Extracellular matrix and cell interactions Flashcards
1
Q
what does ECM stand for
A
extracellular matrix
2
Q
how are tissues held together
A
- cell-cell adhesions
- extracellular matrix
- or both
3
Q
what is the ECM
A
large network of secreted molecules that surround, support, and give structure to cells and tissues
4
Q
what is ECM composed of in plant systems (and give examples)
A
- primarily carbohydrates
- ex cellulose and pectin (predominant in the cell wall)
5
Q
what is ECM composed of in animal systems (and give examples)
A
- primarily proteins
- ex. collagen (most common, but varies by tissue type)
6
Q
what are the four major types of tissues
A
- connective
- epithelial
- nervous
- muscle
7
Q
describe the organization of connective tissue
A
cells are loosely organized, attached to one another, rigid scaffold, or both
8
Q
describe how connective tissue carries mechanical load
A
- EMC is abundant
- carries the mechanical load
9
Q
describe the structure of epithelial tissue
A
sheets of polarized cells with discrete functions at apical and basal ends
10
Q
describe how epithelial tissue carries mechanical load
A
- EMC is sparse
- cells are directly joined to one another and carry the mechanical load
11
Q
is animal connective tissue varied
A
enormously
12
Q
the bulk of connective tissue is composed of what
A
- EMC
- and the cells that produce the matrix are scattered within
13
Q
the tensile strength of connective tissue is provided by what
A
- fibrous proteins
- primarily collagens
14
Q
what is the role of fibrous proteins/ collagens in connective tissue
A
provides tensile strength
15
Q
what determines connective tissue characteristics
A
type and quantity of collagen (as well as other molecules)
16
Q
what are collagens and what is their role
A
- a family of proteins that come in many variety
- supports the structure and function of diff tissues
17
Q
describe the typical structure of collagen molecules
A
- long
- stiff
- triple helices in which 3 polypeptide chains are wound around each other
- sometimes assemble into collagen fibral and collagen fibers
18
Q
what is collagen secreted as
A
- procollagen
- with additional peptide extensions at each end to prevent premature assembly
19
Q
what does procollagen proteinases do
A
cleave the procollagen terminal extensions once in the ECM
20
Q
what cleaves the procollagen terminal extensions once in the ECM
A
extracellular enzymes called procollagen proteinases
21
Q
where are cells that manufacture collagen and other ECM molecules, and how are they named
A
- reside within the connective tissue matrix
- named according to tissue type
22
Q
where are collagen and other ECM molecules produced
A
- mostly intraceullarly
- then secreted via exocytosis before assembly into aggregates
23
Q
what does collagen organization contribute to
A
tissue characterization
24
Q
how is collagen organized in skin and why
A
- woven into alternating layers w diff orientations
- to resist tensile stress in multiple directions
25
how is collagen organized in tendons and why
- aligned in parallel bundles along the major axis of tension
- attaches muscle to bone, only one main axis of tension
26
what organizes collagen as they move along the filaments
cells that secrete collagen
27
cells that interact with collagen in the ECM via transmembrane receptor proteins are called what
integrins
28
what are integrins
cells that interact with collagen in the ECM via transmembrane receptor proteins
29
how do integrins interact with collagen
- **not directly**
- through another ECM protein called fibronectin
30
describe how fibronectin helps bind integrins and collagen
- Fibronectin molecules bind to collagen fibrils outside the cell
- Integrins in the plasma membrane bind to the fibronectin and tether it to the cytoskeleton inside the cell
31
what domain interacts with the cell cytoskeleon
intracellular domain
32
what domain binds to components of the matrix
extracellular domain
33
formation and breakage of attachments at either end of an integrin molecule allows what
many cells to crawl through tissues
34
integrin binding to a molecule on one end leads to what
- **conformational changes at the other end**
- extends in an activated state so that it can latch onto a molecule on the opposite side
35
what are the main ways to activate an integrin
- intracellular signaling molecule can activate it from the cytoplasmic side
- binding to an external structure can trigger itracellular signaling pathways by activating protein kinases that associate w the intracellular end of the integrin
36
what do GAGs stand for
glycosaminoglycans
37
what is the role of GAGs
aid tissues in resisting compression
38
describe the structure of GAGs
- negatively charged polysaccharide chains made of repeating disaccharide units
- in each disaccharide, one of the monomers is an amino sugar
39
describe the structure of proteoglycans
- **chains of GAGs covalently linked to a core protein**
- resembles a bottle brush
40
what makes GAGs good space fillers
tend to adopt extensive conformations which occupy large volumes relative to their mass
41
how do GAGs increase swelling pressure
- strongly hydrophillic
- multiple neg charges attract cations which draw water into the ECM
- this gives rise to swelling pressure
42
