membranes and membrane proteins

What is the basic structure of cellular membranes?

Lipid bilayers formed from amphipathic lipids

What does amphipathic mean?

Having both hydrophilic and hydrophobic regions

Why do lipid bilayers form spontaneously in water?

Hydrophobic tails avoid water while hydrophilic heads interact with it

What are the three major types of membrane lipids?

Glycerophospholipids, sphingolipids, sterols

What is the structure of glycerophospholipids?

Phosphorylated head group, glycerol backbone, two fatty acid tails

What polar head groups are commonly found in glycerophospholipids?

Choline or serine

How do unsaturated fatty acids affect membranes?

Double bonds create kinks that increase fluidity

What is the structure of sphingolipids?

Phosphorylated head group, sphingosine backbone, fatty acid chain

Where are sphingolipids most abundant?

Myelin sheath surrounding nerve cells

What sterol is found in animal cell membranes?

Cholesterol

What is the role of sterols in membranes?

Regulate membrane fluidity and rigidity

Can the inner and outer leaflets of membranes differ?

Yes, they can have different lipid compositions

What are lipid rafts?

Clusters of lipids involved in signalling and transport

How does membrane composition affect membrane properties?

It influences thickness, curvature, and fluidity

Why are membranes described as self-sealing?

They reseal after disruption to maintain cell integrity

Why is selective permeability important?

It maintains internal conditions different from the external environment

What substances can cross membranes without proteins?

Water, gases, urea

Why are aquaporins needed if water can diffuse?

Simple diffusion is often too slow for cell needs

Which molecules require membrane proteins to cross membranes?

Ions, sugars, amino acids

What are the two major classes of membrane transport proteins?

Channels and transporters

What is passive transport?

Movement down a concentration gradient without energy

What is active transport?

Movement against a concentration gradient using energy

What factors influence diffusion across membranes?

Gradient steepness, temperature, size, surface area, distance, number of transporters

Why do most nutrients require active transport?

Their external concentrations are usually low

What energy sources drive active transport?

ATP hydrolysis or ion gradients

What is a uniporter?

A transporter moving one molecule in one direction

What is a symporter?

A co-transporter moving two molecules in the same direction

What is an antiporter?

A co-transporter moving molecules in opposite directions

What is facilitated diffusion?

Passive transport via specific membrane proteins

What are gated ion channels?

Channels that open or close in response to signals

What are examples of gated ion channels?

Ligand-gated, voltage-gated, mechanosensitive

What are gap junctions?

Channels connecting neighbouring cells directly

Why are gap junctions important in cardiomyocytes?

They allow rapid ion movement for coordinated contraction

What is the sodium-potassium pump?

An ATPase that pumps Na⁺ out and K⁺ into cells

How many ions are moved per ATP by the Na⁺/K⁺ pump?

3 Na⁺ out, 2 K⁺ in

Why is the Na⁺ gradient important?

It drives secondary active transport

What are ABC transporters?

ATP-binding cassette transporters using ATP hydrolysis

Where are ABC transporters found?

Prokaryotic and eukaryotic cells

What disease is linked to a defective ABC transporter?

Cystic fibrosis

What is multidrug resistance in cancer cells?

ABC transporters pumping drugs out of cells

What do membrane receptors do?

Bind extracellular ligands and transmit signals

Do receptor ligands usually cross the membrane?

No

How do receptors transmit signals inside the cell?

By conformational change or clustering leading to signalling cascades

What are second messengers?

Intracellular signalling molecules like cAMP or cGMP

What is exocytosis?

Secretion of materials out of the cell via vesicle fusion

Which organelle packages proteins for exocytosis?

Golgi apparatus

What are constitutive vs regulated exocytosis?

Constant secretion vs stimulus-dependent secretion

What is endocytosis?

Uptake of extracellular material into the cell

What is pinocytosis?

Continuous uptake of extracellular fluid

What is phagocytosis?

Engulfment of large particles by immune cells

Which cells commonly perform phagocytosis?

Macrophages and neutrophils

What is receptor-mediated endocytosis?

Uptake using specific receptors and clathrin

What is clathrin?

A protein forming coated pits and vesicles

Why is membrane knowledge important in drug design?

Drugs must cross membranes or bind membrane proteins

What is a drug agonist?

A molecule that activates a receptor

What is a drug antagonist?

A molecule that blocks receptor activation

Why are membrane proteins common drug targets?

They control transport, signalling, and cell communication

What roles do adhesion molecules play?

Cell-cell adhesion and interaction with extracellular matrix

What are examples of adhesion molecules?

Cadherins and integrins

What immune functions are associated with membranes?

Recognition, signalling, and defense mechanisms.