regulation of gene expression

• A stem cell 


  is a cell that can divide (by mitosis) an unlimited number of times
• • Each new cell that is produced when a stem cell divides has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or a muscle cell (by a process known as differentiation)
  • This ability of stem cells to differentiate into more specialised cell types is known as potency
  • There are three types of potency:
  • Totipotency
  • Pluripotency
  • Multipotency
• Totipotent Stem Cells


  Cells that can divide and produce any type of body cell
• Totipotent cells are also referred to as 'embryonic stem cells'
• Totipotent cells


  • Exist for a limited time in early mammalian embryos
  • Exist in extra-embryonic cells (the cells that make up the placenta)
• Zygote


  The cell formed when a sperm cell fertilises an egg cell, which is totipotent
• Morula


  The 16-cell stage of human embryo development, where the cells are totipotent
• Cell specialisation

  1. Totipotent cells begin to translate only part of their DNA

  2. Specialised cells then form tissues

  3. Cells lose their ability to differentiate into any cell type
• There are no totipotent cells present in the later stages of development
• Pluripotent embryonic stem cells

  • Pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells (the cells that make up the placenta)
  • Pluripotent stem cells can divide in unlimited numbers and keep replacing themselves
  • They can be used in treating human disorders
• somatic cell


  any cell that is not a gamete
• Induced pluripotent stem cells (iPS cells)

  • iPS cells can be produced from adult somatic cells using appropriate protein transcription factors
  • These transcription factors cause specific genes to be expressed which dedifferentiate a cell back to its pluripotent state
  • Each individual can have their own pluripotent stem cell line produced from their body's cells and these could potentially be used to generate transplants without the risk of immune rejection
• Multipotent adult stem cells


  Stem cells that remain in adult tissues and can divide an unlimited number of times, but can only produce a limited range of cell types
• Cell differentiation and specialisation

  1. Cells become more and more specialised as tissues, organs and organ systems develop

  2. Cells gradually lose their ability to divide until they can no longer divide
• Adult stem cells

  • Small numbers remain to produce new cells for growth, cell replacement and tissue repair
  • Can divide by mitosis an unlimited number of times
  • Can only produce a limited range of cell types - they are multipotent
• Multipotent adult stem cells

  • Stem cells found in bone marrow that can only differentiate into blood cells (red blood cells, monocytes, neutrophils and lymphocytes)
• In adults, stem cells can be found throughout the body (eg. in the bone marrow, skin, gut, heart and brain)
• Stem cell therapy


  The introduction of adult stem cells into damaged tissue to treat diseases (eg. leukemia) and injuries (eg. skin burns)
• Unipotent cells

  • Unipotent cells are adult cells that can only differentiate into their own lineage
  • For example, heart muscle cells (cardiomyocytes) can generate new cardiomyocytes through the cell cycle to build and replace heart muscle
  • Most cells in animal bodies are unipotent
• in vitro


  experiment occurring outside normal biological context, e.g. test tube or petri dish
• Multipotent adult stem cells


  Adult stem cells that can divide an unlimited number of times but are only able to produce a limited range of cell types
• Adult stem cells

  • Can divide (by mitosis) an unlimited number of times
  • Are only able to produce a limited range of cell types
• Tissues containing small numbers of adult stem cells

  • Bone marrow
  • Brain
• Adult stem cells

  Remain to produce new cells for the essential processes of growth, cell replacement and tissue repair
• Stem cell therapy


  Introduction of adult stem cells into damaged tissue to treat diseases (eg. leukaemia) and injuries (eg. skin burns)
• The use of adult stem cells is less controversial than embryonic stem cells because the donor is able to give permission
• Donation of adult stem cells

  • Bone marrow donation to help treat leukaemia patients
• If multipotent stem cells are being donated from one person to another they need to be a close match in terms of blood type and other body antigens
• There is a chance that the cells used are rejected by the patient's immune system
• embryonic stem cell

  on the inside of an embryo

  undifferentiated/ unspecialised

  can produce different types of specialised cells in body
• adult stem cells

  • bone marrow- limited specialisation, mainly RBC if immune system
  • skin- limited specialisation, found in different layers of skin, hair follicles
  • organs such as liver or brain- limited specialisation, cells found in organs
  • umbilical cord blood- limited specialisation, cells of blood RBC, WBC, muscle and nerve tissue
• meristem cells


  found in tips of roots and shoots (growing regions of plants)

  fully undifferentiated

  one cell has ability to divide to produce whole new plant
• Induced pluripotent stem (iPS) cells


  Cells developed by scientists using an adult's somatic cells that are unipotent (fully differentiated)
• Producing iPS cells

  1. Scientists use specific transcription factors to target the genes that control pluripotency

  2. Scientists 'switch on' these genes that are usually silenced in differentiated cells

  3. This allows the cells to revert back to pluripotent cells
• iPS cells


  • The resultant pluripotent cells can then be used to produce any type of cell required for repair/treatment of the body
  • Could be used instead of embryonic cells
  • Avoids the ethical issues associated with using embryonic stem cells
• During research on iPS cells

  They have caused tumour formation
• Reason for tumour formation in iPS cells

  Some of the genes switched on will control the cell cycle and its regulation, which if uncontrolled will lead to tumour formation
• uses of stem cells in diabetes and paralysis:

  • diabetes (type 1):
  • pancreas unable to produce insulin to control blood sugar levels
  • stem cells could be differentiated into insulin- produces pancreatic cells which are transplanted into the patients body
  • source from stem cell donors or therapeutic cloning
  • paralysis
  • damage to nerve cells in brain, spinal cord, preventing signals from brain reaching muscles in parts of body
  • stem cells could be differentiated into nerve cells which are transplanted into damaged region of nervous system
  • source from stem cell donors or therapeutic cloning
• transcription factor

  protein that controls transcription of gened by binding to specififc region of DNA
• The structure of a gene

  • 'Upstream' refers to the DNA before the start of the coding region
  • The promoter is a section of DNA upstream of the coding region that is the binding site for proteins that control the expression of the gene, including:
  • RNA polymerase
  • Transcription factors
  • While DNA is translated in the 3' to 5' direction, it is transcribed in the 5' to 3' direction to produce messenger RNA (mRNA)