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?

can differentiate into any type of cell except placenta/embryo.

divide in unlimited numbers

from inner layer of cells from blastocyst stage of developing embryo.

what is a multipotent stem cell

can only differentiate into a few different tissue types

found associated with different organs.

what is potency

ability of a stem cell to differentiate

what happens to totipotent cells during embryonic development?

DNA selectively translated- only some genes switched on, so cell can differentiate into specific type + form 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.

happens at the end of specialisation when cell can only propagate its own type. e.g. 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 of organs/embryos

what are pluripotent stem cells produced from?

why can they differentiate?

mature, fully specialised (somatic) cells, regain capacity to differentiate by using transcription factors

what is a transcription factor?

protein that controls transcription of genes so only certain parts of DNA are expressed, e.g. ito 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/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 nucleus, acts as a transcription factor, facilitate binding of RNA polymerase

where to find unipotent stem cells?

often found in organs

how are stem cells useful?

medicine, particularly transplants- prevents rejection since own tissues are used. human stem cells grown in vitro can be used to test the effects of new drugs without harming humans/animals

what are 3 sources of stem cells?

embryonic- e.g. unused embryos from IVF.

adult stem cells- extracted from body tissues

induced pluripotent stem cells- specialised adult somatic cells

what is the process of making an induced pluripotent stem cell? (iPS)

take genes active only in stem cells, not in differentiated cells

introduce 4 back into differentiated cells (multipotent from bone marrow),

makes them behave like stem cells

the 4 genes switch on genes that were shut down during differentiation

transcription factors activate genes

give some advantages of iPS (induced pluripotent stem cells)

unlimited- however limited supply of embryonic

no embryo used so no ethical issues

no immune response if ips from own body

no rejection of tissue so immunosuppressant not needed

what is therapuetic cloning

stem cells can be grown for the purpose of using them therapeutically (in treatments) e.g. muscular degeneration uses retina cells

what are the potential uses of embryonic stem cells?

treat genetic diseases- stem cells with normal genes- not their own- used to treat tissues effected by the disorder

issues with embryonic stem cells

rejection

can grow uncontrollably- mass of cells = tumour

could develop cancer as cells metastasise

ethical issues

describe two defining features of stem cells

self-renewal- ability to maintain an unspecialised state

potency- ability of a stem cell to differentiate

where can we find plant stem cells?

from meristem- contains many rapidly dividing undifferentiated cells. found behind tip of growing shoot, root, cambion

what does meristem tissue contain?

totipotent cells

what are in vitro plant cells (tissue culture)

can be induced to undifferentiated cells and redifferentiate into whole plants

need nutrients/plant growth regulators

used to clone plants

what is the cambium?

tissue layer, provides partially differentiated cells for plant growth, found between xylem and phloem

give 2 advantages and 1 disadvantage of cloning plants

offspring are genetically identical meaning less variation

achieve consistently high yield that are resistant to pests and pathogens.

new disease could cause death of whole crop

suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues.

greater blood supply to damaged areas

more O2 brought for respiration

blood also brings amino acids for protein synthesis to repair tissues