The Cell

Topic 2.5 Cell Division

Mitosis Cellular division in eukaryotic cells. Chromatin is arranged into chromosomes. Chromosomes double. Cell grows in size. Cells divide. Is cellular cloning.

Phases of the Cell Cycle the ‘life cycle’ of a cell. There are 2 phases: 1.Interphase 2.M phase (mitotic phase) a.Prophase b.Metaphase c.Anaphase d.Telophase & cytokinesis

1. Interphase The non-dividing phase in a cell Lasts about ~ 90% of the cell cycle. The cell grows and replicates DNA preparing for Mitosis. There are three periods:

3 periods of Interphase 1. G o – a cell functioning as normal 2. G1 phase – first growth phase 3. S phase- synthesis of DNA 4. G2 phase- 2 nd growth phase Mitosis is a reliable process. Only one error occurs Per 100,000 cell divisions.

2. Mitosis: Prophase The nucleolus disappears. Chromatin condenses into visible chromosomes. There are two sister chromatids held together by a centromere. The mitotic spindle forms in the cytoplasm.

“Pro”metaphase The nuclear envelope disappears. Spindle fibers extend from each pole to the cell’s equator. Spindle fibers attach to the centromeres.

Metaphase Chromosomes are lined up in the equator (middle) of the cell. This is called the metaphase plate.

Anaphase Characterized by movement. It begins when pairs of sister chromatids pull apart. Sister chromatids move to opposite poles of the cell. Chromosomes look like a “V” as they are pulled. At the end of anaphase, the two poles have identical number and types of chromosomes.

Telophase and Cytokinesis Microtubules elongate the cell. Daughter nuclei begin to form at the two poles. Nuclear envelopes re-form. Nucleolus reappears. Chromatin uncoils. Cells split their cytoplasm. It is basically the opposite of prophase.

Role of Mitosis Growth: Multicellular organisms increase their size through growth. This growth involves increasing the number of cells through mitosis. These cells will differentiate and specialize their function. Tissue Repair: As tissues are damaged they can recover through replacing damaged or dead cells. This is easily observed in a skin wound. More complex organ regeneration can occur in some species of amphibian. Asexual Reproduction: This the production of offspring from a single parent using mitosis. The offspring are therefore genetically identical to each other and to their “parent”- in other words they are clones. Asexual reproduction is very common in nature, and in addition we humans have developed some new, artificial methods

Tumors The cancer cells are a mass of cells produced from uncontrolled cell division and can occur in an tissue. These cells disrupt biological order and function. If left unchecked, to bring the whole complex, life sustaining edifice that is the human body crashing down' This mass is called a tumor. There are two major types of tumor: 1.Benign Tumors this is a mass of cancerous cells that do not invade other areas of the body. These are not as dangerous to health but may still require removing to prevent effects on neighboring tissue

2. Malignant Tumors is a mass of cancer cells that may invade surrounding tissues or spread to distant areas of the body. Cancer cells replace normal functioning cells in distant sites: e.g. replacing blood forming cells in the bone marrow, replacing bones leading to increased calcium levels in the blood, or in the heart muscles so that the heart fails. 1.Image is a normal CT. Images 2, 3 & 4 Are PET scans, Light green/blue areas show cancer cells