Gene Mutation Flashcards
What is a mutation?
Any change to the base sequence of DNA.
Mutations in body cells are not passed on to the next generation.
Mutations occurring during the formations of gametes may be inherited.
How can mutations be caused?
Mutations can be caused by errors during DNA replication.
or
mutagenic agents.
Name three types of mutation.
Substitution
Deletion
Addition
What is substitution mutation?
One base is substituted with another, e.g ATGCCT because ATTCCT.
What is deletion mutation?
One base is deleted, e.g ATGCCT becomes ATCCT.
What is addition mutation?
One or more bases are added in, e.g ATGCCT becomes ATGACCT.
What determines the order of amino acids in a particular protein?
The order of DNA bases in a gene.
What can happen to a protein if the sequence of amino acids are altered?
It may affect the protein’s tertiary structure so the protein might not function the way it’s supposed to.
Do all mutations affect the order of amino acids in a protein?
No- the degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet meaning not all substitution mutations will result in a change to the amino acid sequence of the protein.
Why does deleting or inserting a base always lead to changes in the amino acid sequence?
Deleting or inserting a base will change the number of bases present, which will cause a shift in all the base triplets after it.
What are mutagenic agents?
Things that cause an increase in the rate of mutations.
For example, UV radiation, ionising radiation, some chemicals and some viruses.
How do mutagenic agents increase the rate of mutations?
- Acting as a base- chemicals called base analogs can substitute for a base during DNA replication.
- Altering bases- some chemicals can delete or alter bases.
- Changing the structure of DNA- causes problems during DNA replication.
What are hereditary mutations?
You inherit them from your parents.
They are present in the gametes, so if a gamete is fertilised the fetus will have the mutation.
What are acquired mutations?
You develop them during your lifetime.
Acquired mutations occur in individual cells after fertilisation.
When might a mutation occur spontaneously?
During DNA replication.
Substitution mutation: depending on which new base is substituted for the original base there are three possible consequences…
A nonsense mutation
A mis-sense mutation
A silent mutation
Substitution mutation: What is a nonsense mutation?
Occurs if the base change results in the formation of one of the three stop codons that mark the end of a polypeptide chain.
e.g GTC -> ATC means that it is transcribed as UAG in mRNA (a stop codon)- polypeptide chain formation would stop.
Substitution mutation: What is a mis-sense mutation?
Arises when the base change results in a different amino acid being coded for.
Substitution mutation: What is a silent mutation?
Occurs when the substituted base has no effect of the function because they code for the same amino acid
What are proto-oncogenes?
Genes that stimulate cell division.
What are tumour supressor genes?
Genes that slow cell division.
How can proto-oncogenes affect cell division?
The receptor protein on the cell surface membrane can be permanently activated, so that cell division is switched on even in the absence of growth factors.
The oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division.
Explain why a deletion gene is more likely to result in a change to an organism than a substitution gene mutation?
In a deletion all the codons after are affected (frame shift).
In substitution only a single codon (therefore a single amino acid) will be affected.
