Control of Gene Expression- BP Flashcards
What is a stem cell?
a unspecialised/undifferentiated cell
potential to form different types of cells
How does a stem cell become specialised?
differentiation
3 changes: cell shape, number of organelles, new content
occurs by controlling gene expression (some gene are activated, other genes are inhibited)
Stem Cell in Animals/Mammals/Humans?
- embryonic
- umbilical cord blood stem cells
- placental stem cells
- adult stem cells
What are Induced Pluripotent Stem Cells (iPS Cells)?
- turning unipotent body cells into pluripotent cells (like embryonic stem cells)
- involves activating certain deactivated genes using transcription factors
Stem Cell Therapy in Humans? (2 uses)
use stem cells to produce tissues/organs for transplant
use stem cells to treat irreversible diseases e.g. heart disease, type 1 diabetes, paralysis (inject stem cells at site of disorder – will differentiate to become local specialised cells e.g. heart muscle cells, beta cells of pancreas, neurones)
what is a totipotent stem cell?
- found in the early embryo
- can differentiate into any type of cell
what is a pluripotent stem cell?
- found in embryos
- can differentiate into almost any type of cell
what is a multipotent stem cell?
- found in adults
- can differentiate into a limited number of specialised cells
- eg. adult stem cells and umbilical cord blood stem cells
what are unipotent stem cells?
- can only differentiate into a single type of cell
- derived from multipotent stem cells
- made in adult tissue
- eg. cardiomyocytes
Stem Cell in Plants?
In embryo = Zygote/Embryonic Stem Cells
In adult = Meristem Cells in Stem/Shoot/Root
Uses of Stem Cells from Plants?
traditionally cuttings were taken from plants (stem/shoot/root) and used to grow genetically identical plants – possible due to presence of meristem cells
tissue culture (micro propagation) = large scale application of cuttings
process of growing genetically identical plants?
take cutting from shoot/stem/root (called explant)
place explant in nutrient rich medium so meristem cells divide by mitosis
produces a mass of meristem cells (called callus)
take each meristem cell and grow in plant growth factor medium to promote differentiation and formation of shoot/root
transfer plant to soil and greenhouse
then transfer to field
what is controlling gene expression?
either Activating or Inhibiting a Gene
activating gene = protein made
inhibiting gene = protein not made
Example of activating genes? (using oestrogen)
oestrogen can enter a cell by simple diffusion and bind to receptors on the transcriptional factor
causes transcriptional factor to change shape
so transcriptional factor can now enter nucleus and bind to promoters on the DNA to activate transcription
= activated genes (protein to be made)
Example of inhibiting genes?
- using siRNA (small interfering RNA)
- double stranded RNA cut down into small sections
- made single stranded
- then attaches to an enzyme
- siRNA will bind to complementary sections on mRNA
- the enzyme will cut the mRNA so translation cannot occur
- gene inhibited (protein not made)
What is Epigenetics?
Heritable changes in gene function without changes to base sequence of DNA
Changes may due to lifestyle, stress, diet
How does Methylation affect the Genome?
Increased Methylation :
- adding methyl groups
- this attracts proteins which condense the DNA-Histone Complex
- transcription factors cannot gain access (gene inhibited)
What is a Gene Mutation?
a change in the base sequence of DNA
2 types = substitution and insertion/deletion
what is subsitution?
- substitution = replace one base for another, changes one triplet code
- can be silent (new triplet code codes for same AA), mis-sense (codes for a different AA, so protein shape changes slightly), non-sense (codes for a stop codon, so polypeptide chain not produced)
where are stem cells found in plants?
meristems
what is the epigenome and what does it determine?How?
Chromatin (DNA-Histone Complex) is surrounded by an Epigenome (chemical layer)
Epigenome can either cause the Chromatin to become more condensed or more loose
Chromatin becoming more condensed means transcription factors cannot reach the DNA and the gene will be inactivated
Chromatin becoming more loose means transcription factors can reach the DNA and the gene will be activated
These changes may be brought about by Acetylation or Methylation
Cancer?
caused by mutation of genes that control cell division
causes of mutation = random or mutagens (chemicals/radiation)
mutation of proto-oncogene leads to formation of a oncogene = over production of growth factor or receptor proteins permanently active = over stimulation of cell division (uncontrolled cell division)
mutation of tumour-suppressor gene = loss of protein to inhibit cell division (uncontrolled cell division)
Oestrogen and Cancer?
Oestrogen leads to activation of genes – high levels of oestrogen can lead to over activation of Proto-Oncogene forming an Oncogene = Cancer (uncontrolled cell division)
Oestrogen and Cancer?
Oestrogen leads to activation of genes – high levels of oestrogen can lead to over activation of Proto-Oncogene forming an Oncogene = Cancer (uncontrolled cell division)
Epigenetics and Cancer?
Main Example = increased methylation of tumour suppressor genes leads to inhibition of tumour suppressor genes leading to cancer (uncontrolled cell division)
How does Acetylation affect the Genome?
Decreased Acetylation:
- removing acetyl groups
- increases positive charges on the Histone
- increases the attraction to the phosphate groups on DNA
- condense the DNA-Histone Complex
- transcription factors cannot gain access (gene inhibited)
