Proteins

There are 20 naturally occuring amino acids, some the body makes but some have to be obtained from the diet. Amino acids contain sulpher, carbon, hydrogen, oxygen, nitrogen and phosphorus. Protein molecules are built from amino acids. Proteins function as enzymes, hormones and oxygen transplants. 

Some proteins are known as conjugated proteins- they have another chemical group associated with their polypeptide chains. For example, the polypeptide that makes up myoglobin is associated with an iron-containing group. 

Amino acid structure

Amino acids link together via a condensation reaction to form a peptide bond similar to the glycoside. 2 amino acids bonded together are called dipeptides. 

Primary- Peptide chain 

Secondary- helical coiling of chain, Held together by hydrogen bonds, alpha helix and beta plated sheet. 

Tertiary structure: Compact globular structure formed by the folding of polypeptide chains. Unique and determines properties and function of the protein. Held together by bonds in the R group. Hydrogen bonds which are weak, ionic bonds between R groups between positive or negative charges, quite strong, sulpher bridges, covelent S-S bonds between crystalline amino acids. 

Quaternary structure- Several tertiary structures linked together e.g. haemoglobin. 

Polypeptide chains folded into rough globular shapes e.g. enzymes

soluable

hydrochloric chains

important in metabolic reactions e.g. enzymes, membrane transport proteins, haemoglobin [in red blood cells],

highly diverse,

spherodial molecules in water,

relatively straight runs of secondary structure joined by polypeptides which abruptly change directions. 

Insoluable long chain like proteins usually with a structural role e.g. Keratin (hair, nails, hooves, horns) or a connective tissue role (elastin and collagen) also in muscle tissue. 

Cross linked structures keep them together 

They remain as long chains 

Collagen (in skin, tendons, muscle, bones, blood vellels) 

They are important structural proteins