Mitosis

• Chromosomes

  • Found in the nucleus
  • Contains genetic material
  • Are coiled up lengths of DNA molecules
• Body cells have two copies of each chromosome - making them ‘diploid’ cells

  • Once chromosome from ‘mother and one from ‘father’
• When a cell divides by mitosis, it makes two cells identical to the original - contains the same number of chromosomes as the original
• The stage cycle when the cell divides is called mitosis
• Organisms use mitosis to grow or to replace cells that have been damaged

  • Some organisms use mitosis to reproduce - asexual reproduction
• Order of mitosis -

  1. Interphase
  2. Prophase
  3. Metaphase
  4. Anaphase
  5. Telophase
  6. Cytokinesis
• Interphase - the cell is growing and increasing the amount of subcellular structures ie. mitochondria so that the DNA can be duplicated
• Interphase - DNA is copied and forms X-shaped chromosomes

  • Each ‘arm’ of the chromosome is an exact duplicate of the other
  • Arm - called a chromatid
• Prophase -

  • Chromosomes condense (get shorter and fatter)
  • Membrane around the nucleus breaks down and chromosomes lie free in the cytoplasm
• Metaphase -

  • The chromosomes line up at the centre of the cell
• Anaphase -

  • Spindle fibres pull the chromosomes apart.
  • The chromatids are pulled to the opposite ends of the cell
• Telophase -

  • Membranes form around each of the sets of chromosomes
  • These become the nuclei or the two new cells - the nucleus has divided
• Mitosis produces genetically identical daughter cells from one parent cell.
• Meiosis produces haploid gametes with half the number of chromosomes as the diploid parent cell
• Cytokinesis -

  • Part of telophase
  • The cytoplasm and cell membrane divide to form two seperate cells
• To calculate the final number of cells - 2 x the number of cells produced in the first division like 2^n - n being the number of divisions
• Growth - increase in size or mass
• Cell differentiation - the process where a cell changes to become a specialised cell for its job - works more efficiently
• Cell division - by mitosis
• Cell elongation - in plants

  • Plant cells expands, making the cell bigger and so making the plant grow
• Animals -

  • All growth happens by cell division
  • Young - cells divide at a fast rate
  • Old - stop growing so cell division is for repair - to replace old or damaged cells
  • Cell differentiation is lost at an early age
• Plants -

  • Growth in height due to cell elongation - cell division normally just happens in meristems (tips of roots and shoots)
  • Plants grow continuously - continue to differentiate to develop new parts
• Percentile charts -

  • So that an overall pattern in development can be seen and any problems highlighted
  • To make sure it is growing normally/monitor growth
  • Doctors are likely to investigate if a baby’s size is above the top percentile line or below the bottom percentile line, or it their size increases or decreases by 2 or more percentile lines over time, or if there is an inconsistent pattern
• Stem cells differentiate into different types of cells
• Undifferentiated cells = stem cells
• Stems cells can divide by mitosis to become new cells, which then differentiate
• Stem cells are found in early human embryos:

  • Have the ability to divide and produce any kind of cell
• Adult stem cells only produce certain types of cells
• Embryonic stem cells come from embryos and have the potential to turn into all kinds of body cells
• Stem cells are really important for the growth and development of organisms
• Stem cells in adults are only found in places such as bone marrow

  • Aren’t as versatile as embryonic stem cells - can’t produce any cell type at all
  • Used to replace damaged cells
• Meristems contain plant stem cells -

  • Only place where cells can divide by mitosis
  • Found in areas of the plant that are growing e.g. the tips of the roots and shoots
  • Produces unspecialised cells that are able to divide and form any cell type - act like embryonic cells but can divide and differentiate to generate any type of cell for as long as the plant lives
  • Forms specialised tissues ie. xylem and phloem
• Stem cells can be used in medicine

  1. Some adult stem cells used to cure diseases by transplants e.g. sickle cell anaemia
  2. Doctors experimenting with early human embryos and growing stem cells - can be stimulated to differentiate into specialised cells
  3. Might be possible to use stem cells to replace those which have been damaged by disease or injury
• Stem cells used in medicine risks:

  • Rejection - if transplanted cells aren’t grown using patient‘s own stem cells, the patients body may recognise them as foreign and trigger an immune response. Can take drugs to suppress this response - makes them more susceptible to disease
  • Tumour development - uncontrolled division could lead to developments of tumours
  • Disease transmission - viruses live inside cells - virus could be passed on to the recipient and make them sicker
  • Ethical issues: some argue embryos shouldn’t be used because each one is a potential human life