in dense + compact connective tissues (bone or tendon), what is the ratio of GAGs and collagen
- low amount of GAGs
- high amount of collagen
43
in loose connective tissues (inside of eye), what is the ratio of GAGs and collagen
- high amount of GAGs
- low amount of collagen
44
describe the overall structure of epithelia
- multicellular sheets in which adjacent cells are joined tightly together
- cells present in many diff forms, a sheet may be homogenous or comprised of diff types
45
what is stratified epithelia
multicellular sheet is many cells thick
46
what is simple epithelia
multicellular sheet is one cell thick
47
what are 4 types of epithelia cells
- columnar
- cuboidal
- squamous
- stratified
48
what is the function of epithelia
- many functions including secretion and nutrient uptake
- nearly all sheets form a barrier
- same significance to multicellular organisms and plasma membranes do to a single cell
49
what are the 2 faces of epithelial sheets
- **apical** exposed to air or bodily fluid
- **basal** attached to basal lamina
50
what is the basal lamina
thing, tough sheet of the ECM
51
describe the structure of the basal lamina
mainly composed of type IV collagen and a protein laminin
52
what does laminin do
provides linkage sites for integrin molecules in basal plasma membrane
53
describe the polarity of epithelia
- reflects the polarized organization of its individual epithelial cells
- each w an apical and basal surface w diff properties and functions
54
is polarity important for epithelial function
yes
55
what cell type is present in mammalian small intestin
- **simple columnar epithelium** primarily consisted of 2 cell types
- *absorptive cells*
- *goblet cells*
56
what do absorptive cells do
- take up nutrients at their apical surface
- export to underlying tissues at the basal surface
57
what do goblet cells do
- synthesize mucus
- discharge it at the apical surface to lubricate and protect the gut lining
58
the polarity of the simple columnar epithelium depends on what
- the junctions formed between neighbouring cells
- the basal lamina
59
what are the different kinds of epithelial cell junctions
- tight junctions
- adherens junction
- desmosome
- gap junction
- hemidesmosome
60
what is the role of tight junctions
- seals neighbouring cells together, preventing water-soluble molecules from leaking
61
where are tight junctions formed from
proteins called **claudins** and **occludins** arranged in strands to create a seal
62
how do tight junctions maintain polarity
- prevent diffusion of membrane proteins from the apical surface to the basolateral surface
- serve as assembly sites for protein complexes that govern polarity
63
what are the types of cytoskeleton-linked junctions
- adherens
- desmosomes
- hemidesmosomes
64
which cytoskeleton-linked junctions bind one epithelial cell to another
- adherens
- desmosomes
65
which cytoskeleton-linked junctions bind epithelial cells to the basal lamina
hemidesmosomes
66
how do adheren junctions work
- uses transmembrane proteins from the cadherin family, which require Ca2+ to interact w one another
- each cadherin is tethered inside to actin filaments via linker proteins
- junctions form a continuous belt around interacting cells near the apical end
67
what allows epithelium to change shape in adherens junctions
actin network
68
how does the actin network change the shape of epithelium
- contracting along one axis, rolling itself into a tube
- or by contracting along multiple axes, the sheet can form a hollow sphere
69
when is the formation of epithelial cell tubes critical
- during embryonic development
- gives rise to structures including the neural tube and lens vesicle
70
describe desmosome junctions
- different set of cadherin molecules connect to keratin filaments
- bundles of keratin filaments are anchored via desmosome junctions to similar bundles in adjacent cells
71
what provides great tensile strength to the epithelial sheet
- the arrangement of keratin filaments in desmosome junctions
- key characteristic of exposed epithelia (skin)
72
why are hemidesmosomes named
they look like half of a desmosome
73
how do hemidesmosomes work
- anchor cells to the basal lamina via integrins in the cell basal membrane
- integrins bind to laminin in the basal lamina and bind to keratin via linker proteins inside the cell
74
where are gap junctions found
in all epithelia and many other animal tissues
75
what do gap junctions form
water-filled channels that allow inorganic ions and small water-soluble molecules to move directly from the cytosol of one cell to another
76
where are gap junctions located
- regions where the plasma membranes of 2 cells lie close together (and exactly parallel)
- they span by protruding ends of transmembrane protein complexes called connexons
77
the flow of ions and small molecules between cells creates what
an electric and metabolic coupling between them
78
when can gap junctions be opened and closed
in response to extra- or intracellular signals
79
what allows for spread of electrical current through cardiac cells triggering coordinated contractions
- **gap junction permeability**
- the flow of ions and small molecules between cells
80
what do gap junctions connect
the cytosol of one cell to another
81
