Mutations Flashcards
Missense mutation
Change of a single base: change from one amino acid to another
What is a conserved change as opposed to a nonconservative change?
Replacing an aa by one in the same class: has less effect on protein structure
What mutation is sickle cell anemia?
Single base mutation: from GAG to GTG leading to the production of valine instead of glutamic acid
Nonsense mutation
change from one amino acid to a stop codon
Truncated protein
a protein that lacks a c-terminal part depending on where the premature stop codon falls
What happens in nonsense-mediated mRNA decay?
the cell does not produce the truncated protein
What do we have at each exon-exon boundary?
Exon junction complex
What happens when the ribosome starts translation in normal conditions?
It removes the exon junction complexes
What happens when the ribosome starts translation when there is a premature stop codon?
The ribosome stops translation, but there are downstream exon junction complexes that have not been removed: sensing the presence of them will lead to degradation of the transcript
What are the consequences of nonsense mutation?
- The transcript is degraded because it is sensed as a premature stop codon and we activate nonsense-mediated mRNA decay
- Producing a truncated protein in conditions in which the sensing mechanisms is not working: last exons of a gene
Neutral mutation
where an aa is changed into another aa with similar chemical property
Silent mutation
mutation occurring in the third position, not changing the amino acid that is actually encoded by that specific protein so the same amino acid is encoded
What does it mean that the genetic code is redundant?
64 codons for 20 aa + 3 stop codons
What is the difference between silent and neutral mutations?
Silent mutation does not change the aa sequence of the encoded protein whereas neutral protein has no observable affect on fitness
What are introns characterised by?
By the presence of 2 very conserved nucleotides at the 5’ (gt) and at the 3’ (ag) end
