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DMD 5243 > Extracellular matrix (complete) > Flashcards

Extracellular matrix (complete) Flashcards

1
Q

What is the extracellular matrix

A

The interstitial fluid that contains ions, proteins, proteoglycans, and signaling molecules

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2
Q

What are the two main components of the extracellular matrix

A

proteins and proteoglycans

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3
Q

What are the three main proteins in the extracellular matrix

A
  1. collagen
  2. fibronectin
  3. elastin
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4
Q

What are the five main proteoglycans found in the extracellular matrix

A
  1. hyaluronic Acid
  2. Chondroitin sulfate
  3. Dermatan sulfate
  4. Heparan sulfate
  5. Keratan sulfate
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5
Q

What are the four main functions of the proteins and proteoglycans of the extracellular matrix

A
  1. provide shape and structure to the interstitial space
  2. lubrication and cushioning of cells and other things
  3. provides an anchor point for cellular adhesion
  4. allows communication between cells
  5. controls cell life cyles (proliferation, differentiation, apoptosis, migration, etc)
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6
Q

What do the proteins of the Extracellular matrix provide

A

Structure and allow cellular adhesion

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7
Q

Do proteins or proteoglycans prevent compression of the ECM (extracellular matrix)

A

Proteoglycans

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8
Q

what is the major protein of the ECM

A

collagen

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9
Q

What are proteoglycans

A

highly charged protein/saccharide polymers that are 95% carbohydrates

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10
Q

What is the specific structure of collagen

A
  1. forms a left-handed helix
  2. 3 amino acids per turn
  3. each turn has the sequence Gly-X-Y
  4. Three helical collagen proteins come together to make a triple stranded, right handed superhelix
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11
Q

What type of helix does a strand of collagen form

A

a left handed helix

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12
Q

how many amino acids per turn are there in collagen

A

3

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13
Q

what is the specific sequence of amino acids that is found in collagen

A

Gly-X-Y
X = proline (usually)
Y = hydroxyproline (usually)

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14
Q

What is the quaternary structure of collagen

A

a triple-stranded right handed superhelix

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15
Q

Where are the glycine residues of a collagen strand located in the triple helix

A

toward the center of the triple helix

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16
Q

why are the glycine residues of a collagen strand situated toward the center of the triple helix

A

because of their very small side chain

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17
Q

Why are proline and hydroxyproline used with glycine in a collagen strand

A

they provide strength to the collagen structure due to their bulk and rigidity

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18
Q

What are the two classes of collagen

A

fibrillar (fibril-forming) and nonfibrillar

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19
Q

What is the most common type of collagen in the body

A

Type 1

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20
Q

Can collagen fibers be a mixture of collagen types

A

yes

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21
Q

What is the main function of fibrillar collagen

A

provide tensile strength to skin, tendons, and ligaments

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22
Q

What are three types of nonfibrillar collagen

A
  1. basement membrane collagen (type 4)
  2. fibril-associated collagens with interrupted triple helices (FACITs)
  3. Multiplexins
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23
Q

What happens when nonfibrillar collagen interacts with fibrillar collagen

A

they produce network, or mesh like structures

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24
Q

What type of collagen is the primary structure of the basement membrane

A

type 4 collagen

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25
Q

What is the main function of the basement membrane

A

to prevent migration of certain cell types between different tissue types

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26
Q

What are the steps of collagen synthesis

A
  1. Preprocollagen is synthesized with a signal sequence and is directed to the lumen of the ER
  2. Signal sequence is removed to make Procollagen
  3. Post translational modifications occur
    • proline –> hydroxyproline
    • sugars are attached to the protein
    • Disulfide linkages are incorporated
  4. Disulfide linkages trigger formation of triple helical structure
  5. tropocollagen then moves to the golgi and is exocytosed
  6. tropocollagen is converted into mature collagen
  7. mature collagen can be crosslinked to form insoluble collagen fibrils
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27
Q

What occurs in converting preprocollagen into procollagen

A

the signal sequence is removed

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28
Q

what post-translational modifications are made to precollagen

A
  1. prolines are converted to hydroxyprolines
  2. sugars are attached to the protein
  3. disulfide linkages are incorporated
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29
Q

What is scurvy

A

a defect in collagen synthesis that is caused by insufficient vitamin C

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30
Q

How does low vitamin C lead to defective collagen synthesis

A

Vitamin C is a cofactor for the enzymes that produce hydroxyproline, without vitamin C hydroxyproline isn’t made

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31
Q

What are the symptoms of Scurvy

A
  1. Subcutaneous hemorrhages
  2. muscle weakness
  3. soft, swollen, and bleeding gums
  4. osteoporosis
  5. poor wound healing
  6. anemia
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32
Q

