Cell Biology: Structure, Function, and Membrane Dynamics

Vocabulary practice flashcards covering cell characteristics, prokaryotic vs. eukaryotic structures, organelle functions, membrane fluidity regulation, and transport mechanisms.

Homeostasis

The active maintenance of a set of internal conditions within ideal ranges in response to environmental changes.

Archaea

A domain of prokaryotic extremophiles that inhabit extreme environments, such as salt water and deserts.

Economics of Cell Size

The principle stating that cell volume represents metabolic demand and surface area represents supply; because volume increases faster than surface area as cell size increases, cells must remain small so that $\text{Supply} \ngeq \text{Demand}$.

Nucleoid

The region within a prokaryotic cell where chromosomal DNA is located without being enclosed by a membrane.

Peptidoglycan

The substance that composes the prokaryotic cell wall, providing protective structural support.

Nuclear Envelope

A double lipid bilayer membrane that defines the eukaryotic nucleus; its outer lipid bilayer is directly continuous with the rough and smooth endoplasmic reticulum.

Nuclear Pores

Passages traversing the nuclear envelope that regulate transport into and out of the nucleus.

Chromatin

Chromosomal DNA complexed with DNA-binding proteins located within the nucleus.

Nucleolus

A non-organelle region inside the nucleus where ribosomes are assembled.

Endomembrane System

A network of internal lipid bilayer membranes that includes the endoplasmic reticulum, Golgi apparatus, and vesicles.

Smooth Endoplasmic Reticulum (SER)

A network of interconnected lipid bilayer tubules lacking ribosomes that serves as the site for lipid synthesis, fatty acid desaturation, cholesterol synthesis, and some carbohydrate synthesis.

Rough Endoplasmic Reticulum (RER)

A network of interconnected lipid bilayer tubules studded with ribosomes that synthesizes proteins destined for cellular export, the plasma membrane, or the endomembrane system.

Cis Face (Golgi Apparatus)

The receiving region of the Golgi apparatus that fuses with transport vesicles arriving from the endoplasmic reticulum.

Trans Face (Golgi Apparatus)

The shipping face of the Golgi apparatus from which vesicles exit to deliver modified and sorted molecules to their cellular destinations.

Exocytosis

The cellular process by which vesicle-enclosed materials, such as mature insulin, fuse with the plasma membrane to be exported out of the cell.

Endocytosis

The process by which the plasma membrane encloses extracellular substances to bring them into the cell, either non-specifically or via specific receptors.

Lysosome

A digestive vesicle with an acidic internal pH containing enzymes that perform hydrolysis reactions to break down internalized substances and defective organelles.

Primary Lysosome

A newly synthesized lysosome that has not yet fused with an endocytic vesicle or defective organelle.

PIP3 Lipid

A membrane lipid that facilitates the fusion of endocytic cycle vesicles with primary lysosomes; target of destruction by Tuberculosis bacterium enzymes to escape degradation.

Endosymbiotic Theory

The theory that mitochondria and chloroplasts originated from free-living prokaryotic cells that were engulfed by a ancestral host cell and established a permanent endosymbiotic relationship.

Cristae

The extensive inward folds of the inner mitochondrial membrane that house machinery for energy metabolism and ATP production.

Mitochondrial Matrix

The fluid center enclosed by the inner mitochondrial membrane containing mitochondrial DNA and ribosomes.

Thylakoid

A single-membrane disk inside a chloroplast where the light-capturing steps of photosynthesis occur.

Granum

A stack of individual thylakoid disks located within the chloroplast.

Stroma

The fluid-filled space surrounding grana within the inner membrane of the chloroplast.

Cytoskeleton

An intracellular network of diverse proteins providing internal structural support, facilitating intracellular transport, and enabling cell motility.

Extracellular Matrix (ECM)

A network of extracellular proteins outside the cell that provides structural support, anchors cells into higher-order tissues and organs, and assists in cell-cell communication.

Dr. Gorter's RBC Experiment

An experiment that extracted red blood cell lipids and found their surface area as a monolayer was exactly $2\times$ the surface area of the intact cells, demonstrating that cell membranes are phospholipid bilayers.

Fluid Mosaic Model

The structural model describing biological membranes as a fluid phospholipid lake in which proteins and other molecules float dynamically.

Cell Fusion Experiment (1970)

An experiment in which human and mouse cells with distinct fluorescently labeled surface proteins were fused, resulting in intermixed proteins over time and proving membrane fluidity.

Unsaturated Fatty Acids (Membrane Fluidity)

Fatty acid hydrocarbon tails containing kinks that prevent tight packing, thereby increasing membrane fluidity at low temperatures.

Saturated Fatty Acids (Membrane Fluidity)

Straight hydrocarbon tails without double bonds that pack tightly together, decreasing membrane fluidity and increasing solidity at high temperatures.

Cholesterol

An amphipathic eukaryotic membrane lipid consisting of a polar hydroxyl head, a rigid steroid ring, and a nonpolar hydrocarbon tail that buffers membrane fluidity across varying temperatures.

Simple Diffusion

The passive net movement of permeable nonpolar molecules directly across the lipid bilayer down their concentration gradient without energy input or transport proteins.

Facilitated Diffusion

The passive transport of polar or charged substances down their concentration gradient through the assistance of channel or carrier proteins without cellular energy expenditure.

Channel Proteins

Transmembrane proteins that act as open or gated pores, allowing specific solutes to pass without binding and displaying linear transport kinetics.

Carrier Proteins

Membrane transport proteins that specifically bind to the solutes they transport, exhibiting saturation kinetics.

Uniporter

A carrier protein configured to transport only a single type of molecule across the plasma membrane.

Symporter

A carrier protein that cotransports two different types of molecules across the membrane in the same direction.

Antiporter

A carrier protein that transports two different types of molecules across the membrane in opposite directions.

Active Transport

Energy-requiring cellular transport (anti-diffusion) that moves molecules against their concentration gradient to establish or maintain chemical gradients.