Chapter 8: An Introduction To Metabolism

Front 1

Activation energy

Back 1

The amount of energy that reactants must absorb before a chemical reaction will start

Front 2

Active site

Back 2

The specific portion of an enzyme that binds the substrate by means of multiple weak interactions and that forms the pocket in which catalysis occurs.

Front 3

Adenosine triphosphate (ATP)

Back 3

An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

Front 4

Allosteric regulation

Back 4

The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.

Front 5

Anabolic pathway

Back 5

A metabolic pathway that consumes energy to synthesize a complex molecule from simpler compounds.

Front 6

Bioenergetics

Back 6

(1) The overall flow and transformation of energy in an organism. (2) The study of how energy flows through organisms.

Front 7

Catabolic pathway

Back 7

A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds.

Front 8

Catalyst

Back 8

A chemical agent that increases the rate of a reaction without being consumed by the reaction.

Front 9

Chemical energy

Back 9

Energy available in molecules for release in a chemical reaction

Front 10

Coenzyme

Back 10

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

Front 11

Cofactor

Back 11

Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis.

Front 12

Competitive inhibitor

Front 13

Cooperativity

Back 13

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.

Front 14

Endergonic reaction

Back 14

A nonspontaneous chemical reaction, in which free energy is absorbed from the surroundings.

Front 15

Energy

Back 15

The capacity to cause change, especially to do work (to move matter against an opposing force).

Front 16

Energy coupling

Back 16

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

Front 17

Entropy

Back 17

A measure of disorder, or randomness.

Front 18

Enzyme

Back 18

A macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.

Front 19

Enzyme-substrate complex

Back 19

A temporary complex formed when an enzyme binds to its substrate molecule(s).

Front 20

Exergonic reaction

Back 20

A spontaneous chemical reaction, in which there is a net release of free energy.

Front 21

Feedback inhibition

Back 21

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

Front 22

First law of thermodynamics

Back 22

The principle of conservation of energy

Front 23

Free energy

Back 23

The portion of a biological system’s energy that can perform work when temperature and pressure are uniform throughout the system. (The change in free energy of a system is calculated by the equation ΔG = ΔH – TΔS, where H is enthalpy [in biological systems, equivalent to total energy], T is absolute temperature, and S is entropy.)

Front 24

Heat

Back 24

The total amount of kinetic energy due to the random motion of atoms or molecules in a body of matter

Front 25

Hemoglobin

Back 25

An iron-containing protein in red blood cells that reversibly binds oxygen.

Front 26

Induced fit

Back 26

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

Front 27

Kinetic energy

Back 27

The energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter.

Front 28

Metabolic pathway

Back 28

A series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule into simpler compounds (catabolic pathway).

Front 29

Metabolism

Back 29

The totality of an organism’s chemical reactions, consisting of catabolic and anabolic pathways, which manage the material and energy resources of the organism.

Front 30

noncompetitive inhibitor

Back 30

A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme’s shape so that the active site no longer functions effectively.

Front 31

Order

Back 31

In classification, the taxonomic category above the level of family.

Front 32

Phosphorylated

Back 32

Referring to a molecule that is covalently bonded to a phosphate group.

Front 33

Potential energy

Back 33

The energy that matter possesses as a result of its location or spatial arrangement (structure).

Front 34

Ribose

Back 34

The sugar component of RNA nucleotides.

Front 35

Second law of thermodynamics

Back 35

The principle stating that every energy transfer or transformation increases the entropy of the universe. Ordered forms of energy are at least partly converted to heat.

Front 36

Substrate

Back 36

The reactant on which an enzyme works.

Front 37

Thermal energy

Back 37

See heat.

Front 38

Thermodynamics

Back 38

The study of energy transformations that occur in a collection of matter. See first law of thermodynamics and second law of thermodynamics.

Front 39

The relationship of free energy to stability, work capacity, and spontaneous change.

Back 39

Usable systems (top diagrams) are rich in free energy, G. They have a tendency to change spontaneously to a more stable state (bottom), and it is possible to harness this "downhill" change to perform work.

Hint 39

Gravitational motion: Objects move spontaneously from a higher altitude to a lower one.

Diffusion: Molecules in a drop of dye diffuse until they are randomly dispersed.

Chemical reaction: In a cell, a sugar molecule is broken down into simpler molecules.

Front 40

Exergonic reaction

Back 40

Proceeds with a net release of free energy.
o Because chemical mixture loses free energy (G decreases).
o ∆G is negative for an exergonic reaction, using ∆G as a standard for spontaneity; exergonic reactions are those that occur spontaneously. (Remember that the word spontaneous does not imply that a reaction will occur instantaneously or even rapidly.)
• The magnitude of ∆G for an exergonic reaction represents the maximum amount of work the reaction can perform.
o The greater the decrease in free energy, the greater the amount of work that can be done.

Hint 40

Exergonic and Endergonic Reactions in Metabolism

Based on free energy changes, chemical reactions can be classified as either exergonic (“energy outward”) or endergonic (“energy inward”).

Front 41

The structure of adenosine triphosphate (ATP).

In the cell, most hydroxyl groups of phosphates are ionized (-O).

Back 41

The hydrolysis of ATP.

The reaction of ATP and water yields inorganic phosphate and ADP and releases energy.