Chapter 13: Cell Cycle
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Chapter 13: The Cell Cycle
Cell Continuity:
- Cells that arise from cells of the same type
- Living organisms maintain cell continuity by mitosis and cell division
Chromatin and Chromosomes
- Chromatin is elongated DNA
- Chromosomes are composed of DNA and protein
- Chromosomes are arranged into homologous pairs – pairs of chromosomes that contain genes that control the same characteristics
Haploid and diploid
- Haploid means one set of chromosomes
- Diploid means two sets of chromosomes
- In humans the haploid number is 23
- The diploid number is 46 – arranged into 23 pairs
The Cell cycle
- The cell cycle occurs under three distinct stages:
- Interphase
- Mitosis
- Cell division
1. Interphase
- Interphase is the stage where a cell is not dividing and a cell spends the vast majority of its time in this stage
- Chromosomes are elongated and the cell goes about its daily functions
- Towards the end of interphase the cell organelles and DNA are replicated
End of interphase
- The DNA is replicated and condenses into duplicated chromosomes which are held together by centromeres
2. Mitosis
- Mitosis is nuclear division that leads to the formation of two identical daughter cells
Stages:
- Stage 1: Prophase
- Stage 2: Metaphase
- Stage 3: Anaphase
- Stage 4: Telophase
Stage 1: Prophase
- The nuclear membrane begins to disappear and spindle fibres begin to appear from the centrioles:
Stage 2: Metaphase
- The replicated chromosomes line up along the equator of the cell held in place by spindle fibres:
Stage 3: Anaphase
- The spindle fibres begin to contract pulling one chromosome from each pair to each pole:
Stage 4: Telophase
- The chromosomes at each pole begin to unravel and lengthen; spindle fibres disappear; and the nuclear membranes reform at each pole:
3. Cell Division (Cytokinesis)
- Cell division occurs immediately after mitosis and involves formation of cleavage furrow (in animals cells) or cell plate (in plant cells) prior to cell splitting
Cell division – Meiosis:
- Meiosis is nuclear division whereby four new daughter cells are produced each with half the number of chromosomes as the parent cell
Cancer
- Cancer is a disease whereby a cell loses its ability to control both the rate of mitosis and cell division
- Mitosis is normally carefully controlled but when it is out of control it can result in cancer
- Cancer can be either benign or malignant
- Benign cancer involves cells that divide out of control for a limited period of time and do not spread
- Malignant cancers involve cells that divide rapidly uncontrollably and spread and invade other tissues – destroying that tissue in the process
- Anything that has the potential to cause cancer is called a carcinogen – which damage DNA
- Two carcinogens:
- UV light – damages DNA of skin cells
- Cigarette smoke – damages the DNA of cells lining the mouth, airways and lungs