Mutations Flashcards
Description of gene mutation
- definition: involves a (1) permanent heritable change
(2) in one or a few bases in the nucleotide/base sequence
(3) of one gene - could be the substitution of one nucleotide pair with another
- resulting in missense / neutral / silent / nonsense mutation
- could also be the addition or deletion of one or more nucleotide pair
- which if not in multiples of 3, will result in a frame shift mutation
- where all nucleotides downstream of insertion/deletion site will be improperly grouped into codons
- resulting in extensive missense mutation
- which if in multiples of 3, will result in missense / nonsense mutation
elaboration of missense mutation (in nucleotide sub)
- results in a different mRNA codon
- causing the translation of a different amino acid
- leads to a change in aq seq
- leads to change in 3d conformation
- thus leads to change in protein function
elaboration of missense mutation (in nucleotide insertion or deletion)
- results in mRNA codon being added or deleted
- causing the polypeptide to have an amino acid added or deleted
- leads to a change in aq seq
- leads to change in 3d conformation
- thus leads to change in protein function
elaboration of nonsense mutation (in nucleotide sub)
- results in a stop codon
- causing premature termination of translation
- truncated protein -> non-functional
elaboration of silent mutation (in nucleotide sub)
- results in a different mRNA codon
- causing the translation of the same aa
- leads to same aa seq
- leads to same 3d conformation
- thus no change in protein function
elaboration of nonsense mutation (in nucleotide insertion or deletion)
- results in stop codon being added
- causing a truncated protein
- truncated protein -> non-functional
Description of chromosomal aberration (structure)
- definition: change in the structure of a chromosome
- which results in reshuffling of alleles on chromosome
Deletion:
- when chromosome breaks in one or more places,
and a portion of it lost
- missing part is referred to as a deletion
Duplication:
- when any part of the genetic material, be it a single locus or a large piece of chromosome,
is present more than once in the genome
- due to unequal crossing over between synapses chromosomes during meiosis /
through a replication error prior to meiosis
Inversion:
- when a segment of a chromosome is turned around 180º within a chromosome
Translocation:
- is the movement of a chromosomal segment to a new location in the genome
Description of chromosomal aberration (no.)
- definition: a change in the number of chromosomes
aneuploidy:
- where there is addition or loss of one or more chromosomes
polyploidy:
- where there is addition of one or more haploid sets of chromosomes
- resulting in autopolyploidy if additional sets of chromosomes come from same species
- or resulting in allopolyploidy if additional sets of chromosomes come from different species
- due to non-disjunction / failure of chromosomes or chromatids
to disjoin and move to opp poles during division
How chromosomal aberration results in Down syndrome
- gain of an extra chromosome 21 (X chromosome)
- but not a complete set
- due to non-disjunction / failure of chromosomes or chromatids to disjoin and move to opp poles
- during anaphase I of meiosis I or anaphase II of meiosis II
- disrupting normal distribution of chromosomes into gametes
- forming abnormal gametes containing two members of the affected chromosome
- fertilising these with a normal haploid gamete produces a zygote with 3 members of this chromosome
Symptoms of Down syndrome
- characteristically short
- stocky bodies / thick necks
- low intelligence level
- short life expectancy
elaboration on how mutation may change structure and function of protein
- change in 3d conformation of protein
- change in R grp interactions (HI or hydrogen bonds)
- change in the binding/interaction of protein with other molecules
differences between GOF mutation and LOF mutation
- no of mutations (needed for effect on phenotype)
- GOF: single mutation
- LOF: 2 mutations
- type of allele
- GOF: dominant allele
- LOF: recessive allele
- effect
- GOF: activates/stimulates process
- LOF: inactivates process
- example
- GOF: oncogene
- LOF: tumour suppressor gene
differences between chromosomal and gene mutations
- extent
- chromosomal: may involve transfer of whole genes
- gene: change in base
- effect
- chromosomal: changes regulation / control of expression of gene
- gene: changes protein produced
when does mutations have no effect on activity of enzyme
- silent mutations which result in no change in aa seq
OR neutral mutation where change in aa is to another with similar properties - mutations that could result in a change in aa in a region away from binding site of enzyme
- thus does not affect conformation / binding properties of binding site
