Structure of a chromosome (CIE A-level Biology)

This lesson describes the structure of the chromosome, including DNA, histone proteins, chromatids, centromeres and telomeres. The PowerPoint and accompanying worksheets have been primarily designed to cover point 5.1 (a) of the CIE A-level Biology specification but has been specifically planned to provides links to the upcoming topics of the cell cycle, mitosis, meiosis and DNA replication.

The lesson begins with a prior knowledge check, where the students have to recall why the DNA in prokaryotic cells is described as being naked. This re-introduces histone proteins, and then time is taken to describe that the wrapping of DNA molecules around these proteins forms the linear chromosomes in the nucleus of eukaryotic cells. A series of 7 exam-style questions are used throughout the lesson and challenge the students to apply their knowledge and understanding to unfamiliar situations and challenge their knowledge of topics 1 and 2 (cell structure and biological molecules). The mark schemes for all of these questions are embedded into the PowerPoint to allow the students to assess their progress. Moving forwards, a quiz competition is used to introduce the terms diploid, chromatid and centromere and the S phase of interphase in a fun and memorable way. Students will learn that the duplication of chromosomes results in pairs of identical sister chromatids that are joined by a centromere. The importance of the splitting of the centromere in mitosis is explained and then the students are challenged to explain why the non-sister chromatids are involved in crossing over, when variation is needed. The final part of the lesson considers the repetitive nucleotide sequences found on the end of chromosomes that are known as telomeres and students will gain an initial understanding about their structure so they are prepared for the upcoming lesson on their significance