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Cell biology > Week 7: ECM > Flashcards

Week 7: ECM Flashcards

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1
Q

extracellular matrix (ECM)

A

network of macromolecules (proteins/polysaccharides) that are secreted and assembled into an organized meshwork

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2
Q

how is the ECM regulated?

A

the ECM is dynamically regulated because cells keep making new components or degrading older components ⇒ helps to regulate cell behavior
- Cells control the ECM but the ECM also controls cells ⇒ mutual relationship

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3
Q

how do cells survive?

A

cells won’t survive unless they bind to a tissue culture dish floor/walls or the ECM ⇒ they divide and grow but stop when the cells are conformed to one another (stop)

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4
Q

anchorage dependent proliferaiton

A

Most cells want to attach to something but Fully cancerous cells will just grow however and aren’t specific
- Half cancerous cells still want to bind to a substrate ⇒ tissue culture plates are coated specially

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5
Q

are tissue cultures in vitro or in vivo?

A

The tissue culture mimics the ECM in the body for normal cell behavior => this is in vivo

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6
Q

functions of the ECM (3)

A
  • Scaffold to support and stabilize tissues
  • Substrates for cell adhesion and migration
  • Regulation of cell survival, proliferation, differentiation, and functions
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7
Q

what are the 3 major macromolecule classes in the ECM?

A
  1. Glycosaminoglycans (GAGs) ⇒ sugars
  2. Fibrous proteins (insoluble) ⇒ collagen family
  3. Non Collagen glycoproteins
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8
Q

what do we call glycoproteins with unique sugars in the ECM specifically

A

proteoglycans

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9
Q

proteoglycans

A

core proteins with glycosaminoglycans

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10
Q

what is special about hylauronan?

A

it is just a glycosaminoglycan itself because is has no protein core

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11
Q

glycosaminoglycans

A

unbranched polysaccharide chains composed of repeating disaccharide units ⇒ an amino sugar usually sulfated and an uronic acid

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12
Q

what makes glycosaminoglycans unique? (2)

A
  • Depending on the disaccharide species we classify them different
  • Due to sulfate and carboxyl groups, GAGs carry a very high negative charge
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13
Q

4 main glycosaminoglycan groups?

A
  1. hyaluronan
  2. Chondroitin sulfate (aging supplements) and dermatan sulfate
  3. Heparan sulfate and heparin
  4. Keratan sulfate
    → 6 different types of GAGs but classified into 4 because some share the same core sugar backbone structure which make it the same repeated disaccharide with modifications
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14
Q

what do many GAGs have?

A

complex modifications on them where many sugar chains are highly sulfated ⇒ sulfate groups have neg charge

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15
Q

Hyaluronan (hyaluronic acid)

A

extremely large GAG with no sulfating and no core protein
- Forms a hydrogel in your body for resistance to compressive forces in tissues, joints, and soft parts of the body

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16
Q

what does Hyaluronan bind to?

A

water molecules (many)

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17
Q

how do GAGs link to core proteins? and what kind of bond is this?

A

covalently linked to a specific serine residue on the core protein (usually GAGs are 80 residues long)

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18
Q

T/F GAGs immediately start repeating their disulfide after linking to serine?

A

False; has a tetrasaccharide prior to the repeating

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19
Q

linkage tetrasaccharide

A

linkage of 4 sugars in proteoglycans that has to happen and be specific before the repeating disaccharide
- xylose - galactose x2 - glucoronic acid

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20
Q

decorin

A

(CS or DS) binds to collagen fibrils and regulates their assembly
- small with oney 1 GAG

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21
Q

aggrecan

A

major proteoglycan in cartilage that makes tissue flexible
- has many GAGS including chondroitin sulfate and keratan sulfate

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22
Q

what is the most abundant protein in animals?

A

collagen

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23
Q

fibrous proteins

A

major components of skin/bone providing tensile strength to tissues⇒ type 1 is the most common
- 25% of total protein mass and highly regulated for fiber formation

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24
Q

what are collagen molecules made of?

