Gene Expression

• What is a stem cell?

  Undifferentiated cells, that can divide indefinitely and turn into other specific cell types.
• Name and define the 3 types of stem cell?

  1. Totipotent - can develop into any cell type including placenta and embryo
  2. Pluripotent - can develop into any cell type excluding placenta and embryo
  3. Multipotent - can only develop into a few different types of cells
• What happens to totipotent cells during embryonic development?

  • Certain parts of DNA are selectively translated
  • In order to differentiate the cell into a specific type
• Give a unique feature of pluripotent cell and the use of this feature?

  They can divide in unlimited numbers, and can therefore be used to repair or replaced damaged tissue
• What is a unipotent cell and give an example?

  • A cell that can only develop into one type of cell
  • Cardiomyocytes (heart cells)
• Which types of stem cells are found in embryos?

  • Totipotent and pluripotent
  • Multipotent and unipotent cells are only found in mature mammals
• Give some uses of stem cells?

  • Medical therapies
  • Drug testing on artificially grown tissues
  • Research
• How are induced pluripotent cells produced?

  • From mature, fully specialised cells
  • The cell can differentiate through the use of proteins
• What is a transcription factor?

  A protein that controls the transcription of genes so that only certain parts of the DNA are expressed
• How do transcription factors work?

  1. Move from the cytoplasm into the nucleus
  2. Bind to promoter region upstream of DNA
  3. Makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases rate of transcription.
• Give an example of a hormone that affects transcription and explain how it works?

  1. Steroid hormone oestrogen diffuses through cell membrane
  2. Forms hormone-receptor complex with ER and receptor in the cytoplasm
  3. Complex enters the nucleus & acts as transcription factor to facilitate binding of RNA polymerase
• What is meant by epigenetics?

  A heritable change in gene function without change to base sequence of DNA
• How does increased methylation of DNA affect gene transcription?

  Prevents transcription factors from binding. Therefore gene transcription is suppressed.
• How does decreased acetylation of histones affect gene transcription?

  Binding becomes too tight and prevents transcription factors from accessing the DNA. Therefore gene transcription is suppressed.
• How might epigenetics changes affect humans?

  They can cause disease, either by over activating a gene's function (such as in cancer) or by suppressing it.
• Give an application of epigenetics?

  • Treatments of various diseases
  • Development of ways to reverse epigenetic changes
• Describe the process of RNA interference, including the organisms in which it occurs?

  RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated. Occurs in eukaryotes and some prokaryotes.
• Give some characteristics of benign tumours?

  • Slow growth
  • Cells retain function and normal shape
  • Don't spread easily
  • Easy to treat
  • Defined by a clear boundary due to cell adhesion molecules
• Give some characteristics of malignant tumours?

  • Rapid, uncontrollable growth
  • Ill-defined boundary
  • Cells do not retain function and often die
  • Spreads quickly and easily (metastasis)
  • Difficult to treat
• Describe the role of tumour suppressor genes?

  • Code for proteins that control cell division
  • Stop the cell cycle when damage is detected
  • Involved in programming apoptosis
• Explain how tumour suppressor genes can be involved in developing cancer?

  • Mutation in the gene could code for a nonfunctional protein
  • Increased methylation or decreased acetylation could prevent transcription
  • Cells will divide uncontrollably resulting in a tumour
• Describe the role of proto-oncogenes?

  • Control cell division
  • Code for proteins that stimulate cell division
• Explain how proto-oncogenes can be involved in developing cancer?

  • Mutation in the gene could turn it into a permanently activated oncogene
  • Decreased methylation or increased acetylation can cause excess transcription
  • Resulting in uncontrollable cell division and formation of a tumour
• Explain how abnormal methylation of genes can cause cancer?

  Hyper-methylation of tumour suppressor genes or oncogenes can impair their function and cause the cell to divide uncontrollably
• Explain how oestrogen can be involved in developing breast cancer?

  Oestrogen is an activator of RNA polymerase. In areas of high oestrogen concentration (adipose tissue in the breasts) cell division can become uncontrollable