what is a mutation
a random change to the genetic material
what do some mutations involve changes to
the structure or number of chromosomes.
what is a gene mutation and what is disrupted if this occurs
a change to the DNA
disrupts protein synthesis
what is special about the DNA structure
its stable and resistant to corruption of the genetic material stored within it
when may errors in the DNA sequence occur
during DNA replication
what are somatic mutations
mutations associated with mitotic divisions and not passed to offspring - may be associated with development of cancerous tumours
which mutations can be inherited by offspring
mutations associated with meiosis and gamete formation
what does the position and involvement of the amino acid in R group interactions within the protein determine
the impact of the new amino acid on the functions of the protein
what are the two main classes of gene mutations
point mutation and insertion/deletion mutation (indel)
what is a point mutation
one base pair replaces another
what is an insertion/deletion mutation (indel)
one or more nucleotides are inserted or deleted from a length of DNA. these may cause a frameshift
what does the genetic code consist of
nucleotide base triplets within the DNA
what is the sequence of codons on the mRNA a copy of
the sequence of base triplets on the gene (coding strand of DNA)
what are the 3 types of point mutations
- silent
- missense
- nonsense
what makes the genetic code degenerate
all amino acids involved in protein synthesis apart from methionine have more than one base triplet code. this reduces the effect of point mutations as they dont always cause a change to sequence of amino acids in a protein
what is a silent mutation
a point mutation involving a change to the base triplet where that triplet still codes for the same amino acid.
does a silent mutation alter the primary, secondary or tertiary structure of the protein
no
what is a missense mutation
a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.
what is the effect of a missense mutation
altering the primary structure via changing the amino acid sequence alters the tertiary structure and prevents it from carrying out its usual function
what is sickle cell anaemia
results from a missense mutation on the 6th base triplet of the gene for the beta polypeptide chains of haemoglobin - the amino acid valine instead of glutamic acid is inserted at this position. this results in deoxygenated haemoglobin crystallising within erythrocytes causing them to become sickle shaped blocking capillaries and depriving tissues of oxygen
what is a nonsense mutation
a point mutation that alters a base triplet so it becomes a termination (STOP) triplet. results in a truncated protein that will not function and most likely be degraded within the cell
what is Duchenne muscular dystrophy a result of
a nonsense mutation
what do insertions and deletions cause
a frameshift
what is a frameshift
if nucleotide base pairs (not multiples of 3) are inserted in the gene or deleted from the gene because the code is non overlapping and reads in groups of 3, all the subsequent base triplets are altered
