Fibrous Proteins

Question 1

Connective tissue

Answer 1

Function= support/connect organs and other structures
Key components=
-Collagen
-Elastin
-Fibrillin

Question 2

Collagen

Answer 2

-most abundant in the body (25% of protein mass)
-extensively mod by post trans mod
-organise and strengthen ECM
-synth/secreted by connective tissue cells
-triple helix (alpha chains)
- Proline, Lysine, Glycine

Question 3

Collagen type I= skeleton

Answer 3

-most common (90%)
-bone (made by osteoblasts)
-skin
-tendon
-dentin
-fascia
-cornea
-late wound repair

Question 4

Defective production of Type 1

Answer 4

Osteogenesis imperfecta

Question 5

Type II collagen

Answer 5

-cartilage
-intervertebral discs (nucleus pulposus)
-vitreous humor (eye) (vitreous body)

Question 6

S.C.A.B

Answer 6

Type I- skeleton
Type II- cartilage
Type III- arteries
Type IV- basement membrane

Question 7

Collagen type III

Answer 7

Reticulin- skin, blood vessles, uterus, fetal tissue, early wound repairs

Question 8

Type III Collagen defect found in

Answer 8

Ehlers- Danlos syndrome

Question 9

Collagen Type IV

Answer 9

-under Basemental membrane/basal laminate (glomerulus cochlea)
-lens

Question 10

Defects in type IV collagen

Answer 10

-defect in Alpert syndrome
-targeted by autoantibodies in Goodpasture syndrome
-Myofibroblasts are responsible for secretion and wound contraction

Question 11

Alpert Syndrome

Answer 11

-hereditary nephritis
-defect Type IV collagen= mutation to alpha3-5 chains
-x linked
Classic triad= hematuria, hearing loss & ocular disturbances

Question 12

Collagen synthesis

Answer 12

-extensive post translation modification
alpha chains synth in rough ER=
-enter RER lumen as pre-procollagen
-get cleaved becoming pro-alpha chains

Question 13

How are prolines and lysines synthesised

Answer 13

-hydroxylated
-requires vitamin C (cofactor for hydroxylase enzymes)
-deficiency of vitamin C —> scurvy

Question 14

Additional synthesis for hydroxylysine

Answer 14

Glycosylated
-adding sugar molecule

Question 15

Scurvy

Answer 15

-vit c deficiency
-defective pro alpha chains
-not forming triple helix
-degraded in cell (not secreted)
-fragile blood vessels (bleeding/bruising
-loss of teeth
-loss of wound healing

Question 16

Propeptides

Answer 16

-extra amino acids at N and C end of pro alpha chains
-form in Type I,II,III (fibrillar Collagen Alpha chains)
-form disulphide bonds to stabilise alpha chains
3 pro alpha chains - pro collagen

Question 17

ECM modifications of collagen

Answer 17

-moves through Golgi
-procollagen excreted by exocytosis
-propeptides are cleaved (N and C ends)
Tropocollagen formed

Question 18

Collagen fibrils form

Answer 18

-tropocollagen is less soluble than procoll
-fibrils self assemble
-lysine crosslinking= strengthen
-EC enzyme= lysyl oxidase
-copper= cofactor

Question 19

Collagen Fibers

Answer 19

Bunch of triple helices

Question 20

From preprocollagen to collagen Fiber

Answer 20

-Preprocollagen
-Hydroxylations of proline or lysin (with help of vit C)
-Glycosylation
-Triple helix formed
-Exits RER and Golgi
-Exocytosis
-cleaved C and N ends
-assmeble into collagen fibers
-forms cross links making collagen fibers
(stabilised by lysyl oxidase)

Question 21

Aging wrinkles-

Answer 21

-decreased production of elastin and collagen in dermis
-collagen and elastin fibres thicken and clump

Question 22

Osteogenesis imperfects

Answer 22

-brittle bone disease
-genetic disorder
-rage of severity
-osteoporosis and fractures
-defect in collagen production

Question 23

Types of osteogenesis imperfecta

Answer 23

-Type I= most common
-Type II=lethal in utero
-Type III= more severe than I
-Type IV= more sever than I
Severity= II, III, IV, I

Question 24

Type I Osteogenesis imperfecta

Answer 24

-autosomal dominant
-mutation in COL1A1 to COL1A2
-genes encode for alpha chains Type I coll
-abnormal/absent alpha chains
-triple H not formed normally
decreased production of Type I coll

Question 25

Clinical features of osteogenesis imperfecta

Answer 25

-recurrent fractures (confused with child abuse)
-blue sclera (clear connective tissue over veins)
-hearing loss (abnormal malleus, incus and stapes (ossicles))

Question 26

Other features of OI

Answer 26

dentinogensis imperfecta
-rare in Type I
-common in type III, IV
-discoloured teeth
-translucent teeth
-weak teeth

-bone deformity
-short stature