These are my notes for the eighth unit of alevel biology - the control of gene expression!
I got an A in my alevel AQA biology exam using these notes.
Happy revising :)
,Gene mutation
• GENETIC MUTATION - any change to the base sequence of DNA in
organism
• Arises spontaneously during DNA replication
,Types of
genetic
mutations
Base substitution, base deletion and base addition
,Base substitution
• Type of genetic mutation where one nucleotide in DNA sequence is
replaced by another nucleotide
,3 possible consequences
1. Formation of a codon for the same amino acid and the polypeptide
produced will be the same. This is because the genetic code is degene
(amino acids have more than one codon). The mutation has no effect o
the polypeptide produced. This is a silent mutation
2. Formation of a codon for a different amino acid and the polypeptide
produced will be different. The protein produced will be non-functiona
For example if it is an enzyme, the active site may no longer fit the
substrate and no reaction will occur. This is a missense mutation
3. Formation of a stop codon and the polypeptide chain ends. This leads
the formation of a non-functional protein. This is a nonsense mutation
,Base deletion (frame shift mutation
• Type of genetic mutation where one nucleotide is lost from the
normal DNA sequence
,Consequence
1. One deleted nucleotide causes all triplets in sequence to be read
differently because each has been shifted to the left by one base
2. The triplets will code for different amino acids
3. This leads to the formation of a non-functional protein
4. This will affect the hydrogen/ionic/disulphide bonds
5. This will change the tertiary structure of the protein
,
,Base addition (frame shift mutation
• Type of mutation where one nucleotide is added to the normal DN
sequence
, Consequence
1. One added nucleotide causes all triplets in sequence to be read
differently because each has been shifted to the right by one bas
2. The triplets will code for different amino acids
3. This leads to the formation of a non-functional protein
4. This will affect the hydrogen/ionic/disulphide bonds
5. This will change the tertiary structure of the protein
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