L9- Protein Processing

Question 1

What are the two precursors of insulin?

Answer 1

Preproinsulin and proinsulin.

Question 2

What kind of bond holds the two peptide chains of collagen to one another?

Answer 2

Disulfide bonds and non-covalent interactions.

Question 3

What are the two modified amino acids present in collagen?

Answer 3

Hydroxyproline and hydroxylysine.

Question 4

Which cells produce collagen type III?

Answer 4

Fibroblasts.

Question 5

Type I collagen is typically found in which tissues?

Answer 5

Bone, skin, tendons, heart valve.

Question 6

Type III collagen is typically found in which tissues?

Answer 6

Newborn skin and blood vessels.

Question 7

List the steps of collagen biosynthesis in order.

Answer 7

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.

Question 8

What type of enzyme (and co-factor) is required for hydroxylation of proline and lysine during collagen formation?

Answer 8

Hydroxylases. Ascorbic acid (Vitamin C is the co-factor).

Question 9

What effect does hydroxyproline have on collagen stability?

Answer 9

It makes it more stable.

Question 10

What causes collagen to form a triple helix rather than a standard alpha helix or beta sheet?

Answer 10

The steric repulsion between the prolines and hydroxyprolines.

Question 11

What amino acid is typically found at every third residue in collagen?

Answer 11

Glycine.

Question 12

What form of collagen is made after hydrolysis of procollagen?

Answer 12

Tropocollagen.

Question 13

What enzyme helps catalyze the formation of cross links in collagen fibers?

Answer 13

Lysyl oxidase oxidizes lysine to allysine. This forms a cross-link with unmodified lysines.

Question 14

What is the cause of scurvy?

Answer 14

A lack of ascorbic acid (Vitamin C) which leads to a decrease in the hydroxylation of lysines and prolines in collagen.

Question 15

What are the symptoms of scurvy?

Answer 15

Damage and fragility of many tissues and organs such as the gums, as well as skin lesions and blood vessel fragility.

Question 16

Which condition usually results from a mutation in type I collagen?

Answer 16

Osteogenesis Imperfecta. In some of the most severe forms, a glycine is replaced with Cys, interfering with the collagen triple helix.

Question 17

What are the symptoms of Osteogenesis Imperfecta?

Answer 17

Symptoms include bone deformities, brittle bones, and teeth and fragile blood vessels.

Question 18

What are two causes of Ehlers-Danlos Syndrome?

Answer 18

1. Improper processing of collagen caused by lack of enzyme (i.e. lysyl oxidase deficiency) and 2. genetic defects in the collagen genes.

Question 19

What are the symptoms of Ehlers-Danlos Syndrome?

Answer 19

Symptoms include hyperelastic joints and skin hyperextendibility.

Question 20

Keratin is a protein rich in which amino acid?

Answer 20

Cysteine.

Question 21

What is the basic structural unit of collagen?

Answer 21

The collagen triple helix.

Question 22

True or False. Different types of collagen arise from alternative splicing.

Answer 22

False. Different types of collagen are encoded by separate genes.

Question 23

Type II collagen is typically found in which tissues?

Answer 23

Cartilage.

Question 24

Type IV collagen is typically found in which tissues?

Answer 24

Basement membranes.

Question 25

Which enzyme catalyzes the hydroxylation of proline into hydroxyproline?

Answer 25

Prolyl hydroxylase.

Question 26

Which enzyme catalyzes the hydroxylation of lysine into hydroxylysine?

Answer 26

Lysyl hydroxylase.

Question 27

Vitamin C is a cofactor for the hydroxylation of which amino acid present in collagen?

Answer 27

Proline.

Question 28

How does the hydroxyproline content of collagen relate to the stability of the collagen molecule?

Answer 28

The more the hydroxyproline, the more stable the collagen molecule (as defined by higher melting point).

Question 29

What kind of bond predominates between the three chains of a collagen triple helix?

Answer 29

Hydrogen bonding between the NH groups of glycine on one chain and the carboxyl groups on another chain.

Question 30

True or False. Collagen processing and assembly occur outside the cell (i.e. in the extracellular space).

Answer 30

True.

Question 31

What is the difference between procollagen and tropocollagen?

Answer 31

Tropocollagen molecules lack the N- and C- terminus of procollagen and can spontaneously assemble into collagen fibrils.

Question 32

In which tissues are elastin fibers typically found?

Answer 32

In elastic tissues such as the lungs.

Question 33

What is the most common cross-linkage between elastin molecules?

Answer 33

Desmosine linkage, which involves four lysines.

Question 34

In which tissues is keratin typically found?

Answer 34

Hair and nails.