Biomembranes and Transport Mechanisms

Flashcards covering the functions, composition, signaling, fluidity, and transport mechanisms of biomembranes based on lecture notes.

Biomembrane Functions

Acting as selectively permeable barriers, facilitating ion and molecule transport, intercellular signaling (gap junctions), intercellular adhesion (tight junctions), cell identity/antigenicity, and conductivity.

Gap junctions

Structures involved in intercellular signaling and communication.

Tight junctions

Structures responsible for intercellular adhesion and the anchoring of cells.

Tear film (eye)

A simple layer of lipids (including cholesterol) that forms a phase boundary between air and liquid to prevent evaporation and reduce surface tension.

Ear drum (tympanic membrane)

A membrane formed by cells and extracellular matrix that acts as an air-to-air interface.

Glycocalyx

The extracellular part of the membrane composed of glycolipids and gangliosides (spec. oligosaccharides) that define cell identity and antigenicity.

Sialylation

The covalent modification of lipids or proteins with sialic acid, which attracts $H_2O$ to the cell surface and is part of mucins.

Phosphatidylinositol

A glycerophospholipid involved in cell signaling via phosphorylation on its polar head.

Phosphatidylserine

A glycerophospholipid that serves as a signal for apoptosis.

Membrane Fluidity

A property of the lipid bilayer influenced by temperature, fatty acid chain length ($MK$), and the degree of fatty acid saturation.

Cholesterol (in membranes)

A modulator of membrane fluidity that interacts with the hydrophobic parts of transmembrane proteins and decreases interaction between neighboring hydrophobic chains.

Lipid rafts

Specialized microdomains within the membrane that interact with hydrophobic parts of transmembrane proteins.

Passive Transport

Movement including diffusion and osmosis driven by a concentration gradient across the membrane without the use of ATP; allows gases, $H_2O$, and lipophilic molecules to pass.

Aquaporins

Proteins that facilitate the diffusion of $H_2O$; genetic defects in these can lead to nephrogenic diabetes insipidus.

Uniport

A transport mechanism characterized by facilitated diffusion of a single substance.

Symport

A transport protein that moves two molecules or ions in the same direction simultaneously, such as $SGLT1$ transporting $Na^+$ and glucose.

Antiport

A transport protein that moves molecules or ions in opposite directions, such as the $Na^+/K^+$ pump or Nigericin.

Electroneutral Transport

Transport resulting in zero net charge change, such as the exchange of an identical number of ions with the same charge or the movement of uncharged molecules.

Electrogenic Transport

Transport that causes a change in membrane potential by moving ions or charged molecules across the membrane.