mutation

Question 1

what are mutagenic agents?

Answer 1

substances that increase frequency/ rate of gene mutations

Question 2

2 examples of mutagenic agents

Answer 2

-high energy ionising radiation, such as alpha beta or gamma
-chemicals such as nitrogen dioxide or tobacco smoke (carcinogens)

Question 3

Explain why some mutations do not result in changed amino acid sequence

Answer 3

Genetic code is degenerate, so some mutations will not change sequence.
Also some may only alter it slightly or not at all because amino acid doesn’t always change base. When only altered slightly the appearance and function doesn’t always change, however a small number of mutations code for a significantly altered polypeptide with a different shape

Question 4

Substitution mutation

Answer 4

When a base in the DNA sequence is randomly swapped for a different base

Question 5

Types of substitution (SMN)

Answer 5

Silent: the mutation does not alter amino acid sequence of polypeptide (certain codons code for same amino acid)
Missence: the mutation alters a single amino acid in the polypeptide chain
Nonsense: mutation creates a premature stop codon causing polypeptide chain to be incomplete

Question 6

Deletion

Answer 6

When a nucleotide is randomly deleted from the DNA sequence, changing amino acid that would have been coded for. Has a knock on effect (frame shift)

Question 7

Addition

Answer 7

When a nucleotide (with a new base) is randomly inserted into the DNA sequence. Changing amino acid that would have been coded for originally. Changes tripletfurther in DNA sequence (frameshift)

Question 8

Duplication

Answer 8

A whole gene or section is duplicated so that two copies of the gene/section appear on the same chromosome. Original gene intact- so not harmful

May develop new functions

Question 9

Inversion

Answer 9

Usually occurs during crossing over in meiosis. The DNA of a single gene cut in 2 places. Rotated by 180 then rejoined in same place. Large section backwards multiple amino acids affected. Frequently result in non functional protein. Harmful.

Question 10

Translocation

Answer 10

Gene is cut in 2 places the section cut off attaches to a separate gene. Cut off gene and separate gene both non functional.

If a section of a proto oncogene is translocated onto a gene controlling cell division it could boost expression- leading to tumours