AskDefine | Define biomolecule

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  1. molecules, such as amino acids, sugars, nucleic acids, proteins, polysaccharides, DNA, and RNA, that occur naturally in living organisms

Extensive Definition

A biomolecule is a molecule that naturally occurs in living organisms. Biomolecules consist primarily of carbon and hydrogen, along with nitrogen, oxygen, phosphorus and sulfur. Other elements sometimes are incorporated but are much less common.


All known forms of life are composed solely of biomolecules. For example, humans possess skin and hair. The main component of hair is keratin , an agglomeration of proteins which are themselves polymers built from amino acids. Amino acids are some of the most important building blocks used in nature to construct larger molecules. Another type of building block are the nucleotides, each of which consists of three components: either a purine or pyrimidine base, a pentose sugar and a phosphate group. These nucleotides mainly form the nucleic acids.
Besides the polymeric biomolecules, numerous organic molecules are absorbed by living systems.

Nucleosides and nucleotides

Nucleosides are molecules formed by attaching a nucleobase to a ribose ring. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine.
Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides, which are the molecular building blocks of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).


Monosaccharides are the simplest form of carbohydrates. They essentially contain an aldehyde or ketone group in their structure. Examples of monosaccharides are the hexoses glucose, fructose, and galactose and pentoses, ribose, and deoxyribose
Disaccharides are formed when two monosaccharides form a bond with removal of water. Examples of disaccharides include sucrose, maltose, and lactose
Monosaccharides and disaccharides are sweet, water soluble, and crystalline.
Polysaccharides are polymerized monosaccharides, complex, unsweet carbohydrates. Examples are starch, cellulose, and glycogen. They are generally large and often have a complex, branched, connectivity. They are insoluble in water and do not form crystals. Shorter polysaccharides, with 11-40 monomers, are sometimes known as oligosaccharides.


Lipids are chiefly fatty acid esters, and are the basic building blocks of biological membranes. Another biological role is energy storage (e.g., triglycerides). Most lipids consist of a polar or hydrophilic head (typically glycerol) and one to three nonpolar or hydrophobic fatty acid tails, and therefore they are amphiphilic. Fatty acids consist of unbranched chains of carbon atoms that are connected by single bonds alone (saturated fatty acids) or by both single and double bonds (unsaturated fatty acids). The chains are usually 14-24 carbon groups long, but it is always an even number.
For lipids present in biological membranes, the hydrophilic head is from one of three classes:
  • Glycolipids, whose heads contain an oligosaccharide with 1-15 saccharide residues.
  • Phospholipids, whose heads contain a positively charged group that is linked to the tail by a negatively charged phosphate group.
  • Sterols, whose heads contain a planar steroid ring, for example, cholesterol.
Other lipids include prostaglandins and leukotrienes which are both 20-carbon fatty acyl units synthesized from arachidonic acid. They are also known as fatty acids

Amino acids

Amino acids are molecules that contain both amino and carboxylic acid functional groups. (In biochemistry, the term amino acid is used when referring to those amino acids in which the amino and carboxylate functionalities are attached to the same carbon, plus proline which is not actually an amino acid).
Amino acids are the building blocks of long polymer chains. With 2-10 amino acids such chains are called peptides, with 10-100 they are often called polypeptides, and longer chains are known as proteins. These protein structures have many structural and functional roles in organisms.
There are twenty amino acids that are encoded by the standard genetic code, but there are more than 500 natural amino acids. When amino acids other than the set of twenty are observed in proteins, this is usually the result of modification after translation (protein synthesis). Only two amino acids other than the standard twenty are known to be incorporated into proteins during translation, in certain organisms:
  • Selenocysteine is incorporated into some proteins at a UGA codon, which is normally a stop codon.
  • Pyrrolysine is incorporated into some proteins at a UAG codon. For instance, in some methanogens in enzymes that are used to produce methane.
Besides those used in protein synthesis, other biologically important amino acids include carnitine (used in lipid transport within a cell), ornithine, GABA and taurine.

Protein structure

The particular series of amino acids that form a protein is known as that protein's primary structure. This sequence is determined by the genetic makeup of the individual. Proteins have several, well-classified, elements of local structure formed by intermolecular attaraction, this forms the secondary structure of protein. They are broadly divided in two, alpha helix and beta sheet, also called beta pleated sheets. Alpha helices are formed of coiling of protien due to attaraction between amine group of one amino acid with carboxylic acid group of other. The coil contains about 3.6 amino acids per turn and the alkyl group of amino acid lie outside the plane of coil. Beta pleated sheets are formed by strong continous hydrogen bond over the length of protein chain. Bonding may be parallel or antiparallel in nature.Stucturally,natural silk is formed of beta pleated sheets. Usually, a protien is formed by action of both these structures in variable ratios. Coiling may also be random. The overall 3D structure of a protein is termed its tertiary structure. It is formed as result of various forces like hydrogen bonding, disulphide bridges, hydrophobic interactions, hydrophilic interactions, van der Waals force etc. When two or more different polypeptide chains cluster to form a protein, quaternary structure of protein is formed. Quarternary structur is a unique attribute of polymeric and heteromeric proteins like haemoglobin, which consists of two alpha and two beta peptide chains.


An apoenzyme is the inactive storage and generally secretory form of a protein. This is required to prtect the secretory cell from the activity of that protein. Apoenzymes becomes active enzyme on addition of a cofactor. Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds, (e.g., flavin and heme). Organic cofactors can be either prosthetic groups, which are tightly bound to an enzyme, or coenzymes, which are released from the enzyme's active site during the reaction.


Isoenzymes are the enzymes with similar function but different structure. they are products of different genes. They are produced in different organs to perform same function. LDH are examples of such enzymes. Their varied levels in blood are used to determine any deformity in the organ of secretion.


A vitamin is a compound that is generally not synthesized by a given organism but is nonetheless vital to its survival or health (for example coenzymes). These compounds must be absorbed, or eaten, but typically only in trace quantities. When originally discovered by a Polish doctor, he believed them to all be basic. He therefore named them vital amines. The l was later dropped to form the word vitamines.


biomolecule in Catalan: Biomolècula
biomolecule in Czech: Biomolekula
biomolecule in German: Biomolekül
biomolecule in French: Biomolécule
biomolecule in Scottish Gaelic: Bith-mhoileciuil
biomolecule in Indonesian: Biomolekul
biomolecule in Japanese: 生体物質
biomolecule in Slovak: Biomolekula
biomolecule in Sundanese: Biomolekul
biomolecule in Swedish: Biomolekyl
biomolecule in Thai: ชีวโมเลกุล
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