Cell Continuity
Cell continuity: Living cells arising from living cells of the same type
Chromosome: Tightly coiled and highly organised structure of DNA and protein
Chromosomes contain the information necessary for the production of a new cell. Humans have 46 chromosomes = 23 homologous pairs - Chromosomes which contain genes that control the same characteristics
Gene: Short region of DNA which contains the code for the production of a particular protein
1st 22 pairs are called autosomes
23rd pair = sex chromosomes
Haploid: One set of chromosomes
Diploid: Two sets of chromosomes
Cell Cycle
1) Interphase
Long period of the cell cycle during which the cell spends most of its time and carries out its everyday activities
- DNA dublicates itself at the end of Interphase
2) Mitosis
Nuclear division in which the number of chromosomes in the daughter nuclei is the same as the parent nuclei
- For growth and repair
Stages of Mitosis
1) Prophase:
- Chromatin condenses and becomes clearly visible chromosomes
- Duplicated DNA are attached to each other at the centromere
- Nuclear membrane begins to break down
- At each pole end of the cell centrioles produce spindle fibres, which attach to the chromosomes at the centromere
- Chromosomes line up along the middle of the cell, they are held in place by spindle fibres
- Spindle fibres organise chromosomes so each new nucleus will receive the same amount
3) Anaphase
- Centromeres which were holding the chromosomes together split and the chromosomes move apart
- \Spindle fibres contract to move the chromosomes to either ends of the cell
4) Telophase
- Once the chomosomes are at either ends of the cell the nuclear membrane begins to reform around them
- The chromosomes unravel and elongate to become chromatin once more
- The spindle fibres dissolve and the cell prepares itself for cell division
Cell Division
- Process of cell division differs between plants and animals
Animals: A cleavage furrow forms which is an indentation of the cytoplasm, starts on the outside and proteins such as actin and myosin pull the membrane in
Plants: A cell plate forms, small intra-cellular vesicles line up where at the sit of the new cell wall and membrane and fuse together to become them
Cancer
Group of disorders in which cells lose control of mitosis and cell division
Benign: Cells form a tumour but do not move or invade other tissues. In general not life threatening but can develop into malignant cancer
Malignant: Cells have the ability to leave the tumour, this process is called metastasis and left untreated can be life-threatening
Causes of Cancer
Cancer causing agents are refered to as carcinogens
- UV light
- Cigarette smoke
- Radon gas
- Asbestos fibres
Meiosis
Type of nuclear division that leads to four daughter cells being produced each containing a haploid number of chromosomes
- Required for sexual reproduction, in humans its products are the sperm and egg cells
- Involved in gamete formation in all multicellular organisms that reproduce sexually
Differences between meiosis and mitosis
1) Mitosis only involves division of the nucleus, meiosis involves two rounds of nuclear division
2) Mitosis maintains number of chromosomes in the daughter cells, meiosis halves the number of chromosomes in the daughter cells
3) Mitosis produces genetically identical cells, meiosis creates variation through rearrangement of genetic material
4) Mitosis occurs in all living organisms, meiosis can only occur in multicellular organisms
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