mutations

gene mutation and chromosome mutation

what is a mutation?

a change in the base sequence of a chromosome

which types of mutation are there?

substitution, deletion, insertion

substitution mutation

a nucleotide in a DNA molecule is replaced by a nucleotide with a different base code

will a substitiution mutation affect the polypeptide formed?

not necessarily, because the genetic code is degenerate so a mutation doesn’t always form a different amino acid

deletion mutation

a nucleotide is removed from the DNA sequence

will a deletion mutation affect the polypeptide formed?

yes because it causes a frame shift and usually the amino acid sequence of the polypeptide is completely different

how does a mutation affect a protein?

it will change the sequence of amino acids (primary structure), causing the rest of the structure to change shape

why is a mutation bad for proteins that become enzymes?

proteins that become enzymes may control metabolic rate, the active site of a protein has a very specific shape for its role

effects of mutations

metabolic pathways no longer regulated, enzyme action slows/stops, active site changes shape

chromosome mutation

a change in the structure or number of chromosomes

types of chromosome mutation

non-disjunction

non-disjunction

homologous pairs of chromosome fail to separate during meiosis

why is non-disjunction bad?

it means gametes are produced with an abnormal number of chromosomes, meaning offspring have more or fewer chromosomes in all body cells