Biology AS - Cell Division

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Cell Cycle

- M Phase – Mitosis and Cytokinesis

- Metaphase Checkpoint – checks all Spindle is attached before continuing 

- GAP Phase 1 – grows new organelles and proteins - two of everything needed

- G1 Checkpoint – checks chemicals for replication are present

- Synthesis – cell replicates DNA for Mitosis

- GAP Phase 2 – keeps growing Proteins needed for cell division

- G2 Checkpoint – checks for DNA damage to prevent mutations from being passed on

     - if Mutation is detected at any point, the cell undergoes Apoptosis (Kills itself)

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Mitosis - For Repair and Growth

Prophase: Centrioles move to opposite sides of the cell (creates a Spindle - Protein Fibres)– nuclear envelop breaks down (to allow Spindle to form and DNA to ove in Cytoplasm) and Chromosomes become shorter and fatter

Metaphase: Chromosomes line up at Spindle Equator and become attached to Spindle at Centromere

Anaphase: Centromere divides and Spindles contract pulling Chromatids to opposite ends

Telophase: Spindle uncoils (break down) and chromosomes return to normal shape (long and thin) – Nuclear Envelope forms around each group (two different Nuclei)

Cytokinesis: Cytoplasm divides (Animal forms a Cleavage furrow) – divides Cell Membrane and two daughter cells are formed

Chromosomes: Have Centromere and Sister Chromatids (Half of chromosome - identical)

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Meiosis - For production of Gametes

Haploid Nucleus: Hvae one chromosome from each pair - e.g. Egg and Sperm

Zygote: Gametes form together - this forms new cells and becomes an organism

Alleles: Different versions of genes 

Homologous Chromosomes: Matching chromosomes

Normal body cells have a pair of chromosomes (Diploid)

Chromatids now swap and contain different combination of Alleles (Genetic Variation)

Independent Assortment: Different combination of alleles in each Daugter cell (Genetic Variation)

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Stem Cells and Differentiation

Stem Cells: Unspecialised cells - can develop into different types of cells

Differentiation: When Stem cell becomes specialised for a job - e.g. Bone Marrow Stem Cells turn into White and Red Blood Cells - replaces dead or damaged cells throughout body

Self-Renewal: Maintains Stem Cell pool

Potency: How many tyoes of specialised cells can a Stem Cell make

Embryonic Stem Cells: Early embryo -can be put into any cell (used to help in renewal or treat disease) - Cells from Blastocyst form particular organs based off of Stem cells around them (Cell Signalling)

Pluripotent: Can form any specialised cell

Multipotent: Can only form some specialised cells

Ethical Issues: Potential for life, Sancity of Life (Save everyone - the many outway the few)

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