Chapter 3

Question 1

Activation Energy

Answer 1

The energy barrier that blocks the tendency for a chemical reaction to occur.

Question 2

Active Site

Answer 2

The region on the surface of an enzyme or ribozyme where the substrate binds, and where catalysis occurs.

Question 3

Adenine (A)

Answer 3

A nitrogen-containing base found in nucleic acids, ATP, NAD, and other compounds. Purine.

Question 4

Allosteric Regulation

Answer 4

Regulation of the activity of a protein (usually an enzyme) by the binding of an effector molecule to a site other than the active site.

Question 5

Amino Acid

Answer 5

An organic compound containing both NH2 and COOH groups. Proteins are polymers of amino acids.

Question 6

B (beta) pleated sheet

Answer 6

A type of protein secondary structure; results from hydrogen bonding between polypeptide regions running antiparallel to each other.

Question 7

Base

Answer 7

(1) A substance that can accept a hydrogen ion in solution. (Contrast with acid.) (2) In nucleic acids, the purine or pyrimidine that is attached to each sugar in the sugar-phosphate backbone.

Question 8

Catalyst

Answer 8

A chemical substance that accelerates a reaction without itself being consumed in the overall course of the reaction. Catalysts lower the activation energy of a reaction. Enzymes are biological catalysts.

Question 9

Competitive Inhibitor

Answer 9

A nonsubstrate that binds to the active site of an enzyme and thereby inhibits binding of its substrate.

Question 10

Complementary Base Paring

Answer 10

The AT (or AU), TA (or UA), CG, and GC pairing of bases in double-stranded DNA, in transcription, and between tRNA and mRNA.

Question 11

Cytosine (C)

Answer 11

A nitrogen-containing base found in DNA and RNA. In DNA, pairs with guanine. (Pyrimidine)

Question 12

Denaturation

Answer 12

Loss of activity of an enzyme or nucleic acid molecule as a result of structural changes induced by heat or other means.

Question 13

Deoxyribose

Answer 13

A five-carbon sugar found in nucleotides and DNA.

Question 14

Disulfide Bridge

Answer 14

The covalent bond between two sulfur atoms (—S—S—) linking two molecules or remote parts of the same molecule.

Question 15

DNA (Deoxyribonucleic Acid)

Answer 15

The fundamental hereditary material of all living organisms. In eukaryotes, stored primarily in the cell nucleus. A nucleic acid using deoxyribose rather than ribose.

Question 16

Enzyme-Substrate Complex (ES)

Answer 16

An intermediate in an enzyme-catalyzed reaction; consists of the enzyme bound to its substrate(s).

Question 17

Feedback Inhibition

Answer 17

A mechanism for regulating a metabolic pathway in which the end product of the pathway can bind to and inhibit the enzyme that catalyzes the first committed step in the pathway. Also called end-product inhibition.

Question 18

Gene

Answer 18

A unit of heredity. Used here as the unit of genetic function which carries the information for a polypeptide or RNA.

Question 19

Genome

Answer 19

The complete DNA sequence for a particular organism or individual.

Question 20

Guanine (G)

Answer 20

A nitrogen-containing base found in DNA, RNA, and GTP. Pairs with C. Purine.

Question 21

Noncompetitive Inhibitor

Answer 21

A nonsubstrate that inhibits the activity of an enzyme by binding to a site other than its active site.

Question 22

Nucleic Acid

Answer 22

A polymer made up of nucleotides, specialized for the storage, transmission, and expression of genetic information. DNA and RNA are nucleic acids.

Question 23

Nucleotide

Answer 23

The basic chemical unit in nucleic acids, consisting of a pentose sugar, a phosphate group, and a nitrogen-containing base.

Question 24

Peptide Linkage

Answer 24

The bond between amino acids in a protein; formed between a carboxyl group and amino group (—CO—NH—) with the loss of water molecules.

Question 25

Phosphodiester Linkage

Answer 25

The connection in a nucleic acid strand, formed by linking two nucleotides.

Question 26

Primary Structure

Answer 26

The specific sequence of amino acids in a protein.

Question 27

Purine

Answer 27

One of the two types of nitrogenous bases in nucleic acids. Adenine and guanine.

Question 28

Pyrimidine

Answer 28

One of the two types of nitrogenous bases in nucleic acids. Each of the pyrimidines—cytosine, thymine, and uracil—pairs with a specific purine.

Question 29

Quaternary Structure

Answer 29

The specific three-dimensional arrangement of protein subunits.

Question 30

R Group

Answer 30

The distinguishing group of atoms of a particular amino acid; also known as a side chain.

Question 31

Ribose

Answer 31

A five-carbon sugar in nucleotides and RNA.

Question 32

RNA (Ribonucleic Acid)

Answer 32

An often single-stranded nucleic acid whose nucleotides use ribose rather than deoxyribose and in which the base uracil replaces thymine found in DNA. Serves as genome for some viruses.

Question 33

Secondary Structure

Answer 33

Of a protein, localized regularities of structure, such as the ? helix and the ? pleated sheet.

Question 34

Substrate

Answer 34

(1) The molecule or molecules on which an enzyme exerts catalytic action. (2) The base material on which a sessile organism lives.

Question 35

Tertiary Structure

Answer 35

In reference to a protein, the relative locations in three-dimensional space of all the atoms in the molecule. The overall shape of a protein.

Question 36

Thymine (T)

Answer 36

Nitrogen-containing base found in DNA. In DNA, pairs with adenine. Pyrimidine

Question 37

Transition State

Answer 37

In an enzyme-catalyzed reaction, the reactive condition of the substrate after there has been sufficient input of energy (activation energy) to initiate the reaction.

Question 38

Uracil (U)

Answer 38

A pyrimidine base found only in nucleotides of RNA.

Question 39

A (alpha) helix

Answer 39

A prevalent type of secondary protein structure; a right-handed spiral.