Cell Membrane: Transport Campbell and Lecture

• What do you call a phospholipid in a membrane that has both a hydrophilic and hydrophobic region?

  Amphipathic
• What is the model wherein the membrane is a "mosaic" of protein molecules bobbing in a fluid bilayer of phospholipids?

  Fluid mosaic model
• What does the phospholipid bilayer need to be rich in so that as temperatures decrease, the fluidity of the membrane remains fluid?

  unsaturated hydrocarbon tails
• What component of the plasma membrane helps resist changes in membrane fluidity when exposed to different temperatures?

  Cholesterol
• Membrane - collage of different proteins, often clustered together in groups, embedded in a fluid matrix of the lipid bilayer
• Integral proteins - penetrate the hydrophobic interior of the lipid bilayer
• What integral protein is associated with spanning the membrane?

  Transmembrane proteins
• Peripheral proteins - not embedded in the lipid bilayer as they're loosely bound to surface of the membrane
• What are the six major functions of membrane proteins?

  Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix.
• Cells recognize other cells by binding to molecules containing what kind of macromolecule on the extracellular surface of the plasma membrane?

  carbohydrates
• Membrane carbohydrates - function as markers that distinguish one cell from another
• When a membrane allows some substances to cross more easily than others what does the membrane exhibit?

  Selective permeability
• What are nonpolar molecules that can cross the plasma membrane easily without the aid of proteins?

  CO2, O2
• Transport proteins - Have hydrophilic channel that certain molecules or ions use as a tunnel through the membrane
• What channel protein is specific for water molecules travelling across the plasma membrane?

  Aquaporins
• Carrier proteins - hold on to their passengers and change their shape in a way that shuttles them across the membrane
• Diffusion - movement of particles of any substance from an area of high concentration to an area of low concentration down their concentration gradient
• Passive transport - diffusion of a substance across a biological membrane with no energy required.
• Osmosis - diffusion of free water across a selectively permeable membrane, whether artificial or cellular
• Tonicity - ability of a surrounding solution to cause a cell to gain or lose water
• Isotonic solution - a solution that has the same solute concentration as the cell
• Hypertonic solution - cell will lose water, then shrivel afterwards
• Hypotonic solution - Water will enter the cell faster than it leaves and the cell will swell and eventually burst
• Osmoregulation - control of solute concentrations and water balance
• Turgor pressure - inelastic cell wall will expand before it exerts a back pressure on the cell that opposes further water uptake
• Plasmolysis - for hypertonic environments, the plasma membrane pulls away from cell at multiple places and can lead to cell death
• Facilitated diffusion - polar molecules and ions blocked by the lipid bilayer of the membrane diffuse passively with the help of transport proteins
• Ion channels - proteins that transport ions and function as gated channels which open or close in response to a stimuli
• Active transport - pump a solute across a membrane against its concentration gradient which needs energy.
• For active transport, what membrane proteins are usually associated?

  Carrier proteins
• What usually supplies energy for most active transport?

  ATP hydrolysis
• Sodium-potassium pump - exchanges sodium ions for potassium ions across the plasma membrane
• Voltage - electrical potential energy which is characterized by the separation of opposite charges
• Membrane potential - voltage across a membrane
• Electrochemical gradient - combination of chemical forces and electrical forces acting on an ion
• Electrogenic pump - a transport protein that generates voltage across a membrane
• Cotransport - transport protein can couple the downhill diffusion of the solute to the uphill transport of a second substance against its own concentration gradient
• What molecules are involved in bulk transport across the plasma membrane?

  Proteins; polysaccharides
• Exocytosis - cell secretes certain molecules by the fusion of vesicles with plasma membrane
• Endocytosis - cell takes in molecules and particulate matter by forming new vesicles from plasma membrane