Chapter 5: The Working Cell

Question 1

active site

Answer 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.

Question 2

active transport

Answer 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).

Question 3

adenosine triphosphate (ATP)

Answer 3

Main energy source for cells.

Question 4

aquaporin

Answer 4

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

Question 5

cellular respiration

Answer 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).

Question 6

chemical energy

Answer 6

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

Question 7

coenzyme

Answer 7

An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.

Question 8

cofactor

Answer 8

A nonprotein molecule or ion that is required for the proper functioning of an enzyme. See also coenzyme.

Question 9

competitive inhibitor

Answer 9

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.

Question 10

concentration gradient

Answer 10

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.

Question 11

diffusion

Answer 11

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

Question 12

endergonic reaction

Answer 12

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.

Question 13

endocytosis

Answer 13

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

Question 14

energy

Answer 14

The capacity to perform work, or to rearrange matter.

Question 15

energy coupling

Answer 15

In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.

Question 16

entropy

Answer 16

A measure of disorder. One form of disorder is heat, which is random molecular motion.

Question 17

enzyme

Answer 17

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.

Question 18

exergonic reaction

Answer 18

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.

Question 19

exocytosis

Answer 19

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

Question 20

facilitated diffusion

Answer 20

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

Question 21

feedback inhibition

Answer 21

A method of metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

Question 22

first law of thermodynamics

Answer 22

The principle of conservation of energy. Energy can be transferred and transformed, but it cannot be created or destroyed.

Question 23

fluid mosaic

Answer 23

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.

Question 24

heat

Answer 24

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.

Question 25

hypertonic solution

Answer 25

Referring to a solution that, when surrounding a cell, will cause the cell to lose water.

Question 26

hypotonic solution

Answer 26

Referring to a solution that, when surrounding a cell, will cause the cell to take up water.

Question 27

induced fit

Answer 27

The change in shape of the active site of an enzyme, induced by entry of the substrate so that it binds more snugly to the substrate.

Question 28

isotonic solution

Answer 28

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

Question 29

kinetic energy

Answer 29

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

Question 30

metabolism

Answer 30

The totality of an organism’s chemical reactions.

Question 31

noncompetitive inhibitor

Answer 31

A substance that impedes the activity of an enzyme without entering an active site. By binding elsewhere on the enzyme, a noncompetitive inhibitor changes the shape of the enzyme so that the active site no longer functions.

Question 32

osmoregulation

Answer 32

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

Question 33

osmosis

Answer 33

The diffusion of water across a selectively permeable membrane.

Question 34

passive transport

Answer 34

The diffusion of a substance across a biological membrane, without any input of energy.

Question 35

phagocytosis

Answer 35

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

Question 36

phosphorylation

Answer 36

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

Question 37

pinocytosis

Answer 37

Cellular “drinking”; a type of endocytosis in which the cell takes fluid and dissolved solutes into small membranous vesicles.

Question 38

potential energy

Answer 38

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

Question 39

receptor-mediated endocytosis

Answer 39

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.

Question 40

second law of thermodynamics

Answer 40

The principle whereby every energy conversion reduces the order of the universe, increasing its entropy. Ordered forms of energy are at least partly converted to heat.

Question 41

selective permeability

Answer 41

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

Question 42

substrate

Answer 42

(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.

Question 43

thermodynamics

Answer 43

The study of energy transformation that occurs in a collection of matter. See first law of thermodynamics; second law of thermodynamics.

Question 44

tonicity

Answer 44

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