Computer modelling software can be used to explore the structure of molecules that have been mapped via X-ray crystallography

• Jmol is an applet that can render 3D images from appropriate computer files (.pdb) – click on the files to load the applet

Carbohydrates

Carbohydrates are composed of cyclic subunits called monosaccharides. Glucose is an example of a hexose sugar because it forms a hexagonal shape. Cellulose, glycogen and starch (amylose or amylopectin) are all examples of polysaccharides composed of glucose monomers. 

Lipids

Lipids are not composed of recurring monomers, but most will contain either a linear chain (fatty acid) or fused rings (steroids). Fatty acids can be saturated (no double bonds) and form a straight chain or unsaturated (has double bonds) and form a kinked chain. The more double bonds (polyunsaturated), the greater the kink. Triglycerides consist of three fatty acid chains linked to a single glycerol. In phospholipids, one of the fatty acid chains is replaced by a phosphate group. Because phosphate is a polar molecule, it orientates away from the non-polar fatty acid tails. Phospholipids can form hydrophobic interactions between the non-polar tails and consequently will arrange themselves into a bilayer when placed in an aqueous solution.

Proteins

Proteins are composed of amino acids (monomer), which join together to form a polypeptide chain. The amino acids may have different chemical properties (depending on their variable side chain). The order of amino acids will determine the way the polypeptide folds into a complex 3D shape. Some proteins may consist of more than one polypeptide chain.

Nucleic Acids

Nucleic acids are made up of recurring nucleotides (consisting of a sugar, phosphate and nitrogenous base). These nucleotides form long chains and in DNA will form a double-stranded helix due to complementary base pairing. ATP is a modified nucleotide and functions as an immediate source of energy within a cell.