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CTO2 - Cells to Organism > Cell Adhesion > Flashcards

Cell Adhesion Flashcards

1
Q

What are the 3 architecture of tissues

A
  1. mechanical construction
  2. plumbing and wiring
  3. renewal and repair
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2
Q

How do cells in multicellular organisms adhere?
2 key points:
1. How differences in adhesiveness and specificity of adhesion help to maintain ___ between tissues
2. how associations between ____ are needed for the normal function of adult tissues

A
  1. boundaries
  2. different cell types
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3
Q

stress transmission with multicellular organisms:
1. for small flimsy cells to join together into large structures they must…

A
  1. have ways to transmit physical stress
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4
Q

Outline the 2 strategies to transmit stress and whether they are adopted by animal or plant cells

A
  1. Extracellular matrix (ECM) - plants and animal cells
  2. cytoskeleton & cell-cell adhesions - animals
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5
Q

In plant tissue, what is the supportive matrix?

A

cell wall

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6
Q

Explain how plant cells control the production of their cell walls?

A
  • newly formed plant cells = primary cell wall only
  • relatively thin and flexible, can expand as cells grow
  • once cell growth stops, secondary cell wall made
  • thicker more rigid and no longer expands
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7
Q

what is the common additional polymer in cell wall?

A

Lignin

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8
Q

What gives the cell wall its tensile strength? Explain in detail and structure of the macromolecule

A

Cellulose microfibrils
- most abundant macromolecule on earth
- long unbranched chains of linked beta glucose subunits
- 16 cellulose molecules forms microfribril
- predominates in secondary cell wall

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9
Q

What macromolecule provides resistance to compressive forces in plant cells? Explain in detail its structure

A

Pectin
- long complex polysaccharides
- Rich in galacturonic acid
- highly hydrated
- space filling similar to ECM
- crosslinks with cellulose to form matrix
- abundant in primary cell walls

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10
Q

What macromolecules are predominant in primary vs secondary cell wall?

A

Pectin = primary
Cellulose = secondary

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11
Q

Scale model of primary cell wall:
____ provides tensile strength
____ provides resistance to compression

A
  1. cellulose microfibrils
  2. pectin
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12
Q

In primary cell wall, what is middle lamella and what does it do?

A

It is rich in pectin and cements cell walls together

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13
Q

Describe the structure of wood and what macromolecules it is made out of

A
  • cells have thick walls which remain when cell dies, forming long channels running vertically within the tree
  • cell wall composed of lignin (complex polymer of cross linked phenolic compounds, high wet strength rigid when wet)
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14
Q

Orientation of cellulose microfibrils in plant cell wall
- cellulose microfribrils resists ____
- orientation of cellulose microfibrils influences the ___ of cell elongation

A
  • stretching
  • direction
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15
Q

what is needed for cellulose deposition and cellulose synthesis? explain in detail how it is used in each scenario

A

microtubules
- aligned with cellulose microfibril to direct the deposition of cellulose
- microtubules serve as tracks that guide enzyme complexes so cytoskeleton indirectly controls architecture of plant tissue

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16
Q

Regarding animal tissue, describe the difference in comsposition between connective tissues and epithelial tissues?

A
  • connective = abundant ECM
  • epithelial = less ECM, cytoskeleton filaments helps to carry mechanical stress
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17
Q

Connective tissue: Bone, cartilage, vitreous humour (describe each composition)

A

Bone = contains bone forming cells called osteoblasts, makes osteons composed of concentric rings of matrix
cartilage = present in many joints, absorbs impact without breaking, abundant ECM and collagen and proteoglycan
vitreous humour = between lens & retina, viscous gel

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18
Q

What is the major part of ECM? How is it produced? where is it abundant? How is it organised

A
  • Collagen
  • produced by specific cell types within tissue called fibroblasts
  • abundant in bones tendons and skin
  • organised into bundles
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19
Q

How is collagen arranged in skin vs tendon?

