Chapter 7: Membrane Structure and Function

Selective Permeability

The membrane allows some substances to cross it more easily than others.

Amphipathic

Has both a hydrophilic region and a hydrophobic region.

Fluid Mosaic Model

Membrane is a fluid structure with a "mosaic" of various proteins embedded in or attached to a bilayer of phospholipids.

Integral Proteins

Typically transmembrane proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane.

Peripheral Proteins

Protein appendages loosely bound to the surface of the membrane and not embedded in the lipid bilayer.

Glycolipids

Lipid substances with linked sugar groups that are key structural elements in cell membranes and precursors of other biologically active molecules important in cell signaling.

Glycoproteins

Proteins with short chains of sugars attached to them; in eukaryotic cells they are important membrane proteins that allow cell-cell recognition and interaction.

Transport Proteins

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

Channel Proteins

Transport proteins which have a hydrophilic channel that molecules or ions can use to pass through the plasma membrane.

Aquaporins

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane.

Carrier Proteins

Another type of transfer protein.

Diffusion

Movement of molecules of any substance so that they spread out evenly into the available space.

Concentration Gradient

The region along which the density of a chemical substance decreases.

Passive Transport

The diffusion of a substance across a biological membrane. The cell does not have to expend energy to make it happen.

Osmosis

Diffusion of water across a selectively permeable membrane.

Tonicity

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

Isotonic

Having the same or equal osmotic pressure.

hypertonic

Having a higher osmotic pressure than a comparison solution.

Hypotonic

Having a lower osmotic pressure than a comparison solution.

Osmoregulation

The control of water balance.

Turgid

Very firm. Healthy state for most plant cells.

Flaccid

Limp.

Plasmolysis

When a cell is in a hypertonic environment, the cell will lose water to its surroundings, shrink, and its plasma membrane will pull away from the wall.

Facilitated Diffusion

Movement of specific molecules across cell membranes through protein channels.

Ion channels

Channel proteins - operate as gated channels - open or close in response to a stimulus.

Sodium-potassium pump

Cotransporter that actively moves sodium out of a cell and passively moves potassium into it.

Membrane potential

The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

Electrochemical Gradient

The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

Electrogenic Pump

A transport protein that generates voltage across a membrane.

Proton Pump

An active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process.

Cotransport

The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.

Exocytosis

process by which a cell releases large amounts of material.

Endocytosis

The cell takes biological molecules and particulate matter by forming new vesicles formed from the plasma membrane.

Phagocytosis

cellular eating.

Pinocytosis

cellular drinking.

receptor mediated endocytosis

The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

Ligands

Term for any molecule that binds specifically to the receptor site of any other molecule.