Chapter 3 Biology Key Terms

Front 1

α-helix (alpha-helix)

Back 1

A protein secondary structure in which the polypeptide backbone coils into a spiral shape stabilized by hydrogen bonds between atoms.

Front 2

activation energy

Back 2

The amount of energy required to initiate a chemical reaction; specifically, the energy required to reach the transition state.

Front 3

active site

Back 3

The portion of an enzyme molecule where substrates (reactant molecules) bind and react.

Front 4

allosteric regulation

Back 4

Regulation of a protein's function by binding of a regulatory molecule, usually to a specific site distinct from the active site, causing a change in the protein's shape.

Front 5

amino acid

Back 5

A small organic molecule with a central carbon atom bonded to an amino group (–NH3), a carboxyl group (–COOH), a hydrogen atom, and a side group. Proteins are polymers of 20 common amino acids

Front 6

β-pleated sheet (beta-pleated sheet)

Back 6

A protein secondary structure in which the polypeptide backbone folds into a sheetlike shape stabilized by hydrogen bonding.

Front 7

catalysis

Back 7

(verb: catalyze) Acceleration of the rate of a chemical reaction due to a decrease in the free energy of the transition state, called the activation energy.

Front 8

catalyst

Back 8

Any substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.

Front 9

coenzyme

Back 9

A small organic molecule that is a required cofactor for an enzyme-catalyzed reaction. Often donates or receives electrons or functional groups during the reaction.

Front 10

cofactor

Back 10

A metal ion or small organic compound that is required for an enzyme to function normally. May be bound tightly to an enzyme or associate with it transiently during catalysis.

Front 11

competitive inhibition

Back 11

Inhibition of an enzyme's ability to catalyze a chemical reaction via a nonreactant molecule that competes with the substrate(s) for access to the active site.

Front 12

condensation reaction

Back 12

A chemical reaction in which two molecules are joined covalently with the removal of an –OH from one and an –H from another to form water. Also called a dehydration reaction. Compare with hydrolysis.

Front 13

dehydration reaction

Back 13

A chemical reaction in which two molecules are joined covalently with the removal of an –OH from one and an –H from another to form water.

Front 14

dehydration reaction

Back 14

(verb: denature) For a macromolecule, loss of its three-dimensional structure and biological activity due to breakage of hydrogen bonds and disulfide bonds, usually caused by treatment with excess heat or extreme pH conditions.

Front 15

denaturation

Back 15

(verb: denature) For a macromolecule, loss of its three-dimensional structure and biological activity due to breakage of hydrogen bonds and disulfide bonds, usually caused by treatment with excess heat or extreme pH conditions.

Front 16

disulfide bond

Back 16

A covalent bond between two sulfur atoms, typically in the side groups of some amino acids (e.g., cysteine). Often contributes to tertiary structure of proteins.

Front 17

enzyme

Back 17

A protein catalyst used by living organisms to speed up and control biological reactions.

Front 18

hydrolysis

Back 18

A chemical reaction in which a molecule is split into smaller molecules by reacting with water. In biology, most hydrolysis reactions involve the splitting of polymers into monomers. Compare with condensation reaction.

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hydrophilic

Back 19

Interacting readily with water. Hydrophilic compounds are typically polar compounds containing charged or electronegative atoms. Compare with hydrophobic.

Front 20

hydrophobic

Back 20

Not interacting readily with water. Hydrophobic compounds are typically nonpolar compounds that lack charged or electronegative atoms and often contain many C – C and C – H bonds. Compare with hydrophilic.

Front 21

induced fit

Back 21

Change in the shape of the active site of an enzyme, as the result of the initial weak binding of a substrate, so that it binds substrate more tightly.

Front 22

initiation

Back 22

In an enzyme-catalyzed reaction, the stage during which enzymes orient reactants precisely as they bind at specific locations within the enzyme's active site.

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macromolecule

Back 23

Any very large organic molecule, usually made up of smaller molecules (monomers) joined together into a polymer. The main biological macromolecules are proteins, nucleic acids, and polysaccharides.

