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Cells To Organisms > Cell Adhesion > Flashcards

Cell Adhesion Flashcards

1
Q

What material is found in the second plant cell wall and what are its properties?

A

Lignin. It is a phenolic compound, thus hydrophobic, thus plants remain strong even when wet. It is prominant in wood.

Plant cell wall = hardened ECM

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2
Q

What material is found in the first plant cell wall and what are its properties?

A

Cellulose microfibrils (tensile strength & combats tugor pressure)

Plant cell wall= hard ECM

16 cellulose polymers make 1 microfibril, and the orientation of cellulose dictates which direction cell will grow. Their tensile strength is stronger than steel.

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3
Q

What material is found in the first/second plant cell wall and what are its properties?

A

Pectin. Lots of galacturonic acid. Really hydrated (negative charge) and binds cations. Middle lamella is FULL of pectin

Plant cell wall= hard ECM. Predominates 2nd wall

Pectin has a space filling effect. Pectins are linked to cellulose via cross-linking glycans. Middle Lamella is the bit that cements adjacent cell walls together. If Ca2+ was added to a bunch of pectin it would form a jello/jam structure

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4
Q

What is rate limiting for growth of cell wall?

A

Fixing N2.

N is essential for protein synthesis.

Cell wall contains proteins for remodelling growth. This is in contrast to animals who use lots of proteins

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5
Q

Cytoskeleton function in plants

A

Located underneath cellulose and directs depostion of cellulose by guiding enzymes during cellulose synthesis

Cellulose is spun out from the plasma membrane whereas most matrix macromolecules are made in the ER& Golgi and then secreted, Microtubules needed to move cellulose around

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6
Q

What carries the mechanical load in connective tissues?

A

ECM.

Connective tissues are bones/tendons etc

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7
Q

What carries the mechanical load in epithelial cells?

ECM? Or Cytoskeleton?

A

Cytoskeleton. Epithelial cells have little ECM

Cytoskeleton is attached through adhesion belts connected by adheren junctions.

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8
Q

Examples of connective tissues

A

Knee (cartlidge/bone/tendon/skin), eye (vitreuous humor), Bone (osteoblasts)

Osteoblasts secrete a collagen matrix. Bone has mineralization cartlidge does not. Cartlidge made of collagen and proteoglycans. Vitreous humor made of collagen and hyaluronic acid

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9
Q

How is collagen arranged in the body?

What happens if this is disrupted?

A

In skin: forms a criss cross (resist tension in multiple directions)
In tendon: very long, paralell fibres
Incorrect collagen assembly results in Ehlers Danlos syndrome

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10
Q

How is collagen formed?

A

Secreted by fibroblasts as procollagen with added peptides (stop premature assembely) and secreted outside of cell.

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11
Q

What do fibroblasts do?

A

Pull on and shape the collagen they secreted. Done through pos feedback. Important in wound healing

Fibroblasts get signals to migrate in the cell, and drag collagen behind it which in turn influences where fibroblast is going.

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12
Q

Bone composition

A

Made from osteoblasts, secrete collagen, Ca Mg and P incorperated =hydroxyapatite. Make osteons

Not brittle at all. Mineralization occurs to form osteons. Bones are cell sparse.

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13
Q

Composition of ECM in animals

A

collagen and GAG (proteoglycans)
and laminin

GAG=glycosamineglycans

Tendon/bone= less GAG more collagen (&CaPO4 in bone)
Vitreous humor= more GAG and barely any collagen
Laminin mainly found in the basal lamina

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14
Q

Function of GAG

GAG=glycosamineglycans

A

GAG swelling pressure releives tension in collagen. GAG is hydrophillic so fills space in connective tissue. Proteoglycans binds GF and controls cell migration thru the ECM.

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15
Q

Why does GAG resist compression?

A

Bc glucuronic acid is negitively charged so binds cations and draws in water which creates a swelling pressure and forms a gel like matrix

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16
Q

How does fibronectin attach to the cell + ECM?

A

Links to collagen and integrin which is in the cell memebrane

It has a ECM binding site (for collagen) and a cell attachement site (for integrin). Its an extracellular protein

17
Q

How does integrin attach to the ECM?

A

Links to fibronectin and cytoskeleton. Conformation change results in strong binding.

Has a and b subunits, these subunits kind of curled into themselves, and when intra/extracellular signals activate integrin it unfurls and the a and b subunits bind strongly to fibronectin and stronly to adaptor proteins that are connected to actin.

18
Q

What are the different types of epithelial tissues?

A
  • Columnar: secretion/absorption (lining of intestine)
  • Squamous: filration (lining of lung)
  • Stratified: protection (epidermis of skin)
  • Cuboidal: secretion/absorption (lining of kidney tubules)
19
Q

What does the basal lamina do?

A
  1. supports epithelium cells
  2. is a barrier between epithelial cells and connective tissue
20
Q

Whats the basal lamina made of?

