A biomolecule or biological molecule is a loosely used term for
molecules and ions that are present in organisms, essential to some
typically biological process such as cell division, morphogenesis, or
development. Biomolecules include large macromolecules (or
polyanions) such as proteins, carbohydrates, lipids, and nucleic
acids, as well as small molecules such as primary metabolites,
secondary metabolites, and natural products. A more general name for
this class of material is biological materials. Biomolecules are
usually endogenous but may also be exogenous. For example,
pharmaceutical drugs may be natural products or semisynthetic
(biopharmaceuticals) or they may be totally synthetic.
Biology and its subsets of biochemistry and molecular biology study
biomolecules and their reactions. Most biomolecules are organic
compounds, and just four elements—oxygen, carbon, hydrogen, and
nitrogen—make up 96% of the human body's mass. But many other
elements, such as the various biometals, are present in small amounts.
The uniformity of specific types of molecules (the biomolecules) and
of some metabolic pathways as invariant features between the diversity
of life forms is called "biochemical universals" or "theory of
material unity of the living beings", a unifying concept in biology,
along with cell theory and evolution theory.
1 Types of biomolecules
Nucleosides and nucleotides
7 See also
9 External links
Types of biomolecules
A diverse range of biomolecules exist, including:
Lipids, fatty acids, glycolipids, sterols, monosaccharides
Monomers, oligomers and polymers:
Covalent bond name between monomers
Polypeptides, proteins (hemoglobin...)
Polyterpenes: cis-1,4-polyisoprene natural rubber and
Polynucleotides, nucleic acids (DNA, RNA)
Nucleosides and nucleotides
Nucleosides and Nucleotides
Nucleosides are molecules formed by attaching a nucleobase to a ribose
or deoxyribose ring. Examples of these include cytidine (C), uridine
(U), adenosine (A), guanosine (G), thymidine (T) and inosine (I).
Nucleosides can be phosphorylated by specific kinases in the cell,
producing nucleotides. Both
RNA are polymers, consisting of
long, linear molecules assembled by polymerase enzymes from repeating
structural units, or monomers, of mononucleotides.
DNA uses the
deoxynucleotides C, G, A, and T, while
RNA uses the ribonucleotides
(which have an extra hydroxyl(OH) group on the pentose ring) C, G, A,
and U. Modified bases are fairly common (such as with methyl groups on
the base ring), as found in ribosomal
RNA or transfer RNAs or for
discriminating the new from old strands of
DNA after replication.
Each nucleotide is made of an acyclic nitrogenous base, a pentose and
one to three phosphate groups. They contain carbon, nitrogen, oxygen,
hydrogen and phosphorus. They serve as sources of chemical energy
(adenosine triphosphate and guanosine triphosphate), participate in
cellular signaling (cyclic guanosine monophosphate and cyclic
adenosine monophosphate), and are incorporated into important
cofactors of enzymatic reactions (coenzyme A, flavin adenine
dinucleotide, flavin mononucleotide, and nicotinamide adenine
DNA structure is dominated by the well-known double helix formed by
Watson-Crick base-pairing of C with G and A with T. This is known as
B-form DNA, and is overwhelmingly the most favorable and common state
of DNA; its highly specific and stable base-pairing is the basis of
reliable genetic information storage.
DNA can sometimes occur as
single strands (often needing to be stabilized by single-strand
binding proteins) or as A-form or Z-form helices, and occasionally in
more complex 3D structures such as the crossover at Holliday junctions
Stereo 3D image of a group I intron ribozyme (PDB file 1Y0Q); gray
lines show base pairs; ribbon arrows show double-helix regions, blue
to red from 5' to 3' end; white ribbon is an
RNA, in contrast, forms large and complex 3D tertiary structures
reminiscent of proteins, as well as the loose single strands with
locally folded regions that constitute messenger
RNA molecules. Those
RNA structures contain many stretches of A-form double helix,
connected into definite 3D arrangements by single-stranded loops,
bulges, and junctions. Examples are tRNA, ribosomes, ribozymes, and
riboswitches. These complex structures are facilitated by the fact
RNA backbone has less local flexibility than
DNA but a large set
of distinct conformations, apparently because of both positive and
negative interactions of the extra OH on the ribose. Structured RNA
molecules can do highly specific binding of other molecules and can
themselves be recognized specifically; in addition, they can perform
enzymatic catalysis (when they are known as "ribozymes", as initially
discovered by Tom Cech and colleagues.
Monosaccharides are the simplest form of carbohydrates with only one
simple sugar. They essentially contain an aldehyde or ketone group in
their structure. The presence of an aldehyde group in a
monosaccharide is indicated by the prefix aldo-. Similarly, a ketone
group is denoted by the prefix keto-. Examples of monosaccharides
are the hexoses, glucose, fructose, Trioses, Tetroses, Heptoses,
galactose, pentoses, ribose, and deoxyribose. Consumed fructose and
glucose have different rates of gastric emptying, are differentially
absorbed and have different metabolic fates, providing multiple
opportunities for 2 different saccharides to differentially affect
food intake. Most saccharides eventually provide fuel for cellular
Disaccharides are formed when two monosaccharides, or two single
simple sugars, form a bond with removal of water. They can be
hydrolyzed to yield their saccharin building blocks by boiling with
dilute acid or reacting them with appropriate enzymes. Examples of
disaccharides include sucrose, maltose, and lactose.
