Introduction
Cells are made up mostly of water molecules (about 99%) and usually contain more protein than DNA.
Abnormalities in biomolecules, chemical reactions, or biochemical pathways can lead to diseases in animals.
Almost all known organic biomolecules are formed by combining hydrogen, oxygen, nitrogen, carbon, sulphur and phosphorus. These biomolecules can be categorised into four key areas: nucleic acids, proteins, lipids, and carbohydrates.
Lipids
Lipids make up half of the phospholipid bilayer within cells. Some lipids, known as glycolipids, possess oligosaccharide chains that extend outwards from the cell membrane surface.
The non-polar nature of membrane lipids means that the ends are kept towards the middle of the membrane, forcing the phosphate heads to the outside. This is because water is highly polar.
The major classes of cellular lipids are:
Phospholipids
Glycolipids
Fatty acids
Phosphoglycerides
Sphingolipids
Sterols
Proteins
There are two categories of protein within cells: integral and peripheral.
Integral proteins sit within the phospholipid bilayer. They can span the membrane one or more times.
All proteins are bonded to the membrane by hydrophobic reactions between the lipids and the non-polar amino acids on the outer regions of the proteins.
Many of these proteins act as receptors. Their main function is to bind to signalling molecules and induce a biochemical response in the cell.
Cell wall proteins also give stiffness and rigidity to the cell. Some globular proteins perform this role.
Some proteins also serve as motor proteins. Myosin in muscles is an example. These proteins generate mechanical forces.
Some types of proteins include:
Skeletal proteins
Muscle proteins
Blood plasma proteins
Soluble proteins
Compound proteins
Chemically, proteins consist of many amino acids joined together in long chains. About 20 different amino acids naturally occur in proteins.
Nucleic Acids
Nucleic acids are macromolecules that are made up of chains of monomeric nucleotides. The most common nucleic acids are RNA and DNA.
Nucleotides are made up of three components:
A 5-carbon sugar
A phosphate group
A nitrogenous base
The nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C) and thymine (T). RNA contains uracil (U) instead of thymine.
The type of nucleic acid is determined by the structure of the carbon sugar. A nucleic acid with 2-deoxyribose is DNA and one with ribose is RNA.
Nucleic acids can be single or double stranded, though three or more strands can form.