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lec 17- extracellular matrix Flashcards

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1
Q

what is the extracellular matrix?

A

-extracellular matrix = a network of proteins, minerals, sugars, and water outside of the cells

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2
Q

what does the extracellular matrix provide?

A

it provides:
-mechanical support to tissues
-pathways for cellular migration
-survival signals
-sequesters growth factors

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3
Q

what are the 5 classes of macromolecules in the ECM? what can be done to them?

A
  1. collagen
  2. Elastin
  3. glycosaminoglycans and proteoglycans
  4. hyaluronan (a unique glycosaminogylcan)
  5. adhesive glycoproteins

-can be encoded by, can be alternatively spliced, geometrical arrangements can influence cell behavior which gives rise to many different types of ECMs

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4
Q

what makes the ECM?

A

-cells that are in the tissue like fibroblasts
-fibroblasts secrete the fibrous part of the connective tissue and ground substance

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5
Q

what determines how hard or soft a ECM is?

A

-the fibrous part of connective tissue and the ground substance (the material between the fibres made of variable amounts of water and other molecules) which determines the strength of the ECM

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6
Q

what is collagen?

A

-the most abundant protein in the human body and is found across the phylogenetic tree and is very strong

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7
Q

what is the structure of collagen?

A

-rod shaped
-triple helix that can be up to 420 nm long
-contains glycine residues at the core which are small and allow tight packing of the helices

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8
Q

what are the triple helix fibres of collagen that can be made of identical or different chains called?

A

homotrimers for same, heterotimers for 2 or 3 different chains

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9
Q

how many different type of collagens are in humans? how many different proteins that have collagen gene triple repeating segments in them?

A

over 20 types in humans, over 100 proteins with collagen genes

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10
Q

what are the 3 types of collagen?

A
  1. fibrillar collagens
  2. sheet forming collagens
  3. anchoring/Linking collagens
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11
Q

what are the features of fibrillar collagens?

A

-300 nm long
-strong but flexible

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12
Q

where can fibrillar collagens be seen?

A

-in a loose network with more ground substance (water)than collagen, e.x. connective tissue of the intestine
-in a dense network with less ground substance or anything in between, used to reinforce all of the tissues in the body, e.x. tendon

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13
Q

is there collagen in the eye?

A

yes, layers of orthogonal fibers (fibers at angles) and a vitreous body that contains glycosaminoglycans and proteoglycans trapped within collagen

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14
Q

what do fibrillar collagen usually form?

A

-form heteropolymers in vivo with 1 other collagen
-are conserved from sponges to vertebrates

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15
Q

what are the general steps of fibrillar collagen formation?

A

-fibroblasts make collagen 1 and release it from the cells using exocytosis

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16
Q

how is collagen 1 made in 8 steps?

A
  1. very long (42 exons) collagen 1 genes encode collagen 1 chains
  2. preprocollagen translocates to the rough ER
  3. in the ER, the signal sequence is removed, forming the procollagen
  4. sugars are added to the protein
  5. folding of the protein begins
  6. the protein is folded into the long procollagen triple helix and secreted from the ER using COPII vesicles that are modified by accessory proteins to fit the large fibrils
  7. once secreted from the cell, other enzymes called matrix metalloproteinases (MMPs) cleave the procollagen into pieces resulting in collagen
  8. collagen then self assembles into fibrils that have 67 nm stagger and are usually covalently crosslinked at their lysines by the enzyme lysyl oxidase to give the high tensile strength of the collagen fibrils
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17
Q

what are sheet-forming collagens?

A

form sheets instead of fibrils that wrap around organs or tissues (basal lamina) or whole animals (cuticle of earth worms)

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18
Q

what are linking collagens?

A

collagens that link fibrillar ad sheet forming collagens to other structures

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19
Q

what are elastic fibers?

A

fibers that act like rubber bands, give organs the ability to recoil after being stretched

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20
Q

what makes elastic fibers?

A

-embryonic and juvenile fibroblasts

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21
Q

are the elastic fibers you are born with, the ones you keep for the rest of your life?

A

yes, the turn over is very slow if at all

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22
Q

are elastic fibers formed of fibrillin microfibrils that are a scaffold for the protein elastin to bind to?

A

yes

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23
Q

how many genes for fibrillin?

A

3 genes in humans

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24
Q

is elastin only made in humans?

