krishie
Forum Senior
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Hi guys,
Can u please explain what are the different classes of mutations?What is the membrane spanning/cytoplasmic domain?With which exon is it associated?
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krish
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| bluedusk
Forum Elite
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i think a more precise question would help? mutations range from single nuc transitions and transversions to large deletions and insertions. the membrane spanning domain is usually a hydrophobic stretch of protein lying within the cytoplasmic lipid bilayer (as for a receptor). it would have to be an exon to be expressed.
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| krishie
Forum Senior
Topics: 17
Posts: 128
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There are supposed to be 4 classes of mutations.Which are they?What types of mutations are classified in each`class'?These membrane spanning domains are supposed to be associated with ldl receptors.Problems with 2-6 numbered exons can cause receptor troubles.Iwanted to know more about these.The different numbered exons accounting for various problems.
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krish
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| Mars-Aris
Forum Elite
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Mutations :
1) transition mutation : purine is replaced by another purine (adenine for quanine) or a pyrimidine is replaced by another pyrimidine (cytosine is replaced by thymine)
2) Transversion mutation : a purine changes with a pyrimidine (vice versa) e.g adenine changes to cytosin
Mutation types :
Silent : a base is replaced by another but the coding aminoacid remains the same ( one aminoacid has more than 1 corresponding codons in gentic code..Leucin has 4 for example, Valine & Alanine also..occur mainly in the 3rd base of the triplet in mRNA
Clinical significance : none they remain silent! quiet! 
Missense : a base replaced by another and now a different aminoacid is coded ..different aminoacid --> changes the structure & function of a protein --> disease
Clinical example : sickle cell anemia
Nonsense : again change in a base in mRNA results this time to a codon that STOPS transcription ! shorter protein with less aminoacids!
Clinical significance : THE MOST SEVERE MUTATION FROM THOSE MENTIONED (nonsense > missense > silent
Frameshift : a base in mRNA is lost.and the next coming base takes its place, but the whole sequence changes because it is shifted to the left.
Example : GGU-GGA-UGA-GUU (mRNA)
i have put - between the bases to see the change..
Frameshift mutation : deletion of the first guanine base results in
GUG-GAU-GAG-UU
completely different aminoacids will be coded from this sequence --> completely different protein !
hope i helped you :wink: 8)
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| krishie
Forum Senior
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Thank u so much Mars aris!Could u please tell me whether they are classified further into particular classes?Bcos,Iread in a place that there are 4 classes of mutations-like class1 class2,etc!
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krish
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| Mars-Aris
Forum Elite
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i don't know if there 's such classification...
if there are four classes may be the correspond to the different four types of mutations (silent, missense, nonsense, frameshift)
:roll:
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| krishie
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Thank you,Mars aris
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krish
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| Malaysian
Forum Guru
Topics: 28
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Yes I read the diffrent type of classes thing too.....it was regarding Hereditary Hyperlipidaemia and it seems there were a few classes of mutations involved in it and it was in Qbank and I didn't understand a word!
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