Amino acid

In the syllabus and the exam

Amino acid is the monomer unit examined whenever a question builds up to protein structure, and candidates are expected to know that hundreds of amino acid molecules join together, through reactions that release water, to form long chains that then fold into a protein with a specific three-dimensional shape. This links directly to enzyme structure, since an enzyme's active site is a particular arrangement of amino acids that gives it a shape matching only certain substrates, and questions on denaturation are answered correctly only when candidates understand that changing the shape of these amino acid chains, rather than destroying the amino acids themselves, is what stops an enzyme working. A frequent error is describing amino acids as if they were the same thing as protein, rather than the building block from which protein is assembled, similar to how glucose is a building block of starch; another common confusion is between amino acid (the monomer of protein) and fatty acid (part of a lipid molecule), which share a similar-sounding name but belong to entirely different biomolecule categories with different structures and functions. Candidates are also expected to know that some amino acids, called essential amino acids, cannot be made by the human body and must be obtained from protein in the diet, a fact often linked to questions about balanced diet and protein deficiency. A frequently tested extension asks candidates to explain why a change in even one amino acid within a very long chain can alter an enzyme's active site enough to stop it working altogether, a link the syllabus uses to connect protein structure forward to mutation in the genetics chapters.

Example

A protein such as haemoglobin is made of hundreds of amino acids joined together in a specific sequence and folded into a precise three-dimensional shape.

Related terms

ProteinDeoxyribonucleic acid (DNA)

Source:SRC-DSKP-EN