Protein

In the syllabus and the exam

Protein is examined both as a nutrient, tested using the Biuret test which turns a sample from blue to purple in the presence of protein, and as the structural class that enzymes, antibodies, and a number of hormones belong to, which connects this chapter forward to the chapters on enzymes and on body defence. Candidates need to know that proteins are made of amino acids joined together, that the body cannot produce all the amino acids it needs (essential amino acids must come from the diet), and that protein's main biological roles are growth, repair of tissue, and forming the structural and functional molecules such as enzymes and antibodies, rather than serving as the body's first-choice energy source. A common error is mixing up the Biuret test's colour change with the Benedict's test result, writing that a positive protein test produces a brick-red precipitate when in fact it is a colour change to purple or violet with no heating required. Candidates are also often expected to describe protein deficiency diseases such as kwashiorkor, linking a lack of dietary protein to poor growth and muscle wasting, and to explain why growing children and pregnant women have a higher protein requirement than other groups, a point frequently tested in balanced-diet questions. Candidates should also be able to identify protein-rich foods from a given nutritional context, and to explain in an applied question why athletes or recovering patients are often advised to increase protein intake, linking the nutrient back to its role in building and repairing muscle tissue.

Example

Eggs, fish and soybeans are good sources of protein, which the body uses to build muscle tissue and to make enzymes and antibodies.

Related terms

Amino acidCarbohydrateEnzyme

Source:SRC-DSKP-EN