'A' Level Biology Problem Analysis: Amino Acids And Polypeptide locations

QN: How can two amino acids, ‘A’ and ‘B’, that are far apart along the polypeptide chain somehow end up next to each other in an active site?

Thought process:


The primary structure (unique number and linear sequence of amino acids) of the enzyme, which consists of the sequences and lengths of its amino acids, determine the secondary and tertiary structures.

The final shape of the protein is due to its primary structure, which refers to type, number and sequence of amino acids.


The polypeptide chain is folded into its secondary structure, either as an α-helix or β-pleated sheet, through hydrogen bonding between the CO and NH groups, along the polypeptide backbone.

The secondary structure is further folded and twisted into its tertiary structure by various interactions between the different R groups of the different amino acids; via hydrogen bonds, ionic bonds, hydrophobic interactions and disulphide linkages.


The folding and twisting of the polypeptide chain forms the 3D conformation of the enzyme, which results in a globular structure such that the amino acid residues far apart in the primary structure can be brought closer together in the active site.


The above content is contributed by Miss Cordelia Yap, an 'A' Level H2 Biology tutor who graduated from Nanyang Technological University with a Bachelor of Science in Biological Sciences (First Class Honours). Visit her site at www.biologytuition-sg.com for more information.


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