28 Flashcards by M B

describe the structure of a hemidesmosome

specialized structure composed of a dense plaque of PRO (often plectin), keratin fibers are embedded in the fiber

Keratin is linked to the outside of the cell by integrin 

Integrin binds ECM PROs

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what results in tighter attachments to the ECM than focal adhesions?

hemidesmosomes

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what occurs when hemidesmosomes aren’t functioning properly?

Defect in integrin results in epidermolysis bullosa where there’s a loss of hemidesmosomes, the lower layer of the epidermis fails to attach to the basal lamina & chronic blistering is seen

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how many cells is a human comprised of?

20-40 trillion

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how do cells recognize each other?

cell adhesion molecules (CAMs)

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how are CAMs grouped?

2 categories depending on how they pair with each other:

Homophilic or heterophilic

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homophilic

CAMs binds to each other

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heterophilic

bind to diff kinds of PROs

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where are selectins most commonly found?

epithelial cells

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structure of selectins

integral PRO with extracellular domains that bind particular carbs on other cells

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role of selectins

mediate interactions with leukocytes

lymphocytes roll along endothelial cells within capillaries

selectins are involved in one of the first adhesions, then integrins assist in the leukocyte’s entry through the epithelium

adhesion causes intracellular signaling (to indicate to the cell to change shape to allow entry)

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how do selectins bind to white blood cells?

look for the sugar grps

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immunoglobulin

antibodies, immune sys PROs that recognize foreign molecules

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immunoglobulin cell adhesion molecules (ig-CAM)

cell bound integral immunoglobulin PROs

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are Ig-CAMs hetero or homo?

homo & hetero

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when are Ig-CAMs heterophilic?

in immunity-related cells & activities

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Ig-CAM location

lymphocytes, vascular & neural cells

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how does the Rhinovirus use ICAMs? & how is this treated?

it attaches to the cell by binding to Ig-CAMs & then delivers its RNA

ICAM fragments are provided to inhibit the surface & prevent the virus from attaching

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Ig cell adhesion PRO L1 role

assists in growth of nerve cells, mutants have severe neural probs: mental retardation & hydrocephaly (fluid accumulation in ventricles of brain)

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describe the structure of cadherin

integral glycoPRO

have 5 tandem domains

anchored to the actin network with adaptor PROs (such as catenin)

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what is the role of calcium in cadherins?

calcium ions separate the 5 domains

provide subunit stability & ensure they’re in the proper orientation

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are cadherins homophilic or heterophilic?

homophilic

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what determines the strength of a cadherin interaction?

number of cadherins

greater number of cadherins = greater strength of adhesion

what occurs to cadherins during embryogenesis?

when cells need to migrate to growing tissue, they need to separate from each other. Therefore, the cadherins are endocytosed & lose their adhesive properties

as new cell contact develops new cadherins are produced to attach again to form tissues - promotes cells of similar types ot adhere

adherens junctions

junction b/w cells using cadherin molecules attach to the actin network through catenin adaptor PRO connect the actin network to the periphery of the cell

what do adherens junctions look like in epithelial cells?

form a belt around the apical ends of cells - maintains tissue integrity

whre are adherens junctions most commonly found?

epithelial cells

what occurs when there is a loss of function of adherens junctions?

metastasis in cancer cells cancer cells migrate to a diff part of the body

desmosome structure

disc-shaped 2 special types of cadherins: extracellular Intracellular - anchored to plaque PROs, plaque PROs are anchored to IFs (keratin) create point contacts, not a belt

where are desmosomes present?

cells subjected to mechanical stresses (ex: muscles, epithelia etc.)

pemphigus vulgaris

autoimmune disorder attacks cadherin PROs in desmosomes resulting separation of the epithelial cells that form the connective tissue & blistering occurs

where are tight junctions located?

apical ends of epithelia cells

tight junction structure

found at the apical ends CAMs: occludins & claudins form a line of spot welds on both PMs

what is the permeability of claudins?

can be permeable to certain ions allowing for controlled leakage

loss of function of tight junctions

mutation in claudins tissue failure mutation in claudin-1 means the skin epidermis leaks water & animals will die of dehydration (mice) cannot prevent water loss

what is the role of tight junctions in the lungs? & how does this go wrong?

heregulin is a growth factor attached to the apical surface of PMs the heregulin receptors are on the basolateral surface when the sheet of cells are broken, heregulin can reach its receptors & trigger autocrine stimulation of mitosis to heal the wound chronic bronchitis of smokers, asthma & cystic fibrosis increase the permeability of the airway epithelium. This results in an increase of autocrine stimulation & accounts for proliferation. Too much proliferation can result in cancer

describe the structure of gap junctions

integral PRO connexin ring of 6 connexins form a connexon 2 connexons (1 from each cell) bind to form a channel (homophilic)

how many diff connexin PROs are there?

what is the function of gap junctions?

permits flow of small molecules (gated channel, passive flow) enables coordination of cells (rapid signaling for cells to act in synchrony) sweep particulates out of the lungs cAMP & IP3 are delivered to adjacent cells when hormones trigger a single cell (movement of cilia, peristalsis of gut)

describe the movement through gap junction channels?

permits flow of small molecules gate channel passive flow regulated by the number of connexons --> increase the number of connexons = increase the flow

tight junctions

seals gap b/w epithelial cells

adherens junctions

connects actin filament bundle b/w cells

desmosomes

connects IFs b/w cells

gap junctions

allows the passage of small water-soluble molecules from cell to cell

CAMs of tight junctions

occludins & claudins

CAMs of adherens junctions

cadherin

CAMs of desmosomes

2 types of cadherin (intracellular & extracellular)

CAMs of gap junctions

connexin

function of tight junctions

brings PMs to almost the point of fusion, prevent easy flow of liquid & solutes & responsible for integrity

adherens junctions

connects actin filament bundle b/w cells

function of desmosomes

hold cells together that endure mechanical stresses

what are the diffs b/w hemidesmosomes & desmosomes?

hemi --> integral, integrins desmosomes --> not integral, cadherins

plasmodesmata

channels that connect plant cells

how many plasmodesmata does a plant cell have?

b/w 10^3 & 10^5

describe the plasmodesmata structure

Channel is lined with PM & usually contains a desmotubule which is derived from the SER

how is the flow of molecules regulated in plasmodesmata?

Flow is regulated by the desmotubule diameter actin & myosin wrap around the desmotubule & close off the gap

how do viruses use plasmodesmata?

modify plasmodesmata PROs to cause it to open wider to allow the passage of the virus from one cell to the other