Gene Mutation Flashcards
What do mutations form the basis of?
Discontinuous variation
Define mutation
Any change to the quantity or the structure of the DNA of an organism
Define gene mutation
Any change to one or more nucleotide bases, or any rearrangement of the bases in DNA
Define the substitution of bases
Where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
Depending on which new base is substituted for the original base, there are three possible consequences. What are they?
A nonsense mutation, mis-sense mutation or a silent mutation
When does a non-sense mutation occur?
If the base change results in the formation of one of the three stop codons that mark the end of a polypeptide chain which means the protein cannot perform its normal function
When does a mis-sense mutation occur?
When the base change results in a different amino acid being coded for so the polypeptide will differ by one amino acid
When does a silent mutation occur?
When the substituted base, although different, still codes for the same amino acid as before, so the mutation will have no effect
How does a mutation occur by deletion?
A nucleotide is lost from the normal DNA sequence
What does a deleted nucleotide create?
A frame shift
What are mutagens?
Outside factors that increase the mutation rate
Give two examples of mutagens
High-energy radiation that can disrupt the DNA molecule and chemicals that can alter the DNA structure or interfere with transcription
In normal cells, what is the rate of cell division controlled by?
Proto-oncogenes which stimulate cell division and tumour suppressor genes that slow cell division
What can a gene mutation cause proto-oncogenes to mutate into?
Oncogenes
How can oncogenes affect cell division?
The receptor on the cell surface membrane can be permanently activated so that cell division is switched on even in the absence of growth factors or the oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division
