Gene Expression Flashcards
what is a stem cell
undifferentiated cells, that can divide indefinitely and turn into other specific cell types
name and define the three types of stem cell
- totipotent = can develop into any cell type including the placenta and embryo
- pluripotent = can develop into any cell type excluding the placenta and embryo
- multipotent = can only develop into a few different types of cell
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 and can therefore be used to repair or replace damaged tissue
what is a unipotent cell
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
which types of stem cell are found in embryos
totipotent and pluripotent
multipotent and unipotent are only found in mature mammals
give some uses of stem cells
- medical therapies
- drug testing on artificially grown tissues
- research
how are induced pluripotent stem cells produced
from mature, fully specialised (somatic) cells
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
- move from the cytoplasm into nucleus
- bind to promoter region upstream of target gene
- makes it easier or more difficult for RNA polymerase to bind to gene. the increases or decreases rate of transcription
give an example of a hormone that affects transcription and explain how it works
- steroid hormone oestrogen diffuses through cell membrane
- forms hormone-receptor complex with ER alpha receptor in the cytoplasm
- complex enters the nucleus and acts as transcription factor to facilitate binding of RNA polymerase
what is meant by epigenetics
heritable change in gene function without change to the base sequence of DNA
how does increased methylation of DNA affect gene transcription
involves addition of a CH3 group to cytosine bases which are next to guanine.
prevents transcription factors from binding therefore transcription is suppressed
how does decreased acetylation of histones affect gene transcription
- positively charged histones bind to negatively charged DNA
- decreasing acetylation increases positive charge of histones
- binding becomes too tight and prevents transcription factors from accessing the DNA, therefore gene transcription is suppressed
how might epigenetic changes affect humans
they can cause disease, either by over activating a gene’s function (such as cancer) or by suppressing it
give an application of epigenetics
- treatment of various diseases
- development of ways to reverse epigenetic changes
describe the process of RNA interference, including the organisms in which it occurs
- RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated.
- occurs in eukaryotes and some prokaryotes
characteristics of benign tumours (5)
slow growth
defined by a clear boundary due to cell adhesion molecules
cells retain function and normal shape
don’t spread easily
easy to treat
characteristics of malignant tumours (5)
- rapid, uncontrollable growth
- ill-defined boundary
- cells do not retain function and often die
- spreads quickly and easily (metastasis)
- difficult to treat
describe the role of tumor-suppressor genes
- code for proteins that control cell division; in particular, stopping the cell cycle when damage is detected.
- they are also involved in programming apoptosis
explain how tumour-suppressor genes can be involved in developing cancer
- a mutation in the gene could code for a nonfunctional protein
- increased methylation or decreased acetylation could prevent transcription
- cells divide uncontrollably resulting in a tumour
describe the role of proto-oncogenes
- control cell division
- code for proteins that stimulate cell division
explain how proto-oncogenes can be involved in developing cancer
- mutation in the gene could turn it into a permanently activated oncogene
- decreased methylation or increased acetylation can cause excess transcription
- results in uncontrollable cell division and formation of a tumour
explain how abnormal methylation of genes can cause cancer
hyper-methylation of tumour-suppressor genes or oncogenes can impair their function and cause the cell to divide uncontrollably
