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CTO 2 > 1. Cell adhesion > Flashcards

1. Cell adhesion Flashcards

1
Q

How is physical stress transmitted between cells in a tissue?

A
  • ECM
  • cytoskeleton and cell-cell adhesion
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2
Q

What is physical stress in cells?

A

Changes/fluctuations of environment (solutes/ pressure/toxins/light/nutrients)

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3
Q

How is physical stress managed in plant vs animal cells?

A
  • PLANT: predominantly ECM
  • ANIMAL: use both ECM and cytoskeleton + cell-cell adhesion in diff tissues
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4
Q

What are the supportive and space filling matrices in plants?

A

Supportive matrix - cell wall
Space filling matrix - pectin (cell adhesion molecule)

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5
Q

Explain the synthesis of plant cell wall

A
  • plant cells synthesise the cell wall themselves on the outside of the cell by enzyme complexes embedded in the membrane
  • enzyme complexes are directed by microtubules aligned exactly like microfibrils -> cytoskeleton controls the modelling of plant tissues
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6
Q

What is the driving force of plant cell growth?

A

Turgor pressure

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7
Q

What are microfibrils composed of?

A

Cellulose microfibrils - long, unbranched chains of glucose -> 16 cellulose molecules assemble a microfibril

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8
Q

What macromolecules compose the plant cell wall?

A
  • cellulose microfibrils
  • pectin fibers
  • lignin ligning (not all cell walls)
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9
Q

What is pectin composed of? What is the function?

A
  • pectin - long, complex polysaccharide - forms plant cell matrix
  • to resist compression
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10
Q

Compare the structures of primary and secondary plant cell walls

A

PRIMARY:
- weaker - grows into needed size
- pectin
- cellulose
- middle lamella

SECONDARY cell wall - more rigid - starts forming when primary wall reaches the size - secondary wall forms by:
(1) thickening of primary wall
(2) deposition of new layers under old layers (ex: lignin in wood)
- when plant cells become specialised - produce cell wall specific to the cell type: wax for epidermis / hard, thick, woody for xylem

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11
Q

What does the orientation of cellulose microfibrils influence?

A

Because cellulose microfibrils resist stretching - orientation influences in which direction the cell elongates - length / width

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12
Q

Explain the synthesis of plant cell wall

A
  • plant cells synthesise the cell wall themselves on the outside of the cell by enzyme complexes embedded in the membrane
  • composition of the cell wall depends on the plant (hard thick wall - wood, thin flexible wall - leaf)
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13
Q

Which animal tissue links all other animal tissues?

A

Connective tissue (+ basal lamina / basement membrane)

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14
Q

What are the examples of animal connective tissues and their characteristics?

A

All animal connective tissues are abudant in ECM
- tendons - tough and flexible
- bone - hard
- dermis - soft and flexible
- cartilage - shock absorbing
- vitreous humour - soft and transparent

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15
Q

Explain the structure formed in bones

A

Bone - connective tissue - osteoblasts secrete collagen - Ca / Mg / P ions incorporated into matrix - hard, flexible, not brittle - form osteons

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16
Q

What is an osteon?

A

Osteons - mineralised matrix deposited around central canal with a blood vessel and nerves

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17
Q

Explain the structure of cartilage

A

Large amounts of **ECM **(abudant in collagen and proteoglycan) - no mineralisation

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18
Q

Explain the structure of vitreous humour

A

Clear, viscous gel - water, collagen, hyaluronic acid

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19
Q

What is the major protein of ECM?

A

Collagen - fibrous proteins

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20
Q

What cells synthesise collagen?

A

Fibroblasts

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21
Q

What is the structure of collagen?

A

Triple stranded helical structure - rope like superhelix -> collagen fibril -> collagen fiber
MONOMER -> TRIMER -> FIBRIL -> FIBER

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22
Q

What is collagen arrangement in skin?

A

In skin collagen is arranged both longitudinally + transversally -> allows skin to resist stress in different directions

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23
Q

What is the collagen arrangement in tendons?

A

In tendons collagen fibers are aligned parallely, along the axis of extension

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24
Q

How do fibroblasts influence the alignement of collagen?

