Cell Biology Essentials: Membrane Fluidity, Cell Structure, and Fermentation

A comprehensive set of vocabulary flashcards covering membrane fluidity, cellular structures, and fermentation processes to aid exam preparation.

Membrane Fluidity

The ability of a biological membrane to remain dynamic and flexible, allowing components to move laterally.

Phospholipid Bilayer

Double layer of amphipathic phospholipids that forms the structural basis of all cell membranes.

Lateral Movement

Side-to-side diffusion of lipids or proteins within one leaflet of a membrane; occurs frequently.

Flip-Flop Movement

Rare translocation of a phospholipid from one leaflet of the bilayer to the other.

Fry & Edidin Experiment

1970 cell-fusion study showing that membrane proteins mix over time, demonstrating their lateral mobility.

Determinants of Membrane Fluidity

Temperature, fatty-acid saturation level, and cholesterol content, all of which influence membrane viscosity.

Temperature (Membrane Context)

Higher temperatures increase fluidity by raising kinetic energy; lower temperatures decrease fluidity.

Saturated Fatty Acid

Straight lipid tail with no double bonds that packs tightly, making membranes more rigid.

Unsaturated Fatty Acid

Lipid tail with one or more cis double bonds that create kinks and increase membrane fluidity.

Cis Double Bond

Specific unsaturated bond creating a kink in a fatty-acid tail, preventing tight packing.

Cholesterol

Amphipathic lipid that modulates membrane fluidity—restricts movement at high temperatures and prevents packing at low temperatures.

Antifreeze Effect of Cholesterol

Cholesterol’s ability to stabilize membrane fluidity across temperature changes.

Selective Barrier

Membrane function that allows cells to control the entry and exit of substances.

Prokaryotic Cell

Small (1–5 µm) cell lacking membrane-bound organelles and a nucleus.

Eukaryotic Cell

Larger (10–100 µm) cell containing membrane-bound organelles, including a nucleus.

Nucleoid

Region in a prokaryote where DNA is located; not surrounded by a membrane.

Nucleus

Membrane-bound compartment in eukaryotic cells that houses DNA and transcription.

Endosymbiosis Theory

Model proposing that mitochondria and chloroplasts originated from prokaryotes engulfed by ancestral eukaryotic cells.

Engulfed Prokaryotic Cell

Bacterium taken inside a larger cell during endosymbiosis, precursor to mitochondria or chloroplasts.

Mitochondria

Organelles that perform aerobic respiration and produce ATP; derived from an engulfed bacterium.

Chloroplast

Photosynthetic organelle in plants and algae, derived from an engulfed cyanobacterium.

Plasma Membrane

Phospholipid bilayer that encloses the cell and regulates traffic in and out.

Ribosome

Molecular machine composed of rRNA and protein that synthesizes polypeptides.

Free Ribosome

Ribosome suspended in cytosol that produces proteins for use in the cytosol, nucleus, or organelles.

Rough Endoplasmic Reticulum (Rough ER)

Membrane network studded with ribosomes that synthesizes proteins for secretion or membranes.

Smooth Endoplasmic Reticulum (Smooth ER)

Membranous network without ribosomes that synthesizes lipids and detoxifies compounds.

Golgi Apparatus

Stack of flattened sacs that modifies, sorts, and ships proteins and lipids using vesicles.

Lysosome

Acidic vesicle containing hydrolytic enzymes that digest macromolecules and recycle organelles.

Autophagy

Process by which lysosomes degrade and recycle a cell’s own components.

Microtubule

Cytoskeletal filament made of tubulin, involved in mitosis, cilia/flagella, and organelle transport.

Tubulin

Globular protein subunit that polymerizes to form microtubules.

Microfilament

Thin cytoskeletal filament composed of actin that supports cell shape and movement.

Actin

Globular protein that polymerizes into microfilaments, enabling muscle contraction and cell motility.

Extracellular Matrix (ECM)

Network of proteins and polysaccharides outside animal cells providing structural support and signaling.

Fermentation

Anaerobic pathway that regenerates NAD⁺ to allow glycolysis to continue, producing limited ATP.

Anaerobic

Occurring without molecular oxygen.

Glycolysis

Cytosolic pathway that splits glucose into pyruvate, yielding 2 ATP and NADH.

NAD⁺

Oxidized electron carrier regenerated during fermentation to keep glycolysis running.

NADH

Reduced form of NAD⁺ that donates electrons to pyruvate or its derivatives in fermentation.

Pyruvate

Three-carbon product of glycolysis; substrate for fermentation or aerobic respiration.

Alcoholic Fermentation

Pathway in yeast that converts pyruvate to ethanol and CO₂ while regenerating NAD⁺.

Ethanol

Two-carbon alcohol produced during alcoholic fermentation.

Carbon Dioxide

Gas released during alcoholic fermentation; responsible for bread dough rising.

Lactic Acid Fermentation

Pathway converting pyruvate to lactic acid, common in muscle cells during intense exercise.

Lactic Acid

Organic acid produced in muscles during anaerobic metabolism, contributing to the burning sensation.

ATP

Adenosine triphosphate, the cell’s main energy currency; fermentation nets about 2 ATP per glucose.

Surface Area-to-Volume Ratio

Relationship that limits cell size; decreases as cells grow, making nutrient exchange less efficient.