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Movement and Musculoskeletal Biology Emily > 011 connective tissue and fibrous proteins > Flashcards

011 connective tissue and fibrous proteins Flashcards

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1
Q

what are the 5 types of tissues?

A
  • epithelial tissues
  • connective tissues
  • muscular tissues
  • nervous tissues
  • blood
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2
Q

what 3 types of molecules are abundant in ECM in all tissue types?

A
  • proteoglycans
  • collagens
  • multi adhesive matrix proteins (between cells)
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3
Q

what are the 4 main properties of fibrous proteins?

A
  • extended protein structure
  • insoluble in water or lipid bilayers
  • secondary structure is simple ( either alpha helix or Beta sheet)
  • quaternary structure is held together by covalent bridges
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4
Q

give 3 examples of fibrous proteins

A
  • alpha-keratin
  • elastin
  • collagen
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5
Q

what is alpha-keratin used for?

A
  • external protection, toughness
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6
Q

where is alpha-keratin found?

A
  • hair, nails, outer layer of skin
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7
Q

what cells produce a-keratin?

A
  • epidermal cells
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8
Q

what is the secondary structure of a-keratin?

A
  • a-helix
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9
Q

what property of a-keratin makes it insoluble?

A
  • hydrophobic sidechains
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10
Q

what amino acid is a-keratin rich in to form disulphide bridges?

A
  • cysteine
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11
Q

what is the quaternary structure of a-keratin?

A

-2 parallel supercoiled a-helices to form a dimer
- 2 dimers associate and form a tetramer, a staggered arrangement to form the protofibrils
- the association of 4 protofibrils forms a 4 stranded rope = a fibre of keratin

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12
Q

what are the disulphide bridges for?

A
  • increase strength and stability
  • the more disulphide bridges, the stronger the a-keratin
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13
Q

what is the main property of elastin?

A
  • can stretch several times but still return to original size
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14
Q

where is elastin found?

A
  • blood vessel walls, elastic ligaments, lung walls, bladder
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15
Q

what cells produce elastin?

A
  • fibroblasts, chondrocytes
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16
Q

give 2 examples of diseases where elastin is implicated

A
  • cardiovascular disease, lung emphysema
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17
Q

describe the formation of elastin

A
  • synthesised as pro-elastin
  • converted to tropoelastin
  • lysine amino acid crosslinks tropoelastin = elastin
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18
Q

what are the 2 different cross-linking options for elastin?

A
  • desmosine
  • lysinorleucine
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19
Q

describe the linking in lysinorleucine (elastin)

A

2 Lys residues are cross-linked by oxidation, initially forms a Schiff base intermediate, which then forms lysinoleucine, if both oxidized = adol link, linking 2 tropoelastin molecules

20
Q

describe the linking in desmosine (elastin)

A

formed from 4 Lys residues, 3 are oxidised, linking 2,3, or 4 tropoelastin molecules

21
Q

what is the amino acid composition in a-keratin?

A
  • Cys, Phe,Val, Met, Ala
22
Q

what is the amino acid composition in elastin?

A
  • 33% Gly, 10% Pro and Hyp, 23% Ala, 13% Val
23
Q

what structure/feature of elastin makes it insoluble?

A
  • hydrophobic amino acids Ala, Val, Ile, Leu
24
Q

what is the secondary structure of elastin?

A
  • a helix structure, but different to a-helix
  • it is able to stretch and relax like a coiled spring
  • constructed from helices of Beta-turns based on the sequence Val,Pro,Gly,Val = called the Beta-spiral
25
Q

where is collagen found?

A
  • where tensile strength is needed e.g. tendons, inner skin, cartilage, bones, cornea
26
Q

how many different types of polypeptide chains = collagen types are there?

A
  • 30 different polypeptide chains = 16 collagen types
27
Q

what are the overall 4 stages of collagen synthesis?

A
  1. synthesis as procollagen which is secreted from chondrocytes and fibroblasts
  2. cleaved to tropocollagen by procollagen peptides
  3. assembly of tropocollagen leads to collagen fibre
  4. chemical crosslinking of tropocollagen strengthens fibre
28
Q

what cells synthesise collagen?

A
  • chondrocytes, fibroblasts
29
Q

describe the first stage of collagen synthesis

A
  1. 3 seperate pro-alpha chains are synthesised separately in the cells
    - selected Pro and Lys residues are hydroxylated and then some are glycosylated
    - 3 pro-alpha chains assemble at the C-terminus end, starting with disulphide bridge formation between the 3 chains
    - the 3 chains then ‘zip up’ to form procollagen
    - a typical collagen sequence = 900 residues, and a Gly residue every 3rd position e.g. (Pro, Hyp, Gly)300
    - this relates to osteogenesis imperfect where Gly is in the wrong place
30
Q

what medical problem is related to the first step of collagen synthesis?

