H human bio unit 1

• A somatic cell is any cell in the body other than cells involved in reproduction
• somatic stem cells divide by mitosis to form more somatic cells
• each somatic cell receives an identical copy of the full set of chromosomes and the diploid chromosome number is maintained
• germline cells are cells which eventually lead to the formation of gametes (sex cells) and are found in the testes and the ovaries
• germline cells include haploid gametes and diploid germline stem cells that divide to form these gametes
• the germline cell can undergo two divisions

  • the first seperates homologous chromosomes
  • the second seperates chromatids
• the 1st division of germline cells

  • germline cells divide by mitosis to produce more germline cells
  • nuclear division by mitosis maintains the diploid (23 homologous pairs) chromosome number
• 2nd division of germline stem cells

  • the nucleus of a germline stem cell can divide again by meiosis to produce haploid gametes which contain only 23 single chromosomes
  • this type of cell division leads to 4 genetically different gametes
• mitosis: a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth

  
• meiosis: a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes

  
• somatic stem cells differentiate into specialised cells that form the different types of body tissue
• cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell
• cellular differentiation allows cells to carry out specialised functions
• there are two main types of stem cells, embryonic stem cells and tissue stem cells
• embryonic stem cells are found in embryos at very early stages of development
• tissue stem cells are found throughout the body, also known as somatic or adult stem cells.
• pluripotent - has potential to develop into any human cell type
• cells in the very early embryo can differentiate into all the cell types that make up the individual and so are pluripotent. All of the genes in embryonic stem cells can be switched on so these cells can differentiate into any type of cell
• tissue stem cells are involved in the growth, repair and renewal of the cells foud in that tissue. Tissue stem cells are multipotent.
• multipotent - can differentiate into many different types of cell (not all)
• tissue stem cells can only give rise to a limited range of cell types closely related to the tissue they are normally located in. This is because many of the genes are already switched off
• an example of tissue stem cells are blood stem cells located in bone marrow and can give rise to red blood cells, platelets, phagocytes and lymphocytes
• therapeutic uses of stem cells involve the repair of damaged or diseased organs or tissues
• examples of therapeutic stem cell treatments are uses in corneal repair and the regeneration of damaged skin (e.g. burn victims)
• the research uses involve stem cells being used as model cells to study how diseases develop or being used for drug testing.
• stem cells from the embryo can self-renew, under the right conditions in the lab
• stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work
• use of embryonic stem cells can offer effective treatments for disease and injury; however, it involves the destruction of embryos
• stem cell research is tightly regulated by laws such as the human fertilisation and embryology act and the human reproductive cloning act
• embryos may only be used for 14 days before being destroyed
• cancer cells divide excessively because they do not respond to regulatory signals. This results in a mass of abnormal cells called a tumour.
• usually when a cell is damaged or old they undergo apoptosis
• apoptosis - programmed cell death
• metastasis - cancer cells lose the molecules on their surface that would normally hold them in place and can therefore be detached from their neighbours.
• cells within a tumour may fail to attach to each other, spreading throughout the body where they may form secondary tumours
• DNA is a double-stranded molecule made up of repeating units called nucleotides
• DNA has 4 bases: adenine, thymine, cytosine and guanine. This means it has four different types of nucleotide
• A strong chemical bond forms between the phosphate group of one nucleotide and the carbon 3 of the deoxyribose on another nucleotide

  
• strands of nucleotides form weak hydrogen bonds between complementary paired bases A-T, C-G

  
• DNA is made up of 2 anti-parallel strands. This means that the strands run in opposite directions to eachother