4.1.2 Cell division

4.1.2.1 Chromosomes

  • Chromosomes are the genetic information in nucleus
  • They affect the make-up of the cell
  • They determines which proteins are made
  • DNA is packaged in chromosomes
  • Chromosome are made up of coiled up DNA sections
  • The DNA must not be tangled
  • DNA makes up genes
  • Genes = sequences of DNA
  • Genes code for certain characteristics
  • Each chromosome has many genes

Chromosomes in Pairs

  • Chromosomes come from biological parents
  • Each cell has 23 pairs of chromosome
  • One copy of each set from the father and one copy from the mother
  • Chromosomes are found in pairs
  • If they are not paired, it could lead to genetic disease
  • Many genetic diseases are as result of chromosome pairing problems e.g. Down’s Syndrome – extra 21st chromosome
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4.1.2.2 Mitosis and the cell cycle

Cell Cycle

  • The cell cycle is how cells duplicate and divide
  • Cells divide to replace dead cells for growth or repair
  • The length of the cell cycle varies between organisms
  • Hair follicles, blood, skin and digestive system lining divide fast, and have a very quick cell cycle
  • Interphase – cell are ready to divide, the cell grows, DNA duplicates, organelles are made
  • Metaphase – genetic material separates, the cell is ready to divide into two daughter cells
  • Cytokinesis – the cytoplasm and cell membrane split into two daughter cells

DNA Replication

  • The cell grows to form two copies of each chromosome
  • This cell now has double the DNA
  • Each cell will eventually get the normal share of DNA

Making Organelles

  • Organelles are produced so the cell now has double the organelles
  • There is an increase in mitochondria number for energy
  • There is also an increase in ribosomes for protein synthesis
  • The cell grows, with the cell surface membrane extending and the cytoplasm grows too

Mitosis

  • Chromosomes line up on equator (middle of the cell)
  • Chromosomes are pulled to opposite poles (sides) of the cell
  • Chromosomes are pulled apart by spindle fibres
  • Membranes form around the chromosomes to become two new nuclei

Cytokinesis

  • Division of the cytoplasm and cell membranes to surround the new nuclei are formed
  • This final stage of the cell cycle involves the formation of new cells

Mitosis for Growth

  • Cells are constantly growing and dividing
  • Mitosis allows this with the formation of identical daughter cells
  • Important for all eukaryotes cells as they are needed to grow

Mitosis for Development

  • Replacing skin cells – skin cells damaged constantly, replaced by dividing cells underneath the surface
  • Growth of organism
  • Asexual reproduction – single-celled organisms reproduce to produce two daughter organisms
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4.1.2.3 Stem cells

Types of Stem Cells

  • A stem cell is an undifferentiated cell
  • It has the ability to differentiate and form a specialised cell
  • It can divide by mitosis to form a tissue of stem cells
  • Then different cell clusters can differentiate to many tissues of different specialised cells
  • This is how the human body develops from a single embryonic stem cell

Embryonic Stem Cells

  • Stem cells in embryos are known as embryonic stem cells
  • Embryonic stem cells are found in early embryos
  • They are completely undifferentiated
  • They can be used to turn into any type of cell

Adult Bone Marrow Stem Cells

  • Stem cells can be found in the bone marrow, teeth and other areas
  • These cells cannot differentiate into any type of cells (like embryonic stem cells)
  • They can only differentiate into predetermined cells, such as some blood cells (i.e. red blood cells and white blood cells)

Plant Stem Cells

  • Stem cells are found in plant meristems
  • These cells can differentiate to form any type of plant cell
  • They are present throughout the lifespan of the plant
  • Stem cells from meristems can be used to prevent extinction
  • These cells can be harvested from plants that are threatened by extinction
  • These plants can then be grown in favourable conditions, as clones of the original plant, to keep these rare plants in existence

Stem Cells to Treat Diabetes

  • Patients with diabetes suffer from a lack of insulin, and have high blood glucose levels
  • Stem cells can be made that can produce insulin, for insulin injections
  • Used to treat those who suffer from diabetes (type I)

Stem Cells to Treat Paralysis

  • Stem cells can be differentiated to form nerve cells
  • These cells are used to treat those who suffer from the nerve damage that causes certain types of paralysis

Therapeutic Cloning

  • Immune rejection is an issue in medical treatment
  • There is a risk of the recipient’s immune system rejecting the  ‘foreign’ cells
  • The use of therapeutic cloning can reduce the risk of rejection
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    Therapeutic Cloning

    • Therapeutic cloning uses stem cells from the patient
    • An embryo is produced, to have the same genetical material as the patient, and the stem cells are extracted
    • These cells should not be rejected by the patient’s immune system as they have the same genetic material as the patient

    Ethical Debate

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