Cell Structure and Membranes Vocabulary

Vocabulary flashcards covering cell theory, eukaryotic and prokaryotic organelles, membrane transport, and cytoskeleton components.

Prokaryotic Cells

Cells that lack a nucleus and membrane-bound organelles, possessing circular chromosomes located in a region called the nucleoid, including Bacteria and Archaea.

Eukaryotic Cells

Cells defined by having a nucleus, linear chromosomes, and membrane-bound organelles, typically $10$ to $100\,\text{times}$ larger than prokaryotic cells.

Cell Theory

The unifying biological theory proposed by Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow stating that cells are the fundamental units of life, all organisms are composed of cells, and all cells come from pre-existing cells.

Fluid Mosaic Model

Model of cell membrane structure proposed by Singer and Nicolson in $1972$, describing a fluid phospholipid bilayer embedded with proteins, glycoproteins, and glycolipids.

Cholesterol

A steroid lipid found in animal cell membranes (occupying up to $25\%$ of lipid content) that regulates membrane fluidity by preventing close packing of phospholipids at low temperatures.

Glycolipid

A carbohydrate covalently linked to a membrane lipid, located on the outer surface of the plasma membrane to serve as a cellular recognition site.

Glycoprotein

A carbohydrate covalently linked to a membrane protein, functioning in cellular recognition and interactions on the cell surface.

Lipid Raft

A specialized membrane domain enriched in specific lipids and proteins that plays crucial roles in cell signaling and signal transduction processes.

Simple Diffusion

Passive transport involving the net movement of small or nonpolar molecules directly across a membrane from a region of higher concentration to lower concentration without energy or transport proteins.

Osmosis

The passive net movement of a solvent across a selectively permeable membrane toward a region of higher solute concentration.

Tonicity

A measure of the relative solute concentration across a semi-permeable membrane, categorized into isotonic, hypotonic, and hypertonic states.

Turgor Pressure

Internal fluid pressure exerted by the plasma membrane against the rigid cell wall in plant cells as water enters, keeping the plant upright.

Channel Proteins

Integral membrane proteins that form hydrophilic pores across the membrane to facilitate rapid diffusion of specific ions or molecules.

Carrier Proteins

Membrane transport proteins that bind specific large polar molecules (such as glucose) and undergo a conformational shape change to release them across the membrane.

Sodium-Potassium Pump

An integral membrane protein performing primary active transport by hydrolyzing ATP to move $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell.

Secondary Active Transport

A form of active transport that uses energy stored in an established ion concentration gradient to move a solute against its own concentration gradient.

Exocytosis

The cellular process of secreting macromolecules out of eukaryotic cells through the fusion of secretory vesicles with the plasma membrane.

Endocytosis

The process of bringing macromolecules or particles into eukaryotic cells via invagination of the plasma membrane to form internal vesicles.

Phagocytosis

A form of endocytosis ('cellular eating') in which the plasma membrane engulfs a large particle or cell to form a phagosome.

Pinocytosis

A form of endocytosis ('cellular drinking') where small vesicles invaginate to bring fluids and dissolved substances into the cell.

Receptor-Mediated Endocytosis

Targeted uptake of specific macromolecules depending on ligand binding to membrane receptors, typically utilizing clathrin-coated pits and vesicles.

Ribosomes

Ribonucleoprotein complexes consisting of a small subunit (SSU) and large subunit (LSU) that serve as the universal sites of protein synthesis.

Actin Filaments (Microfilaments)

Cytoskeletal polymers of actin monomers that stabilize cell shape, facilitate cytoplasmic streaming, drive cytokinesis, and assist pseudopodia formation.

Intermediate Filaments

Tough, ropelike protein assemblages that anchor cell structures, hold the nucleus in position, and maintain cellular rigidity.

Microtubules

The largest cytoskeletal components made of tubulin monomers that form internal cell framework, serve as tracks for motor proteins, and structure cilia and flagella.

Nucleus

A eukaryotic organelle enclosed by a double-membrane nuclear envelope containing nuclear pores, housing chromatin and chromosomes.

Nucleolus

A densely staining region inside the eukaryotic nucleus that exhibits high RNA activity and serves as the site of ribosome assembly.

Rough Endoplasmic Reticulum

An interconnected network of flattened membrane sacs studded with ribosomes, responsible for synthesizing proteins targeted for membranes or secretion.

Smooth Endoplasmic Reticulum

Tubular endoplasmic reticulum lacking ribosomes that synthesizes lipids and steroids and chemically modifies small molecules such as drugs and pesticides.

Golgi Apparatus

An organelle consisting of flattened membrane sacs (cisternae) that receives, modifies, concentrates, packages, and sorts proteins from the rough ER.

Primary Lysosome

An organelle originating from the Golgi apparatus containing hydrolytic digestive enzymes capable of breaking down biological macromolecules.

Secondary Lysosome

A digestive vacuole formed by the fusion of a primary lysosome with a phagosome.

Peroxisome

An organelle housing metabolic reactions that generate toxic peroxides and safely convert them into water.

Vacuole

A large membrane-bound organelle prominent in plant and fungal cells that provides storage, catabolism, pigment reproduction, and structural turgor pressure.

Mitochondrion

A double-membrane organelle with folded inner membrane cristae and a fluid matrix, serving as the site of aerobic respiration.

Chloroplast

A double-membrane photosynthetic plastid containing thylakoids stacked into grana suspended in stroma, responsible for converting light energy into chemical energy.

Extracellular Matrix

A network surrounding animal cells consisting of fibrous collagen, gel-like proteoglycans, and linking proteins that provides structural support and cell adhesion.

Nucleoid

The non-membrane-bound region in prokaryotic cells where the circular chromosome is localized.