Molecular Biology - Proteins

Proteins are polymers made of amino acid monomers linked by peptide bonds. Each amino acid consists of a central carbon atom ($C$), an amine group ($-NH_2$), a carboxyl group ($-COOH$), a hydrogen atom ($-H$), and a variable side chain ($-R$ group).

There are 20 different amino acids used by ribosomes to create polypeptides. The sequence of these amino acids is coded for by genes and determines the three-dimensional conformation of the protein.

A condensation reaction occurs between the $-NH_2$ group of one amino acid and the $-COOH$ group of another, releasing one molecule of $H_2O$ and forming a dipeptide.

The primary structure is the linear sequence of amino acids. Secondary structures, such as the $\alpha$-helix and $\beta$-pleated sheet, are stabilized by hydrogen bonds between the carboxyl and amine groups of the peptide backbone.

Tertiary structure is the further folding of the polypeptide caused by interactions between $-R$ groups, including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

Quaternary structure exists in proteins consisting of more than one polypeptide chain, such as Hemoglobin ($Hb$).

Denaturation is a structural change in a protein that results in the loss of its biological properties. It is typically caused by high temperatures or extreme $pH$ levels which disrupt intermolecular bonds.

The proteome is the totality of proteins expressed within a cell, tissue, or organism at a given time. The proteome is always larger than the genome because of alternative splicing and post-translational modifications.

Key examples of protein functions include: Rubisco (catalysis), Insulin (hormone), Immunoglobulins (immunity), Rhodopsin (receptor), Collagen (tensile strength), and Spider silk (structural).