What is Osteogenesis imperfecta

A

a defect in collagen synthesis that causes brittle bones

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33
Q

What causes Osteogenesis imperfecta

A

it is caused by a genetic defect in the genes coding for alpha 1 or alpha 2 collagen chains

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34
Q

Osteogenesis imperfectia is caused by a point mutation in the gene that causes a different amino acid to be in the spots that are usually glycine in collagen. Why is that problematic

A

because the amino acid replacing glycine will usually have a bulky side chain. which wouldn’t allow the collagen to coil and form the triple helical structure

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35
Q

What are the symptoms of Osteogenesis imperfecta

A
  1. fragile bones
  2. thin skin
  3. abnormal teeth
  4. weak tendons
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36
Q

What is the primary function of elastin

A

it is responsible for the elastic (stretchy) nature of blood vessels, lungs, ligaments, and skin

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37
Q

What is the structure of elastin

A

a single protein with very little post translational modifications

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38
Q

What is a desmosine

A

a complex two dimensional lattice work formed by crosslinked elastin monomers

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39
Q

What does the formation of a desmosine (from elastin monomers) permit these elastin fibers to do

A

it permits the elastin polymers to stretch in two directions

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40
Q

What does fibronectin do in the ECM

A

it acts as an attachment point for other cellular and ECM components

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41
Q

Is there only one form of fibronectin, or are there multiple, tissue and developmental stage specific

A

there are multiple tissue and developmental stage specific types of fibronectin

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42
Q

What is fibronectin involved in

A

cell adhesion
cell migration
embryonic morphogenesis
cytoskeletal and ECM organization

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43
Q

What do proteoglycans form in the ECM

A

they are the gel-forming portion of the ECM, sometimes called the ground substance

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44
Q

What are proteoglycans? what is their structure

A

they are protein chains with large amounts of carbohydrates attached

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45
Q

about what percentage of proteoglycans are carbohydrates and proteins

A

they are 95% carbs, 5% proteins

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46
Q

What do you call the carbohydrate portion of proteoglycans

A

Glycosaminoglycans (GAGs)

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47
Q

What are the 5 major proteoglycans in the ECM

A
  1. Hyaluronic Acid
  2. Chondroitin sulfate
  3. dermatan sulfate
  4. heparan sulfate
  5. keratan sulfate
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48
Q

Where are proteoglycans primarily constructed

A

in the Golgi

  • Protein portion is delivered from the ER
  • the Carb portion is added in the golgi
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49
Q

Where are proteoglycans degraded

A

in the lysosome

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50
Q

are proteoglycans degraded in a specific sequence, or just randomly

A

they are degraded in a specific sequence

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51
Q

What occurs if the process of constructing or degrading proteoglycans is disrupted

A 
it leads to a broad class of diseases called
Mucopolysaccharidosis
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52
Q

What are lysosomal storage diseases

A

defects in the lysosomes ability to break down proteoglycans

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53
Q

What is the main function of proteoglycans

A

to provide structural support to tissues, especially cartilage and connective tissue

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54
Q

What is the effect that proteoglycans have on compression stress

A

they are largely responsible for preventing compression stress

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55
Q

what makes proteoglycans effective at reducing compression stress

A

their large negative charges

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56
Q

What are aggrecans

A

large macromolecular bottle-brush like structures formed by many different proteoglycans interacting with each other

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57
Q

What is the typical overall charge of proteoglycans

A

its a large negative charge

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58
Q

how do proteoglycans neutralize their large negative charge

A

by binding numerous counter ions (cations)

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59
Q

What does the high charge density on proteoglycans cause to happen in the ECM

A

the high charge density of proteoglycans leads to an influx of water into the ECM

60
Q

What results from the influx of water into the ECM by proteoglycans

A

stiffness and swelling of the ECM due to the balancing of osmotic forces

61
Q

What are the properties of the ECM that are directly caused by the highly charged proteoglycans

A
  1. Rigidity of the ECM
  2. Flexibility of the ECM
  3. Compressibility of the ECM
62
Q

What does the rigidity, flexibility and compressibility of the ECM allow tissues to do

A

withstand torsion and shock

63
Q

What is Hyaluronic Acid

A

a GAG on proteoglycans

64
Q

What are the characteristics of hyaluronic acid

A
  1. longest chain of the GAGs
  2. only GAG with no protein core
  3. only GAG with no sulfonation
  4. major component of synovial fluid and vitreous humor
  5. found in ECM of cartilage and skin
65
Q