Polysaccharides are polymerized monosaccharides, or complex
carbohydrates. They have multiple simple sugars. Examples are starch,
cellulose, and glycogen. They are generally large and often have a
complex branched connectivity. Because of their size, polysaccharides
are not water-soluble, but their many hydroxy groups become hydrated
individually when exposed to water, and some polysaccharides form
thick colloidal dispersions when heated in water. Shorter
polysaccharides, with 3 - 10 monomers, are called
oligosaccharides. A fluorescent indicator-displacement molecular
imprinting sensor was developed for discriminating saccharides. It
successfully discriminated three brands of orange juice beverage.
The change in fluorescence intensity of the sensing films resulting is
directly related to the saccharide concentration.
Lignin is a complex polyphenolic macromolecule composed mainly of
beta-O4-aryl linkages. After cellulose, lignin is the second most
abundant biopolymer and is one of the primary structural components of
most plants. It contains subunits derived from p-coumaryl alcohol,
coniferyl alcohol, and sinapyl alcohol and is unusual among
biomolecules in that it is racemic. The lack of optical activity is
due to the polymerization of lignin which occurs via free radical
coupling reactions in which there is no preference for either
configuration at a chiral center.
Lipids (oleaginous) 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
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,
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 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
Modified amino acids are sometimes observed in proteins; this is
usually the result of enzymatic modification after translation
(protein synthesis). For example, phosphorylation of serine by kinases
and dephosphorylation by phosphatases is an important control
mechanism in the cell cycle. 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
Besides those used in protein synthesis, other biologically important
amino acids include carnitine (used in lipid transport within a cell),
GABA and taurine.
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. It specifies the order of side-chain
groups along the linear polypeptide "backbone".
Proteins have two types of well-classified, frequently occurring
elements of local structure defined by a particular pattern of
hydrogen bonds along the backbone: alpha helix and beta sheet. Their
number and arrangement is called the secondary structure of the
protein. Alpha helices are regular spirals stabilized by hydrogen
bonds between the backbone CO group (carbonyl) of one amino acid
residue and the backbone NH group (amide) of the i+4 residue. The
spiral has about 3.6 amino acids per turn, and the amino acid side
chains stick out from the cylinder of the helix. Beta pleated sheets
are formed by backbone hydrogen bonds between individual beta strands
each of which is in an "extended", or fully stretched-out,
conformation. The strands may lie parallel or antiparallel to each
other, and the side-chain direction alternates above and below the
Hemoglobin contains only helices, natural silk is formed of
beta pleated sheets, and many enzymes have a pattern of alternating
helices and beta-strands. The secondary-structure elements are
connected by "loop" or "coil" regions of non-repetitive conformation,
which are sometimes quite mobile or disordered but usually adopt a
well-defined, stable arrangement.
The overall, compact, 3D structure of a protein is termed its tertiary
structure or its "fold". It is formed as result of various attractive
forces like hydrogen bonding, disulfide bridges, hydrophobic
interactions, hydrophilic interactions, van der Waals force etc.
When two or more polypeptide chains (either of identical or of
different sequence) cluster to form a protein, quaternary structure of
protein is formed.
Quaternary structure is an attribute of polymeric
(same-sequence chains) or heteromeric (different-sequence chains)
proteins like hemoglobin, which consists of two "alpha" and two "beta"
An apoenzyme (or, generally, an apoprotein) is the protein without any
small-molecule cofactors, substrates, or inhibitors bound. It is often
important as an inactive storage, transport, or secretory form of a
protein. This is required, for instance, to protect the secretory cell
from the activity of that protein. Apoenzymes becomes active enzymes
on addition of a cofactor. Cofactors can be either inorganic (e.g.,
metal ions and iron-sulfur clusters) or organic compounds, (e.g.,
[Flavin groupflavin] 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, or isozymes, are multiple forms of an enzyme, with
slightly different protein sequence and closely similar but usually
not identical functions. They are either products of different genes,
or else different products of alternative splicing. They may either be
produced in different organs or cell types to perform the same
function, or several isoenzymes may be produced in the same cell type
under differential regulation to suit the needs of changing
development or environment. LDH (lactate dehydrogenase) has multiple
isozymes, while fetal hemoglobin is an example of a developmentally
regulated isoform of a non-enzymatic protein. The relative levels of
isoenzymes in blood can be used to diagnose problems in the organ of
Molecular and cellular biology portal
List of biomolecules
Multi-state modeling of biomolecules
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