GENE MUTATION Flashcards
Gene Mutation
change to one or more bases or arrangement of bases
Nonsense Mutation: a base changes resulting in the formation of a stop codon, therefore polypeptide production stopped prematurely
Mis-Sense Mutation: a base changes resulting in a different amino acid being coded for
How a Mis-Sense Mutation causes only one different amino acid in the polypeptide chain
Three bases code for one amino
However here only one codon is changed, i.e. there is NO frame shift
Therefore the other codons are not affected
Silent Mutation: a base changes however the resulting codon still codes for the same amino acid due to the degeneracy of the generic code, this substitution will be on the third base as degeneracy is found on the third base
Deletion Mutation: when a base/s is completely removed from the DNA sequence, resulting in a ‘frame shift’ to the left
Why mutation involving deletion of a base is more severe than mutation involving substitution of a base
Deletion causes frame shift
This changes many amino acids
Substitution alters only one amino acid
Substitution at times causes no problems due to the degeneracy of the triplet code
So overall, mutation affects the structure of a gene by adding, substituting or deleting a base.
How mutation of a gene may result in a non-functional enzyme
Mutation causes change in base of DNA
This results in a change in base sequence of mRNA, thus changing the codons
Incorrect tRNA molecules coded for
Incorrect amino acids coded for
Different amino acids results in different tertiary structure of the enzyme
The different tertiary structure means the active site has a different shape due to different bonds being formed
The active site shape no longer complimentary to shape of substrate
How mutation of base may cause the production of a complete new protein (a bit like the above):
Base sequence is changed
Different mRNA
mRNA attracts different tRNA
Different amino acid is inserted into protein
Why mutant genes are more easily identified in haploid cells than diploid cells
Haploid cells have one set of chromosomes whereas diploid have two sets of chromosomes (homologous pair)
In haploid cells, all the alleles are expressed, whereas in diploid cells recessive alleles are often hidden
How mutation can be detected from a sample of cells
Extract DNA
Remove specific section using Restriction Endonucleases
Find the base sequence using a gene probe
Compare the base sequence with a normal base sequence
Causes of mutation
They can occur spontaneously. How mutation rate is increased by factors known as Mutagenic Agents, these agents ionise the bases so that they don’t form the correct base pairs:
Ultraviolet Light
X-Rays
α and β radiation
Chemicals such as mustard gas and cigarette smoke
Mutations produce the genetic diversity needed for natural selection and speciation.
Proto-Oncogenes: stimulate cell division
Growth factors attach to receptor protein on cell-surface membrane
This allows relay proteins to switch on the genes necessary for DNA Replication
Mutation can turn Proto-Oncogene into Oncogenes
Oncogenes
Permanently activate receptor proteins even without growth factors leading to cell division
Codes for growth factors that are then produced in excess stimulating cell division
Tumour Suppressor Genes
slows cell division and overrides the effect of oncogenes
If a Tumour Suppressor Gene becomes mutated, it becomes inactivated. This mutation can be inherited too.
Tumour Suppressor Genes may also be inactivated when cells with genetically modified genes are added to the body, this is because the Tumour Suppressor Genes will not have recognised the new genes, therefore will not know how to stop division
Why all cancer cells must be destroyed in a tumour
Cells can metastasise
It can spread to other parts of the body
Remaining cells continue to divide
All cells contain the same genes however only certain genes are expresses in any cell at one time. Some gene are permanently switched off, whilst others come on and off according to requirement.
