6.1.1 (a)

Question 1

What is a mutation?

Answer 1

Mutation – change in sequence of nucleotide bases in DNA.

If a mutation occurs, protein synthesis is disrupted – this change in sequence can occur by either: substitution, deletion or insertion of one or more nucleotides

Question 2

What is a point mutation and what is the effect of substitution?

Answer 2

• If only one nucleotide is affected, it is called a point mutation
• Substitution of one nucleotide can result in a new codon, the degenerate nature of genetic code means you may or may not get a new amino acid, which in turn gives a new primary structure of a protein
• This new protein structure, having an effect on the organism is dependant on how involved the amino acid is with the R-Group interactions.

E.g. if the protein is an enzyme, the active site won’t be complementary anymore.

Question 3

What is a frameshift mutation?

Answer 3

• Codons are transcribed in non-overlapping groups of 3, if one nucleotide is inserted, or deleted, this changes the frame that the codons are read.
• If nucleotides are changed in groups of 3, this is not a frameshift mutation

Question 4

Generally, how can different mutations affect organisms?

Answer 4

No effect: No affect on phenotype, normally functioning proteins are still synthesised

Damaging: Phenotype affected in a negative manner. Proteins no longer synthesised, or non-functional proteins are synthesised

Beneficial: Protein is synthesised that is new and useful (rare). E.g. Mutation on a protein on plasma membrane means HIV cannot bind and enter cells

Question 5

What are the causes of mutation?

Answer 5

• Mutations are spontaneous, occur during DNA replication
• Mutagens (chemical, physical or biological agent causing a mutation) can increase the rate of mutation

Question 6

What is the effect of depurination and/or depyrimidation?

Answer 6

Depurination* (loss of purine base) or *depyrimidination (loss of pyrimidine base) leads to insertion of incorrect base at complementary base pairing during DNA replication

Question 7

What are examples of beneficial mutations?

Answer 7

• Digesting lactose (the sugar in milk) is a recent beneficial mutation
• It supports with preventing osteoporosis (digesting lactose when drinking milk)

Question 8

What are chromosomal mutations and how do their structures change in mutation?

Answer 8

Chromosomal mutations affect the whole chromosome or a number of them. They can be caused by mutagens in meiosis.

Chromosome structure changes:

• Deletion – section of chromosome breaks off and is lost
• Duplication – Sections duplicated on chromosome
• Translocation – Section of one chromosome breaks off and joins a non-homologous chromosome
• Inversion – section of chromosome broken off, inverted, and rejoined