1.1 - 1.4

• Germline cells are gametes (sperm and ova) and the stem cells that divide to form gametes.
• 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
• Germline stem cells divide by mitosis and by meiosis.
• Somatic cells are non-sex cells. meaning they make up all the cells in the human body except the reproductive cells (gametes).
• Somatic cells are the differentiated cells that form the different types of human body tissue such as skin, bones and blood.
• somatic cells in the body contain a diploid number of chromosomes and can undergo mitosis giving rise to daughter cells.
• Germline cells are cells that divide by mitosis and meiosis.
• The nucleus of a germline stem cell can divide by mitosis to produce identical diploid stem cells containing 23 pairs of homologous chromosomes.
• The nucleus of a germline stem cell divides by meiosis and produces haploid gametes.
• Cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell. This allows a cell to carry out specialised functions.
• Cells in the very early embryo can differentiate into all the cell types that make up the individual and so are pluripotent.
• All the genes in embryonic stem cells can be switched on so these cells can differentiate into any type of cell.
• Tissue stem cells are multipotent as they can differentiate into all of the types of cells found in a particular tissue type.
• Examples of multipotent stem cells differentiating are: blood stem cells located in bone marrow can give rise to red blood cells, platelets, phagocytes, and lymphocytes.
• Tissue stem cells are involved in the growth, repair and renewal of the cells found in that tissue. They are multipotent.
• Therapeutic uses of stem cells involve repairing damaged or diseased organs or tissues. Therapeutic uses are exemplified by their use in corneal repair and the regeneration of damaged skin.
• Stem cells from the embryo can self-renew, under the right conditions, in the lab.
• Research uses involve stem cells being used as model cells to study how diseases develop or being used for drug testing
• Use of embryonic stem cells can offer effective treatments for disease and injury; however, it involves destruction of embryos.
• embryonic stem cell research poses a moral dilemma. it forces us to choose between two moral principles being the duty to prevent or alleviate suffering and also the duty to respect the value of human life.
• Cancer cells divide excessively because they do not respond to regulatory signals. This results in a mass of abnormal cells called a tumor.
• Cells within the tumour may fail to attach to each other, spreading through the body where they cause secondary tumours.
• A DNA nucleotide is made from a deoxyribose sugar, phosphate group, and nitrogenous base.

  
• The 5' and 3' designations refer to the number of carbon atoms clockwise from the oxygen to the phosphate group.

  
• DNA has a double helix shape
• The two strands of DNA are anti-parallel structures.
• The base pairings are described complimentary. the base pairings are Adenine - Thymine and Cytosine - Guanine.
• The base sequences of DNA forms the genetic code
• DNA replication is a semi-conservative process. this means that wen DNA is replicated, each newly replicated molecule has an original parental strand and a new synthesised strand
• For DNA replication to occur the nucleus must contain an original DNA, Primers, free nucleotides, DNA polymerase, Ligase, and ATP.
• DNA polymerase can only add nucleotides in one direction resulting in the leading strand being replicated continuously and the lagging strand being replicated discontinuously in fragments.
• DNA replication occurs at several locations. Many replication forks operate simultaneously to speed up the process.
• Step 1 of DNA replication: the double helix is unwound
• Step 2 of DNA replication: DNA unzips to form two template strands - hydrogen bonds between bases are broken.
• Step 3 of DNA replication: DNA primers attach to the strands showing where DNA polymerase to attach itself to
• Step 4 of DNA replication: DNA polyerase attached the free nucleotides to the 3' strand of the template DNA to be copied. At least 2 primers are required - one for each strand.
• Step 5 of DNA replication: Primers attach along the length of the lagging strand - they are extended by DNA polymerase from their 3' end
• Step 6 of DNA replication: The fragments along the lagging strand are joined together by the enzyme ligase - this is a discontinuous process as it happens in fragments.
• Step 1 of PCR: The DNA is heated at between 92-98 °C. This causes the DNA to denature and the strands to seperate.