Metabolism

Definition of Metabolism

Metabolism refers to the sum of all chemical reactions that occur within a living organism to maintain life. These reactions enable organisms to grow, reproduce, maintain their structures, and respond to environmental changes.

• Metabolic Pathways: Series of interconnected chemical reactions catalyzed by enzymes.

• Purpose: Conversion of energy and matter to sustain cellular functions.

• Example: Cellular respiration and photosynthesis are major metabolic pathways.

Catabolic vs. Anabolic Reactions

Types of Metabolic Reactions

Metabolic reactions are classified as either catabolic or anabolic, depending on whether they break down or build up molecules.

• Catabolic Reactions: Break down complex molecules into simpler ones, releasing energy. Example: Breakdown of glucose during cellular respiration.

• Anabolic Reactions: Build complex molecules from simpler ones, requiring energy input. Example: Synthesis of proteins from amino acids.

• Comparison: Catabolism provides energy for anabolism.

Potential Energy vs. Kinetic Energy

Forms of Energy in Biological Systems

Energy exists in two main forms relevant to biology: potential and kinetic energy.

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

• Kinetic Energy: Energy of motion. Example: Movement of molecules during diffusion.

• Application: Cells convert potential energy in food molecules to kinetic energy for cellular work.

First and Second Laws of Thermodynamics

Fundamental Laws Governing Energy

Thermodynamics describes how energy is transferred and transformed in biological systems.

• First Law (Law of Energy Conservation): Energy cannot be created or destroyed, only transformed from one form to another.

• Second Law: Every energy transfer increases the entropy (disorder) of the universe; energy transformations are not 100% efficient.

• Example: During cellular respiration, some energy is lost as heat.

Entropy

Definition and Biological Significance

Entropy is a measure of disorder or randomness in a system. In biological processes, entropy tends to increase, reflecting the second law of thermodynamics.

• High Entropy: More disordered systems (e.g., heat energy).

• Low Entropy: More ordered systems (e.g., organized molecules).

• Application: Living organisms maintain order by expending energy.

Exergonic vs. Endergonic Reactions

Types of Energy Changes in Reactions

Chemical reactions are classified based on energy flow.

• Exergonic Reactions: Release energy; products have less free energy than reactants. Example: Cellular respiration.

• Endergonic Reactions: Require energy input; products have more free energy than reactants. Example: Photosynthesis.

• Equation: for exergonic, for endergonic reactions.

ATP Synthesis

Role and Formation of ATP

ATP (Adenosine Triphosphate) is the primary energy carrier in cells. It stores and provides energy for cellular processes.

• Structure: Composed of adenine, ribose, and three phosphate groups.

• Synthesis: ATP is produced from ADP and inorganic phosphate () during cellular respiration and photosynthesis.

• Hydrolysis: ATP hydrolysis releases energy ().

• Example: Muscle contraction uses ATP.

Enzymes

Nature and Function of Enzymes

Enzymes are biological catalysts that speed up chemical reactions without being consumed. They are typically proteins.

• Mechanism: Lower activation energy required for reactions.

• Specificity: Each enzyme acts on a specific substrate.

• Example: Amylase breaks down starch into sugars.

Enzyme Inhibitors

Regulation of Enzyme Activity

Enzyme inhibitors are molecules that decrease or stop enzyme activity.

• Competitive Inhibitors: Bind to the active site, blocking substrate access.

• Noncompetitive Inhibitors: Bind elsewhere, changing enzyme shape and function.

• Example: Cyanide inhibits cytochrome c oxidase in cellular respiration.

Allosteric Regulation

Control of Enzyme Activity

Allosteric regulation involves the binding of regulatory molecules at sites other than the active site, affecting enzyme activity.

• Allosteric Site: Location on enzyme where regulator binds.

• Effect: Can activate or inhibit enzyme function.

• Example: Feedback inhibition in metabolic pathways.

Cellular Respiration

Process of Energy Production in Cells

Cellular respiration is the process by which cells extract energy from organic molecules, primarily glucose, to produce ATP.

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

• Overall Equation:

• Location: Cytoplasm (glycolysis), mitochondria (Krebs cycle and ETC).

Anaerobic Respiration (Fermentation)

Energy Production Without Oxygen

Anaerobic respiration occurs when oxygen is not available. Fermentation is a common anaerobic process in both plants and animals.

• Plant Fermentation: Produces ethanol and carbon dioxide. Equation:

• Animal Fermentation: Produces lactic acid. Equation:

• Purpose: Regenerates NAD+ for glycolysis, allowing ATP production to continue.

• Example: Muscle cells perform lactic acid fermentation during intense exercise.