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about carbohydrates, lipids, nucleic acids, and proteins


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


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

Condensation reaction

a chemical reaction in which two molecules or moieties (functional groups) combine to form one single molecule, together with the loss of a small molecule

Dehydration reaction

A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule


A chemical reaction that breaks bonds between two molecules by the addition of water; functions 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. Are a multiple of CH2O


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

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 α 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.


Any of a group of large biological molecules, including fats, phospholipids, and steroids, that mix poorly, if at all, with water.

Fatty acid

A carboxylic acid with a long carbon chain.


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

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.

Unsaturated fatty acid

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

trans fat

An unsaturated fat, formed artificially during hydrogenation of oils, 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.


A type of lipid characterized by a carbon skeleton consisting of four fused 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 many hormones.


A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed by the reaction. Most are proteins.


A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction. an enzyme is an example of this


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


A biologically functional molecule consisting of one or more poly-peptides folded and coiled into a specific three-dimensional structure.

Amino acid

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

Peptide bond

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 linear sequence of amino acids.

Secondary structure

a kind of structure with regions of repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bonding between constituents of the backbone (not the side chains).

alpha helix

A coiled region constituting one form of the secondary structure of proteins, arising from a specific pattern of hydrogen bonding between atoms of the polypeptide backbone (not the side chains).

beta 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 between atoms of the polypeptide backbone (not the side chains).

Tertiary structure

a kind of structure a protein molecule due to interactions of amino acid side chains, including hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

Hydrophobic interaction

A type of weak chemical interaction caused when molecules that do not mix with water coalesce to exclude water.

Disulfide bridge

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

Quaternary structure

a structure of a protein of more than one polypeptide.


In proteins, a process in which a protein loses its native shape due to the disruption of weak chemical bonds and interactions, 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, or temperature


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

X-ray crystallography

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

A nucleic acid molecule with deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T); capable of being replicated and determining the inherited structure of a cell's proteins.

Ribonucleic acid

A type of nucleic acid consisting of a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U);


A polymer consisting of many nucleotide monomers in a chain. The nucleotides can be those of DNA or RNA. also called nucleic acid.


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


One of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring. Cytosine (C), thymine (T), and uracil (U) are examples of this.


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 DNA nucleotides, having one fewer hydroxyl group than ribose

Double helix

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


Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5' S 3' directions).

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