A

alpha chains that have a triple helix

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25
Q

alpha chains

A

series of triplet Gly-X-Y in collagen
- X is commonly proline
- Y is commonly hydroxyproline

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26
Q

triple helix

A

3 alpha chains that form a ropelike structure of collagen
- 40 different collagen molecules formed form different combinations of 3 alpha chains

27
Q

what type of collagen is a triple helix?

A

type 1 or 2
- can also be type 4 but that won’t form fibrils

28
Q

which type of collagen is a fibril association collagen?

A

type 9 => link and organize fibrils (2) and help with collagen fibrils interactions with other ECM components

29
Q

which type of collagen is network forming?

A

type 4 => in the basal lamina sheets

30
Q

how does collagen formation occur? (9 steps)

A
  1. Synthesis of pro alpha chain ⇒ polypeptides at the edges (translation)
    - Precursor to collages still
    - N terminal shown in green outside of 3 helix
    - Red portion is the triplet Gly-X-Y structure
  2. Hydroxylation of Pro/Lys
  3. Glycosylation
  4. Self assembly of 3 pro alpha chains
    - Monomer finds a partner and automatically forms the triplets
  5. Procollagen triple helix formation ⇒ in golgi end structure
  6. Secretion ⇒ via a secretory vesicle (still have green portion outside of triple helix structure )
  7. Cleavage of propeptides by extracellular proteases (collagen) ⇒ green is removed because it prevented the self assembly of larger collagen fibrils and then fibers
  8. Self assembly into collagen fibril
  9. Aggregation to form collagen fiber
31
Q

why is fiber formation not triggered until outside of the cell?

A

because these are much larger than the actual cells so this cannot be triggered while in the cell or it is catastrophic

32
Q

where do proteases exist?

A

only exist outside of the cell which helps the process stay tightly regulated
- cuts N terminus which form fibrils and then fibers of collagen

33
Q

procollagen vs fibril vs fiber

A
  • pro collagen includes a propeptide sequence on each of its 3 alpha chains => gets cleaves by proteases
  • fibrils are made of cleaved collagen molecules self assembling together to form one round band like structure
  • fiber is a bunch of fibrils that come together to form a bigger circular structure as the final product
34
Q

what kind of links form within alpha chains and between collagen molecules of alpha chains?

A

intramolecular cross linkage between alpha chain parts and intermolecular modified lysine side chains in the formed fibril

35
Q

Fibril associated collagens

A

types IX (9) and XII (12) do not aggregate into fibrils and are smaller than type 1/2 because they Mediate interactions of collagen fibrils with other ECM molecules and link the type 2 collagen together

36
Q

Network forming collagens

A

type IV (4) that does not form fibrils and instead is composed of 3 alpha chains that interact via terminal domains to assemble into a flexible network that gives tensile strength to the basal lamina
- key component of the basal lamina

37
Q

where do type 4 collagen molecules connect to one another?

A

at 7S boxes to make tetramers

38
Q

multi domain glycoproteins functions (3)

A

functions to organize the matrix, cell ECM attachment, and guide cell movements

39
Q

what do multi domain glycoproteins bind to?

A

have multiple binding sites and many bind specifically to other matrix molecules (collagen, proteoglycans) or receptors on cell surfaces (integrins)

40
Q

fibronectin

A

large glycoprotein composed of 2 (heterodimer) similar but not identical subunits held together by disulfide bonds at their C termini
- functionally distinct domains separated by flexible hinge regions and serves as an organizer and connecter of ECM

41
Q

what kinds of domains do fibronectin have?

A

collagen binding, heparin (heparin sulfate GAGs), and integrin binding
- Both collagen and heparin binding is associated with different ECM components and orchestrates and stabilizes the structure of the ECM
Also binds integrins which makes it a cell binding site

42
Q

what is the cell binding domain?

