Biochemistry Lecture 9 - Protein Processing and Maturation Flashcards
(20 cards)
What amino acid has the smallest R group?
Glycine
What amino acid can form sulfide bonds?
Cysteine
What type of environment is the cytoplasm (reducing vs. oxidizing)? What about the ER lumen and outside the cell?
Reducing. ER lumen and outside cell is oxidizing.
What is the most abundant protein in the body?
Collagen.
What is the basic composition of collagen?
Three alpha chains (not related to alpha helices).
Where is Type I collagen found?
Bone, skin, tendon, heart valves.
Where is Type II collagen found and what is another name for it?
Reticulin - is a supporting mesh in soft tissues and skin.
Where is Type I and III synthesized?
Firbroblast cells
What are the steps in collagen synthesis?
- Polypeptide chain synthesis
- Hydroxylation of the prolines and lysines.
- Glycosylation
- Dsulfide bond formation at c-terminus
- Triple helix formation
- Secretion from the fibroblast cell
- Hydrolysis of propeptides
- Assembly into fibril
- Assembly into fiber and formation of cross-links
What is the consensus amino acid sequence for collagen?
Glycine-proline-hydroxyproline (gly-pro-hyp). It is variable but they all have a gly every third residue.
Explain the molecular basis of Scurvy.
Hydroxylated prolines in collagen correlate with highly stable collagen fibers. Vitamin C is a cofactor for the enzymes that hydroxylate proline and lysine, and in Scurvy, vitamin C deficiency inhibits the hydroxylation, leading to skin lesions, blood vessel fragility, teeth falling out, etc.
Where and how does collagen fold?
It happens in the ER lumen. Folding is initiated at the C-terminus and proceeds in a zipper-like fashion to the N-terminus. It resembles a helical rod.
Where are the glycine residues located in collagen and what does that allow for?
They are located in the center to allow for tight packing.
What is deposited in the “hole” between collagen monomers in the synthesis of bone?
Calcium phosphate.
What causes Osteogenesis Imperfecta?
Point mutation in collagen gene: Glycine in collagen is replaced by cysteine (often), which prevents proper triple helix formation, and the ultimate degradation of collagen and poor bone formation.
What are the symptoms of Ehlers-Danlos Syndrome?
Hyperelastic joints and skin, prone to falling and bruising.
Are heterozygotes with an abnormal collagen gene typically symptomatic? Why?
They are symptomatic because even small amounts of defective collagen will completely disrupt the formation of proper collagen structure.
Are heterozygotes with an abnormal collagen processing enzyme gene typically symptomatic? Why?
These individuals are typically NOT symptomatic because even small amounts of working enzyme will allow for proper collagen formation.
How many lysine residues are involved in cross-links in elastin?
FOUR
How many lysine residues are involved in cross links in collagen?
TWO
