L9- Protein Processing Flashcards
What are the two precursors of insulin?
Preproinsulin and proinsulin.
What kind of bond holds the two peptide chains of collagen to one another?
Disulfide bonds and non-covalent interactions.
What are the two modified amino acids present in collagen?
Hydroxyproline and hydroxylysine.
Which cells produce collagen type III?
Fibroblasts.
Type I collagen is typically found in which tissues?
Bone, skin, tendons, heart valve.
Type III collagen is typically found in which tissues?
Newborn skin and blood vessels.
List the steps of collagen biosynthesis in order.
1) Polypeptide chain synthesis, 2) hydroxylation of proline and lysine, 3) glycosylation, 4) disulfide bond formation at C-terminus, 5) triple helix formation, 6) secretion, 7) hydrolysis of propeptides, 8) fibril assembly, 9) fiber assembly and formation of cross links.
What type of enzyme (and co-factor) is required for hydroxylation of proline and lysine during collagen formation?
Hydroxylases. Ascorbic acid (Vitamin C is the co-factor).
What effect does hydroxyproline have on collagen stability?
It makes it more stable.
What causes collagen to form a triple helix rather than a standard alpha helix or beta sheet?
The steric repulsion between the prolines and hydroxyprolines.
What amino acid is typically found at every third residue in collagen?
Glycine.
What form of collagen is made after hydrolysis of procollagen?
Tropocollagen.
What enzyme helps catalyze the formation of cross links in collagen fibers?
Lysyl oxidase oxidizes lysine to allysine. This forms a cross-link with unmodified lysines.
What is the cause of scurvy?
A lack of ascorbic acid (Vitamin C) which leads to a decrease in the hydroxylation of lysines and prolines in collagen.
What are the symptoms of scurvy?
Damage and fragility of many tissues and organs such as the gums, as well as skin lesions and blood vessel fragility.
Which condition usually results from a mutation in type I collagen?
Osteogenesis Imperfecta. In some of the most severe forms, a glycine is replaced with Cys, interfering with the collagen triple helix.
What are the symptoms of Osteogenesis Imperfecta?
Symptoms include bone deformities, brittle bones, and teeth and fragile blood vessels.
What are two causes of Ehlers-Danlos Syndrome?
- Improper processing of collagen caused by lack of enzyme (i.e. lysyl oxidase deficiency) and 2. genetic defects in the collagen genes.
What are the symptoms of Ehlers-Danlos Syndrome?
Symptoms include hyperelastic joints and skin hyperextendibility.
Keratin is a protein rich in which amino acid?
Cysteine.
What is the basic structural unit of collagen?
The collagen triple helix.
True or False. Different types of collagen arise from alternative splicing.
False. Different types of collagen are encoded by separate genes.
Type II collagen is typically found in which tissues?
Cartilage.
Type IV collagen is typically found in which tissues?
Basement membranes.
Which enzyme catalyzes the hydroxylation of proline into hydroxyproline?
Prolyl hydroxylase.
Which enzyme catalyzes the hydroxylation of lysine into hydroxylysine?
Lysyl hydroxylase.
Vitamin C is a cofactor for the hydroxylation of which amino acid present in collagen?
Proline.
How does the hydroxyproline content of collagen relate to the stability of the collagen molecule?
The more the hydroxyproline, the more stable the collagen molecule (as defined by higher melting point).
What kind of bond predominates between the three chains of a collagen triple helix?
Hydrogen bonding between the NH groups of glycine on one chain and the carboxyl groups on another chain.
True or False. Collagen processing and assembly occur outside the cell (i.e. in the extracellular space).
True.
What is the difference between procollagen and tropocollagen?
Tropocollagen molecules lack the N- and C- terminus of procollagen and can spontaneously assemble into collagen fibrils.
In which tissues are elastin fibers typically found?
In elastic tissues such as the lungs.
What is the most common cross-linkage between elastin molecules?
Desmosine linkage, which involves four lysines.
In which tissues is keratin typically found?
Hair and nails.
