#12. Proteins - amino acids, peptid bonds

Proteins are large molecules made of long chains of amino acids.






1. Amino acids

All proteins have the same basic structure. They consist of an Amino Group (NH2), an Carboxyl group (COOH), and a Carbon in the middle which bonds with a Hydrogen atom and an 'R' group, which is specific to individual amino acids.

There are 20 naturally occurring 'R' groups, making amino acids neutral, acidic, alkaline, aromatic (has a ring structure) or sulphur-containing). The 20 R groups corresponds to 20 different amino acids. Each different amino acid has a specific name. For example, Alanine's 'R' group consists of CH3.

2. Peptid bonds

a. Condensation reaction:

                   2 amino acids are joined by a peptide bond ---> dipeptide + H₂O.

b. Hydrolysis reaction: 

Dipeptides are split into 2 amino acids by breaking the peptide bond using a molecule of H₂0. 

Syllabus 2015 (f) describe the structure of an amino acid and the formation and breakage of a peptide bond;

Syllabus 2016  - 2018 An understanding of protein structure and how it is related to function  is central  to many aspects of biology, such  as enzymes, antibodies and muscle contraction. Globular and fibrous proteins play important roles in biological processes such  as the transport of gases and providing support for tissues. a)   describe the structure of an amino  acid and the formation and breakage of a peptide bond