Brittle Bones Flashcards

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1
Q

What effect does SDS have on the electrophoresis of collagen?

A

The speed of migration of the proteins in the collagen depend on their size not charge

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2
Q

What is 2-mercaptoethanol?

A

A reagent which reduces the disulphide bond between the cystine residues in proteins

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3
Q

What is the affect of the point mutation which occurs in the brittle bones case?

A

Glycine is replaced by cysteine - this causes a different smino acid to be coded for, meaning a spdifferent secondary structure will form - hence protein will fold up differently and different bonds will form

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4
Q

What is the effect on the protein of a different, larger amino acid being coded for in a protein sequence?

A

Thr larger amino acid will cause steric hinderance - this generates a kink in the normally straight chain resulting in defective protein forming

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5
Q

Which is heavier cystine or glycine?

A

Cysteine

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6
Q

In OI, why are only some of the childs collagen chains affected?

A

The child may be heterozygous, so only one allele is mutation and therefore only some collagen molecules will carry the mutation

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7
Q

Why is the pattern of inheritance basically dominant for OI?

A

Because the collagen triple helix contains 2 alpha 1 chains, and is disrupted if even only one chain is affected

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8
Q

Why does abnormal collagen production result in the symptoms and signs seen in OI?

A

Abnormal collagen structure leads to defects in the mineralisation process of bone as hydroxyapetite has nothing to be layed onto

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9
Q

Suggest a suitable prenatal diagnostic test to identify a foetus who may be at risk of OI?

A

Amnio or CVS

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10
Q

What is restriction fragment length polymorphism?

A

When specific probes thta are complenentary to the part with the mutation are set under thr 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

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11
Q

Why does a substitution of glycine for cysteine result in defective assembly of collagen fibres?

A

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.

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12
Q

What does cysteine contain in its side chain?

A

a reactive sulphydryl group

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13
Q

What is the effect of cysteine having a reactive sulphydryl group in its side chain?

A

inappropriate disulphide bonds between the two α1(I) chains in the helix, resulting in a cross linked polypeptide chain

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14
Q

What effect does a cross-linked polypeptide chain have on the speed of migration on an agar plate?

A

polypeptide chains will migrate much more slowly than the individual chains when examined by gel electrophoresis in the presence of SDS

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15
Q

Why is directly sampling the patients collagen protein not a suitable pre-natal testing method?

A

Sampling collagen from a foetus would be impractical and risky

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