A

In collagen secretion fibroblasts pull apart and shape it - different collagen alignments based on tissue (ex: skin vs tendon) - also vice versa collagen alignment influences fibroblast distribution

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25
Explain collagen secretion by fibroblasts
- collagen secreted as precursor form outside the cell - **procollagen** - enzymes add peptide extensions - assembles into collagen into **fibrils**
26
What could be caused by faulty collagen assembly?
Disorders - Ehlers-Danlos syndrome (EDS)
27
How do cells attach to ECM?
Via **integrin proteins** - they attach to **cytoskeleton** inside the cell and **collagen** in ECM
28
What is the mechanism of integrin attachment inside the cell?
Integrin proteins (transmembrane receptor) attaches to the cytoskeleton via **actin filaments** (part of cytoskeleton)
29
What is the mechanism of integrin attachment outside the cell?
Integrins attach to collagen in ECM via **fibronectins**
30
How integrins can be activated / deactivated?
Activated: both **subunits are extended** - triggered by binding to ECM (fibronectin) or adaptor proteins to cytoskeleton inside the cell Deactivated: both **subunits are folded** REVERSIBLE
31
How do integrins coordinate cell movement?
Integrins create new attachment points at the front - attachments at the back are released -> **cell crawls**
32
Compare the functions of collagen and GAGs?
Collagen: provide **tensile strength** to resist stretching GAGs: resist **compression**
33
What are GAGs?
Glycosaminoglycans (GAGs) - neg charged (draws in H2O, ions) **polysaccharide chains** - usually form **proteoglycans** - common brush structure GAG aggregate - more commonly found in **soft ECM** (ex vitreus humour not bone - mostly collagen)
34
What is epithelium and what are its functions?
- epithelium - sheet of cells - **created barriers** - external and internal lining of cavities - controls movement of molecules / microbes - maintains different environments on both sides
35
What are the forms of epithelium cells? Relate to their function, give organ examples
- **Columnar** : secretion, absorption (ex: intestine) - **Cuboidal** : secretion, absorption (ex: kidney) - **Squamous** : filtration (ex: lung) - **Stratified** : protection (ex: skin)
36
What is basal lamina and what is its function?
- basal lamina / basement membrane - thin, tough **sheet of ECM** - separates epithelial cells and connective tissue
37
What is basal lamina composed of? What is its structure?
- **type IV collagen** <- form conn tissue - **laminin** <- from epithelial cells
38
Explain the structure and function of laminin
- laminin - cross-like trimer structure - supplies **adhesive sites** in basal lamina **for integrins** from epithelial cells (linking role)
39
Explain epithelial polarity
- environments on **basal - apical epithelial surfaces** are different (epithelium creates barriers) -> **'POLES' of different environments** are formed => epithelial apical-basal polarity
40
Why is epithelial polarity necessary?
Epithelial polarity maintains barriers - necessary for: - **absorption** : brush-border cells (microvilli) - take up nutrients - **secretion** : goblet cells - secrete mucus
41
What are the main cell junctions between epithelial cells?
- tight junctions - adherens junctions - desmosomes - hemidesmosomes - gap junctions **H**onestly,** T**as **A**domas **G**eria visa **D**iena
42
What is the role of tight junctions in epithelial cells?
- barrier function - **prevent leakage** - maintain **epithelial polarity**
43
What proteins act in tight junctions?
Occludin Claudin
44
How do tight junctions maintain epithelial polarity?
- prevent diffusion of membrane proteins within cell membrane - allow glucose transport both in and out the cell
45
Explain the structure and function of adherens junctions
- **cadherins** (need Ca2+) - key components - link cytoskeletons (**actin**) of adjacent cells - **homophilic** binding (two same cadherins bind)
46
What are adhesion belts?
Adhesion belts - **actin filament bundles** which bind neighbouring cells via **adherens junctions**
47
How are adherens junctions involved in epithelial sheet bending?
Connections between adherens junctions and cytoskeleton (adhesion belts) allow sheets to change shape
48
Explain the structure and function of desmosomes
- join intermediate filaments (**keratin**) of neighbouring cells - join cells - contain **cadherins** (different to adherens junctions)
