Molecular Biology - Proteins

Proteins are composed of long chains of amino acids linked together by peptide bonds through condensation reactions, where a molecule of $H_{2}O$ is released.

There are $20$ different amino acids used by ribosomes to create polypeptides, each differing by its specific $R$ group (side chain).

The primary structure of a protein is the specific sequence of amino acids, which is determined by the $DNA$ base sequence of the gene.

Secondary structure involves the folding of the polypeptide chain into $\alpha$-helices or $\beta$-pleated sheets, stabilized by hydrogen bonds between the $-NH$ and $-C=O$ groups.

Tertiary structure is the further $3D$ folding of the protein caused by interactions between $R$ groups, including disulfide bridges, ionic bonds, hydrogen bonds, and hydrophobic interactions.

Quaternary structure exists in proteins consisting of more than one polypeptide chain, such as Hemoglobin ($4$ subunits) or Collagen ($3$ subunits).

The proteome is the entire set of proteins expressed by a genome, cell, tissue, or organism at a given time and is unique to every individual.

Denaturation is a structural change in a protein that results in the loss of its biological properties, typically caused by high temperatures or deviations from the optimum $pH$.

Key examples of proteins include: Rubisco (enzyme for $CO_{2}$ fixation), Insulin (hormone for glucose uptake), Immunoglobulins (antibodies), and Rhodopsin (light-sensitive pigment).