A

Type IV Collagen and lamininn

Laminin is where integrins in the basal membrane of epithelial cells attach to
Collagen comes from the connective tissue (stromal cells) below and laminin comes from the epithelial cells above

21
Q

Why is polarity important in epithelial tissues?

aka apical v basal

apical = top basal = bottom

A

You might have specialized cell types in one epithelial sheet. Example: gut has goblet and absorpitive cells and microvili (apical) and where they are in the sheet is essential to their function

if microvili were basal they wouldnt work!

22
Q

What junctions are found in epithelial cells?

A

Tight junctions
Adheren junctions
Desmosomes
Gap junctions
Hemidesmosomes

(in that order from apical - basal)

Adherens, desmosomes, hemidesmosomes, all mechanical attachement

23
Q

Tight junctions: function and form

A

Made of occulin and claudin. Prevent leaking in epithelial cells bc bind them tightly. Segregate apical and basal memebrane proteins -> eg glucose transport

glucose is driven UP its conc gradient by Na driven transporters (apical) and then driven down its conc gradient by passive transporter (basal)

24
Q

Adherens: function and form

A

Cadherens (ca dependent) link cytoskeleton together via adhesion belt with linker proteins

linker proteins = middleman

basically a continuous sheet of actin across the epithelial sheet. Actin goes into the vili too. Cadherens will always relocate to a point of cell cell contact

25
Q

How does bending happen?

A

Via cadherens. The adhesion belt contracts and epithelial cells at the apex narrow. This results in tube or vesicle formation. Eg. Neural tube or eye lens vesicle

26
Q

Desmosomes: form and function

A

Connect keratin via cadherens and a big plaque of intracellular linker proteins

Not the same cadherens as in adheren junctions

Found in tough epithelia like skin

27
Q

Hemidesmosomes: form and function

A

Connect keratin via integrins and a plaque of intracellular linker proteins

Integrins bind to the basal lamina (on bottom of cell)

How epithelial cells bind to a substratum

28
Q

Gap junction: form and function

A

Made of two connexon proteins that make water filled channels. Lets small, hydrophillic stuff like metabolites flow from cell to cell. Eg responsible for heart beat bc lets electrical current through to sync the cells. Are gated; eg dopamine closes gap junctions in retinal neurons

Connexon like two tubes going end to end

Inc light= inc dopamine = close of gap junctions meaning eye stops using rod (for the dark) and starts using cone receptors (for light)

29
Q

What junctions are found in plant cells?

A

Only gap junctions called Plasmodesmata

The cell wall does the function of the rest of the junctions found in epithelial cells

30
Q

Describe compaction

(in early embryos)

A

All the cells get on top of each other, and then the boundries disapear and form a blob. This is bc of E-cadherens connecting everything.

E-cadherens restricted to their basolateral cell-cell contact site

basolateral = inside the blob, like end of the cells and across

31
Q

Why are cadherins important in compaction?

A

Because removing cadherins (ie applying cadherin antibody or genetic mutation) results in embryo falling apart and dieing

32
Q

What property is essential in cadherins?

A

Homophillic adhesion. Individual cadherin interactions are weak but lots of them together are strong. (like velcro)

homophillic = like binds like

E-cadherins = epithelial cells
N-cadherins= nerve/muscle/lens cells (mi
P-cadherins= placenta/epidermis (aka Cadherin-6)

33
Q

How do cell migrate in embryonic development

A

Via cadherins. Cadherins stick to each other. (eg. if all jumbled up will create layers). Ex: if you make cells express E-cadherins they will go to each other

Suggests that tissue architecture is maintained by cadherins or cells affinity for each other; and the ECM

34
Q

How is neural tube formed during embyronic development?

A

Ectoderm cells stop expressing E and switch to N when neural tube starts forming. Neural tube cells switch from N to 7 as they start migrating.

No switch from N to 7 means they dont migrate

35
Q

What is EMT?

EMT=epithelial to mesenchyme transition

A

As tissues develop (eg neural crest cell migration) some epithelial cells become mesenchymal cells. (they r more motile and not polarity dependent). Also seen in cancer (carcinomas, ie breast cancer)

Cancers from epithelial cells are called carcinomas

36
Q

Whats the relationship between selectins and integrins and inflammed tissue?

A

Inflamation triggers white blood cells. Selectins are expressed on the surface of white blood cells and endothelial cells, and link actin. White blood cells (leukocytes) use selectins to roll down the endothelial sheet because selectins weakly bind. They use integrins to enter the tissue bc they bind strongly.

Endothelial cells line the blood vessels.

37
Q

In what cases does dysregulated cell adhesion happen?

A

During cancer, cell adhesion is not controlled. ECM-degrading proteases also out of control to make way for the tumor

Proteases are usually tightly controlled. By being secreted in inactive form (plasminogen) or need specfic receptors so confined to where they are (uPA) or inhibited locally (TIMPs)

38
Q

How is ECM remodelled and why?

A

Eg. white blood cells entering tissue makes ECM reshuffle. The ECM is locally degraded/moved. Done by matrixmetalloproteinases (MMP’s) and serring proteases

Localised degradation allows ECM to retain structure but allow white blood cells through

39
Q

Whats the role cell-cell adhesion in the nervous system?

A

Essential for synapse development

Cells To Organisms (8 decks)

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