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39 Cards in this Set

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What type of cells make collagen? where is it destined to function?
Osteoblasts and fibroblasts - make collagen then secrete to ECM.
Where in cells does collagen synthesis start?
Nucleus - transcription of collagen a-helix DNA. N-term signal sequence tags the mRNA for transport to rough ER.
What happens to ribosomes as they translate collagen mRNA into protein?
The collagen protein N-terminus contains a Signal Sequence so they are translocated to the ER
Why collagen mRNA goes to RER:
Because the newly made protein has a signal sequence for it.
What happens to Signal Sequence once protein gets to ER:
Cleaved; yields collagen precursor that must be modified.
2 types of post-translation modifications of pre-collagen propeptides:
1. Hydrolxylation of selected prolines and lysines
2. Glycosylation of selected hydroxylysine residues.
What enzymes hydroxylate Prolines and Lysines?
Prolyl hydroxylase
Lysyl hydroxylase
What do hydroxylation enzymes for collegen require?
Fe2+, Ascorbate, and Oxygen
What happens if Ascorbate is not available?
Scurvy - Vit C is essential for keeping iron reduced, and if lacking collagen fibers cannot crosslink.
Primary Polypeptide Sequence structure of Collagen:
Gly-X-Y
-Y is typically Lysine or Proline
Secondary structure of Collagen:
LH alpha-helix
Quaternary structure of Collagen:
RH superhelix
What happens after post-translation modifications of Collagen a-helices?
Assembly and Secretion
How does the superhelix assemble?
Starting with C-terminus ends, interchain disulfides form and allow the 3 helixes to zip up.
Resulting structure of assembled procollagen
-2 terminal end propeptides (nonhelical)
-Central superhelix (RH)
Where does Procollagen go after assembly:
Secreted from ER to Golgi by vesicular transport; then vesicular transport to cell surface/Extracellular Matrix.
Where are the propeptides of Procollagen cleaved?
In the extracellular matrix.
Enzymes that cleave propeptides from Procollagen:
Procollagen peptidases
What allows Collagen fibrils to form?
Spontaneous association
What allows Collagen Fibrils to Crosslink? (enzyme)
Lysyl oxidase
Products of Lysyl Oxidase:
Allysine
Hydroxyallysine
What is Allysine?
Lysine with its amino group replaced by an aldehyde
How are the R-groups in the primary 2ndary helical structure of collagen oriented?
Every third R-group (Glycine) projects toward helix interior.
Requirements for Prolyl/Lysyl Hydroxylase:
-Procollagen a-helix
-Ascorbate
-Fe2+
-O2
-a-ketoglutarate
Type of reaction catalyzed by Prolyl/Lysyl hydrolyxase:
Dioxygenase
-Oxidative decarboxylation of a-ketoglutarate
-Hydroxylation of Pro/Lys
Purpose of hydroxylating proline:
Increased stability of collagen
Purpose of hydroxylating lysine:
Ability to make interchain crosslinks
Actually 2 reasons for hydroxylating lysine:
1. Site for glycsolyation with Galactose and/or Glucose
2. Enables crosslinking
Difference between N-linked and O-linked glycosylation:
Nlinked: specific residues Asn-x-Ser/Thr, ER, cotransltn.

Olinked: no sequence, Ser/Thr, Golgi, post-translation.
What type of glycosylation occurs on collagen?
O-linked - in the golgi
Rate limiting step in collagen assembly/synthesis:
Cis-trans isomerization of proline - must occur before C-to-N zipperng up can occur.
Type of crosslink that forms between 2 neighboring Allysines:
Aldol condensation
Type of crosslink that forms between an Allysine and Lysine:
1. Schiff base
2. Amadori rearrangement link
3 types of collagen diseases:
1. Inherited
2. Dietary
3. Autoimmune
2 Inherited collagen disorders:
1. Osteogenesis imperfecta
2. Ehlers Danlos
Osteogenesis Imperfecta
-cause
-inheritance
-symptoms
-mutation of gene for type I collagen
-auto dominant
-brittle bones
Difference between OI type I vs. II:
I = normal collagen, less

II = more severe; abnormal collagen
Dietary collagen disease/cause
Scurvy - lack of ascorbate - unstable collagen.
Autoimmune collagen disease:
Bullous pemphigoid