Brittle Bones Flashcards
What effect does SDS have on the electrophoresis of collagen?
The speed of migration of the proteins in the collagen depend on their size not charge
What is 2-mercaptoethanol?
A reagent which cleaves the disulphide bond between the cystine residues in proteins
What is the affect of the point mutation which occurs in the brittle bones case?
Glycine is replaced by cysteine - this causes a different amino acid to be coded for, meaning a different secondary structure will form - hence protein will fold up differently and different bonds will form
What is the effect on the protein of a different, larger amino acid being coded for in a protein sequence?
Thr larger amino acid will cause steric hinderance - this generates a kink in the normally straight chain resulting in defective protein forming
Which is heavier cystine or glycine?
Cysteine
In OI, why are only some of the childs collagen chains affected?
The child may be heterozygous, so only one allele is mutation and therefore only some collagen molecules will carry the mutation
Why is the pattern of inheritance basically dominant for OI?
Because the collagen triple helix contains 2 alpha 1 chains, and is disrupted if even only one chain is affected
Why does abnormal collagen production result in the symptoms and signs seen in OI?
Abnormal collagen structure leads to defects in the mineralisation process of bone as hydroxyapetite has nothing to be layed onto
Suggest a suitable prenatal diagnostic test to identify a foetus who may be at risk of OI?
Amnio or CVS
What is restriction fragment length polymorphism?
When specific probes that are complementary to the part with the mutation are set under the right conditions of temperature and ionic strength - only becomes hybridised if the sequence is exactly complementary which allows mutant and normal sections to be identified
Why does a substitution of glycine for cysteine result in defective assembly of collagen fibres?
The larger amino acid in the mutant molecule will cause steric hindrance which generates a kink in the normally straight triple helix, with a resulting defect in the assembly into fibres.
What does cysteine contain in its side chain?
a reactive sulphydryl group
What is the effect of cysteine having a reactive sulphydryl group in its side chain?
inappropriate disulphide bonds between the two α1(I) chains in the helix, resulting in a cross linked polypeptide chain
What effect does a cross-linked polypeptide chain have on the speed of migration on an agar plate?
polypeptide chains will migrate much more slowly than the individual chains when examined by gel electrophoresis in the presence of SDS
Why is directly sampling the patients collagen protein not a suitable pre-natal testing method?
Sampling collagen from a foetus would be impractical and risky
