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A giant molecule formed by the joining of smaller molecules, usually by a condensation reaction. Polysaccharides, proteins, and nucleic acids are examples of this type of molecule.


A long molecule consisting of many similar or identical monomers linked together.


The subunit that serves as the building block of a polymer.

condensation reaction (dehydration reaction)

A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water, in which case it is also called a dehydration reaction.


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


A chemical process that lyses, or splits, molecules by the addition of water, functioning in disassembly of polymers to monomers.


A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).


The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides. Also known as simple sugars, monosaccharides have molecular formulas that are generally some multiple of CHO.


A double sugar, consisting of two monosaccharides joined by a glycosidic linkage formed during dehydration synthesis.

glycosidic linkage

A covalent bond formed between two monosaccharides by a dehydration reaction.


A polymer of many monosaccharides, formed by dehydration reactions.


A storage polysaccharide in plants, consisting entirely of glucose monomers joined by glycosidic linkages.


An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.


A structural polysaccharide of plant cell walls, consisting of glucose monomers joined by β glycosidic linkages.


A structural polysaccharide, consisting of amino sugar monomers, found in many fungal cell walls and in the exoskeletons of all arthropods.


A lipid consisting of three fatty acids linked to one glycerol molecule; also called a triacylglycerol or triglyceride.


Three fatty acids linked to one glycerol molecule; also called a fat or a triglyceride.

unsaturated fatty acid

A fatty acid possessing one or more double bonds between the carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.

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 are attached to the carbon skeleton.

trans fat

An unsaturated fat containing one or more trans double bonds.


A lipid made up of glycerol joined to two fatty acids and a phosphate group. The hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails, while the rest of the molecule acts as a polar, hydrophilic head. Phospholipids form bilayers that function as biological membranes.


A type of lipid characterized by a carbon skeleton consisting of four rings with various chemical groups attached.


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, such as hormones.


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


A polymer (chain) of many amino acids linked together by peptide bonds.


A functional biological molecule consisting of one or more polypeptides folded and coiled into a specific three-dimensional structure.

amino acid

An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of polypeptides.


The covalent bond between the carboxyl group on one amino acid and the amino group on another, formed by a dehydration reaction.

primary structure

The level of protein structure referring to the specific sequence of amino acids.

secondary structure

The localized, repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bond formation between constituents of the backbone.

a helix

A spiral shape constituting one form of the secondary structure of proteins, arising from a specific pattern of hydrogen bonding.

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.

tertiary structure

Irregular contortions of a protein molecule due to interactions of side chains involved in hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

disulphide bridges

A strong covalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer.

quaternary structure

The particular shape of a complex, aggregate protein, defined by the characteristic three-dimensional arrangement of its constituent subunits, each a polypeptide.


In proteins, a process in which a protein unravels and loses its native shape, thereby becoming biologically inactive; in DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme (noncellular) conditions of pH, salt concentration, and temperature.


A protein molecule that assists in the proper folding of other proteins.

X-ray crystallography

A technique that depends on the diffraction of an X-ray beam by the individual atoms of a crystallized molecule to study the three-dimensional structure of the molecule.


A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).

nucleic acid

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.

deoxyribonucleic acid (DNA)

A double-stranded, helical nucleic acid molecule consisting of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T); capable of replicating and determining the inherited structure of a cell's proteins.

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, gene regulation, and as the genome of some viruses.


A polymer consisting of many nucleotide monomers in a chain; nucleotides can be those of DNA or RNA.


The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group.


One of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring fused to a five-membered ring.


One of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring.


The sugar component of RNA nucleotides.


The sugar component of DNA nucleotides, having one fewer hydroxyl group than ribose, the sugar component of RNA nucleotides.

double helix

The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.


The opposite arrangement of the sugar-phosphate backbones in a DNA double helix.

2 purines

Adenine (A) and guanine (G).

3 pyrimidines

Cytosine (C), thymine (T), and uracil (U).

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