alpha (a) helix
A spiral shape constituting one form of the secondary structure of proteins, arising from a specific hydrogen-bonding structure.
An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of proteins.
beta (b) pleated sheet
One form of the secondary structure of proteins in which the polypeptide chain folds back and forth. Two regions of the chain lie parallel to each other and are held together by hydrogen bonds.
A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).
A chemical agent that changes the rate of a reaction without being consumed by the reaction.
A structural polysaccharide of cell walls, consisting of glucose monomers joined by β-1, 4-glycosidic linkages.
A structural polysaccharide of an amino sugar found in many fungi and in the exoskeletons of all arthropods.
A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.
A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water; also called a dehydration reaction.
A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule.
In proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive. In DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme conditions of pH, salt concentration, and temperature.
deoxyribonucleic acid (DNA)
A double-stranded, helical nucleic acid molecule capable of replicating and determining the inherited structure of a cell's proteins.
The sugar component of DNA, having one less hydroxyl group than ribose, the sugar component of RNA.
A strong covalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer.
The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.
A biological compound consisting of three fatty acids linked to one glycerol molecule.
A long carbon chain carboxylic acid. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form fat.
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).
An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.
A type of weak chemical bond formed when molecules that do not mix with water coalesce to exclude the water.
One of a family of compounds, including fats, phospholipids, and steroids, that are insoluble in water.
A giant molecule formed by the joining of smaller molecules, usually by a condensation reaction. Polysaccharides, proteins, and nucleic acids are macromolecules.
The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides. Also known as simple sugars, the molecular formulas of monosaccharides are generally some multiple of CH2O.
A polymer (polynucleotide) consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.
The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group.
A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.
A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.
A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids.
One of two types of nitrogenous bases found in nucleotides. Adenine (A) and guanine (G) are purines.
One of two types of nitrogenous bases found in nucleotides. Cytosine (C), thymine (T), and uracil (U) are pyrimidines.
The particular shape of a complex, aggregate protein, defined by the characteristic three-dimensional arrangement of its constituent subunits, each a polypeptide.
ribonucleic acid (RNA)
A type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.
saturated fatty acid
A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that can attach to the carbon skeleton.
The localized, repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bond formation between peptide linkages.
A type of lipid characterized by a carbon skeleton consisting of four rings with various functional groups attached.
Irregular contortions of a protein molecule due to interactions of side chains involved in hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.