11 SG: Biological Membranes and Transport

Fluid Mosaic Model

A model describing the structure of cell membranes, where proteins float in or on the fluid lipid bilayer like boats on a pond.

Lipid Transfer Protein

Proteins that facilitate the transfer of lipids between membranes.

Peripheral Proteins

Proteins that are temporarily associated with the lipid bilayer or with integral membrane proteins.

Amphitropic Proteins

Proteins that can exist both in the cytosol and associated with membranes.

Monotopic

Proteins attached to only one side of the membrane.

Bitopic

Proteins that span the membrane once.

Polytopic

Proteins that span the membrane multiple times.

Hydropathy Index

A measure of the hydrophobic or hydrophilic properties of amino acid residues in a protein.

β Barrel

A large beta-sheet that twists and coils to form a closed structure in membrane proteins.

Porin

Proteins that form large pores in the outer membranes of bacteria, mitochondria, and chloroplasts.

Positive-Inside Rule

The observation that positively charged residues are more common on the cytoplasmic side of membrane proteins.

GPI-Anchored Protein

Proteins that are attached to the membrane via a glycosylphosphatidylinositol (GPI) anchor.

Flippases

Enzymes that facilitate the movement of phospholipids from one leaflet of the bilayer to the other (go INSIDE)

Floppases

Enzymes that move phospholipids from the inner to the outer leaflet of the bilayer.

Scramblases

Enzymes that move phospholipids in both directions across the bilayer, disrupting membrane asymmetry.

FRAP (Fluorescence Recovery After Photobleaching)

A technique to study the movement of proteins and lipids within cell membranes.

Microdomains

Small, specialized areas within a cell membrane with distinct lipid and protein composition.

Rafts

Microdomains in the cell membrane rich in cholesterol and sphingolipids, involved in signaling and trafficking.

Caveolae

Small, flask-shaped invaginations in the cell membrane involved in endocytosis and signal transduction.

Caveolin

A protein associated with caveolae that plays a role in their formation and function.

BAR Domain

Protein domains that bind to curved membranes and are involved in membrane remodeling.

Septins

A group of GTP-binding proteins involved in cytokinesis and other cellular processes.

v-SNAREs

Vesicle-associated proteins that mediate vesicle fusion with target membranes.

t-SNAREs

Target membrane-associated proteins that mediate vesicle fusion with target membranes.

Integrin

Transmembrane receptors that facilitate cell-extracellular matrix adhesion.

Selectin

Cell adhesion molecules that bind to carbohydrate molecules on the surfaces of other cells.

Membrane Potential (Vm)

The voltage difference across a cell membrane due to the distribution of ions.

Electrochemical Gradient

The combined effect of an ion's concentration gradient and the electrical potential across a membrane.

Electrochemical Potential

The energy required to move an ion across a membrane, considering both concentration and electrical gradients.

Ion Channels

Proteins that allow the passage of ions across cell membranes.

Electroneutral

Transport processes that do not result in a net charge transfer across the membrane.

Cotransport

The simultaneous transport of two substances across a membrane by a single protein or protein complex.

Antiport

A type of cotransport where two substances are moved in opposite directions across a membrane.

Symport

A type of cotransport where two substances are moved in the same direction across a membrane.

Uniport

The transport of a single substance across a membrane by a transporter.

Electrogenic

Transport processes that result in a net charge transfer across the membrane.

P-Type ATPases

A family of enzymes that transport ions across membranes using ATP hydrolysis.

SERCA Pump

A type of P-type ATPase that transports calcium ions into the sarcoplasmic/endoplasmic reticulum.

Na+K+ ATPase

A P-type ATPase that pumps Na out of cells and K into cells, maintaining the electrochemical gradient.

V-Type ATPases

Enzymes that transport protons across membranes using ATP hydrolysis, found in vacuoles and lysosomes.

F-Type ATPases

Enzymes that synthesize ATP using a proton gradient, found in mitochondria and chloroplasts.

ATP Synthase

An enzyme that synthesizes ATP from ADP and inorganic phosphate using a proton gradient.

ABC Transporters

A family of transporters that use ATP hydrolysis to transport various molecules across membranes.

Multidrug Transporters

ABC transporters that expel drugs and other toxins from cells.

Na+ Glucose Symporter

A transporter that moves sodium and glucose into cells simultaneously.

Ionophore

Molecules that facilitate the transport of ions across cell membranes.

Aquaporins (AQPs)

Channel proteins that facilitate the transport of water across cell membranes.

Ligand-Gated Channel

Ion channels that open or close in response to the binding of a chemical messenger (ligand).

Voltage-Gated Ion Channel

Ion channels that open or close in response to changes in membrane potential.

Patch-Clamping

A technique used to study the ionic currents passing through individual ion channels.