Topic 14.1: Consequences of mutations

Question 1

what is a mutation

Answer 1

a change in nucleotide sequence in DNA

Question 2

What is mutagenesis

Answer 2

the process of mutation generation

Question 3

what causes mutations

Answer 3

exogenous, endogenous sources or spontaneous events which causes defective or error prone DNA repair….mutation

Question 4

what is a spontaneous event

Answer 4

eg: spontaneous deamination - where cytosine becomes uracil or metholated cytosine becomes thymine

Question 5

what are transposable elements

Answer 5

specific dna sequences that move, jumping genes randomly changing the nucleotide sequence, can move within same chromosome or on different chromosome:
can deactivate the gene and reactivate itcan move within same chromosome or on different chromosome
if in promoter region - alter gene expression
also can cause no effect

Question 6

what is the result of a mutation

Answer 6

• may or may not cause a phenotypic change
• may be good, bad, or neutral
• causes genome variation and driving force of evolution
• may cause disease

Question 7

what does a mutation at a nucleotide and gene level cause

Answer 7

deletion - removal of base
insertion - adding of base
subtsitution - swapping of one base for another

Question 8

what is single nucleotide polymorphism and what can it cause

Answer 8

single base change
- no known effect - anonymous SNP
- outside a gene - non coding SNP
- inside a gene - coding SNP
....changes gene product (polypeptide or RNA), polypeptide length and amount of gene product

Question 9

if a single nucleotide/base changes, what can result

Answer 9

Transition - changes to same type of base so purine to purine or pyrimidine to pyrimidine
Transversion - changes to different type of base so purine to pyrimidine and vice versa

Question 10

how is sickle cell anaemia caused

Answer 10

single nucleotide change

transversion of A to T causing amino acid change from glu to val

Question 11

what is a missense mutation

Answer 11

point mutation in which a single nucleotide change results in a codon that codes for a different amino acid

Question 12

what is a silent/neutral single nucleotide sequence

Answer 12

both codons code for the same base - no phenotypic change

Question 13

what causes a change in polypeptide seqeunce

Answer 13

deletion (of non multiples of 3) or insertion - changes reading frame, stop codon not recognised = frameshift mutation, as triplet code is non overlapping so a frameshit can happen
or a mutation in a stop codon - later on read

Question 14

a single point mutation can also

Answer 14

mutation of codon makes a stop codon = shorter = nonsense mutation

Question 15

how is the amount of gene product changed

Answer 15

mutations affecting regulatory sequences

Question 16

deletion and insertions can be

Answer 16

multi-nucleotide mutations ( 3 base pairs or multiple of 3) = more than one base = different amino acid

Question 17

what can lead to trinucleotide expansion and example of a disease

Answer 17

fork slippage

Huntington’s = polyglutamine repeats, usually 6-39 then if diseased 35-121 repeats

Question 18

what is a nonsense mutation

Answer 18

A nonsense mutation is the substitution of a single base pair that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid. The presence of this premature stop codon results in the production of a shortened, and likely nonfunctional, protein.