A

tripeptide RGD (Arg-Gly-Asp) binds to integrins on the surface of cells
- Organizer in the ECM as a connector
- This is captured by alpha beta subunits of integrins

43
Q

basal lamina

A

thin, tough, flexible sheet of specialized extracellular matrix
- under epithelial tissues directly surrounding muscle

44
Q

components of the basal lamina? (4)

A
  • Laminin
  • Type IV collages ⇒ network forming
  • Nidogen ⇒ small glycoprotein
  • Perlecan ⇒ heparan sulfate proteoglycan
45
Q

laminin

A

composed of 3 polypeptide chains (alpha, beta, and gamma) arranged as an asymmetric cross
- Binding sites for integrins and other ECM components
- Heterotrimers self assemble into a network

46
Q

integrin

A

major cell surface receptors that bind the ECM
Transmembrane heterodimers composed of alpha and beta subunits ⇒ similar to cadherins

47
Q

difference between integrin and cadherin

A

integrins are a heterodimer and cadherins don’t form those but bind to one another homophilically

48
Q

what adaptor proteins connect integrin with actin filaments?

A
  1. talin binds to the beta subunit of integrin when active
  2. kindlin also binds to the beta subunit of integrin but doesn’t touch talin and is on the tail end
  3. vinculin binds talin to the actin filaments it isn’t already connected to
49
Q

what allows hemidesmosomes to bind to both collagen on the extracellular side and keratin on the intracellular side?

A

type 4 collagen binds to laminin which binds to type 17 collagen and integrin on the outside of the cell
- on the inside pectin binds to integrin, BP230 binds to pectin and keratin binds to BP230

50
Q

what alpha and beta integrin type receptors are responsible for collagen, fibronectin, and laminin?

A

a1B1 is a collagen receptor
a5B1 is a fibronectin receptor
a6B1 is a laminin receptor
- the binding is determined by the alpha/beta pair
–> different combinations provide specificity of binding particles

51
Q

Glanzmanns disease?

A

B3 subunit deficiency; failure of platelets to bind fibrinogen and results in defective clotting and excessive bleeding

52
Q

Leukocyte adhesion deficiency

A

B2 subunit deficiency; failure of white blood cells to migrate from blood at sites of infection, resulting in repeated bacterial infections

53
Q

inactive integrin state

A

both external and internal segments are unable to bind ligands ⇒ means no binding for either end

54
Q

active integrin state

A

both external and internal segments are able to bind ligands ⇒ means binding occurs when even 1 side is activated to activate the other binding site as well simultaneously

55
Q

outside in activation of integrin

A

binding of an external ligand to extracellular domain leads to activation of the intracellular domain

56
Q

inside out activation of integrin

A

binding of the adaptor protein to intracellular domain leads to activation of the extracellular domain

57
Q

what is unique about integrin?

A

they are only active/inactive on both their intracellular and extracellular segments

58
Q

inside out activation example with platelets

A
  • extracellular signals activate intracellular regulatory signals ⇒ monomeric GTPase Rap1 which activates Talin
  • Rab1 unfolds talin so it binds to integrin intracellular domain as an adaptor protein
  • Talin also interacts with adaptor proteins (vinculin) to form an actin linkage
    → now has a high affinity for the ligand
59
Q

Rab1

A

once activated by GEF, it activates Talin
- GDP to GTP state and binds to talin via RIAM

60
Q

Talin

A

when active it interacts with the beta subunit of the integrin to trigger integrin activation

61
Q

outside in activation example

A

tissue culture cells in the lab are spread on the plate and cells want to attach to the surface which allows them to grow
- The extracellular binding is integrin mediated for proliferation
- FAK is recruited to the site where integrin makes contact with the ECM and FAK molecules undergo cross phosphorylation which signals Src to bind
- when these are activated the FAK will binds to paxillin and talin on the cytosolic membrane side to activate integrin binding with the ECM

62
Q

Focal adhesion kinase (FAK)

A

recruited to the site where integrins are at the site of contact with ECM

63
Q

Ribonuclease

A

Short and branched oligosaccharides chains (Proteoglycan)

Cell biology (15 decks)

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