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Biochem 1 (WPH) > Connective Tissue - Franzblau > Flashcards

Connective Tissue - Franzblau Flashcards

1
Q

when does a polypeptide become a protein?

A

when it has biological activity

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2
Q

“proteus” is the greek root for…

A

“of highest importance”

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3
Q

growth of connective tissue in the lumen of a blood vessel is called

A

atherosclerosis

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4
Q

emphysema is caused by

A

destruction of elastin fibers in lungs

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5
Q

atherosclerosis is caused by

A

growth of connective tissue in the lumen of a blood vessel is called

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6
Q

cirrhosis is caused by

A

fibrosis of liver

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7
Q

ehlers-danlos syndrom is caused by

A

genetic mutation in collagen metabolism

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8
Q

how many distinct collagen polypeptides are there

A

> 18

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9
Q

how many polypeptides in a mature collagen protein

A

3 wound together

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10
Q

what is the length and width of a mature collagen protein

A

300nm by 1.5 nm

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11
Q

molecular weight of mature collagen protein

A

285 kDa

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12
Q

idiopathic means

A

of an unknown cause

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13
Q

collagen accounts for roughly how much vertebrate protein weight?

A

1/4th

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14
Q

one third of all collagen amino acid residues are…

A

glycine

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15
Q

three common and essential aa residues of collagen are….

A

glycine
proline & hydroxyproline
lysine & hydroxylysine

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16
Q

hydroxylysine is hydroxylated on the __ carbon

A

δ

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17
Q

T/F there are no cystein residues in most mature collagen proteins

A

true

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18
Q

what is the general alternating regional sequence of collagen amino acid residues?

A

regions of gly pro x (nonpolar usually)
regions of gly x x (polar usually)
(x can be hydroxypro, hydroxylys, or others)

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19
Q

is proline typically polar or nonpolar?

A

nonpolar

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20
Q

what is the rise per residue of an alpha helix vs collagen alpha chain helix?

A

.15 nm vs .28 nm

1.5 A vs 2.8 A

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21
Q

what is a type II trans helix

A

a left-handed polyproline helix (.28 nm rise)

found in collagen α chains

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22
Q

is the collagen helix left or right-handed?

A

left

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23
Q

how many α chains form a collagen helix?

A

3

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24
Q

are α chains in a collagen helix wound around each other in a left or right-handed fashions

A

right

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25
Q

why is glycine important in triple helix formation?

A

gly is the only aa that can fit in these tightly bound triple helixes

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26
Q

mutations exchanging glycine residues for other aa residues in collagen may result in what kind of pathology?

A

brittle bones e.g. osteogenesis imperfecta

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27
Q

tropocollagen

A

complete functional 3-stranded collagen molecule

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28
Q

how do tropocollagen molecules line up to form a fibril?

A

head to tail and staggered by 25%

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29
Q

how much are adjacent tropocollagen fibrils staggered by?

A

25%

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30
Q

what is the molecular weight of an amino acid on average?

A

100 daltons

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31
Q

how many amino acids in a 100,000 Da polypeptide?

A

1,000

100 daltons / amino acid

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32
Q

how many amino acids in 100 kDa polypeptide

A

1,000
100 daltons / amino acid
.1 kDa / amino acid

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33
Q

are all 3 α chains in a tropocollagen molecule identical?

A

usually not

e.g. collagen I is α1 2α2

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34
Q

what is the α chain structure of collagen I?

A

α1 2α2

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35
Q

T/F the α1 chain of different collagen types are genetically distinct

A

true

α1 just denotes the first type of α-chain in that collagen, it is not universal nomenclature

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36
Q

where is collagen I found

A

skin tendon bone cornea (70% of all collagen)

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37
Q

which is the most common collagen type?

A

collagen I (70% of all collagen)

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38
Q

collagen II is found…

A

in cartilage

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39
Q

collagen III is found…

A

in reticular fibers

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40
Q

collagen IV is found…

A

in basement membranes

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41
Q

outline the entire collagen synthesis pathway from transcription to turnover

A 
transcription
translation
hydroxylation in ER
glycosylation in Golgi
pro-collagen triple helix
extrusion from cell
tropocollagen (termini cleaved)
fiber formation
fiber stabilization
turnover/repair
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42
Q

where are collagen α-chains hydroxylated?

A

ER

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43
Q

where are collagen α-chains glycosylated?

A

Golgi

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44
Q

where is procollagen cleaved into tropocollagen?

A

ECM

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45
Q

what is collagen biosynthetic intermediate that is extruded from the cell?