A

skin = ply wood pattern to resist tensile stress
tendon = attach bone to muscle so they align in parallel along axis of extension

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20
Q

What form are collagen molecules secreted in? explain in detail

A
  • precursor form
  • peptide extensions obstruct premature fibril assembly
  • precursors cleaved to form mature collagen outside the cell
  • collagen can’t form into fibrils in cells, once they are outside they meet the enzyme and cleave so it can be turned into collagen fibril
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21
Q

What does incorrect collagen assembly lead to?

A

Skin being hyper extensible

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22
Q

How do cells attach to the ECM? What does each of the components do?

A
  • fibronectin and integrin
  • fibronectin = molecular bridge between integrin and ECM
  • integrin functions as heterodimers, transmits tension across the plasma membrane
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23
Q

How does integrin regulate itself causing cell to move across membrane?

A
  • by signals from inside and outside the cell changes the integrin conformation
  • on and off integrin connections with ECM enable cells to move through tissue
  • can switch from being inactive (folded) to active (bound to collagen and spring open)
  • binding is reversible
  • new attachment points are established at front of moving cell and old adhesions are released at the back so cell can crawl
24
Q

How does collagen use GAGS to resist compression?

A

chains of GAGs are linked to a core protein to form proteoglycans. GAGs are negatively charged so it keeps high cations in ECM. draws in water and creates swelling pressure. this matrix is tough and resistant to compression.

25
Q

Compare the composition of ECM/GAGs in Tendon/bone vs vitreous humour (connective tissue)

A
  • dense connective tissue (bone/tendon) has less GAGs and more collagen
  • vitreous humour (entirely GAGs and very little collagen)
26
Q

What is an epithelium? what are its functions?

A
  • sheet of cells joined together side by side
  • covers external surfaces and line all internal cavities
  • creates barriers
  • control movement of molecules in and out (has receptors for external signals)
  • protects against fluid loss
27
Q

What are the 3 main functions of the epithelia

A
  1. secretion/absorption
  2. filtration
  3. protection
28
Q

What is a basal lamina? what is it made of? Function?

A

sheet of epithelial cells sits on a mat-like structure
- thin tough sheet of ECM made from collagen and laminin
- separates epithelial cells from collagen fibres in underlying connective tissue

29
Q

Composition of basal lamina:
- composed of mainly 1 and 2
- 1 is supplied by ____
- 2 is supplied by ____

A

1 = type IV collagen, supplied by underlying stromal cells connective tissue
2 = laminin, supplied by overlying epithelial cells

30
Q

How does laminin work?

A
  • interacts with many proteins (e.g. integrins)
  • provides adhesive sites for integrins located in the basal membrane
  • fulfils a linking role similar to that of fibronectin in connective tissue
31
Q

Regarding epithelial sheet, which side is apical which side is basal.

A

apical = free and exposed to air or bodily fluid
basal = attached to basal lamina

32
Q

Polarity is essential for epithelial cell function. Using gut as an example, explain how polarity is crucial

A
  • gut is lined by absorptive epithelial cells
  • contains goblet cells that secrete mucous
  • specialised cell type with diff function in same sheet
  • polarity is crucial for function of both cell types
33
Q

What are tight junctions and what is its function?

A
  • allows epithelial sheets to function as barriers
  • bind the epithelial cells tightly to prevent leakage
  • occluding and Claudia seals interacting cells
34
Q

How do tight junctions segregate membrane proteins

A
  • block diffusion of membrane proteins to keep apical and basal domains separate
  • enables transport of glucose against conc gradient and then down its concentration out into the bloodstream
35
Q

Tight junction stitches cells together. List the 4 different cell-cell junctions and note the ones that have mechanical attachment

A

adherens junctions = joins actin filaments of neighbouring cells
desmosomes = joins intermediate filaments of neighbouring cells
hemidesmosomes = joins intermediate filaments to basal lamna
gap junction = forms tunnels of aqueous connectivity between cells

36
Q

In adherens junctions, what is the key component? what does it do?

