gene expression

• gene mutation: change is base sequence of DNA
• chromosome mutation: change in number of chromosomes caused by non-disjunction
• polyploidy: change in the number of sets of DNA
• aneuploidy: a change in the number of an individual chromosome (3x chromosome 21 causes downs syndrome)
• base substitution: one nucleotide in a section of DNA is replaced by another with a different base
• base deletion: one or more bases are lost from the genetic code, resulting in a frame shift
• base addition: one or more bases added to the genetic code, resulting in a frame shift
• base duplication: one or more bases and up being repeated in the genetic code, resulting in a frame shift
• base inversion: a sequence of bases get separated from the DNA, then are inserted again in the same place but in reverse order
• base translocation: a group of bases are separated from the DNA sequence on one chromosome and inserted into the DNA sequence in another chromosome
• mutagenic agents- things that can increase rate of mutation (chemicals, ionising radiation)
• stem cell- undifferentiated call that can differentiate into different cell types and self renew
• totipotent stem cell: a stem cell that can differentiate into any type of cell --> found in embryo cell and zygotes
• pluripotent stem cells: can differentiate into almost any cell type --> found in foetal cells and inner mass of blastocyst
• multipotent stem cell: stem cells that can differentiate into limited different types of cells
• unipotent stem cell: a stem cell that can only differentiate into one type of cell
• how can we use stem cells?

  research into differentiation

  stem cell transplants (bone marrow- leukaemia)

  developing specialised tissue for transplant (nerve cells- spinal cord)

  developing organs for transplant
• transcription factors: are proteins, they bind to specific section of DNA upstream of the gene (promoter), which either inhibits or stimulares the transcription of a gene
• regulation of gene expression:

  • transcription factors
  • epigenetics
• oestrogen: non-polar and lipid soluble, can diffuse through phospholipid bilayer, bind to receptor molecule inside cell
• how oestrogen effects gene transcription:

  • oestrogen diffuses into the cell by simple diffusion
  • this binds to a receptor molecule inside a cell (transcription factor)
  • the binding of oestrogen causes tertiary structure and shape to change
  • this enters DNA as a transcription factors, as it has been activated
• epigenetics: a heritable change in gene expression that doesn't involve changes to the base sequence
• epigenome: chemical tags attached to the DNA (methyl) and histone proteins (acetyl)
• methylation: methyl groups are added to the DNA, cause DNA to coiled more tightly around histone proteins, making it harder for RNA polymerase to bind
• acetylation: an acetyl group is added into the histone tails, making the DNA coil less tightly around histones, making it easier for RNA polymerase to bind
• RNA interference:

  • virus digests double stranded RNA (dsRNA)
  • digestive enzyme (dicer) digests dsRNA into short interference RNA (siRNA)
  • siRNA loses a strand and combines with digestive enzyme
  • siRNA binds to complementary viral mRNA, enzyme digests the viral mRNA
  • stopping translation of viral mRNA to produce viral proteins
• how hypermethylation of TSG leads to cancer


  hypermethylation is where more methyl groups are added to DNA, causing it to coil more tightly around histone proteins. there is less DNA accessible for transcription so that less RNA polymerase will be able t bind to promoter, TSG is not expressed without this gene, cells grow uncontrollably leading to tumour growing
• proto-oncogene is a gene that can cause cancer if it is mutated
• oncogene is where a proto-oncogene has been permanently switched on
• oncogenes can cause uncontrolled cell growth and division due to growth factor being permanently activated (different gene in different cell).
• tumour suppressor gene (TSG): number of different genes, slow down cell division, repair DNA mistakes. which all help to prevent tumours forming
• mutation of TSG:

  cause genes to be switched off, and rapid growth which can lead to tumours
• menopause- stopping of menstrual cycle, including oestrogen production in ovaries reduced.

  • this oestrogen can activate transcription factors for proto-oncogenes causing uncontrolled cell growth