49
Explain the structure and function of hemidesmosomes
- join intermediate filaments (**keratin**) to basal lamina - use **integrins** to connect keratin - looks like a half desmosome - hemidesmosome
50
Explain the structure and function of gap junctions
- direct **channels** for cytosolic communication - tunnels of **aqueous connectivity** between cells - small, water-soluble molecules pass - **connexon proteins** line up to form the water-filled channel - gap junction
51
How permeable are gap junctions?
- gap junctions are gated - **selective** - permeability regulated by **external signals** (ex dopamine)
52
What is the equivalent of gap junctions in plants?
- **plasmodesmata** in cell walls - no other cell-cell junctions
53
How do cell adhesions influence cell behaviour?
Assist in **cell movement** in tissue growth and development
54
What is compaction in embryo development?
Compaction - the 8-cell stage in embryo development when **adherens junctions (cadherin) form** between adjacent cells
55
What proteins are essential in embryo compaction?
- E-cadherins essential for forming adherens junctions - E-cadherin localisation at basolateral cell-cell conatct sites
56
What are the experiments which defined cadherin mediated adhesions?
1) when cadherin **binding antibodies** were introduced in embryo - cells didn't adhere - fell apart 2) when cadherin **genes were deleted** in embryos - cells didn't adhere, embryo fell apart
57
What are the main types of cadherins? What cells express them?
- E-cadherin (**e**pithelial cells) - N-cadherin (**n**eurons) - R-cadherin (nerve, muscle, lens (**r**etina)) - Cadherin-6 (placenta, epidermis) Different cells express different cadherins **CERN**
58
Explain homophilic vs heterophilic binding
HOMOPHILIC : like-to-like (ex: same cadherins) HETEROPHILIC : different molecule bind (ex: ligand and receptor)
59
How cell adhesions help cells sort out?
- cells sort out according to type - recognise similar cells by cell adhesion molecule - cells adhere expressing **same cadherin types** - **levels of specific cadherin** expression also influence cell-cell interactions - cells with higher cadherin levels adhere more tightly
60
How do cadherins act in cell sorting during development?
In neural tube formation: 1) **e**ctoderm cells express **E-cadherin** 2) when **n**eural tube pinches off - turn off E-cadherin production, turn on **N-cadherin** expression 3) migratin neural crest cells turn off N-cadherin expression and turn on **cadherin-7 expression**
61
Explain epithelial to mesenchymal cell transition
Epithelial-to-mesenchymal transition (EMT): - cell assembly into epithelium is **reversible** - EMT found in developing tissues, tissue regeneration, wound healing - EMT involved in cancer
62
Explain what are selectins and their function
Selectins : - **cell surface proteins** that **bind to carbohydrates** - expressed in **WBCs** and endothelial cells - act in inflammation - form relatively weak cell adhesion in blood
63
Explain selectin and integrin function in inflammation
Selectins **WBC movement** into tissues at **inflammation sites**: - selectins on endothelial cell surface **recognise WBCs sugars** - form weak adhesion and **rolling of WBCs** along endothelial cells - rolling by selectins done - **strong adhesions** formed with **integrins** at the site of inflammation the WBCs **squeeze into tissue**
64
What problems can arise if selectins or integrins are defective?
Affects WBCs recognition at inflammation sites - leukocyte adhesion deficiency (LAD)
65
Why would cells degrade ECM?
- cells degrade ECM to **allow cells to pass** between endothelial cells to the inflammation site - **ECM remodelling** (for development, wound healing)
66
What are the main groups of ECM degrading enzymes?
- matrix metalloproteinases (MMPs) - serine proteases - localised degradation - highly specific enzymes (ex: collagenase)
67
Why does the activity of ECM degrading enzymes must be localised?
ECM degradation must be highly controlled by localising ECM degrading enzymes - not to destroy ECM where not needed
68
How is the activity of ECM degrading enzymes is controlled?
1) Enzymes expressed in **inactive form** (localised activators) 2) Enzymes **confined by cell-surface** receptors 3) Enzymes are **inhibited** by locally secreted inhibitors

CTO 2 (8 decks)

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