The Genetic code (OCR A level Biology)

This lesson focuses on the nature of the genetic code in terms of being near universal, non-overlapping and degenerate and specifically focuses on this latter term to explain how a mutation may not result in a change to the sequence of amino acids. The PowerPoint has been designed to cover point 2.1.3 (f) of the OCR A-level Biology A specification and there are clear links to gene mutations which students will meet in module 6.

The lesson begins by introducing the terms near universal and non-overlapping in addition to degenerate. A quick quiz competition is used to generate the number 20 so that the students can learn that there are 20 proteinogenic amino acids in the genetic code. This leads into a challenge, where they have to use their prior knowledge of DNA to calculate the number of different DNA triplets (64) and the mismatch in number is then discussed and related back to the lesson topic. Moving forwards, base substitutions and base deletions are briefly introduced so that they can see how although one substitution can change the primary structure, another will change the codon but not the encoded amino acid. The lesson concludes with a brief look at the non-overlapping nature of the code so that the impact of a base deletion (or insertion) can be understood when covered in greater detail in module 6.