Biomolecule
A
biomolecule is a
chemical compound 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 these are much less common.
Biomolecules are necessary for the existence of all known forms of
life. 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 is 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 small
organic molecules are absorbed or synthesised by living systems. Many biomolecules may be useful or important
drugs.
A diverse range of biomolecules exist, including:
*Small molecules:
**
Lipid,
Phospholipid,
Glycolipid,
Sterol**
Vitamin**
Hormone,
Neurotransmitter**
Carbohydrate,
Sugar**
Disaccharide*
Monomers:
**
Amino acid**
Nucleotide**
Phosphate**
Monosaccharide*
Polymers:
**
Peptide,
Oligopeptide,
Polypeptide,
Protein**
Nucleic acid, i.e.
DNA,
RNA**
Oligosaccharide,
Polysaccharide*
Macromolecules:
**
PrionNucleosides 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 carbohydrates in the form of simple sugars.
Disaccharides are formed from two monosaccharides joined together. Monosaccharides and disaccharides are sweet, water soluble, and crystalline. Examples of monosaccharides include the
hexoses (
glucose,
fructose, and
galactose) and
pentoses (ribose,
deoxyribose). Examples of disaccharides include
sucrose,
maltose, and
lactose.
Polysaccharides are polymerized monosaccharides, complex unsweet carbohydrates. They are, generally, large and often have a complex, branched, connectivity. They are insoluble in water and do not form crystals. Examples include
starch,
cellulose, and
glycogen. Shorter polysaccharides, with 2-15 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 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.
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.
Hormones are produced in the
endocrine glands, where they are excreted into the
bloodstream. They perform a wide range of roles in the various organs including the regulation of
metabolic pathways and the regulation of membrane transport processes.
Hormones may be grouped into three structural classes:
*The
steroids are one class of such hormones. They perform a variety of functions, but they are all made from cholesterol.
*Simple amines or amino acids.
*Peptides or proteins.
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. Proteins have several, well-classified, elements of local structure and these are termed
secondary structure. The overall
3D structure of a protein is termed its
tertiary structure. Proteins often aggregate into macromolecular structures, or
quaternary structure.
Metalloproteins
A
metalloprotein is a protein that contains a
metal cofactor. The metal may be an isolated
ion or may be
coordinated with a nonprotein
organic compound, such as the
porphyrin group found in
hemoproteins. In some cases, the metal is coordinated with both a
side chain of the protein and an inorganic nonmetallic ion. This type of protein-metal-nonmetal structure is found in
iron-sulfur clusters.
A
vitamin is a compound that can not be synthesized by a given organism but is nonetheless vital to its survival or health. These compounds must be absorbed, or eaten, but typically only in trace quantities.
*
List of biomolecules*
Biological tissue*
Biological matter
