What is the phospholipid bilayer?
A double layer of phospholipids with hydrophilic heads facing outward (cytosol & extracellular fluid) and hydrophobic tails facing inward.
What does it mean that phospholipids are amphipathic?
They contain both hydrophilic (polar) and hydrophobic (nonpolar) regions.
What role does cholesterol play in membrane fluidity?
At high temperatures, it restrains phospholipid movement; at low temperatures, it prevents tight packing and maintains fluidity.
Which type of fatty acid makes membranes more fluid: saturated or unsaturated?
Unsaturated fatty acids make membranes more fluid.
What are peripheral proteins?
Proteins bound to the surface of the membrane.
What are integral proteins?
Proteins that penetrate the hydrophobic core of the membrane.
What are transmembrane proteins?
Integral proteins that span the entire membrane.
What are the six functions of membrane proteins?
Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to cytoskeleton/ECM
What are glycolipids and glycoproteins?
Membrane carbohydrates attached to lipids (glycolipids) or proteins (glycoproteins) that serve as cell identity markers.
What is diffusion?
The passive movement of molecules from high to low concentration until equilibrium is reached.
What is osmosis?
The diffusion of free water across a selectively permeable membrane.
Define tonicity.
The ability of a solution to cause a cell to gain or lose water.
What does hypotonic mean?
A solution with a lower solute concentration than the cell, causing water to enter and the cell to swell.
What does hypertonic mean?
A solution with a higher solute concentration than the cell, causing water to exit and the cell to shrink.
What does isotonic mean?
A solution with equal solute concentration inside and outside the cell; no net water movement.
What is facilitated diffusion?
Passive transport of molecules through membrane proteins (channel or carrier proteins).
What are channel proteins?
Proteins that provide corridors for molecules or ions to pass through (e.g., aquaporins).
What are carrier proteins?
Proteins that bind molecules, change shape, and shuttle them across the membrane.
What is active transport?
Movement of solutes against their concentration gradient using ATP.
What is bulk transport?
Movement of large molecules via vesicles across the membrane.
What is exocytosis?
Process where vesicles fuse with the plasma membrane to release contents outside the cell.
What is endocytosis?
Process where cells take in molecules by forming vesicles from the plasma membrane.
What are the three types of endocytosis?
Phagocytosis (“cell eating”), pinocytosis (“cell drinking”), receptor-mediated endocytosis (specific uptake using receptors).
