28 Flashcards
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
what results in tighter attachments to the ECM than focal adhesions?
hemidesmosomes
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
how many cells is a human comprised of?
20-40 trillion
how do cells recognize each other?
cell adhesion molecules (CAMs)
how are CAMs grouped?
2 categories depending on how they pair with each other:
Homophilic or heterophilic
homophilic
CAMs binds to each other
heterophilic
bind to diff kinds of PROs
where are selectins most commonly found?
epithelial cells
structure of selectins
integral PRO with extracellular domains that bind particular carbs on other cells
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)
how do selectins bind to white blood cells?
look for the sugar grps
immunoglobulin
antibodies, immune sys PROs that recognize foreign molecules
immunoglobulin cell adhesion molecules (ig-CAM)
cell bound integral immunoglobulin PROs
are Ig-CAMs hetero or homo?
homo & hetero
when are Ig-CAMs heterophilic?
in immunity-related cells & activities
Ig-CAM location
lymphocytes, vascular & neural cells
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
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)
describe the structure of cadherin
integral glycoPRO
have 5 tandem domains
anchored to the actin network with adaptor PROs (such as catenin)
what is the role of calcium in cadherins?
calcium ions separate the 5 domains
provide subunit stability & ensure they’re in the proper orientation
are cadherins homophilic or heterophilic?
homophilic
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?
20
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