What is the function of hyaluronic acid in synovial fluid and vitreous humor

A

to increase the viscosity

it is one of the major lubricating components

66
Q

What is the function of hyaluronic acid in the cartilage and skin

A
  1. involved in inflammation and wound repair

2. UVB sunburns = decreased hyaluronic acid = inflammation and erythemia

67
Q

Which GAG doesn’t have a protein core

A

Hyaluronic acid

68
Q

which GAG doesn’t have sulfonation

A

hyaluronic acid

69
Q

Which GAG is the most common GAG

A

Chondroitin sulfate

70
Q

In which tissue is Chondroitin sulfate the major component

A

cartilage

71
Q

What is the function of chondroitin sulfate in cartilage

A

it resists compression of cartilage

72
Q

What happens in the joints when there is a decrease in chondroitin sulfate

A

osteoarthritis

73
Q

Which proteoglycan has the highest charge density

A

Dermatan sulfate

74
Q

Which two proteoglycans are structurally similar

A

Dermatan sulfate and Chondroitin sulfate

75
Q

What are two disorders associated with disruption of Dermatan sulfate synthesis

A
  1. Maroteaux-Lamy syndrome (polydystrophic Dwarfism)

2. Hurler’s syndrome

76
Q

What is Maroteaux-Lamy syndrone

A

polydystrophic dwarfism

77
Q

What is hurlers syndrome

A

a defect in catabolism of dermatan sulfate

78
Q

Which of the proteoglycans is the most highly charged of all proteoglycans

A

heparan sulfate

79
Q

What is the proteoglycans that is the major component of basement membranes

A

Heparan sulfate

80
Q

how is heparin related to heparan sulfate

A

it is structurally similar, just smaller

81
Q

What does heparin do

A

binds to antithrombin III and inhibits the clotting cascade

82
Q

Which is the most heterogeneous GAG

A

Keratan sulfate

83
Q

What are the three different classes of Keratan sulfate

A

KS-1 Found in the cornea of the eye
KS-2 found in skeletal tissue (bone and cartilage)
KS-3 found primarily in the brain

84
Q

What causes the differences between the three classes of keratan sulfate

A

the amino acid of protein attachment

85
Q

What Amino acids are each of the three classes of Keratan sulfate bound to

A

KS-1 Asparganine
KS-2 Serine or Threonine
KS-3 Serine of Threonine

86
Q

How is the ECM like reinforced concrete

A

the collagen is like the rebar providing strength and support
the proteoglycans act like cement to tie everything together and provide rigidity

87
Q

Is the ECM a static environment

A

no, it is constantly being remodeled

88
Q

why is the ECM constantly being remodeled

A

to accommodate cell growth, proliferation, and movement

89
Q

What is responsible for digesting the structural components of the ECM

A

Matrix Metalloproteases (MMPs)

90
Q

Are MMPs always active

A

no they are synthesized as zymogens, and later activated

91
Q

what are the two types of MMPs

A

secreted or membrane bound

92
Q

What can MMPs degrade

A 
collagen
elastin
fibronectin
the protein core of proteoglycans
other MMPs
93
Q

What is different about metaloproteases

A

they rely on a metal cofactor for activity

94
Q

What is the metal that MMPs require as a cofactor

A

ZINC

95
Q

What happens to activity of MMPs with introduction of a powerful metal chelator like EDTA

A

the activity of MMPs is abolished

96
Q

What are the three domains of MMPs

A
  1. Propeptide domain
  2. Catalytic domain
  3. Haemopexin-like C-terminal domain
97
Q

What does the catalytic domain do in MMPs

A

binds the zinc and allows for proteolytic activity

98
Q

Which of the three domains of MMPs is occasionally absent

A

the Haemopexin-like C-terminal domain

99
Q

What is the use of the propeptide domain of the MMPs

A

while it is attached to the MMP, the MMP is inactive. When the propeptide domain is removed the MMP becomes active

100
Q

What is the part of the propeptide domain that keeps the MMP inactivated

A

the cysteine switch

101
Q

how does the cysteine switch on the propeptide domain keep MMPs inactive while the MMP still have the propeptide domain

A

the cysteine switch binds the zinc atom and prevents its use by the enzyme.

