Fibrous Proteins

Question 1

what 3 types of molecules are found in ecm of all tissues

Answer 1

1- proteogylcans
2- collagens
3- multiadhesive matrix proteins

Question 2

what are the two types of proteins in the body

Answer 2

Fibrous

Globular

Question 3

what are the 3 types of fibrous proteins

Answer 3

alpha keratin - external protection
elastin - in connective tissues
collagen - also in connective tissues but related to tensile strength

Question 4

what cells are alpha keratin made by

Answer 4

epidermal cells

Question 5

describe the secondary structure of alpha keratin

Answer 5

alpha helices
rich in amino acids
hydrophobic side chains on the outside that make it insoluble
rich in cys residues which form disulphide bridges between cysts in separate alpha helices to connect them

Question 6

explain the role of disulphide bridges

Answer 6

stabilise the interior of a globular protein and make alpha keratin stronger

Question 7

what is a protofibril

Answer 7

when a dimer associates antiparallel with two other dimers in a staggered arrangement

Question 8

what is elastin made from

Answer 8

fibroblasts and chondrocytes

Question 9

describe formation of elastin

Answer 9

proelastin to tropoelastin

tropoelastin crosslinked via LYSINE residues to give elastin

Question 10

what are the two types of cross links that occur

Answer 10

desomsine - 4 lysine
aldol/lysinonorleucine - 2 lysine
these links are formed by oxidation

Question 11

describe desmosine cross link

Answer 11

formed from 4 lysines 3 of which are oxidised

Question 12

how can elastin deform

Answer 12

because it has a lack of hydrogen bonds

Question 13

what is the secondary structure of elastin

Answer 13

beta spiral

Question 14

what is the most abundant protein in the body

Answer 14

collagen

Question 15

what cells make collagen

Answer 15

fibroblasts and chondrocytes

Question 16

what are the 4 stages of collagen assembly

Answer 16

1- synthesised as procollagen which is secreted from the cell
2- cleaved to tropocollagen by procollagen peptidase
3 - assembly of tropocollagen leads to collagen fibre
then crosslinking strengthens

triple helix structures

Question 17

what type of triple helix is found in collagen

Answer 17

left handed helix (alpha helices are usually right handed

Question 18

does collagen have hydrogen bonds

Answer 18

yes - unlike elastin

Question 19

what property of the polypeptide allows them to be packed together in collagen

Answer 19

glycine R-group is only H

allows chains to be packed together

Question 20

what is the role of the pro and hyp residues on the outside of the helices

Answer 20

they form inter-triple helix contacts to stabilise the collagen fibres

Question 21

what is osteogenesis imperfecta

Answer 21

mutant collagen gene 
Gly becomes Cys 
problem with procollagen formation 
tropocollagen not regularly packed as it remains unfolded 
clinical symptom - brittle bones

Question 22

what is ehlers - danlos syndrome

Answer 22

reduced levels of procollagen peptidase
procollagen is not fully converted to tropocollagens
stretchable skin - imperfect collagen

Question 23

what is scurvy

Answer 23

hydroxyproline needed for correct assembly of collagen - needed for OH group
vitamin c ascorbate is a cofactor for this
leads to skin lesions and damages blood vessels

Question 24

what is lathyrism

Answer 24

it effects the final stages of crosslinking
copper deficiency or ingestion of beta-aminopropionitrile
irreversibly inhibits lysyl oxidase