The mitotic cell cycle
You began life as a single cell, and yet your body now holds trillions of cells that all carry exactly the same instructions. That is the work of mitosis. In this lesson we first take a chromosome apart to see what is being copied - the DNA wound on histone proteins, the two sister chromatids joined at the centromere, and the protective telomeres capping the ends. We then meet mitosis itself, the nuclear division that makes genetically identical cells, and see why the body needs it for growth, cell replacement, repair of tissues and asexual reproduction. We draw the whole cell cycle as a circle - interphase (G1, S and G2), then mitosis, then cytokinesis - and learn why telomeres allow copying to continue without losing genes. Finally we look at stem cells renewing our tissues, at what happens when cell division escapes control and forms a tumour, and at how to prepare a root-tip squash of onion or broad bean to see dividing cells for yourself.
By the end you should be able to (NSSCAS Biology (AS) 3.1.1):
- describe the structure of a chromosome, limited to DNA, histone proteins, chromatids, centromere and telomeres
- explain the importance of mitosis in the production of genetically identical cells, growth, cell replacement, repair of tissues and asexual reproduction
- observe and draw the mitotic stages visible in temporary root tip squash preparations and in prepared slides of root tips of species such as those of Vicia faba and Allium cepa
- outline the mitotic cell cycle, including interphase (growth in G1 and G2 phases and DNA replication in S phase), mitosis and cytokinesis
- outline the significance of telomeres in permitting continued replication and preventing the loss of genes
- outline the role of stem cells in cell replacement and tissue repair by mitosis
- explain how uncontrolled cell division can result in the formation of a tumour
Miss Rachel and Mike talk through the whole topic — with the figure and working drawn live.