Division and Differentiation in Human Cells Flashcards
What is a somatic Cell
A somatic cell is any type of cell in the human body except cells involved in reproduction
Division of Somatic Stem Cells
They divide during tissue repair. Each somatic stem cell contains 46 chromosomes and is diploid prior to mitosis, the genetic material undergoes DNA replication and becomes doubled in quantity for a brief time.
Germline Cells
Germline cells are the cells involved in reproduction. They include haploid gametes and the diploid cells that divide to form these gametes
Division of Germline stem cells
Diploid Germline stem cells first divide by mitosis. The nucleus of each of these cells contain 23 pairs of homologous chromosomes and this genetic material becomes doubled by DNA Replication, following mitosis each identical diploid germline cell formed receives 23 pairs of homologous chromosomes and the chromosome number is maintained.
Each of these diploid Germline stem cells then undergoes a second form of nuclear division called meiosis. This involves a further doubling of the genetic material followed by 2 rounds of nuclear division. The first round separates the homologous chromosomes; the second separates the chromatids. The result is the formation of 4 haploid gametes
Differentiation in human cells
Embryonic cells possess all the genes for constructing the whole organism. However, unlike those in adult cells, all the genes in cells at this early stage are switched on or have potential to be switched on. The unspecialised cells of the early embryo undergo differentiation and become specialised in structure and biochemical properties, making them perfectly adapted for carrying out a particular function
Selective Gene Expression
Once a gene becomes differentiated, it only expresses the genes that code for the proteins characteristic of that particular type of cell.
Stem Cells
Stem cells are unspecialised cells that can:
.Reproduce themselves by repeated mitosis and cell division whole remaining undifferentiated and unspecialised.
.Differentiate into specialised cells when required to do so by the multicellular organism that possesses them.
Embryonic Stem Cells
All of the genes in an embryonic cell have the potential to be switched on, so the cell is capable of differentiating into almost all of the cell types found in the human body. Because of this ability they are described as being PLURIPOTENT
Tissue Stem Cells
Tissue stem cells are found in locations such as skin and red bone marrow. They have a much narrower differentiation potential than embryonic stem cells because many of their genes are already switched off. Tissue stem cells can only give rise to a limited range of cell types closely related to the tissue in which they are normally located, however the are involved in the growth, repair and renewal of all the cell types found in that particular tissue and therefor described as being MULTIPOTENT
Models
A model organism is one that is suitable for laboratory research because it’s biological characteristics are similar to those of a group of related organisms.
Stem cells can be used in research as model cells to investigate:
- The means by which certain diseases and disorders develop
- The responses of cells to new pharmaceutical drugs
Therapeutic use of stem cells
- Cornea Repair
- Skin Graft
- Bone Marrow Transplant
Ethical Issues
The use of stem cells raises several ethical issues. For example, the extraction of human embryonic stem cells to create a stem cell line for research purposes results in the destruction of the human Embryo.
Ethical issues are also raised by the use of induced pluripotent stem cells and by the use of nuclear transfer technique.
Cancer Cells
A cancer is an uncontrolled growth of cells. Cell division in normal healthy cells is controlled but factors such a cell cycle regulators and external chemical signals. Cancerous cells do not respond to these regulatory signals.
Tumours
Cancer cells divide uncontrollably to produce a mass of abnormal cells called a tumour. A tumour is described as benign if it remains as a discrete group of abnormal cells in one place within an otherwise normal tissue. A tumour is said to be malignant if some of its cells lose the surface molecules that keep them attached to the original cell group, enter the circulatory system and spread through the body.
Genetic errors
Most cancers originate for a cell that has undergone a succession of mutations to the genes involved in the control of cell division. As these genetic errors accumulate, a point is reached where control of cell division is lost.
Agents that cause genetic damage:
- Smoking
- pollution
- Skin exposure to UV radiation
