Brittle bones- incomplete

Question 1

What does speed of migration through polyacrylamide gel depend on in the presence of SDS (sodium dodecyl sulphate) in gel electrophoresis?

Answer 1

their size not their charge (Haem-Haemoglobin).

The origin is at the top of the gel, and the smallest proteins migrate the fastest.

Question 2

What does type I collagen consist of?

Answer 2

Type I collagen consists of

• two α1(I) polypeptide chains
• one α2(I) chain

Question 3

What is 2-mercaptoethanol?

Answer 3

sulphydryl reagent which reduces the disulphide bonds between cysteine residues in proteins

i.e. -S-S- becomes 2 -S-H in the presence of the reagent.

Question 4

What is collagen?

Answer 4

extracellular matrix protein synthesised by and secreted from a variety of cells, such as fibroblasts, and organised into insoluble fibres

Question 5

What is a common special feature of collagen?

Answer 5

triple helix structure

Associated with this is the unusual amino acid composition with its high concentration of glycine. Glycine is the smallest of the amino acids and occurs at every third position in collagen where it faces the interior of the helix

Question 6

What is the major consequence of osteogenesis imperfecta?

Answer 6

formation of bone - Bone is formed by laying down hydroxyapatite (a form of calcium phosphate) on an ordered scaffold of collagen-I

The abnormal collagen structure leads to defects in this mineralisation process, so that the patient ends up with skeletal abnormalities and generally weak bones.

Other problems also occur commonly in osteogenesis imperfecta, especially with the eyes, teeth, skin and ears.

Question 7

What skeletal abnormalities arise from col α1 protein mutations?

Answer 7

Initially skeleton is laid down as collagen

Later stage mineralisation

Collagen is defective = bones are defective

Skeleton is an active tissue - whole skeleton turns over every 5-10 years

Question 8

How can RFLP be used to identify foetus that will suffer from osteogenesis imperfecta?

Answer 8

restriction fragment length of polymorphism

• mutation either removes or creates restriction site
• Digest DNA
• gel electrophoresis
• Use a probe to region of DNA near mutation

Question 9

How can PCR be used to identify foetus that will suffer from osteogenesis imperfecta?

Answer 9

Amplify region with mutation
Gel electrophoresis
Use a probe specific for mutation

Or sequence PCR product