1. mutations and variations

Question 1

What is a gene mutation?

Answer 1

a change in the sequence of bases of DNA

substitution of a single nucleotide = different codon. May code for different amino acid, = differences in the primary structure of the protein

insertion or deletion of a nucleotide/s- frameshift mutation, bases read in non-overlapping sets of 3, shifts the reading frame of the sequence, changing every successive codon after the mutation= new amino acid, changing the primary structure of the protein

Question 2

why is DNA a degenerate code?

Answer 2

multiple different codons can code for the same amino acid

Question 3

What are the 3 possible effects of a mutation?

Answer 3

no effect- normal functioning proteins are still synthesised

damaging- phenotype of an organism is affected in a negative way, proteins are no longer synthesised or proteins synthesised are non-functional, interfering with one or more essential processes.

beneficial- new and unusual characteristic in the phenotype- EG some mutations alter the surface membrane of a cell, meaning a person becomes immune to HIV infection. Ability to digest lactose is though to be a mutation.

Question 4

What are the causes of mutations?

Answer 4

often occur spontaneously, during DNA replication

mutagens- a chemical, physical or biological agent, which causes mutations.

the loss of a base often occurs spontaneously, causes insertion of incorrect base during DNA rep

free radicals- oxidising agents- affect structures of nucleotides and disrupt base pairing during replication. Antioxidants (EG vitamins A C E) are anticarcinogens - can negate the effects of free radicals.

Question 5

What is a chromosome mutation?
what causes them?
what are the types of changes to chromosome structure?

Answer 5

affect a whole chromosome or a number of chromosomes within a cell.
can be caused by mutagens and usually occur during meiosis.
can be silent but often lead to developmental difficulties.

TYPES-
1. deletion- section breaks off, lost within the cell
2. duplication- sections become duplicated
3. translocation- section of one, breaks off and joins
another non-homologous chromosome
4. inversion- section breaks off, is reversed, joins
back

Question 6

What’s a point mutation?

Answer 6

Mutation affecting a specific base

Question 7

What are the 3 types of point mutation?

Answer 7

Substitution
Insertion
Deletion

Insertion and deletion are frameshift mutations, displace the triplet code

Question 8

What are nonsense and missense mutations?

Answer 8

Nonsense- stop codon= premature end = shorter protein than expected

Missense- change in amino acid- degenerate coding has failed