Cell Membrane: Transport and Specialised Functions

These flashcards cover cell membrane transport mechanisms, specialised protein functions, signaling receptors, and membrane-related diseases based on the lecture by Dr Alessandro Siani.

Receptor

A membrane protein that binds to chemical messengers such as hormones sent by other cells.

Enzyme (membrane protein)

A protein that breaks down a chemical messenger and terminates its effect.

Ion Channel

A channel protein that is constantly open and allows ions to pass into and out of the cell.

Gated ion channel

A channel that opens and closes to allow ions through only at certain times.

Cell-identity marker

A glycoprotein that distinguishes the body's own cells from foreign cells.

Cell-adhesion molecule (CAM)

A membrane protein that binds one cell to another or to the extracellular matrix.

Phospholipid bilayer

A semipermeable structure that allows small molecules to diffuse following concentration gradients, while electrically charged and polar molecules cannot diffuse easily.

Selective permeability

The property of plasma membranes that regulates molecular traffic by allowing some substances to pass through but not others.

Osmosis

The diffusion of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Passive transport

A type of membrane transport, such as diffusion, that requires no energy input.

Active transport

A directional transport process that moves molecules against their concentration gradients and requires energy input, usually provided by ATP.

Simple diffusion

A type of passive transport where solutes diffuse through the cell membrane following their concentration gradient without requiring specialised proteins.

Facilitated diffusion

A type of passive transport that requires the presence of specialised proteins such as channels and carriers.

Aquaporins

Channel proteins formed by $4$ subunits, each consisting of a transmembrane $6$-helix bundle, that facilitate the single-file movement of water molecules.

Uniporter

A transport protein that moves one substance in one direction.

Symporter

A transport protein that moves two substances in one direction.

Antiporter

A transport protein that moves two substances in opposite directions.

Primary active transport

Transport that is energised directly by the hydrolysis of ATP.

Secondary active transport

Transport that is energised indirectly by the concentration gradient.

Ligand-gated channel

A gated ion channel that opens when the protein is stimulated to change shape by a chemical signal.

Voltage-gated channel

A gated ion channel that opens when the protein is stimulated by an electrical charge difference.

Exocytosis

Bulk transport where material in vesicles is expelled from a cell (inside to outside), such as the release of neurotransmitters or insulin.

Endocytosis

Bulk transport of materials from the outside to the inside of the cell.

Phagocytosis

A type of endocytosis where a cell engulfs a particle in a vacuole which then fuses with a lysosome for digestion.

Pinocytosis

A type of endocytosis where molecules are taken up when extracellular fluid is gulped into tiny vesicles.

Receptor-mediated endocytosis

A type of endocytosis where the binding of ligands to receptors triggers vesicle formation.

Ligands

Specialised molecules that bind to receptors on the cell surface to send a message inside the cell.

Acetylcholine receptor (AChR)

An ion channel receptor where binding of Acetylcholine causes the channel to open, allowing $Na^+$ to flow into the cell to initiate muscle contraction.

Enzyme-linked receptors

Receptors that, upon signal binding, activate a protein kinase domain in the cytoplasm to phosphorylate substrates and trigger a chemical cascade.

G protein coupled receptors (GPCRs)

Receptors that activate a G protein by replacing GDP with GTP, which then activates an effector protein to cause changes in cell function.

Major Histocompatibility Complexes (MHC)

Membrane proteins that play an essential role in the immune response by presenting antigens to lymphocytes.

CFTR (Cystic Fibrosis Transmembrane Conductance Regulator)

A membrane channel that, when mutated, causes Cystic Fibrosis.

Amyloid-beta plaques

Plaques involved in Alzheimer's Disease that disrupt membrane integrity.