Biology Key Terms Chap 5

Front 1

Active Site

Back 1

The part of an enzyme molecule where a substrate molecule attaches (by means of weak chemical bonds); typically, a pocket or groove on the enzyme's surface.

Front 2

Active Transport

Back 2

The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring input of energy (often as ATP).

Front 3

Adenosine Triphosphate - ATP

Back 3

Main energy source for cells.

Front 4

Aquaporin

Back 4

A transport protein in the plasma membrane of some plant or animal cells that facilitates the diffusion of water across the membrane (osmosis).

Front 5

Cellular Respiration

Back 5

The aerobic harvesting of energy from food molecules; the energy-releasing chemical breakdown of food molecules, such as glucose, and the storage of potential energy in a form that cells can use to perform work; involves glycolysis, the citric acid cycle, and oxidative phosphorylation (the electron transport chain and chemiosmosis).

Front 6

Chemical Energy

Back 6

Energy available in molecules for release in a chemical reaction; a form of potential energy.

Front 7

Competitive Inhibitior

Back 7

A substance that reduces the activity of an enzyme by binding to the enzyme's active site in place of the substrate. A competitive inhibitor's structure mimics that of the enzyme's substrate.

Front 8

Concentration Gradient

Back 8

An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, substances tend to move from where they are more concentrated to where they are less concentrated.

Front 9

Diffusion

Back 9

The spontaneous tendency of a substance to move down its concentration gradient from where it is more concentrated to where it is less concentrated.

Front 10

Endergonic Reaction

Back 10

An energy-requiring chemical reaction, which yields products with more potential energy than the reactants. The amount of energy stored in the products equals the difference between the potential energy in the reactants and that in the products.

Front 11

Endocytosis

Back 11

Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane.

Front 12

Enzyme

Back 12

A protein (or RNA molecule) that serves as a biological catalyst, changing the rate of a chemical reaction without itself being changed into a different molecule in the process.

Front 13

Exergonic Reaction

Back 13

An energy-releasing chemical reaction in which the reactants contain more potential energy than the products. The reaction releases an amount of energy equal to the difference in potential energy between the reactants and the products.

Front 14

Exocytosis

Back 14

The movement of materials out of the cytoplasm of a cell by the fusion of vesicles with the plasma membrane.

Front 15

Facillitated Diffusion

Back 15

The passage of a substance through a specific transport protein across a biological membrane down its concentration gradient.

Front 16

Fluid Mosaic

Back 16

A description of membrane structure, depicting a cellular membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer made of phospholipid molecules.

Front 17

Heat

Back 17

Thermal energy; the amount of energy associated with the movement of the atoms and molecules in a body of matter. Heat is energy in its most random form.

Front 18

Hypertonic Solution

Back 18

In comparing two solutions, the one with the greater concentration of solutes; cells in such a solution will lose water to their surroundings.

Front 19

Hypotonic Solution

Back 19

In comparing two solutions, the one with the lower concentration of solutes; cells in such a solution will take up water from their surroundings.

Front 20

Isotonic Solution

Back 20

A solution having the same solute concentration as another solution, thus having no effect on passage of water in or out of the cell.

Front 21

Kinetic Energy

Back 21

The energy of motion; the energy of a mass of matter that is moving. Moving matter does work by imparting motion to other matter.

Front 22

Osmoregulation

Back 22

Method by which organisms regulate solute concentrations and balance the gain and loss of water.

Front 23

Osmosis

Back 23

The diffusion of water across a selectively permeable membrane.

Front 24

Phaygocytosis

Back 24

Cellular "eating"; a type of endocytosis whereby a cell engulfs macromolecules, other cells, or particles into its cytoplasm.

Front 25

Phosphorlation

Back 25

The transfer of a phosphate group, usually from ATP, to a molecule. Nearly all cellular work depends on ATP energizing other molecules by phosphorylation.

Front 26

Potential Energy

Back 26

The energy that matter possesses because of its location or arrangement. Water behind a dam and chemical bonds possess potential energy.

Front 27

Receptor Mediated Endocytosis

Back 27

The movement of specific molecules into a cell by the inward budding of membranous vesicles. The vesicles contain proteins with receptor sites specific to the molecules being taken in.

Front 28

Selective Permeability

Back 28

A property of biological membranes that allows some substances to cross more easily than others and blocks the passage of other substances altogether.

Front 29

Substrate

Back 29

(1) A specific substance (reactant) on which an enzyme acts. Each enzyme recognizes only the specific substrate or substrates of the reaction it catalyzes. (2) A surface in or on which an organism lives.

Front 30

Tonicity

Back 30

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