102
Q

What does the catalytic domain of MMPs use the Zinc it binds to for

A

it uses the zinc to activate a water molecule, the water molecule is then able to react with the amide bond of a protein substrate

103
Q

What are the different classifications of MMPs

A
  1. Collagenases
  2. Gelatinases
  3. Metalloelastases
  4. Stromelysins
  5. Matrilysins
104
Q

What does collagenases degrade

A

fibrillar collagen (only mammalian enzyme that can)

105
Q

what do gelatinases degrade

A

non-fibrillar collagen

106
Q

What do metalloelastases degrade

A

elastin

107
Q

what do stromelysins degrade

A

Most ECM proteins, except fibrillar collagen

108
Q

what do matrilysins degrade

A

mose ECM proteins except collagen

109
Q

Can most MMPs activate other MMPs

A

yes

110
Q

What is enamelysin

A

an MMP that degrades amelogenin

111
Q

What is amelogenin (degraded by enamelysin)

A

a major component of tooth enamel

112
Q

What disease is related to defects in enamelysin

A

Amelogenesis imperfecta

113
Q

What are the symptoms of amelogenesis imperfecta

A

tooth enamel is thin, weak, and discolored

they are more susceptible to cavities, and more sensitive to temperature

114
Q

what are the three proteins that are important in ECM signaling events of MMPs

A

Integrin receptors
Cytokines
Growth factors

115
Q

What are integrins

A

cell surface receptors that link the ECM to the cytoskeleton

116
Q

what leads to activation of the integrin receptor

A

A deformation in the ECM

117
Q

What can the integrin do once it is activated

A
  1. transmit the deformation of the ECM to the cytoskeleton (can affect cellular structure)
  2. Activate cellular transcription factors, modifying gene expression
  3. it can also transmit information out to the ECM
118
Q

What is the structure of integrin

A

dimer with alpha and beta subunits

119
Q

What things can bind to integrins and what do they do

A

cations (Ca or Mg)

they are thought to stabilize the ECM binding to the receptor

120
Q

What two signaling mechanisms can mediate changes in electrical potential

A
  1. stretch activated ion channels

2. environmental electrical potentials

121
Q

What activates stretch activated ion channels

A

deformation of the cell membrane

122
Q

What does ion flow into the cell cause

A
  1. it can activate intracellular secondary signaling mechanisms, which can lead to transcriptional events
  2. it can lead to voltage sensitive signaling events through gap junctions
123
Q

What do gap junctions allow to pass between the cytosol of two adjacent cells

A

ions and small molecules. when ions flow into one cell they can directly pass to another through gap junctions

124
Q

what structures make up gap junctions

A

connexons

125
Q

Besides integrins, what are three other classes of signaling molecules for the ECM

A
  1. cytokines
  2. Growth factors
  3. specific ECM modulators
126
Q

what are cytokines generally thought to be involved in

A

inflammatory processes

127
Q

What are the two common classes of cytokines

A

interleukins (IL)

interferons (IF)

128
Q

can cytokines signal cells to secrete MMPs

A

yes

129
Q

What affect can growth factors have on cells

A
  1. cell growth
  2. cell proliferation
  3. cell differentiation
130
Q

are growth factors and cytokines easily distinguishable

A

no

131
Q

How are growth factors used in dentistry

A

a bone growth factor has began being placed in implants to promote bone growth

132
Q

What are the two parts of bone ECM

A
  1. calcified bone matrix

2. Osteoid

133
Q

Which part of the bone ECM is mineralized (mostly inorganic)

A

the calcified bone matrix

134
Q

What cell types are found in the calcified bone matrix

A

only osteocytes

135
Q

Which part of the bone ECM is nonmineralized

A

the osteoid

136
Q

What happens to the osteoid when it is fully matured

A

it may become calcified bone matrix

137
Q

What is the primary substance in the osteoid

A

type 1 collagen

138
Q

What is the function of osteoblasts

A

to build new bone matrix

139
Q

what is the function of osteoclasts

A

to breakdown existing bone

140
Q

What is the function of osteocytes

A

transmit signals to osteoclasts and blasts to initiate bone remodeling

141
Q

in normal bone how does osteoclast and osteoblast activity compare

A

they are balanced

142
Q

what can cause an imbalance in osteoclast and osteoblast activity

A

outside stimulus on the bone

orthodontics)(osteoporosis

143
Q

What attaches the tooth to the alveolar bone

A

the Periodontal ligament (PDL)

144
Q

what is the primary cell type in the PDL

A

fibroblasts

145
Q

what is the function of fibroblasts in the PDL

A

to create an intricate collagen structure to secure the tooth to the bone

146
Q

What happens when the PDL is put under tensile stress

A
  1. it releases IL-1, IL-6, and VEGF
  2. ILs activate MMPs and inactivate TIMP (MMP inhibitor)
  3. VEGF stimulates angiogenesis
  4. MMPs degrade ECM to facilitate cell proliferation and capillary growth
  5. PDL cells and osteoblasts proliferate and grow more bone
147
Q

What happens when the PDL is compressed

A
  1. PDL releases IL1 and 6
  2. ILs stimulate release of RANKL and MMPS
  3. MMPs degrade non mineralized surface of osteoid and the ECM
  4. RANKL stimulates maturation of osteoclasts
  5. osteoclasts break down bone

DMD 5243 (17 decks)

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