Module 8: Genes Flashcards
stem cell definition
unspecialised/undifferentiated cell
potential to form different types of cells
how can a stem cell become specialised
differentiation
3 changes: cell shape, number of organelles, new content
occurs by controlling gene expression (some genes are activated and some are inhibited)
3 changes a stem cells needs to make to become specialised
cell shape
number of organelles
new content
stem cells in animals/mammals/humans
totipotent
pluripotent
multipotent
unipotent
totipotent
zygote
pluripotent
embryonic stem cells
multipotent
bone marrow stem cell
unipotent
tissues
what does iPS stand for
Induced Pluripotent Stem cells
what are induced pluripotent stem cells?
turning unipotent body cells into pluripotent cells (like embryonic stem cells), involves activating certain deactivated genes using transcription factors
What are the uses of stem cell therapy in humans
Use stem cells to produce tissues/organs for transplant
Use stem cells to treat irreversible diseases (inject stem cells at the site of disorder- will differentiate to become local specialised cells)
Stem cells 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 the presence of meristem cells Tissue culture (micro propagation)= large scale application of cuttings
Process of taking cuttings from a plant
Take cutting from shoot/stem/root (explant)
Place explant in the nutrient rich medium so meristem cells divide by mitosis
Produces a mass of meristem cells (callus)
Take each meristem cell and grow in a 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 a gene
Activating= protein made
Inhibiting= protein not made
Example of activating gene
Using oestrogen
Can enter a cell by simple diffusion and bind to receptors on the transcriptional factor
Causes transcriptional factor to change shape
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) Making siRNA= double stranded RNA cut down into small sections, made single stranded, then attaches to an enzymes Will then bind to complementary sections on mRNA= the enzyme will cut the mRNA so translation can’t occur- gene inhibited (protein not made)
What is epigenetics
Heritable changes in gene function without changes to the base sequence of DNA
Changes may occur due to stress, lifestyle or diet
Chromatin and epigenome
What is chromatin
DNA- histone complex
What is an epigenome
Chemical layer
Chromatin and epigenome
Chromatin is surrounded by an epigenome
The epigenome can either cause the chromatin to become more condensed or more loose
More condensed= transcription factors can’t reach the DNA and the gene will become inactivated
More loose= transcription factors can reach the DNA and the genes will be activated
Changes may be brought about by acetylation or methylation
How does methylation affect the genome
Increased methylation= Adding methyl groups This attracts proteins Condensed the DNA-Histone complex Transcription factors can’t gain access Gene inhibited
How does acetylation affect the genome
Decreases acetylation=
Removing acetyl groups
Increases positive charges on the histone
Increases the attraction to the phosphate group on DNA
Which condense the DNA-Histone complex
Transcription factors can’t gain access
Gene inhibited
Gene mutation definition
A change in the base sequence of DNA
2 types of gene mutations
Substitution
Insertion/deletion
Substitution
Gene mutation
Replaces one base for another, changes one triplet code
(Can be silent, mis-sense or non-sense)
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 cmon so polypeptide chain not produced