AQA A level Biology Topic 8 – The control of gene expression notes (A* achieved)

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




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, 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




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, 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
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