Chapter 4 - Principals of Biology

plasma membrane

Membrane surrounding the cytoplasm that consists of a phospholipid bilayer with embedded proteins; functions to regulate the entrance and exit of molecules to and from the cell.

homeostasis

Maintenance of normal internal conditions in a cell or an organism by means of self-regulating mechanisms.

Fluid-mosaic model

Model for the plasma membrane based on the changing location and pattern of protein molecules in a fluid phospholipid bilayer.

glycolipids

Lipid in plasma membranes that contains an attached carbohydrate chain; assembled in the Golgi apparatus.

glycoprotein

Protein in plasma membranes that has an attached carbohydrate chain; assembled in the Golgi apparatus.

channel proteins

Protein that forms a channel to allow a particular molecule or ion to cross the plasma membrane.

carrier protein

Protein in the plasma membrane that combines with and transports a molecule or ion across the plasma membrane.

cell recognition protein

Glycoproteins in the plasma membrane that identify self and help the body defend itself against pathogens.

receptor proteins

Protein located in the plasma membrane or within the cell; binds to a substance that alters some metabolic aspect of the cell.

Enzymatic proteins

Protein that catalyzes a specific reaction; may be found in the plasma membrane or the cytoplasm of the cell.

selectively permiable

Property of the plasma membrane that allows some substances to pass, but prohibits the movement of others.

diffusion

Movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution (equilibrium).

solute

Substance that is dissolved in a solvent, forming a solution.

Solvent

Liquid portion of a solution that serves to dissolve a solute.

osmosis

Diffusion of water through a selectively permeable membrane.

osmotic pressure

Measure of the tendency of water to move across a selectively permeable membrane; visible as an increase in liquid on the side of the membrane with higher solute concentration.

isotonic solution

Solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis.

hypotonic solution

Solution that contains a lower solute (more water) concentration than the cytoplasm of a cell; causes cell to gain water by osmosis.

hypertonic solution

Higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis.

facillitated transport

Passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a protein carrier.

active transport

Use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy.

sodium-potassium pump

Carrier protein in the plasma membrane that moves sodium ions out of, and potassium ions into, cells; important in the function of nerve and muscle cells in animals.

exocytosis

Process in which an intracellular vesicle fuses with the plasma membrane so that the vesicle's contents are released outside the cell.

endocytosis

Process by which substances are moved into the cell from the environment; includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

phagocytosis

Process by which cells engulf large substances, forming an intracellular vacuole.

pinocytosis

Process by which vesicle formation brings macromolecules into the cell.

receptor-mediated endocytosis

Selective uptake of molecules into a cell by vacuole formation after they bind to specific receptor proteins in the plasma membrane.

extracellualr matrix

Nonliving substance secreted by some animal cells; is composed of protein and polysaccharides.

adhesion junctions

Junction between cells in which the adjacent plasma membranes do not touch but are held together by intercellular filaments attached to buttonlike thickenings.

Tight junctions

Junction between cells when adjacent plasma membrane proteins join to form an impermeable barrier.

gap junctions

Junction between cells formed by the joining of two adjacent plasma membranes; it lends strength and allows ions, sugars, and small molecules to pass between cells.

plasmodesmata

In plants, cytoplasmic connections in the cell wall that connect two adjacent cells.