Front 24

molecular chaperone

Back 24

A protein that facilitates the three-dimensional folding of newly synthesized proteins, usually by an ATP-dependent mechanism.

Front 25

monomer

Back 25

A small molecule that can covalently bind to other similar molecules to form a larger macromolecule. Compare with polymer.

Front 26

multienzyme complex

Back 26

A group of enzymes that are physically attached to each other, even though each of the enzymes catalyzes a separate?but usually related?chemical reaction.

Front 27

myosin

Back 27

Any one of a class of motor proteins that use the chemical energy of ATP to move along actin filaments in muscle contraction, cytokinesis, and vesicle transport.

Front 28

oligopeptide

Back 28

A chain composed of fewer than 50 amino acids linked together by peptide bonds. Often referred to simply as peptide.

Front 29

peptide

Back 29

A chain composed of fewer than 50 amino acids linked together by peptide bonds. Often referred to simply as peptide.

Front 30

peptide bond

Back 30

The covalent bond (C–N) bond formed by a condensation reaction between two amino acids; links the residues in peptides and proteins.

Front 31

polymer

Back 31

Any long molecule composed of small repeating units (monomers) bonded together. The main biological polymers are proteins, nucleic acids, and polysaccharides.

Front 32

polymerization

Back 32

The process by which many identical or similar small molcules (monomers) are covalently bonded to form a large molecule (polymer).

Front 33

polypeptide

Back 33

A chain of 50 or more amino acids linked together by peptide bonds. Compare with oligopeptide and protein.

Front 34

prebiotic soup

Back 34

A hypothetical solution of sugars, amino acids, nitrogenous bases, and other building blocks of larger molecules that may have formed in shallow waters or deep-ocean vents of ancient Earth and given rise to larger biological molecules.

Front 35

primary structure

Back 35

The sequence of amino acids in a peptide or protein; also the sequence of nucleotides in a nucleic acid. Compare with secondary, tertiary, and quaternary structure.

Front 36

prion

Back 36

An infectious form of a protein that is thought to cause disease by inducing the normal form to assume an abnormal three-dimensional structure. Cause of spongiform encephalopathies, such as mad cow disease.

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protein

Back 37

A macromolecule consisting of one or more polypeptide chains composed of 50 or more amino acids linked together. Each protein has a unique sequence of amino acids and, in its native state, a characteristic three-dimensional shape.

Front 38

quaternary structure

Back 38

The overall three-dimensional shape of a protein containing two or more polypeptide chains (subunits); determined by the number, relative positions, and interactions of the subunits. Compare with primary, secondary, and tertiary structure.

Front 39

secondary structure

Back 39

In proteins, localized folding of a polypeptide chain into regular structures (e.g., a-helix and b-pleated sheet) stabilized by hydrogen bonding between atoms of the backbone. In nucleic acids, elements of structure (e.g., helices and hairpins) stabilized by hydrogen bonding and other interactions between complementary bases. Compare with primary, tertiary, and quaternary structure.

Front 40

substrate

Back 40

(1) A reactant that interacts with an enzyme in a chemical reaction. (2) A surface on which a cell or organism sits.

Front 41

termination

Back 41

In enzyme-catalyzed reactions, the final stage in which the enzyme returns to its original conformation and products are released.

Front 42

tertiary structure

Back 42

The overall three-dimensional shape of a single polypeptide chain, resulting from multiple interactions among the amino acid side chains and the peptide backbone. Compare with primary, secondary, and quaternary structure.

Front 43

transition state

Back 43

A high-energy intermediate state of the reactants during a chemical reaction that must be achieved for the reaction to proceed. See activation energy.

Front 44

transition state facilitation

Back 44

The second stage (after initiation) in enzyme-catalyzed reactions, in which the enzyme enables formation of the transition state.

Front 45

van der Waals interactions

Back 45

A weak electrical attraction between two hydrophobic side chains. Often contributes to tertiary structure in proteins.