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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.




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




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.




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 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.



primary structure


secondary structure


a helix


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


disulphide bridges

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

quaternary structure



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




nucleic acid


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)







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




The sugar component of RNA nucleotides.



double helix



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

2 purines

Adenine (A) and guanine (G).

3 pyrimidines


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