Cell Biology & Bioenergetics – Vocabulary Review

A comprehensive set of vocabulary flashcards covering membrane structure, transport mechanisms, cytoskeletal components, organelles, cellular respiration, enzyme regulation, and related bioenergetic concepts to aid exam preparation.

Fluid Mosaic Model

Currently accepted description of the cell membrane as a fluid phospholipid bilayer with embedded proteins that can move laterally.

Hydrophobic Interior

Non-polar core of the phospholipid bilayer that blocks most water-soluble (polar) molecules from freely crossing.

Integral Membrane Proteins

Proteins partially or completely embedded in the lipid bilayer; often span the membrane.

Peripheral Membrane Proteins

Proteins loosely attached to the membrane surface or to integral proteins; do not penetrate the hydrophobic core.

Membrane Fluidity

Measure of how easily lipid molecules move within the bilayer; increases with more unsaturated fatty acids and short chains, and is modulated by cholesterol.

Unsaturated Fatty Acid

Fatty acid containing one or more double bonds; introduces kinks that increase membrane fluidity.

Cholesterol (in membranes)

Steroid molecule that buffers membrane fluidity—reduces fluidity at high temperatures and prevents solidification at low temperatures.

Simple Diffusion

Passive movement of molecules down their concentration gradient without the need for transport proteins or energy.

Facilitated Diffusion

Passive transport down a gradient that requires specific carrier or channel proteins but no ATP.

Passive Transport

Movement of substances across a membrane without energy input (includes simple and facilitated diffusion).

Active Transport

Energy-requiring movement of substances against their concentration gradient, usually via ATP-powered pumps.

Pinocytosis

Form of endocytosis where the cell “gulps” extracellular fluid and dissolved solutes into small vesicles.

Phagocytosis

Endocytic process in which the cell engulfs large particles or other cells, forming a phagosome.

Receptor-Mediated Endocytosis

Highly specific uptake of molecules via receptor binding and clathrin-coated vesicle formation.

Exocytosis

Process by which intracellular vesicles fuse with the plasma membrane to release contents outside the cell.

Microfilaments

Thin cytoskeletal fibers composed of actin; involved in cell shape, movement, and cytokinesis.

Microtubules

Hollow tubes of tubulin that form tracks for motor proteins, make up cilia/flagella, and organize chromosomes during cell division.

Cell Wall

Semirigid structure outside the plasma membrane of plants, fungi, and some prokaryotes; provides support and determines shape.

Prokaryotic Cell

Cell type lacking a nucleus and membrane-bound organelles but containing DNA and ribosomes (e.g., bacteria, archaea).

Eukaryotic Cell

Cell type with a nucleus and membrane-bound organelles such as mitochondria and ER.

Mitochondria

Organelle that harvests energy from glucose and other fuels to produce ATP via cellular respiration.

Rough Endoplasmic Reticulum (Rough ER)

Organelle studded with ribosomes; site of synthesis and initial modification of secreted and membrane proteins.

Smooth Endoplasmic Reticulum (Smooth ER)

Organelle lacking ribosomes; involved in lipid synthesis, detoxification, and calcium storage.

Nucleolus

Dense region within the nucleus that produces ribosomal RNA (rRNA) and assembles ribosomal subunits.

ATP (Adenosine Triphosphate)

Cell’s primary energy currency; releases energy when hydrolyzed to ADP and inorganic phosphate.

Exergonic Reaction

Chemical reaction that releases free energy (ΔG < 0); e.g., ATP hydrolysis.

Glycolysis

First stage of glucose metabolism; occurs in the cytosol and produces pyruvate, ATP, and NADH.

Pyruvate Oxidation

Conversion of pyruvate to acetyl-CoA in the mitochondrial matrix, producing NADH and CO₂.

Citric Acid Cycle

Series of mitochondrial reactions that oxidize acetyl-CoA, generating NADH, FADH₂, and ATP (or GTP).

Oxidative Phosphorylation

Process in which the electron transport chain and ATP synthase produce the bulk of cellular ATP using a proton gradient.

Fermentation

Anaerobic pathway that regenerates NAD⁺ from NADH and produces limited ATP when oxygen is absent.

Proton Gradient

Difference in H⁺ concentration across the inner mitochondrial membrane created by the electron transport chain.

ATP Synthase

Membrane enzyme that uses the flow of protons down their gradient to phosphorylate ADP, forming ATP.

Amino Acids (in catabolism)

Monomers produced by protein hydrolysis that can enter metabolic pathways for energy production.

Allosteric Regulation

Modulation of enzyme activity by binding of a molecule at a site other than the active site, causing a conformational change.

Oxidation

Loss of electrons (or hydrogen) from a molecule; often releases energy.

Reduction

Gain of electrons (or hydrogen) by a molecule; often stores energy.

NAD⁺/NADH

Coenzyme pair that shuttles electrons in redox reactions; NADH is the reduced, energy-rich form.

Hydrolysis of ATP

Reaction in which ATP + H₂O → ADP + Pᵢ + energy; powers many cellular processes.