Macromolecules

There are four types of macromolecules that make up all living matter: carbohydrates, lipids, proteins, and DNA.

They are all composed of long complex chains of molecules (polymers) made up of simpler, smaller subunits (monomers). They are joined together in a process known as dehydration, in which a covalent bond is formed between two monomers, releasing a water molecule.

Carbohydrates:

• Carbohydrates are made up of sugars and their polymers. Simple sugars  are chains of hydrocarbons of varying length that possess a hydroxyl (OH) group on each carbon.
• Glucose and galactose are two types of monomers that form a hexagonal ring because of its aldehyde structure. Fructose forms a pentagonal ring because of its keytone structure.
• Carbohydrates are essential for both energy storage and structure. Starch is the chief energy source for plants and glycogen is the main energy source for animals.Cellulose in plants and chitin in invertebrate animals help to provide structure and support.

Lipids:

Lipids ccan be divided into three main categories: fats, steroids, and phospholipids.

• A fat (tryglyceride) is composed of a glycerol molecule (a short hydrocarbon) bonded to three fatty acids through dehydration synthesis.
• If there are no double covalent bonds between the carbons of the fatty acids, the fat is said to be saturated, because the maximum number of hydrogens are bonded to the carbon skeleton. IF the fatty acid has any double bonds, it is said to be unsaturated.
• Phospholipids are composed of a glycerol molecule bonded to two fatty acids and a phosphate group. This phosphate group is polar although the rest of the molecule is hydrophobic.
• Steriods are made of four interconnecting carbon rings and cholesterol is the most common steroid.
• Lipids are excellent sources of energy, insulation, and, in the case of the dual nature of the phospholipid, they are crucial elements of membranes.

Proteins:

Proteins have many levels of structure.

• Their primary level of structure is the sequence of amino acids linked together in a peptide chain. There are only 20 amino acids, each with a hydrogen, an amino group (NH2-), a carboxyl group (COO -), and an R group.
• The secondary level of structure in proteins is the bending of this peptide chain into either an alpha helix (coil) or a beta sheet (plaited sheet) as a result of hydrogen bonding.
• The tertiary structure is based on the folding of the secondary structure caused by interactions between amino acid side chains. These include ionic and covalent bonds, disulphide bonds, and hydrophobic interactions.
• A protein's quaternary structure is based on the interaction between many peptide chains. 

DNA:

• DNA is composed of a nitrogenous base, a five-carbon sugar (a pentose), and a phosphate group.
• There are five nitrogenous bases: adnine, guanine, thymine, uracil, and cytosine. Adenine only binds with thymine, guaning only binds with cytosine. Thymine is only found in DNA and uracil is a substitude for thymine in RNA.
• The pentose in RNA is ribose and deoxyribose in DNA. A phosphate group is linked to the sugar via a phosphodiester bond and the three nucleotides have become a nucleic acid.  
• DNA holds the generic information necessary for protein synthesis and RNA carries this information to the actual site of protein production.