Cell Unit

Endomembrane system

A group of membrane and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins.

Phagocytosis

A process where a white blood cell or phagocyte surrounds and destroys foreign substances, like bacteria, and removes dead cells.

Tonoplast

The membrane that surrounds the large vacuole in a mature plant cell.

Cristae

Functional dynamic compartments whose shape and dimensions modulate the kinetics of chemical reactions and the structure of protein complexes.

Mitochondrial matrix

The inner space surrounded by the mitochondrial inner membrane, containing several proteins involved in various biochemical reactions.

Granum

A coin-shaped stack of thylakoids found inside the chloroplasts of plant cells.

Stroma

The cells and tissues that support and give structure to organs, glands, or other tissues in the body.

Peroxisome

Intracellular organelle in eukaryotic cells that functions as a degradative organelle, containing oxidases for chemical oxidation reactions.

Dynein

A family of cytoskeleton motor proteins that move along microtubules, converting chemical energy stored in ATP to mechanical work.

Actin

A protein that contributes to the contractile property of muscle and other cells.

Pseudopodia

Temporary arm-like projections of a eukaryotic cell membrane used in movement.

Proteoglycans

Glycoproteins where the carbohydrate units are polysaccharides containing amino sugars.

Integrins

The principal receptors used by animal cells to bind to the extracellular matrix.

Tight junction

Membranes of neighboring cells pressed together, preventing leakage of extracellular fluid.

Desmosomes

Anchoring junctions that fasten cells together into strong sheets.

Gap junction

Communicating junctions that provide cytoplasmic channels between adjacent cells.

Amphipathic molecule

A compound comprising a hydrophilic head and a hydrophobic tail.

Fluid mosaic model

Describes the main characteristics of the plasma membrane.

Integral proteins

Proteins that reside within the bilayer membranes, playing critical roles in the movement of molecules and transduction of energy.

Peripheral proteins

Proteins found temporarily attached to the cell or mitochondrial membrane.

Osmoregulation

Active regulation of the osmotic pressure of an organism’s body fluid to maintain homeostasis.

Aquaporins

Proteins that facilitate the diffusion of water.

Endocytosis

The cellular process that allows a cell to bring substances into itself by forming a vesicle around the material.

Receptor-mediated endocytosis

A highly efficient mechanism for cellular uptake of membrane-impermeant ligands.

Exocytosis

The process for moving large molecules out of the cell to the cell exterior.

Signal-transduction pathway

A series of molecular interactions triggered by the binding of a signaling molecule to its receptor.

Local regulator

Chemical signals that act over short distances, reaching target cells by diffusion.

G-protein-linked receptor

A large family of proteins acting as cell surface receptors for various signals.

Tyrosine kinase

Enzymes that selectively phosphorylate tyrosine residues in different substrates.

Protein kinase

Enzymes that regulate the biological activity of proteins by phosphorylation of specific amino acids.

Protein phosphatases

Enzymes that remove phosphate groups from proteins, essential for regulating cell signaling.

Second messenger

A small molecule or ion that transmits signals from cell-surface receptors to effector proteins.

Cyclic AMP

A cellular signal important for many biological processes.

Adenylyl cyclase

An enzyme that catalyzes the conversion of ATP into cyclic adenosine monophosphate.

DAG

Diacylglycerol, an important lipid that acts as both an intermediate in lipid biosynthesis and a signaling lipid.

Inositol trisphosphate

A molecule controlling many cellular processes by releasing calcium from intracellular stores.

Scaffolding proteins

Proteins that bind to multiple other proteins to organize them into functional units.

Osmosis

The process by which water molecules move across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration, achieving equilibrium.

Diffusion

The movement of molecules from an area of higher concentration to an area of lower concentration, resulting in an even distribution.

Facilitated Diffusion

The process by which molecules pass through a cell membrane via special proteins, without using energy, often moving from higher to lower concentration.

Hypotonic

A solution that has a lower solute concentration compared to another solution, leading to water moving into the cell.

Hypertonic

A solution that has a higher solute concentration compared to another solution, causing water to move out of the cell.

isotonic

A solution that has the same solute concentration as another solution, resulting in no net movement of water into or out of the cell.

Tonicity

The measure of a solution's ability to affect the volume of a cell by altering its water content, based on solute concentration.

Phosphorylation cascade

A series of biochemical events in which one enzyme activates another through the addition of phosphate groups, amplifying a cellular response.