osteogenesis imperfecta

Question 1

composition of T1 collagen

Answer 1

2 a1(1) chains 
1 a2(1) chain

Question 2

gene that encodes procollagen precursor for a1(1) collagen

Answer 2

COL1A1

Question 3

effect of sodium dodecyl sulphate on electrophoresis

Answer 3

speed of migration depends on size not charge

Question 4

2-mercaptoethanol

Answer 4

sulphydryl reagent
reduces disulphide bonds between cysteine residues
-s-s- becomes 2x -s-h

Question 5

collagen

Answer 5

ECM protein synthesised and secreted by many cells eg fibroblasts
organised into insoluble fibres - give mech strength and rigidity
give tensile strength to bone, cartilage, tendons, ligaments

Question 6

structure of collagen

Answer 6

triple helix
high conc of glycine - smallest AA, face interior
have hydroxyproline and hydroxylysine

Question 7

features of osteogenesis imperfecta

Answer 7

fracture of long bones
misdiagnosed with child abuse
malformed bones

Question 8

mutation associated woth osteogenesis imperfecta

Answer 8

range - most impact glycine residues, altering assembly
eg G->T for collagen T1 - point mutation
means sub of glycine for cysteine

Question 9

affect of cystine in collagen

Answer 9

larger than glycine
cause steric hinderance = kink = defect in assembly of fibres
sulphydryl agent - inappropriate sulphide bridges between the 2 a1(1) chains
cross linked polypeptide chains will migrate much more slowly when examined with SDS
with 2-mercaptoethanol migrate normally becaasue disulphide bridges are cleaved

Question 10

retio from being heterozygous

Answer 10

not actually 50:50 for normal:mutated
differences in rate of transcription, translatioin, stability of mRNA or protein which causes a diff ratio
because there are 2 a1(1) chains, and structure disrupted if 1 is mutated - majority of collagen fibres affected = dominant phenotype

Question 11

consequence of osteoporosis

Answer 11

formation of the bone
bone formed by laying down hydroxyapatite (form of Ca phosphate) on scaffold of collagen-1
abnormal collagen = defects in mineralisation process = skeletal abnormalities and weak bones
problems with eyes, skin and ears

Question 12

prenatal screening

Answer 12

screening of collagen would be impractical and risky
instead use CVS/amniocentesis
probes used which comp to sequence where mutation should occur
at right temp and ionic strength probe and DNA only hybridise if exactly complementary
if mutation altered restriction enzyme recognition site - only one form would be cleaved by enzymes
methods rely on mutation being known - could be checked on by family members

Question 13

AA sequence in collagen

Answer 13

glycine, x, y

glycine, proline, hydroxyproline/hydroxylysine

Question 14

what type of disease is osteogenesis imperfecta genetically

Answer 14

autosomal dominant

de novo

Question 15

synthesis of collagen

Answer 15

pre-procollagen is what is translated
procollagen - after hydroxylation and glycosylation
ends are cleaved
tropocollagen - insoluble fibrils -> insoluble fibres