A
  • osteogenesis imperfecta (aka brittle bone disease, blue sclera of eye)
  • genetic defect
  • due to Gly residue mutation to Cys
  • triple helix is partially unfolded at n terminal
  • tropocollagen cannot pack together properly = weaker formation
31
Q

describe the second stage of collagen synthesis

A
  • cleavage of procollagen to tropocollagen by procollagen peptidase
  • the N-terminals and C-terminal peptides of procollagen are cleaved
  • related to Ehlers-Danlos syndrome
  • tropocollagen is procollagen without the N and C terminals, length = 300nm
  • secondary structure of tropocollagen = triple helix
32
Q

what is the secondary structure of tropocollagen?

A
  • triple helix
33
Q

describe the 6 features of the tropocollagen triple helix (briefly)

A
  1. 3 separate polypeptide chains arranged as a left-handed helix
  2. 3.3 residues per turn
  3. each chain forms h bonds to other 2 chains
  4. Gly residues every 3rd position
  5. side chains point towards centre of triple helix
  6. Pro, Hyp residues are imino acids, helps form ring structure to stiffen triple helix
  7. Gly residues are buried, Pro and Hyp are outside on surface
34
Q

is the tropocollagen helix right or left handed?

A
  • left handed
35
Q

how many residues are there per turn in tropocollagen helix?

A

3.3.

36
Q

what bonds are between the 3 tropocollagen helix chains?

A

hydrogen bonds

37
Q

what amino acid is every 3rd position on tropocollagen helix?

A

Glycine

38
Q

where does the sidechain with Gly face in tropocollagen triple helix?

A
  • towards centre of helix
39
Q

what effect does the structure of Gly have on the tropocollagen helix?

A
  • Gly R group = only H = pack 3 chains closely together
  • Gly NH forms H bond to CO of adjacent polypeptide
40
Q

what effect do Pro and Hyp residues have on the structure of the tropocollagen helix?

A
  • their sidechain forms a covalent link with the mainchain N atom, forming a ring structure and stiffening the triple helix
  • inter-triple helix contacts = stabilize collagen fibre
41
Q

where are Gly and Pro, Hyp in the tropocollagen triple helix?

A
  • Gly is buried, inside of helix
  • Pro and Hyp are outside on the surface of helix
42
Q

what medical problem is related to the second stage of collagen synthesis?

A
  • Ehlers-Danos syndrome (type 7)
  • decreased levels of procollagen peptidase , so not fully converted into tropocollagen
  • high levels of procollagen found in skin and tendons
  • 40nm gaps between tropocollagen molecules become blocked by uncleaved peptides which prevent lysyl oxidase from acting on tropocollagen to form crosslinks
  • symptoms = stretchable skin, hypermobile joints, short stature
43
Q

describe the 3rd stage of collagen synthesis

A
  • assembly of tropocollagen
  • repetitive cross-striations every 67nm
  • each tropocollagen is displaced lengthwise by 1/4 of its length, so they are all overlapping
  • 40nm gaps between tropocollagen molecules, where calcium phosphate is deposited in bone formation
  • assembly forms via noncovalent hydrogen bond involving OH group of hydroxyproline
  • related to scurvy
44
Q

what medical problem is related to the 3rd stage of collagen synthesis?

A
  • scurvy
  • hydroxyproline is needed for the assembly of collagen fibres
  • hydroxyproline is only formed from Pro residues after procollagen has formed
  • this reaction of Pro with prolyl hydroxylase needs ascorbate cofactor, which is Vitamin C
  • lack of Vit C = poor collagen fibril formation = skin lesions, weak blood vessel walls
45
Q

describe the 4th stage of collagen synthesis

A
  • the collagen fibres are stabilised by covalent crosslinks between lysine residues
  • (same as elastin) action of lysyl oxidase generates an aldehyde (CHO) form of lysine from Lys residue
  • joining of 1 CHO and 1 NH2 group (1 oxidised) on 2 Lys residues = lysinorleucine
  • joining of 2 CHO groups (both oxidised) = adol link
  • related to medical problem lathyrism
46
Q

what is the medical problem related to the 4th stage of collagen synthesis?

A
  • lathyrism
  • in uk = animal disease from ingestion of sweet pea seeds with Beta-aminopropionitrile or copper deficiency or low lysyl oxidase (another form of Ehlers-Danlos syndrome)
  • Beta-aminopropionitrile prevents conversion of lys to aldehyde form by irreversibly inhibiting lysyl oxidase
  • lysyl oxidase requires copper for fill activity
  • lack of cross-link formation in collagen = lathyrism
    = pain in calf muscles, especially at night, acute muscle spasms produce painful lumps or ‘lodokas’ which last 10-15mins

Movement and Musculoskeletal Biology Emily (23 decks)

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