Chapter 3 Flashcards
Activation Energy
The energy barrier that blocks the tendency for a chemical reaction to occur.
Active Site
The region on the surface of an enzyme or ribozyme where the substrate binds, and where catalysis occurs.
Adenine (A)
A nitrogen-containing base found in nucleic acids, ATP, NAD, and other compounds. Purine.
Allosteric Regulation
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.
Amino Acid
An organic compound containing both NH2 and COOH groups. Proteins are polymers of amino acids.
B (beta) pleated sheet
A type of protein secondary structure; results from hydrogen bonding between polypeptide regions running antiparallel to each other.
Base
(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.
Catalyst
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.
Competitive Inhibitor
A nonsubstrate that binds to the active site of an enzyme and thereby inhibits binding of its substrate.
Complementary Base Paring
The AT (or AU), TA (or UA), CG, and GC pairing of bases in double-stranded DNA, in transcription, and between tRNA and mRNA.
Cytosine (C)
A nitrogen-containing base found in DNA and RNA. In DNA, pairs with guanine. (Pyrimidine)
Denaturation
Loss of activity of an enzyme or nucleic acid molecule as a result of structural changes induced by heat or other means.
Deoxyribose
A five-carbon sugar found in nucleotides and DNA.
Disulfide Bridge
The covalent bond between two sulfur atoms (—S—S—) linking two molecules or remote parts of the same molecule.
DNA (Deoxyribonucleic Acid)
The fundamental hereditary material of all living organisms. In eukaryotes, stored primarily in the cell nucleus. A nucleic acid using deoxyribose rather than ribose.
Enzyme-Substrate Complex (ES)
An intermediate in an enzyme-catalyzed reaction; consists of the enzyme bound to its substrate(s).
Feedback Inhibition
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.
Gene
A unit of heredity. Used here as the unit of genetic function which carries the information for a polypeptide or RNA.
Genome
The complete DNA sequence for a particular organism or individual.
Guanine (G)
A nitrogen-containing base found in DNA, RNA, and GTP. Pairs with C. Purine.
Noncompetitive Inhibitor
A nonsubstrate that inhibits the activity of an enzyme by binding to a site other than its active site.
Nucleic Acid
A polymer made up of nucleotides, specialized for the storage, transmission, and expression of genetic information. DNA and RNA are nucleic acids.
Nucleotide
The basic chemical unit in nucleic acids, consisting of a pentose sugar, a phosphate group, and a nitrogen-containing base.
Peptide Linkage
The bond between amino acids in a protein; formed between a carboxyl group and amino group (—CO—NH—) with the loss of water molecules.
Phosphodiester Linkage
The connection in a nucleic acid strand, formed by linking two nucleotides.
Primary Structure
The specific sequence of amino acids in a protein.
Purine
One of the two types of nitrogenous bases in nucleic acids. Adenine and guanine.
Pyrimidine
One of the two types of nitrogenous bases in nucleic acids. Each of the pyrimidines—cytosine, thymine, and uracil—pairs with a specific purine.
Quaternary Structure
The specific three-dimensional arrangement of protein subunits.
R Group
The distinguishing group of atoms of a particular amino acid; also known as a side chain.
Ribose
A five-carbon sugar in nucleotides and RNA.
RNA (Ribonucleic Acid)
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.
Secondary Structure
Of a protein, localized regularities of structure, such as the ? helix and the ? pleated sheet.
Substrate
(1) The molecule or molecules on which an enzyme exerts catalytic action. (2) The base material on which a sessile organism lives.
Tertiary Structure
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.
Thymine (T)
Nitrogen-containing base found in DNA. In DNA, pairs with adenine. Pyrimidine
Transition State
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.
Uracil (U)
A pyrimidine base found only in nucleotides of RNA.
A (alpha) helix
A prevalent type of secondary protein structure; a right-handed spiral.
