CR1 KCP1 Cell Membrane & Transport

What are the fundamental building blocks of the cell membrane?

Amphiphilic lipids, such as phospholipids or sphingolipids.

How are phospholipids arranged in the lipid bilayer?

Hydrophilic (polar) heads face the watery ICF and ECF, while hydrophobic (nonpolar) tails meet in the inner region to exclude water.

Contrast Integral and Peripheral membrane proteins.

Integral proteins strongly bind and penetrate the bilayer (e.g., transmembrane channels). Peripheral proteins bind weakly to the surface via electrostatic affinity or hydrogen bonds.

What is the Glycocalyx and where is it located?

A "sugar coating" of glycoproteins and glycolipids found exclusively on the exterior surface of the cell.

What are three main functions of the Glycocalyx?

Protects from dehydration, provides antigenic function (immune recognition), and differentiates blood groups on RBCs.

Define the Fluid Mosaic Model.

The lipids and proteins in the cell membrane are not rigidly locked in place; the membrane remains fluid and dynamic.

How does cholesterol regulate membrane fluidity at high vs. low temperatures?

High temps: Stabilizes membrane and raises melting point. Low temps: Intercalates between phospholipids to prevent clustering.

What is Simple Diffusion and what molecules use it?

Movement of small or lipophilic/nonpolar molecules down their concentration gradient without energy (e.g., O2, CO2).

What is Facilitated Diffusion?

Movement of large or charged molecules down a gradient via specific membrane proteins (channels or carriers).

What are Aquaporins?

Specialized channel proteins that regulate the flow of water molecules across the membrane.

What is the difference between Voltage-gated and Ligand-gated ion channels?

Voltage-gated open in response to changes in membrane potential; Ligand-gated open in response to binding of a neurotransmitter/ligand.

What is Primary Active Transport?

Movement of materials against a concentration gradient using direct metabolic energy (ATP hydrolysis).

Give a primary active transport example and its ion exchange ratio.

The Na+/K+ pump extrudes 3 Na+ from the cell and imports 2 K+ per ATP cycle.

What is Secondary Active Transport?

Couples the movement of a molecule against its gradient with another molecule moving down its electrochemical gradient (does not directly hydrolyze ATP).

Differentiate between Phagocytosis and Pinocytosis.

Phagocytosis: Non-selective ingestion of large particles. Pinocytosis: Non-selective ingestion of fluids and small particles.

What triggers Receptor-Mediated Endocytosis?

Highly selective uptake occurs only when specific ligands bind to external membrane receptors.

Uniporter?

A carrier that transports a single molecule at a time down its concentration gradient (e.g., glucose or amino acids).

Symporter (Cotransporter)?

A carrier that simultaneously transports two different molecules in the same direction.

Antiporter?

A carrier that simultaneously transports two different molecules in opposite directions.

Pathophysiology of Cystic Fibrosis?

Mutation in the CFTR gene (chloride ion channel) leads to defective ion transport, causing thick, sticky mucus in lungs and digestive tract.

Pathophysiology of Familial Hypercholesterolemia?

Mutations in the LDL receptor gene prevent the internalization of LDL by endocytosis, leading to early heart disease.

Pathophysiology of Hereditary Spherocytosis?

Mutations in cytoskeletal proteins (spectrin/ankyrin) cause structural membrane instability, making RBCs fragile and prone to rupture (hemolytic anemia).

Pathophysiology of Myasthenia Gravis?

Autoimmune attack degrades or blocks acetylcholine receptors at neuromuscular junctions, causing muscle weakness and fatigue.

Pathophysiology of Cholera?

Bacterial toxin modifies G-proteins in intestinal cells, overstimulating ion channels and causing massive water efflux (diarrhea).