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What are the two phases of nano-composite of bone?
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What consists of organic phase of bone?
Collagen- makes bone flexible, ductile and tough
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What consists mineral phase of bone?
Hydroxyapatite crystals- makes bones rigid, stiff and hard
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What is collagen?
- Most abundant animal protein
- Organic phase of bone
- Major component of connective tissue
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What is tropocollagen?
The molecular component/ building block of collagen fibril – three peptide chains coiled around each other
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What is the amino acid sequence of tropocollagen peptide?
3-amino acid repeating motif of Glycine-Proline-Proline, or GXY
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What does it mean that Glycine is conserved in tropocollagen peptide?
100% of the time there Glycine will be in the first amino acid of the repeating GXY motif
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Where in the cell is this repeating motif made?
Ribosome during translation
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Where in the cell is the amino acid modified?
Hydroxylation occurs in the endoplasmic reticulum
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What is the organization of tropocollagen?
Three collagen peptides, each with 1000 amino acids length, wrap together to form the triple helical building block of collagen
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How many repeats in the tropocollagen amino acid sequence motif?
350 times
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Which amino acid donates the H-bond in tropocollagen?
Amino acids at X or Y positions that are not proline or hydroxyproline
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What is the most common cause of osteogenesis imperfecta?
Mutation at the glycine position
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Why is glycine completely conserved?
Only glycine has a sidechain small enough to pack into the core of the helix
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What exists in the gaps between tropocollagen?
Hydroxyapatite mortar
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Describe what happens to the tropocollagen peptide in the ER
- Preprocollagen peptide gets hydroxylated at proline/lysin, then glycosylation occurse of the hydroxylysine
- Helices wrap around the hydroxylated and glycosylated residues forming the triple helix
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How many tripeptide repeats per helical turn?
7
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How are tropocollagen molecules packed?
- In a staggered pattern to form long, wide fibrils.
- Repeats every 67 nm
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Which collagen type(s) are associated with bone
Types I, II, III
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Which gene mutations result in osteogenesis imperfecta
COL1A1 or COL1A2
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Substitution of which amino acid at the glycine position would cause less severe form of osteogenesis imperfecta?
Alanine, the next smallest AA other than glycine
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What is an co-enzyme required for prolylhdyroxylase to work?
Vitamin C
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What does allysine mean?
Post-translational modification of lysin by lysyl oxidase which replaces the side chain amine with aldehyde
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What is a treatment for scurvy?
Take vitamin C
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What is scruvy?
Chronic vitamin C deficiency
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