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Summary AQA A level Biology Paper 2 Topic 8 notes
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A detailed summary of the AQA A level Biology paper 2 topic 8 which has been edited to learn help the content and the mark scheme too.
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🌿T8: control of gene expression
mutations
what are the 3 mutations we already know?
-addition= causes frameshift
-deletion= causes frameshift
-substitution
what are the 3 new mutations?
-duplication= addition of the previous or next base
-inversion= when a codon is inverted
-translocation= sequence of bases have moved from 1 location in the
genome to another which could be within the same chromosome or a
different one
what are three types of point mutations?
-silence= no effect on protein sequence
-missense= results in amino acid substitution
-nonsense= substitutes amino acid with stop codon
stem cells
what is a blastocyst?
-ball of cells consisting of an outer layer with an inner cell mass which
is pluripotent
-formed 3-8 days after fertilisation
what is a stem cell?
-undifferentiated dividing cells in adult tissues
what does totipotent mean?
-cells which can differentiate into any other type of cell
T8: control of gene expression 1
, what does pluripotent mean?
-found in embryos and can differentiate into almost any other cell
what does multipotent mean?
-found in adults and can differentiate into a limited number of
specialised cells
what does unipotent mean?
-can differentiate into 1 type of cell
what are induced pluripotent stem cells?
-unipotent stem cells turned into pluripotent stem cells using proteins
regulation of transcription and translation
what is a transcription factor and its role?
-regulatory proteins
-regulate (turn on or off) genes to ensure theyre expressed in right cell
at right time in right amount
how do they work?
1- gene that codes for required protein is stimulated by a specific
transcription factor (TF)
2- there are many TFs and they all have a DNA binding site that is
specific to a certain gene
3- after it binds to the correct region of DNA transcription begins
4- this then produces mRNA which is translated into a protein
what happens when the gene isnt expressed?
-DNA binding site on complementary TF is blocked
-inhibitor stops TF from binding to DNA so no transcription
how does oestrogen initiate transcription?
1- oestrogen diffuses across the cell membrane as its lipid soluble
2- oestrogen binds to a complementary receptor on surface of a TF
3- DNA binding site on the TF changes shape
T8: control of gene expression 2
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