Intermediates: Molecules that are substrates for subsequent reactions.

Regulation of Metabolic Pathways

Cells regulate metabolism by controlling enzyme concentrations, producing modulators, using feedback inhibition, compartmentalizing enzymes, and maintaining ATP/ADP ratios.

ATP and Energy Transfer

ATP stores energy in high-energy phosphate bonds and transfers energy between reactions.

• Aerobic Metabolism: Yields 30-32 ATP per glucose, requires oxygen.

• Anaerobic Metabolism: Yields 2 ATP per glucose.

Aerobic Respiration Steps

1. Glycolysis: Occurs in cytosol, produces 2 ATP and 2 pyruvate.

2. Citric Acid Cycle: Produces NADH, FADH2, and 2 ATP.

3. Electron Transport Chain: Produces 26-28 ATP, uses O2 as final electron acceptor.

Fate of Pyruvate

With insufficient oxygen, pyruvate undergoes anaerobic respiration:

• Humans: Produces lactic acid.

• Yeast: Produces alcohol.

Protein Synthesis and Genetic Information

DNA, RNA, and Protein Synthesis

Proteins are synthesized based on instructions encoded in DNA. The process involves:

• Transcription: DNA is transcribed to mRNA.

• Translation: mRNA is translated into a protein chain by ribosomes.

Alternative Splicing

mRNA processing allows multiple proteins to be produced from one DNA sequence via alternative splicing.

Posttranslational Modification

Proteins undergo folding, cross-linking, cleavage, addition of groups, and assembly into polymers after translation.

Summary Table: Types of Chemical Reactions

Type	General Equation	Description
Decomposition	$AB \rightarrow A + B$	Breaks down molecules
Synthesis	$A + B \rightarrow AB$	Combines molecules
Exchange	$AB + C \rightarrow A + BC$	Exchanges functional groups