bio chapter 7

Amphipathic

Having both a hydrophilic region and a hydrophobic region (such as phospholipids).

Fluid mosaic model

Membrane is a fluid structure with a 'mosaic' of various proteins embedded in it / proteins are not randomly distributed.

Membrane fluidity

Most lipids and some proteins drift laterally / flip-flop across the membrane is rare. Membranes are about as fluid as salad oil.

Unsaturated vs. saturated fatty acid tails (membrane)

Unsaturated tails (kinks) prevent tight packing so the membrane is more fluid / saturated tails pack together so it is more viscous.

Cholesterol and membrane fluidity

At warm temperatures (37°C) it restrains phospholipid movement / at cool temperatures it maintains fluidity by preventing tight packing.

Peripheral proteins

Membrane proteins bound to the surface of the membrane.

Integral proteins

Membrane proteins that penetrate the hydrophobic core / those that span the membrane are transmembrane proteins (nonpolar amino acids often coiled into alpha helices).

Six major functions of membrane proteins

Transport / enzymatic activity / signal transduction / cell-cell recognition / intercellular joining / attachment to the cytoskeleton and ECM.

Membrane carbohydrates

Bonded to lipids (glycolipids) or more commonly to proteins (glycoproteins) on the external face / used in cell-cell recognition / vary among species - individuals - and cell types.

Sidedness of membranes

Inside and outside faces differ / the asymmetry is determined when the membrane is built by the ER and Golgi apparatus.

Selective permeability

Plasma membranes regulate molecular traffic: hydrophobic (nonpolar) molecules cross rapidly / hydrophilic molecules (ions - polar molecules) do not cross easily without transport proteins.

Channel protein

Transport protein with a hydrophilic channel that certain molecules or ions use as a tunnel (such as aquaporins for water).

Aquaporin

Channel protein that facilitates passage of water.

Carrier protein

Transport protein that binds to a molecule and changes shape to shuttle it across the membrane.

Passive transport

Diffusion of a substance across a membrane with no energy investment by the cell.

Diffusion

Tendency of molecules to spread out evenly into the available space / substances move down their concentration gradient.

Dynamic equilibrium

As many molecules cross the membrane in one direction as in the other.

Osmosis

Diffusion of water across a selectively permeable membrane - from lower solute concentration to higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water.

Isotonic solution

Solute concentration same as inside the cell / no net water movement. Animal cell: normal. Plant cell: flaccid.

Hypertonic solution

Solute concentration greater than inside the cell / cell loses water. Animal cell: shriveled. Plant cell: plasmolyzed.

Hypotonic solution

Solute concentration less than inside the cell / cell gains water. Animal cell: lysed. Plant cell: turgid (normal).

Turgid

Firm plant cell / in a hypotonic solution it swells until the wall opposes further water uptake.

Flaccid

Limp plant cell / occurs in an isotonic environment (no net water movement).

Plasmolysis

In a hypertonic environment - the plant cell membrane pulls away from the cell wall - causing wilting / usually lethal.

Osmoregulation

Control of solute concentrations and water balance (such as Paramecium's contractile vacuole).

Facilitated diffusion

Passive transport in which transport proteins (channel or carrier) speed movement of molecules down their gradient / no energy required.

Active transport

Moves substances against their concentration gradients / requires energy - usually ATP / performed by specific membrane proteins.

Sodium-potassium pump

Active transport protein that moves Na+ out and K+ into the cell using ATP (the major electrogenic pump of animal cells).

Membrane potential

The voltage difference across a membrane - created by differences in the distribution of positive and negative ions.

Electrochemical gradient

Combination of a chemical force (concentration gradient) and an electrical force (membrane potential) driving ion diffusion.

Electrogenic pump

Transport protein that generates voltage across a membrane (Na+/K+ pump in animals / proton pump in plants - fungi - bacteria).

Cotransport

Active transport of one solute indirectly drives transport of another (such as the plant sucrose-H+ cotransporter using the proton pump's H+ gradient).

Exocytosis

Transport vesicles fuse with the plasma membrane and release their contents outside the cell.

Endocytosis

Cell takes in macromolecules by forming vesicles from the plasma membrane. Three types: phagocytosis - pinocytosis - receptor-mediated.

Pinocytosis

'Cellular drinking' / the cell takes in extracellular fluid and dissolved solutes in vesicles.

Receptor-mediated endocytosis

Endocytosis in which receptors bind specific molecules - forming coated pits and coated vesicles