Chromosomes, mitosis and stem cells

• All plant and animal cells are eukaryotic which means that they have a nucleus that controls the activities of the cell.
• The nucleus contains long structures called chromosomes that are made of DNA
• What is DNA?


  Also known as deoxyribonucleic acid. It is a polymer made up of two strands that bond together to form a double helix
• A short section of DNA that controls a characteristic is called a gene. Each chromosome is made up of many genes
• How many chromosomes does each body cell of a human contain?

  46
• There are 23 matching pairs of chromosomes in a human body cell
• One chromosome from each pair is inherited from each parent, meaning that every person has two copies of each gene
• What is a sex cell?

  Sperm cells in human males and egg cells in human females which are called gametes
• How many chromosomes are found in sex cells?

  Half of the chromosomes found in the body so 23 in humans.
• Why do sex cells only have half of the chromosomes than in the body cells?

  As everyone inherits half of their DNA from their mother and half from their father
• Everyone has a unique set of DNA meaning DNA can be used to identify people. However identical twins are the only people in the world that do not have unique DNA
• What is mitosis ?

  The process of making new body cells
• New body cells are needed for growth and repair. They are made by a form of cell division called mitosis which is part of the cell cycle
• What are the three stages of the cell cycle?

  • Cell grows, more mitochondria and ribosomes are made. DNA is copied
  • Mitosis where the nucleus divides and chromosomes separate onto opposite sides of the cell
  • Cell division where the cell membrane and cytoplasm divides producing two genetically identical cells
• Why is mitosis important for growth and development?

  It allows a single fertilised egg cell to develop into a multicellular organism. It produces new body cells for growth and repair.
• How do you calculate how long a cell cycle stage lasts?

  Fractional of cells X time
• What are stem cells?

  Unspecialised cells with the potential to become any type of cell
• Stem cells can divide by mitosis to produce more stem cells, or can differentiate into specialised cells
• What are three sources of stem cells?

  • Embryonic stem cells (religious objections)
  • Adult bone marrow (only become blood cells)
  • Meristem tissue in plant stems (only become plant cells)
• Why are stem cells useful?

  If the spinal cord is damaged in an accident, it can lead to permanent paralysis. If stem cells could be used to replace potentially damaged never tissue, then the paralysis could potentially be reversed
• How would stem cells repair paralysis?

  • Spinal cord is broken so no information can pass between the brain and legs
  • Stem cells can be injected into the bottom of the spine
  • Stem cells will differentiate into new neurones and the spinal cord re joins
• What is therapeutic cloning?

  In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are genetically identical so are not rejected by the body and can be useful in medical treatment
• What happens in therapeutic cloning?

  • From a patients body cell the nucleus is extracted
  • A nucleus is removed from an egg cell from a donor
  • An electric shock is used to insert a patients DNA into an egg cell
  • By mitosis an embryo of stem cells is made, genetically identical to the the patient
• What are three problems with stem cells?

  • Risk of rejection
  • Risk of infection ( passing on pathogens when stem cells are injected)
  • Ethical objections (e.g religious groups who believe destroying an embryo destroys a life)
• What are the benefits of using stem cells?

  • Can treat a wide variety of diseases from diabetes and paralysis
  • Organs developed from a patient’s own stem cells reduces the risk of organ rejection