Semi-conservative DNA replication (OCR A-level Biology)

This fully-resourced lesson describes how DNA is replicated during interphase of the cell cycle and explains why it is known as semi-conservative replication. Both the detailed PowerPoint and accompanying resources have been designed to cover the details of point 2.1.3 (e) of the OCR A-level Biology A specification and the occurrence of spontaneous mutations is also discussed in the latter part of the lesson.

As detailed in the specification, the focus of this lesson is the role of the enzymes DNA helicase and polymerase and students are also introduced to DNA ligase to enable them to understand how this enzyme functions to join the nucleic acid fragments. Time is taken to explain key details such as the assembly of strands in the 5’-to-3’ direction so that the continuous manner in which the leading strand is synthesised can be compared against that of the lagging strand. The students are constantly challenged to make links to previous topics such as DNA structure, phosphorylated nucleotides and hydrolysis reactions through a range of exam questions and answers are displayed so any misconceptions are quickly addressed. The final part of the lesson focuses on the occurrence of mistakes by DNA polymerase and also on the quantity of DNA in the cell following replication so that future links can be made to the cell cycle (as covered in module 2.1.6)