A

procollagen (triple helix with terminal tangles)

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46
Q

what process in collagen biosynthesis gives rise to microheterogeneity of α-chains?

A

hydroxylation in ER

glycosylation in Golgi

47
Q

what is the enzymes that modify collagen in the ER?

A

prolyl hydroxylase

lysyl hydroxylase

48
Q

T/F prolyl hydroxylase and lysyl hydroxylase modifie free proline and lysine

A

false - only hydroxylate proline and lysine in pp chains

49
Q

which is more commonly hydroxylated on proline, C3 or C4?

A

C4, but C3 possible

50
Q

what is the cofactor for prolyl hydroxylase?

A

ascorbate (from diet)

lack causes scurvy

51
Q

ascorbate is a cofactor of which collagen biosynthetic enzyme?

A

prolyl hydroxylase

52
Q

the cofactor in the collagen biosynthetic pathway that causes scurvy if lacked is called __ and it interacts with enzyme __

A

ascorbate

prolyl hydroxylase

53
Q

why does ascorbate lack result in scurvy?

A

ascorbate is a cofactor for prolyl hydroxylase

lack = fewer hydroxylations, failure to stabilize collagen fibrils through x-linking

54
Q

which number C does lysyl hydroxylase hydroxylate?

A

C5 (δ)

55
Q

ehlers-danlos syndrome is caused by a mutation in which collagen biosynthetic enzyme?

A

lysyl hydroxylase

prolyl hydroxylase problems are fatal in utero

56
Q

what is a cofactor for lysyl hydroxylase?

A

ascorbate

57
Q

is ascorbate a cofactor for prolyl hydroxylase or lysyl hydroxylase?

A

both

58
Q

what interactions stabilize procollagen through the terminal extensions?

A

disulfide bonds

59
Q

where in collagen are disulfide bonds found?

A

on the terminal ends of procollagen

but these are cleaved off in functional tropocollagen and mature collagen fibers

60
Q

which terminal extensions bind together first in procollagen formation?

A

C-terminals (through disulfide bonds)

then procollagen wraps up to N-terminus

61
Q

with reference to collagen, Tm is the temperature at which…

A

50% of the helical structure is lost

62
Q

the temperature at which 50% of collagen helical structure is lost is called

A

Tm (melting temperature)

63
Q

what is the Tm of:
gly-pro-pro collagen sequences
gly-pro-hyp collagen sequences
collagen as a whole

A 
gly-pro-pro = 24 degrees C
gly-pro-hyp = 58 degrees C
overall        = 37 degrees C
64
Q

what is the melting temperature of collagen

A

37 degrees C

roughly physiologic, we teeter on the edge of stability… but there are other stabilizing forces present

65
Q

T/F the collagen triple helix is remarkable stable under physiological conditions

A

true - but it will denature when heated

66
Q

what does the typical melting curve (heat denaturation curve) of collagen look like

A

~100% helix content until sudden drop-off near 37 degrees C (Tm)
50% helix content at 37 degrees C

67
Q

what enzyme cleaves procollagen into tropocollagen?

A

procollagen peptidases

68
Q

what is the function of procollagen peptidases in collagen biosynthesis?

A

cleave terminal extensions from procollagen and it becomes tropocollagen

69
Q

what collagen type is not cleaved from procollagen to tropocollagen by procallagen peptidase?

A

type IV collagen (basement membranes)

70
Q

gaps between head-tail tropocollagens in fibers are __ nm

A

42 nm

71
Q

adjacent tropocollagen rows are displaced __ nm in fibers

A

68 nm

roughly 1/4th of 300nm total

72
Q

what forces drive the quarter stagger of tropocollagen in collagen fibrils?

A

polar and non-polar forces

73
Q

how are collagen fibers formed vs stabilized?

A

formed: polar and non-polar interactions line tropocollagen up head-tail and quarter stagger
stabilized: covalent cross-linking through lysil oxidase and aldol condensations and also 3 lysyl hydroxypyridinium rings

74
Q

2 types of x-linkage to stabilize collagen

A
  • aldol cross links: lysyl oxidase LOX turns lysyl amino groups into aldehyde groups, which bind to each other through aldol condensations
  • hydroxypyridinium ring (pyridinoline) formation betwen two hydroxylysyl and one lysyl residue
75
Q

how does osteogenesis imperfecta come about and what are the symptoms

A
  • mutations impair collagen triple helix formation (gly substituded with sterically bulkier residues), leads to over hydroxylation & glycosylation because helices are not wound as tightly
  • brittle bones, frequent fractures
76
Q

what happens in the disease lathyrism caused by ingestion of β-aminopropionitirile BAPN which is found in sweet peas?

