Whole of Unit/Module 8, control of gene expression for AQA A level Biology based on class notes, specification, textbooks, websites, videos and revision sessions. Summarised into bullet point notes that are quick and to the point with just information you need for the exam.
a unspecialised/undifferentiated cell
potential to form different types of cells
How does a stem cell be come a specialised cell?
differentiation
3 changes: cell shape, number of organelles, new content
occurs by controlling gene expression (some gene are activated, other genes are
inhibited)
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)
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,
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)
making siRNA = 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
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
How does Methylation and Acetylation affect the Genome?
Increased Methylation = adding methyl groups, this attracts proteins which condense the
DNA-Histone Complex so transciption factors cannot gain access (gene inhibited)
Decreased Acetylation = removing acetyl groups, increases positive charges on the
Histone which increases the attraction to the phosphate groups on DNA which condense
the DNA-Histone Complex so transciption factors cannot gain access (gene inhibited)
What is a Gene Mutation?
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