Protein consists of carbon, hydrogen, oxygen and nitrogen molecules arranged in specific ways. Nitrogen as part of what in known as an ‘amino group’ distinguishes protein from carbohydrates and fats.
The smallest unit of protein is an amino acid. These consist of four different but distinct molecular groups:
- an amino group
- a carboxly group
- a central carbon group
- a side chain called the R group
The side chain or ‘R’ group differentiates each amino acid from one another. In glycine, for example, the ‘R’ group is simply a hydrogen molecule.
When amino acids bond together they form what are called peptides or peptide chains and these make up the structure of primary proteins.
Structural proteins give cells or organelles their shape, for example, actin in the muscle cell. Functional proteins catalyze or support biochemical reactions in the body, an example is enzymes. Many proteins in the body are both structural and functional. Dietary protein is mainly the structural protein we consume from plants and animals whereas dairy protein is strictly a dietary protein.
Most dietary proteins are a complex combination of primary proteins. In these protein structures the primary proteins are twisted and folded into increasing complex shapes known as secondary, tertiary and quaternary structures.
However, protein quality is based on amino acid content not the structural formation.
Protein digestion begins in the stomach were gastric hydrochloric acid denatures the protein. Denaturing protein involves untangling or unfolding the complex shapes so that digestive enzymes can act on the peptide bonds in the primary protein.
As long as adequate amino acids and energy is consumed the appropriate secondary, tertiary and quaternary structures can be formed in the body.