A

yes, but insects and molluscs have evolved different proteins to make elastin-type fibers

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25
do humans have 1 elastin gene that is alternatively spliced?
yes
26
are elastin proteins covalently linked to one another through actions of the lysyl oxidase enzyme?
yes
27
how does elastin stretch?
the segments between the cross-linked elastin protein segments align with others when stretched
28
what are glycosaminoglycans?
long polysaccharides
29
what are proteoglycans?
proteins that are covalently post transitionally modified with glycosaminoglycans
30
are glycosaminoglycans and proteoglycans made in all vertebrate cells and are they secreted into the ECM?
yes
31
what are glycosaminoglycans and proteoglycans a major part of?
-cartilage -loose connective tissue -basement membranes
32
do glycosaminoglycans and proteoglycans vary in length and sequence of their sugar groups?
yes
33
what are glycosaminoglycans and proteoglycans thought to do in the ECM?
trap water
34
how much water can glycosaminoglycans and proteoglycans attract?
50g of water per proteoglycan
35
what is hyaluronan (hyaluronic acid)? what are its characteristics?
-the largest glycosaminoglycan (a string of sugars) that is released extracellularly -when hydrated it has a diameter of 200nm -it is not post-transitionally modified -a crucial element of cartilage -can block microbes in other tissues
36
what acts as lubricant for joints? are they located in the eye?
-hyaluronan and other Gags -yes, they are transparent
37
can high levels of hyaluronan protect us from cancer?
yes
38
what is thought to be the function of adhesive glycoproteins?
-they are thought to control interactions between proteins and sugars in the ECM -bind to integrins in the cell
39
what are the two well studied adhesive glycoproteins?
1. fibronectin 2. tensactin
40
what is fibronectin?
-a large V-shaped proteins linked at their C termini by disulfide bonds
41
what does fibronectin bind to?
collagen, cell surface receptors, proteoglycans, and other proteins
42
what are the 2 alternatively spliced types of fibronectin and what do they do?
1. tissue fibronection: makes insoluble fibrils in connective tissue which are used during wound healing 2. plasma fibronectin: in body fluids which are used for blood clots
43
is tensactin found in all vertebrates?
yes, not in invertebrates
44
what is tensactin composed of?
-N-termini from 3 subunits that self associate -disulfide bonds link 2 of the 3 unit arms together to form a 6nm protein
45
what is tensactin found in?
-embryonic tissues -wounds -tumors
46
what does tensactin bind to?
-fibronectin -integrins -proteoglycans -immunoglobulin-superfamily receptors
47
what is the basal lamina?
a 2 dimensional, thin arrangment of ECM proteins that lies very close to the plasma membrane
48
what does the basal lamina form?
a layer under all epithelia
49
what does the basal lamina wrap around?
wrap around muscle cells (sarcolemma)
50
can the basal lamina filter macromolecules?
yes, filters blood plasma into urine in kidneys
51
how does the basal lamina attach to connective tissue?
via collagens
52
what is the basement membrane?
basal lamina + collagen
53
what is laminin?
-another protein in the basal lamina
54
what does laminin bind to?
binds to integrin
55
what does laminin self assemble into?
a 2D network by binding non-covalently to other laminins
56
what secretes laminin?
muscle and epithelial cells
57
the 2D laminin and collagen networks lie parallel to one another and are reinforced by other proteins such as:
-nidogen attaches laminin to collagen -perlecan binds to itself, laminin and collagen
58
what 3 things do the basal lamina cross links provide?
1. the size selectivity of the basal lamina to filter macromolecules 2. a barrier for cell migration 3. the mechanical support to the cells/tissues, force transmission
59
what are Matrix Metalloproteinases (MMPs) used for?
used to break down the ECM
60
how many members of MMPs?
24
61
what are MMPs composed of? what are its characteristics
-have a zinc protease domain -have an autoinhibitory propeptide that binds to zinc ion in the catalytic domain of the enzyme -substrate specificity comes from a regulatory domain at the C-terminus -there are also fibronectin domains in many of them
62
what do MMPs bind to? what do they dock to?
-bind to membrane receptors -dock into the plasma membranre using C -terminal transmebrane domain
63
each MMP is selective and cleaves specific components of the ECM resulting in what two things?
1. weakening of ECM 2. release of bio-active protein fragments

bio 428 (21 decks)

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