SECTION 8 THE CONTROL OF GENE EXPRESSION
SUMMARY NOTES TO SPEC POINT 3.8
STEPHEN HARDEN-WILSON 19/05/23
Muta%ons 3.8.1 --------------------
Can be both detrimental and advantageous to an organism
• SubsPtuPon
• DelePon
• InserPon – this and delePon can cause frame shi*s where every codon aUer the mutaPon is read
one less/more so each amino acid coded for subsequently will be wrong
• DuplicaPon
• Inversion
• TranslocaPon
Caused by…
• Random – occur conPnuously as cells duplicate DNA or produce proteins
• Mutagenic agents
either A/ high energy ionising radiaPon or B/ chemicals
Stem Cells 3.8.2.1 --------------------
ClassificaPon of potency…
• To-potent – only found in embryos and have ability to specialise into any cell
• Pluripotent – found in embryo and bone marrow, many cell type
• Mul-potent – bone marrow, can be specialised into various Pssues
• Unipotent – can only divide by mitosis to form copies of one cell type
eg. Cardiomyocytes are heart muscle cells that can regenerate to form new cells of the same type
-------------------------
But there is a way to transform somaPc (body) cells to become stem cells, they are called induced
pluripotent stem cells/ iPS. This has to be done because specialisaPon is irreversible naturally, ie a
unipotent cell cannot go back to become mulPpotent.
Regula%on of Transcrip%on and Transla%on 3.8.2.2 --------------------
TranscripPonal factors are chemicals that bind to the binding site called a promoter region (which is a
parPcular base sequence) of a gene on the DNA which signal for it to be transcripted into mRNA. If the
transcripPonal factor has not binded, the gene will not be expressed.
This is one the basic mechanisms that decides what genes are expressed in a cell, because all cells of an organism are
gene8cally iden8cal, but the genes that are ac8vated within them varies greatly
-------------------------
Example of oestrogen: lipid soluble so easily diffuses into the cell, then binds to its receptor molecule in
the cytoplasm, causing the receptor’s DNA binding site to change shape, as it has made a
complimentary fit. This transcripPonal factor (binded and changed molecule with oestrogen acached) now
enters the nucleus through a nuclear pore and s"mulates the transcrip"on of the specific (targeted) gene
-------------------------
TranslaPon is regulated with small molecules called RNAi, or interfering RNA that bind to the target
mRNA (the RNAi has been converted into a single stranded molecule to enable this to happen by an
enzyme found in cell’s cytoplasm). It is binded with an enzyme that cuts mRNA, meaning it can no longer
be translated into a polypepPde chain (using tRNA and a ribosome).
SUMMARY NOTES TO SPEC POINT 3.8
STEPHEN HARDEN-WILSON 19/05/23
Muta%ons 3.8.1 --------------------
Can be both detrimental and advantageous to an organism
• SubsPtuPon
• DelePon
• InserPon – this and delePon can cause frame shi*s where every codon aUer the mutaPon is read
one less/more so each amino acid coded for subsequently will be wrong
• DuplicaPon
• Inversion
• TranslocaPon
Caused by…
• Random – occur conPnuously as cells duplicate DNA or produce proteins
• Mutagenic agents
either A/ high energy ionising radiaPon or B/ chemicals
Stem Cells 3.8.2.1 --------------------
ClassificaPon of potency…
• To-potent – only found in embryos and have ability to specialise into any cell
• Pluripotent – found in embryo and bone marrow, many cell type
• Mul-potent – bone marrow, can be specialised into various Pssues
• Unipotent – can only divide by mitosis to form copies of one cell type
eg. Cardiomyocytes are heart muscle cells that can regenerate to form new cells of the same type
-------------------------
But there is a way to transform somaPc (body) cells to become stem cells, they are called induced
pluripotent stem cells/ iPS. This has to be done because specialisaPon is irreversible naturally, ie a
unipotent cell cannot go back to become mulPpotent.
Regula%on of Transcrip%on and Transla%on 3.8.2.2 --------------------
TranscripPonal factors are chemicals that bind to the binding site called a promoter region (which is a
parPcular base sequence) of a gene on the DNA which signal for it to be transcripted into mRNA. If the
transcripPonal factor has not binded, the gene will not be expressed.
This is one the basic mechanisms that decides what genes are expressed in a cell, because all cells of an organism are
gene8cally iden8cal, but the genes that are ac8vated within them varies greatly
-------------------------
Example of oestrogen: lipid soluble so easily diffuses into the cell, then binds to its receptor molecule in
the cytoplasm, causing the receptor’s DNA binding site to change shape, as it has made a
complimentary fit. This transcripPonal factor (binded and changed molecule with oestrogen acached) now
enters the nucleus through a nuclear pore and s"mulates the transcrip"on of the specific (targeted) gene
-------------------------
TranslaPon is regulated with small molecules called RNAi, or interfering RNA that bind to the target
mRNA (the RNAi has been converted into a single stranded molecule to enable this to happen by an
enzyme found in cell’s cytoplasm). It is binded with an enzyme that cuts mRNA, meaning it can no longer
be translated into a polypepPde chain (using tRNA and a ribosome).
