Cellular Energy, Membrane Transport, and Enzyme Function: Study Notes for General Biology

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This section introduces fundamental concepts related to energy, thermodynamics, and their roles in biological systems.

Nanotechnology: The manipulation of matter on an atomic or molecular scale, often used in biotechnology and medicine.
Energy: The capacity to do work or cause change.
Potential Energy (PE): Stored energy due to position or structure; e.g., chemical bonds in molecules.
Kinetic Energy (KE): Energy of motion; e.g., movement of molecules.
Entropy: A measure of disorder or randomness in a system; increases as energy is transformed.
Heat: Energy transferred between objects due to temperature difference.
Law of Conservation of Energy (First Law of Thermodynamics): Energy cannot be created or destroyed, only transformed from one form to another.
Chemical Energy: Energy stored in chemical bonds of molecules.
Calorie: A unit of energy; the amount of energy needed to raise the temperature of 1 gram of water by 1°C.
kcal: Kilocalorie; 1 kcal = 1000 calories. Food energy is measured in kilocalories.

Potential Energy: Water behind a dam, chemical bonds in glucose.
Kinetic Energy: Flowing water, muscle contraction, movement of ions across membranes.

When energy is transformed (e.g., chemical to kinetic), some is lost as heat, increasing entropy.
Living systems maintain order by using energy, but overall entropy of the universe increases.

Calorie (cal): Scientific unit of energy.
Food Calorie (Cal or kcal): Equal to 1000 scientific calories; used in nutrition.

Cells break down food molecules (e.g., glucose) via cellular respiration to produce ATP, the cell's energy currency.
Major steps: Glycolysis, Krebs cycle, Electron Transport Chain.

ATP (Adenosine Triphosphate) is the primary energy carrier in cells.

ATP hydrolysis releases energy for cellular processes (e.g., muscle contraction, active transport).
Phosphorylation: Transfer of a phosphate group from ATP to another molecule, making it more reactive.

Chemical Work: Building or breaking molecules (e.g., synthesis of proteins).
Transport Work: Moving substances across membranes (e.g., active transport).
Mechanical Work: Physical movement (e.g., muscle contraction, movement of cilia).

Metabolism: All chemical reactions in a cell.
Enzyme: Biological catalyst that speeds up chemical reactions without being consumed.
Activation Energy: The energy required to start a chemical reaction.
Substrate: The reactant an enzyme acts upon.
Active Site: Region on the enzyme where the substrate binds.
Induced Fit: The enzyme changes shape slightly to fit the substrate more snugly.
Enzyme Inhibitor: A molecule that decreases enzyme activity.
Competitive Inhibitor: Binds to the active site, blocking substrate binding.
Noncompetitive Inhibitor: Binds elsewhere on the enzyme, changing its shape and reducing activity.

Activation energy is needed to break bonds in reactants.
Enzymes lower activation energy, allowing reactions to occur faster and at lower temperatures.

Substrate binds to the enzyme's active site, forming an enzyme-substrate complex.
Enzyme changes shape (induced fit) to facilitate the reaction.
Products are released, and the enzyme is free to catalyze another reaction.

Competitive Inhibition: Inhibitor competes with substrate for the active site.
Noncompetitive Inhibition: Inhibitor binds to a different site, altering enzyme shape and function.

Transport Protein: Protein that helps move substances across the cell membrane.
Diffusion: Movement of molecules from high to low concentration.
Facilitated Diffusion: Passive transport of molecules via transport proteins.
Passive Transport: Movement of substances without energy input.
Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).
Concentration Gradient: Difference in concentration of a substance across a space.
Dynamic Equilibrium: State where concentrations are equal but molecules continue to move.
Osmosis: Diffusion of water across a selectively permeable membrane.
Solution: Homogeneous mixture of solute and solvent.
Solute: Substance dissolved in a solution.
Solvent: Substance that dissolves the solute (usually water in biology).
Isotonic: Solution with equal solute concentration as the cell; no net water movement.
Hypertonic: Solution with higher solute concentration than the cell; water moves out, cell shrinks.
Hypotonic: Solution with lower solute concentration than the cell; water moves in, cell swells.
Osmoregulation: Control of water balance in cells/organisms.

Exocytosis: Process by which cells expel materials in vesicles.
Endocytosis: Process by which cells take in materials by engulfing them in vesicles.
Phagocytosis: "Cell eating"; a type of endocytosis where large particles are engulfed.
Liposomes: Artificial vesicles used in research and medicine to deliver substances to cells.

Series of molecular events by which a cell responds to signals from its environment.
Often involves membrane receptors, secondary messengers, and cellular responses.

Type	Energy Required?	Direction	Example
Diffusion	No	High to Low	Oxygen entering cells
Facilitated Diffusion	No	High to Low	Glucose transport via carrier proteins
Active Transport	Yes (ATP)	Low to High	Sodium-potassium pump
Osmosis	No	Water: High to Low	Water movement in plant cells
Exocytosis	Yes (ATP)	Out of cell	Secretion of hormones
Endocytosis	Yes (ATP)	Into cell	Uptake of nutrients