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AQA AL Biology notes Topic 8 – The control of gene expression
Topic 8 – The control of gene expression
Table of Content
8.1 Alteration of the sequence of bases...........................................................2
8.2 Gene expression is controlled by a number of features..............................3
8.2.1 Most of a cell’s DNA is not translated....................................................................................................................................3
8.2.2 Regulation of transcription and translation............................................................................................................................5
8.2.3 Gene expression and cancer...................................................................................................................................................9
8.3 Using genome projects.............................................................................11
8.4 Gene technologies...................................................................................11
8.4.1 Recombinant DNA technology..............................................................................................................................................11
8.4.2 Differences in DNA between individuals of the same species can be exploited for identification and diagnosis of heritable
conditions.......................................................................................................................................................................................15
8.4.3 Genetic fingerprinting...........................................................................................................................................................16
1
, AQA AL Biology notes Topic 8 – The control of gene expression
8.1 Alteration of the sequence of bases
Define gene mutation
Change in base (sequence of DNA)
Results in formation of new allele
Can arise spontaneously during DNA replication (interphase)
A mutation can lead to the production of a non-functional enzyme. Explain how. (6)
Change in DNA base, change in sequence on mRNA codon
Change in amino acid sequence
Change in position of hydrogen bonds
Changes in tertiary structure
Changes in active site
Substrate isn't complementary to active site (so can't bind, so no ES complex formed)
Base deletion & addition
1. Base removed / added causes frameshift
2. Change sequence of DNA base, change sequence on mRNA codon…
If 3 bases removed / added
No frameshift
But extra codons → extra amino acid
Substitution
1. DNA base replaced with another base
2. Changes 1 mRNA codon & 1 amino acid, changes sequence of amino acid…
3. Due to degenerate nature of genetic code, the new triplet may still code for same amino acid so
sequence of amino acids remains unchanged
Inversion
Sequence of bases is separated from DNA & inserted at the same position, backwards
No frameshift coz no. of bases stays the same
2
, AQA AL Biology notes Topic 8 – The control of gene expression
Duplication
Sequence of bases is inserted twice or multiple times causes frameshift
Change sequence on mRNA codon
Change amino acid sequence…
If 3 bases added
No frameshift
But extra codons → extra amino acid
Translocation
Sequence of bases taken out & inserted at different position on the same or different chromosome
Significant impact on gene expression as changes in both old & new location
Mutagenic agents
Increase rate of mutation
Eg ultraviolet light or alpha particles (high energy radiation / ionising particles)
8.2 Gene expression is controlled by a number of features
8.2.1 Most of a cell’s DNA is not translated
Stem cells
Unspecialised cells that can divide & differentiate into different type of cells
Give two characteristic features of stem cells (2)
Keep dividing to replace themselves
Can differentiate into other cell
ESCs is used to treat damage to heart. Suggest two reasons why putting ESCs into a person's heart might
lead to more harm to the person (2)
Differentiating into wrong types of cells
Might divide out of control, leading to cancer
Stem cell specialisation
1. Stimulus eg chemical
2. Causes selective activation of genes - some genes activated while others inactivated
o Eg muscle cells genes coding for actin & myosin need to be activated
3. mRNA only transcribed from active genes - translated on ribosomes = proteins
4. These proteins modify cell permanently & determine cell structure / function
Potency - types of stem cells
3
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