Membranes and membrane proteins

What is the basic structure of cellular membranes?

A phospholipid bilayer composed of amphipathic lipids with hydrophilic heads and hydrophobic tails.

What does amphipathic mean?

A molecule with both hydrophilic and hydrophobic regions.

What are the three major classes of membrane lipids?

Glycerophospholipids

What is the structure of a glycerophospholipid?

Glycerol backbone

What is the structure of a sphingolipid?

Sphingosine backbone

What is the main sterol in animal membranes?

Cholesterol.

How do unsaturated fatty acids affect membranes?

They create kinks that increase fluidity.

How does cholesterol affect membrane fluidity?

It stabilises membranes by reducing fluidity at high temperatures and preventing rigidity at low temperatures.

What are lipid rafts?

Microdomains enriched in cholesterol and sphingolipids involved in signalling and trafficking.

Why are membranes self‑sealing?

To maintain cell integrity during processes like division

What are the main functions of the cytoplasmic membrane?

Selective permeability

What molecules can diffuse freely across membranes?

Gases (O₂

What molecules require transport proteins?

Ions

What are the two major classes of membrane transport proteins?

Channels and transporters.

What is passive transport?

Movement of molecules down their concentration gradient without energy input.

What is facilitated diffusion?

Passive transport via channels or carriers.

What is active transport?

Movement of molecules against their gradient using energy.

What factors influence diffusion rate?

Concentration gradient

What is a uniporter?

A transporter that moves one molecule at a time.

What is a symporter?

A co‑transporter that moves two molecules in the same direction.

What is an antiporter?

A co‑transporter that moves molecules in opposite directions.

What is primary active transport?

Transport powered directly by ATP hydrolysis.

What is secondary active transport?

Transport powered by ion gradients created by ATP‑dependent pumps.

What is the Na⁺/K⁺ ATPase?

A pump that moves 3 Na⁺ out and 2 K⁺ into the cell per ATP hydrolysed.

What is the role of proton gradients?

Driving ATP synthesis in mitochondria and powering secondary transport.

What are ABC transporters?

ATP‑Binding Cassette transporters that use ATP to move molecules across membranes.

What human disease involves an ABC transporter?

Cystic fibrosis (CFTR Cl⁻ channel defect).

What is multidrug resistance?

Cancer cells overexpress ABC transporters that pump drugs out.

What are ligand‑gated ion channels?

Channels that open when a ligand binds (e.g.

What are voltage‑gated ion channels?

Channels that open in response to membrane potential changes.

What are mechanosensitive channels?

Channels that open in response to mechanical stress.

What are gap junctions?

Channels connecting neighbouring cells for rapid communication.

What is exocytosis?

Fusion of vesicles with the plasma membrane to release contents outside the cell.

What is constitutive exocytosis?

Continuous secretion of molecules.

What is regulated exocytosis?

Secretion triggered by a signal.

What is endocytosis?

Uptake of extracellular material into the cell via vesicles.

What is pinocytosis?

Continuous uptake of extracellular fluid.

What is phagocytosis?

Engulfment of large particles or microbes by specialised cells like macrophages.

What is receptor‑mediated endocytosis?

Selective uptake using clathrin‑coated pits.

What is clathrin?

A triskelion‑shaped protein forming coated vesicles.

What is cell signalling?

Communication via receptors detecting extracellular ligands and activating intracellular pathways.

What are agonists?

Molecules that activate receptors.

What are antagonists?

Molecules that block receptor activation.

Why are membrane proteins major drug targets?

They control signalling

What are adhesion molecules?

Proteins like cadherins and integrins that mediate cell‑cell and cell‑matrix interactions.

What are the main functions of membrane proteins?

Transport