Stem Cells And Differentiation Flashcards
What is a totipotent stem cell
Totipotent cells in humans are the zygote which has the potential to form all of the 216 different cell types needed for an entire new person
What takes place in the early stages of development
The first stage of embryonic development is known as cleavage. This is a special kind of mitosis where cells divide repeatedly without normal interphase for growth between divisions. The result is a mass of small identical and undifferentiated cells forming a hollow sphere known as a blastocyst. This process takes 5-6 days and it takes place as the zygote is moved along the oviduct towards the uterus. One large zygote cell forms a large number of small cells in the early embryo known as embryonic stem cells. By the time the blastocyst is formed the cells in the inner layer are no longer totipotent the inner layer is now said to be pluripotent
What are stem cells
Stem cells are undifferentiated cells that have the potential to develop into many different types of specialised cells from the instructions in their DNA
What are pluripotent stem cells
Cells which can form almost all of the cell types needed in the future but not tissue like the placenta
What happens as embryonic stem cells develop
They will become more specialised as the embryo develops e.g forming blood stem cells which gives rise to blood cells
What are umbilical cord stem cells
The blood that drains from the placenta and umbilical cord after birth is a rich source of pluripotent stem cells. If frozen and stored in theory those stem cells will be available throughout the life of the child. However this would be expensive and would require storage space
What are adult stem cells
Some adult stem cells remain as undifferentiated cells in a tissue or organ. They can differentiate when needed to produce any one of the major cell types found in that particular tissue or organ. Another term for adult stem cells is somatic stem cells. There’s only a very small number of adult stem cells in each different tissue and they only form a very limited range of stem cells. They are said to be multipotent
What are multipotent stem cells
A cell that can form a very limited range of differentiated cells within a mature organism
How are different cell types formed in development
Cell determination is closely linked to the position of the cells in the embryo. If cells are surgically removed from the embryo and grown on they will still produce the predetermined cell unless they are in the very earliest stages
What are some of the epigenetic control mechanisms
- Histone acetylation appears to activate the gamma globin gene in the fetus
- dna methylation appears to play a major role in silencing the fetal gamma globin just before and after birth
- histone methylation has the same affect as dna methylation
- a number of transcription factors have been shown to be key in the switch to the production of beta globin in the spleen and bone marrow as the fetus approaches full term
How does DNA methylation work
This is the addition of a methyl group where the cytosine occurs next to the guanine in the DNA chain. It is added by using the DNA methyltransferase enzyme and DNA methylation can modify the structure of his tones. There is also DNA demetnylation which is the removal of the methyl group
What factors affect the modification of histones
Histone acetylation - where an acetyl group is added which opens up the structure and activates the chromatin allowing genes to be transcribed
Histone methylation - where a methyl group is added and can cause inactivation of the DNA a or activation of a region
What is epigenetics
Genetic control by factors other than the base sequences on the DNA
