Principles of DNA sequencing (OCR A-level Biology)

This detailed lesson describes the principles of DNA sequencing and has been designed to cover the first part of point 6.1.3 (a) of the OCR A-level Biology A specification. Fred Sanger’s chain termination method is used as the example to guide the students through the details of each step.

The lesson begins with a focus on the common ingredients of the process such as DNA polymerase, DNA nucleotides and primers. Links are made to module 2.1.3 where nucleic acids were initially met through a series of prior knowledge check questions. Time is then taken to explain why these short lengths of synthesised nucleotides are necessary and this will support students when primers are met in the PCR and genetic engineering. Moving forwards, students will recognise how the modification to the nucleotide means that the chain terminates once a modified nucleotide is added into the sequence and that these have been radioactively labelled. Gel electrophoresis is introduced and an outline of the process given to provide knowledge to build on when this is encountered later in the module. A series of exam-style questions allow students to assess their understanding of this potentially difficult topic before students are encouraged to consider the limitations of the method so they are prepared to meet the new methods in upcoming lessons.

A number of quiz competitions run throughout the lesson to maintain engagement and to introduce terms and values in a memorable way