Brittle Bones

Question 1

What does COL1A1 encode

Answer 1

Procollagen precursor of a1 collagen

Question 2

What do fibroblasts secrete

Answer 2

Collagen (extracellular matrix protein)

Question 3

What do the insoluble fibres do

Answer 3

Mechanical strength and rigidity to tissues

Provide tensile strength of skeletal tissues

Question 4

How often is glycine present in collagen

Answer 4

Every third position in collagen

Faces the interior of the helix

Question 5

Main feature of osteogenesis imperfecta

Answer 5

Repeated fracture of long bones

Question 6

What defect is present in osteogenesis imperfecta

Answer 6

G instead of T for collagen type 1
Cystine instead of glycine
Causes steric hinderance and kink in triple helix
Cystine can also form inappropriate disulphide bonds between the two a1 chains

Question 7

Why is someone who is heterozygous for OI not be 50% abnormal

Answer 7

Different translation rate
Different transcription rate
Stability of mRNA
Stability of protein

Question 8

What happens to the formation of bone is OI

Answer 8

Hydroxyapatite cannot be layed down and mineralised on collagen

Question 9

How can you diagnose OI

Answer 9

Restriction fragment length polymorphism

PCR - use probe specific for mutation