IB Biology 1.6 – Cell Division

Important Terms Mitosischromatids Cytokinesiskintochore Cell cyclemicrotubule Interphasecentriole Prophasecentromere Metaphasecyclins Anaphaseoncogenes Telophasemutagens G1, S, G2metastasis Chromosomesmitotic index

Learning Goals 1.To be familiar with the events and structures involved in all stages of mitosis 2.To be familiar with the stages of the cell cycle 3.To understand the role of cyclins in regulating the cell cycle 4.To know the characteristics of cancer cells and the associated terminology

Expected Knowledge Mitosis is division of the cells nucleus into two genetically identical daughter nuclei Chromosomes condense by supercoiling Cytokinesis occurs after mitosis and is different in plant and animal cells Interphase is a crucial and very active phase of the cell cycle Cyclins help control the cell cycle Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours

The Cell Cycle Consists of G1, S, G2, mitosis and cytokinesis phases

Mitosis Review Interphase Very active phase between cell divisions DNA replication in nucleus and protein synthesis occur during interphase Consists of G1 phase, S phase and G2 phase

Mitosis Review Prophase Chromosomes supercoil to become shorter and thicker Microtubules form to link the poles Nuclear membrane breaks down and nucleus disappears

Supercoiling of Chromosomes

Mitosis Review Metaphase Chromosomes line up along equator of cell Microtubes attach to centromeres of chromosomes Each individual chromatid attaches to a microtubule and tension occurs to test attachment

Mitosis Review Anaphase Centromere divides and sister chromatids are pulled to opposite sides of the cell Half of the chromatids go to one side and half to the other so each side as identical genetic material

Mitosis

Mitosis Review Telophase The cell elongates, nuclear membranes reform in each cell and nucleoli reappear Centrioles disappear chromosomes elongate and thin out Two genetically identical daughter cells have been formed

Cytokinesis Mitosis is the process whereby the genetic material divides Other parts of the cell; the cytoplasm and the organelles also must divide This is called cytokinesis

Cytokinesis – Animals vs Plants in an animal cell, the membrane pinches off and forms two round cells This can’t happen in a plant cell because of the rigid cell wall. So a plate begins to form at the centre of the cell and extends both ways to cut the cell in two

jPcT1uUZiE

Cyclins Regulate the Cell Cycle Cyclins activate proteins called “Cyclin dependent Kinases” or CDKs which allow a cell to progress though the cell cycle They allow the cell to proceed from G1 to S and from G2 to M If there is damage to the cell then the cycle will not proceed These are called “check- points”

Cancer Cell division and mitosis is tightly controlled by the cell Sometimes cell DNA will mutate and the cell will develop certain characteristics. These include: The ability to divide without a “start” signal The ability to overide “stop dividing” signals The ability to get blood vessels to grow towards it (angiogenesis)

Cancer Other features of cancerous cells

Cancer Cancer cells are formed because of mutations in certain genes in the cell. These cancerous genes are often formed because of environmental agents called mutagens. Cancerous genes are called oncogenes. One of the most potent mutagens is cigarette smoke

Cancer Since cancer cells divide faster than normal cells, they spend more time undergoing mitosis. Mitotic index is a method used to tell if cancer cells are present. It is a measurement of the fraction of cells that are undergoing mitosis. Mitotic index = # cells in mitosis ÷ total #cells

Cancer Mitotic Index Calculate the mitotic index of this sample

Cancer Metastasis Cancer cells will originate in a single part of the body and form a lump called a tumour. However, some of them may get transported in the blood to other parts of the body. This is called metastasis. That is why tumours will often show up in other parts of the body after the primary tumour has been removed. These are called secondary tumours