A

BAPN is suicide inhibitor of LOX, so aldol cross-linking of collagen fibers reduced

77
Q

T/F collagen is a static protein

A

false - synthesis and degredation are dynamic and balanced, not static

78
Q

what enzymes participate in collagen turnover and repair?

A

collagenases

79
Q

how do collagenases work in collagen turnover and repair?

A

-cleave collagen, decreasing Tm from ~37 to ~30 degrees C

80
Q

escribe 3 steps of collagen turnover and repair

A
  • collagenases cleave collagen, decreasing Tm from ~37 to ~30 degrees C
  • denatured collagen α-chains are degraded non-specifically by other proteases
  • degredation products may feedback to new collagen production
81
Q

what is the approximate rate of collagen turnover?

A

~50% turnover every 3-4 weeks

82
Q

how does the quaternary structure of elastin differ from collagen?

A 
elastin = no quaternary structure (single pp only)
colagen = 3 α-chains
83
Q

elastin contains __-rich non-polar regions that participate in hydrophobic interactions

A

valine

84
Q

elastin fibers associate with one another through what kind of interactions?

A

covalently cross-links

85
Q

what is the principle stabilizes elastin fibers?

A

entropy - stretched = less entropy, wants to recoil

86
Q

the monomeric precurser to to elastin fibers is called

A

tropoelastin

87
Q

tropoelastin is

A

the monomeric precurser to to elastin fibers

88
Q

in what form is elastin when it moves from intracellular to ECM?

A

tropoelastin

89
Q

where is tropoelastin found?

A

ICM, secreted to ECM to cross-link and form elastin fibers

90
Q

what enzyme facilitates elastin cross-links?

A

LOX lysyl oxidase

91
Q

does LOX lysyl oxidase facilitate cross-linking of elastin or collagen?

A

both

92
Q

what is an alysyne residue

A

a lysine with amino turned aldehyde

93
Q

how does elastin corss-linking occur?

A
  • lysyl oxidase LOX oxidises 3 lysine residues into aldehyde (alysine) residues
  • these 3 alysine react with a fourth lysine to form desmosine, a 4 lysyl ring structure
94
Q

what is a desmosine

A

a 4 lysyl ring structure that cross-links elastin fibers

95
Q

marfan syndrome is cause by

A

missing fibrillin gene (fibrillin is a component of collagen)

96
Q

what is the half-life of elastin?

A

70-80 years

97
Q

what is the half-life of collagen?

A

3-4 weeks

98
Q

how does the half-life of elastin compare to that of collagen?

A

much longer

70-80 years vs 3-4 weeks

99
Q

what are 2 possible causes of emphysema?

A

smoking

α-1 antitrypsin deficiency

100
Q

what amino acid residues to GAGs bind to?

A

serine residues (O-linked)

101
Q

GAGs are polysaccharides formed by repeating __ __ units

A

repeating amino-disaccharide units

102
Q 
chondroiotin sulfate
heparan sulfate
keratan sulfate
hyalurononan
are all examples of
A

GAGs

103
Q

what is a proteoglycan

A

protein + GAGs

104
Q

aggrecan and decorin are examples of

A

proteoglycans

105
Q

which has more GAG chains, aggrecan or decorin

A

aggrecan - 100 GAGs

decorin - 1 GAG (with N-linked oligosaccharides)

106
Q

what is the charge of GAGs

A

negative (sulfate and carboxyl groups)

107
Q

what gives GAGs their negative charge?

A

sulfate and carboxyl groups

108
Q

this protein binds cells and collagen fibers together

A

fibronectin

109
Q

name 4 components of a typical proteoglycan

A

hyaluronic acid backbone
linker protein (hylauronic acid to core proteins)
core proteins (branching off hyaluronic acid)
GAGs (branching off core proteins)

110
Q

T/F H-bonds between aa’s in neighboring collagen chains stabilize the structure

A

true

111
Q

T/F proteoglycans function in all of the following:

  • structure
  • aid cell adhesion
  • determine viscoelastic properties
  • withstand compression
  • facilitate contact between ligands and receptors
  • serve as reservoir of growth factors
  • protect proteins from proteolytic degredation
A

true

112
Q

T/F proteoglycand facilitate protein degredation

A

false - they protect proteins from proteolytic cleavage

113
Q

what is the difference between:
hydroxypyridinium (pyridinoline)
desmosine

A

hydroxypyridinium (pyridinoline) - collagen cross links (3 lysyl residues)
desmosine - elastin cross links (4 lysyl residues)

Biochem 1 (WPH) (15 decks)

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