Chapter 5: The Dynamic Cell — Energy, Metabolism, and Transport

Vocabulary flashcards covering energy, thermodynamics, metabolism, enzymes, and cell transport from the lecture notes.

Energy

The capacity to do work; exists in multiple forms (mechanical, thermal, chemical, electromagnetic, sonic, gravitational); the biosphere derives its energy mainly from the sun.

Kinetic energy

Energy of motion; one of the two basic forms of energy; can be converted to potential energy and vice versa; some energy is lost as heat during conversions.

Potential energy

Stored energy; can be converted to kinetic energy; interconversion with kinetic energy occurs with some energy lost as heat.

Calorie (kilocalorie)

Unit of heat; energy in food is measured in Calories; 1 Calorie = 1 kilocalorie = 1,000 calories; value listed on food packages.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed from one form to another.

Second Law of Thermodynamics

Energy transformations involve loss of usable energy; heat is the least usable form of energy.

Entropy

A measure of disorder; every energy transformation increases entropy; maintaining order requires adding energy.

ATP (adenosine triphosphate)

Energy currency of cells; powers nearly all cellular activities; hydrolysis produces ADP and Pi and releases energy.

ADP

Adenosine diphosphate; formed when ATP loses a phosphate; can be rephosphorylated to ATP.

Coupled reaction

An energy-releasing reaction (often ATP breakdown) drives an energy-requiring reaction.

Enzyme

Protein catalyst that speeds up a reaction; not consumed in the reaction.

Active site

Part of an enzyme where the substrate binds; specificity described by lock-and-key or induced fit; returns to original shape after the reaction.

Substrate

Molecule that binds to an enzyme’s active site and is transformed by the enzyme.

Metabolic pathway

A series of linked enzyme-catalyzed reactions leading to an end product.

Enzyme inhibition

Prevents an enzyme from binding its substrate; can be competitive or noncompetitive; examples include cyanide inhibiting cytochrome c oxidase and penicillin inhibiting bacterial enzymes.

Feedback inhibition

Product of a pathway inhibits the first enzyme by binding to an allosteric site, shutting the pathway down.

Activation energy

Energy required to start a reaction; enzymes lower this barrier by bringing reactants together or participating in the reaction.

Passive transport

No energy required; substances move down their concentration gradient; includes simple diffusion and facilitated diffusion via transport proteins.

Simple diffusion

Movement of small or nonpolar molecules directly through the lipid bilayer down a concentration gradient; no energy used.

Facilitated diffusion

Diffusion through a membrane via carrier or channel proteins; no energy required; water uses aquaporins.

Osmosis

Diffusion of water across a selectively permeable membrane; from higher to lower water concentration; influenced by solute concentrations.

Isotonic

Solutions that cause no net water movement; equal solute/water concentrations; example: 0.9% saline with red blood cells.

Hypotonic

Solution with higher outside water concentration; cells gain water; animal cells may swell or lyse; plant cells become turgid.

Hypertonic

Solution with lower outside water concentration; cells lose water; animal cells shrink; plant cells may plasmolyze.

Active transport

Movement of substances against a concentration gradient requiring energy; uses transport proteins; example: sodium–potassium pump maintains ion gradients.

Sodium–potassium pump

A transport protein that moves Na+ out and K+ in; uses ATP; 3 Na+ out and 2 K+ in per cycle; maintains essential ion gradients.

Bulk transport

Movement of large macromolecules via vesicles; exocytosis exports material; endocytosis brings material in.

Exocytosis

Vesicle fuses with the plasma membrane to release contents outside the cell.

Endocytosis

Cell takes in substances via vesicles; includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Phagocytosis

Endocytosis that engulfs solid particles; cell surrounds and digests them.

Pinocytosis

Endocytosis that ingests liquids or small particles via vesicles.

Receptor-mediated endocytosis

Selective endocytosis using receptor-coated pits to uptake specific substances.

Photosynthesis

Process by which plants convert solar energy to chemical energy (carbohydrates) using water and carbon dioxide; releases oxygen; occurs in chloroplasts.

Cellular respiration

Process by which cells break down carbohydrates to generate ATP; occurs in mitochondria; releases CO2 and water.