Summary AQA A LEVEL BIOLOGY CHAPTER 20 GENE EXPRESSION NOTES
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Course
Unit 8 - The control of gene expression
Institution
AQA
I created these notes throughout y12&13 and used them for my A level 2022 exams. I got a grade 9 in GCSE and am awaiting for my a level biology result. These notes were made using the CGP revision guide, AQA Biology textbook and class notes in order to cover everything in the course. I have also ad...
20.1 GENE MUTATION
Saturday, 5 February 2022
21:11
Gene mutation - Change to one or more nucleotide bases or the arrangement of
bases.
Inversion mutation - A group of bases become separated from the DNA sequence
and rejoin at the same position but in the inverse order.
Duplication - One or more bases are repeated, producing a frame shift to the right.
Translocation of bases - A group of bases become separated from the DNA sequence
of one chromosome and become inserted into a DNA sequence of a different
chromosome.
Gene mutations can arise spontaneously during DNA mutations.
Spontaneous mutations are permanent changes in DNA without any outside
influence.
Mutagenic agents can increase the rate of mutations.
● High energy ionising radiation can disrupt the structure of DNA.
● Chemicals such as NO2 which can directly alter the structure of DNA or
interfere with transcription.
, 20.2 STEM CELLS & TOTIPOTENCY
Saturday, 5 February 2022
22:14
Differentiation - Cell develops into a specialised structure suited to the role that it
will carry out.
Stem cells are unspecialised dividing cells which can differentiate into specialised
cells.
Totipotent stem cells can differentiate into any type of body cell.
● Fertilised eggs or early cells derived from the fertilised egg are totipotent.
For a cell to become specialised, certain genes are needed to be expressed as they
only need to produce the specific proteins needed to carry out its specialised
function.
● Only part of the DNA is translated into proteins and are expressed, the other
genes are silenced.
● These proteins can determine the cell structure and control cell processes.
There are stem cells in some adult tissues that differentiate into specialised cells
which need to be replaced.
In most animal cells, cell specialisation is irreversible.
● Adult stem cells constantly need to be replaced, and so can divide to form an
identical copy of themselves. This is self-renewal.
Plants have many totipotent cells which retain the ability to differentiate again after
specialisation.
● Plants can be cloned by taking cuttings and tissue culture techniques.
There are various stem cell sources in mammals:
● Embryonic stem cells.
● Umbilical cord stem cells.
● Placenta stem cells.
● Adult stem cells found in body tissues.
Totipotent stem cells - Found in early embryo and can differentiate into any cell.
● All body cells are formed from a zygote, so zygote said to be totipotent.
Pluripotent stem cells - Found in the embryo and can differentiate into almost any
cell.
Multipotent stem cells - Found in adults and can differentiate into a limited number
of specialised cells.
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