gene expression- stem cells

what is a stem cell/

undifferentiated cells that can divide and differentiate into other specialised cells`

name the 3 types of stem cells

totipotent, pluripotent, multipotent

what is a totipotent stem cell?

only found in first view divisions of a developing embryo. can develop into any cell type

what is a pluripotent stem cell?

in inner layer of cells from blastocyst stage of a developing embryo. can differentiate into any type of cell except placenta/embryo. divide in unlimited numbers

what is a multipotent stem cell

found associated with different organs. can only differentiate into a few different tissue types

what is potency

ability of a stem cell to differentiate

what happens to totipotent cells during embryonic development?

certain parts of the DNA are selectively translated so that only some genes are switched on in order to differentiate the cell into a specific type and form the tissues that make up the foetus.

give a unique feature of pluripotent cells and the use of this feature

they can divide in unlimited numbers, can therefore be used to repair or replace damaged tissue

what is a unipotent cell? give an example

a cell that can only develop into one type of cell. this happens at the end of specialisation when the cell can only propagate its own type. an example is cardiomyocites- heart cells

which types of stem cell are found in embryos?

totipotent and pluripotent. multipotent and unipotent only found in mature mammals

give some uses of stem cells

medical therapies e.g. bone marrow transplants, treating blood disorders. drug testing on artificially grown tissues. research e.g. on formation on organs and embryos

how are pluripotent stem cells produced?

from mature, fully specialised (somatic) cells. the cell regains capacity to differentiate through the use of proteins, in particular transcription factors

what is a transcription factor?

a protein that controls the transcription of genes so that only certain parts of the DNA are expressed, e.g. in order to allow a cell to specialise.

how do transcription factors work? (3)

move from cytoplasm into nucleus. bind to promoter region upstream of target gene. makes it easier or more difficult for RNA polymerase to bind to  gene- this increases/decreases rate of transcription

give an example of a hormone that affects transcription and explain how it works.(3)

steroid hormone oestrogen diffuses through cell membrane. forms hormone-receptor complex with ER a receptor in the cytoplasm. complex enters the nucleus and acts as a transcription factor to facilitate binding of RNA polymerase