A

Cadherins (calcium dependent adherence protein)
provides mechanical strength by linking cytoskeleton of adjoining cells. cadnerin protein binds together (each one is bound to the cytoskeletal filament via linker proteins

36
Q

Adhesion belts:
- where are adherens junctions usually located (apical/basal), just below ___ junctions
- what is an adhesion belt, how does it bend

A
  • located near apical cell surface just under tight junctions
  • continuous belt of actin cytoskeleton across epithelial sheet, actin filament is joined using the sheets forming actoncytoskeleton
  • apical bundles of actin filaments can contract, epithelium rolls into tube or forms vesicle
37
Q

Desmosomes:
- connect ____ filaments in neighbouring cells
- contains ____ , different set to those in adherin junctions
- mainly found in _____ epithelia

A
  • keratin
  • cadherins
  • tough, exposed (e.g. skin)
38
Q

Hemidesosomes:
- half a ___1__, without cadherins instead has ___2___
- __2__ used to bind epithelial sheet to __3___
- ___2___ in the epithelial membrane connect __4__ filaments in the cell to 3

A

1 = desmosome
2 = integrins
3 = basal lamina
4 = keratin

39
Q

How do gap junctions work?

A
  • if 2 cells are very close to each other and in parallel, small water soluble molecules can flow through
  • connexon protein in each cell line up to form water filed channel
40
Q

Gated gap junction: ______ of gap junctions can be regulated by extracellular signals

A

permeability

41
Q

What carries out the role of gap junctions in plants?

A

Plasmodesmata

42
Q

How do cells sort themselves and move in the migration of neural crest cells in vertebrate embryos?

A

They sort themselves into specific arrangement based on expression of specific cadherins

43
Q

During compaction of early embryo, what type of cadherin is used in the formation of adherens junctions and is it in the apical or basolateral contact sites?

A

E-cadherin & basolateral

44
Q

What does adhesion binding antibodies and expression and deletion of cadherin lead to

A

embryo falls apart (die if its deletion)

45
Q

List the 3 different types of cadherins and where they are expressed.

A
  • E-cadherin, mainly expressed on epithelial cells
  • N-cadherin, expressed on nerve, muscle and lens cells
  • P-cadherin, expressed in placenta and epidermis
46
Q

What is the mechanism by which cells can recognise and stick to similar cells

A

Homopholic adhesion

47
Q

Describe the selecive assembly of cells, 2 ways cells get sorted.

A
  1. sorts itself with other cells expressing same cadherin as distinctive pools
  2. level of cadherin expression: high level = more tightly compacted in the centre
48
Q

How does cadherins aid in cell sorting in development of neural tube.

A
  • Ectoderm cells express E-cadherin
  • As neural tube pinches off, cells turn off E-cadherin and turn on N-cadherin
  • Migrating neural crest cells turn off N-cadherin and turn on cadherin-7
  • Overexpression of N-cadherin leads to cells failing to leave the neural tub
49
Q

what is the diff between epithelial and mesenchymal cells?

A

epithelial = regular columnar morphology, high adhesion with junctions
mesenchymal = irregular rounded morphology, loss of apical basal polarity

50
Q

What is EMT and is it reversible?

A

epithelial to mesenchymal transition and yes it is reversible

51
Q

What are selectins? where is it found? what does it do?

A
  • cell surface protein that binds carbohydrates
  • expressed in WBC & endothelial cells
  • linked to actin cytoskeleton
  • mediate cell-cell adhesions in bloodstream
52
Q

How does transition from selection dependent -> integrin dependent induce inflammation

A

WBC with selection-dependency rolls along endothelial cells due to weak adhesion. leukocytes activates interns which mediate stronger adhesion and invades the tissue

53
Q

Why does ECM need to be degraded and how? is it localised or wide-spread?

A

to allow cells to pass between endothelial cells
- enzymes: MMPs and serine proteases
- localised degration

54
Q

What are the 3 ways activity of ECM degrading proteases is kept tightly localised

A
  1. secreted in an inactive form, localised activator activates them
  2. confined by cell surface receptors
  3. inhibited by actions of locally secreted inhibitors
55
Q
A

CTO2 - Cells to Organism (8 decks)

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