book 5 (mutations) Flashcards
1
Q
state the definition of gene mutation
A
it is the change in the base sequence of the DNA
2
Q
describe the different types of mutations and explain it’s consequences
A
- substitution - the replacement of one nucleotide by another nucleotide. this results in the change of 1 codon
- inversion - 2 or more nucleotides are inverted. this results in 1 or more codon changed
- addition - one or several nucleotides are inserted into a sequence. this results in a shift in reading frame from point mutation
- deletion - one or several nucleotides are removed to form a sequence. this results in a shift in reading frame from point of mutation
3
Q
what is silent mutation?
A
- refers to mutations that do not result in a change to the amino acid sequence of a protein
- the altered codon still codes for the same amino acid and protein’s properties and functions still remain the same
- brought about by base substitution
4
Q
what is neutral mutation?
A
- refers to mutations that results in no changes to the functional properties of the proteins
- altered codon encodes for a different amino acid with similar chemical properties as original amino acid OR altered codon encodes for a different amino acid that is found in the region of the protein where the exact sequence of amino acid is not essential for the protein’s function
- brought about by base substitution
5
Q
what is missense mutations
A
- refers to mutations in which the altered codon encodes for a different amino acid which has different chemical properties as the original amino acid, such that the properties of the protein changes
- may produce a non-functional protein or reduces the functional activity of protein
- brought about by base substitution
6
Q
what is nonsense mutation
A
- refers to mutations that produces truncated proteins
- the altered codon encodes for a stop codon which results in the premature termination of translation, polypeptide synthesised will be shorter than original polypeptide
- brought about by base substitution, insertion or deletion
7
Q
what is frameshift mutation
A
- refers to mutation that cause the triplet reading frame of mRNA to be shifted
- produce non-functional proteins
- brought about by base substitution or deletion
8
Q
explain how sickle cell anaemia comes about
A
- due to a change in DNA sequence due to a base substitution in the haemoglobin beta chain gene
- this causes a change in mRNA codon
- resulting in the change of 6th amino acid from glutamic acid to valine
- this changes the amino acid sequence of HbS protein
- glutamic acid is hydrophilic whereas valine is hydrophobic
- R group of valine forms different interactions with other amino acid
- resulting in different 3D conformation, affecting the property of haemoglobin
9
Q
define chromosomal abberation
A
it is defined as a change in structure of a chromosome or the number of chromosomes
10
Q
what is the mechanism of chromosomal abberation
A
- chromosomal abberation is brought about by deletion, inversion, translocation or duplication of the chromosome
- non-disjunction of homologous chromosomes or chromatids during meiosis and mitosis
11
Q
what results is aneuploidy?
A
- failure of sister chromatids of one or several chromosomes to separate during anaphase in mitosis OR
- failure of one of several pairs of homologous chromosomes to separate during anaphase I in meiosis
OR - failure or chromatids of one or several chromosomes to separate during anaphase II in meiosis
12
Q
what results in polyploidy?
A
- failure of sister chromatids of ALL chromosomes to separate during anaphase in mitosis
OR - failure of ALL homologous pairs of chromosome to separate during anaphase I in meiosis
OR - failure of chromatids of ALL chromosomes to separate during anaphase II in meiosis
13
Q
what causes down syndrome?
A
- due to non-disjunction in meiosis I or II in the mother’s ovary, producing an ovum containing 2 chromosome 21
- results in extra chromosome 21 thus the affected person will have 47 chromosomes (2n+1)
