Cell adhesion 3

what do tight junctions do

stitch cells together

what do adherens junctions do

join actin filaments of neighbouring cells

what do desmosomes do

join intermediate filaments of neighbouring cells

what do hemidesmosomes do

join intermediate filaments to the basal lamina

what are key components in adherens junctions

cadherins

what are cadherins

calcium dependent adherence proteins

what do adherens junctions do

provide mechanical strength by linking cytoskeletons of adjoining cells

in very simple terms, how do adherens junctions form

cadherins relocate to positions of cell to cell contact

where are adherens junctions usually located

near apical cell surface, just below tight junctions

what type of junctions form adhesion belts

adherens junctions

what do connections between adherens junctions and the cytoskeleton allow

sheets of epithelial cells to change shape

what does the contraction of apical bundles of actin filaments cause

epithelial cells to narrow at their apex, the epithelium rolls up into a tube or invaginates to form a vesicle

how can the process of epithelial tube formation be described

begins with a flat sheet of epithelial cells, invagination of the epithelial sheet is caused by an organised tightening along adhesion belts in selected regions of cell sheet, this sheet contains an adhesion belt that is associated with actin filaments, the epithelial tube eventually pinches off from overlying sheet of cells to form an epithelial tube

what occurs when the neural tube fails to close or form

spina bifida

what does spina bifida lead to

abnormalities of the spinal cord, often neurological deficits, affecting motor and sensory function

what do desmosomes do

connect keratin filaments in neighbouring epithelial cells

what do desmosomes contain that are different to to adherens junctions

they contain cadherins that are different to those found in adherens junctions

where are desmosomes mainly found

in tough exposed epithelia

what is the structure of a desmosome

keratin filaments are anchored to cytoplasmic plaque on both sides of two interacting plasma membranes, the cytoplasmic plaque is made of intracellular linker proteins, at the centre are cadherin proteins that hold epithelial cells together

what is the difference between hemidesmosomes and desmosomes

have integrin instead of cadherins

where do integrins in the epithelial cell membrane connect keratin filaments in the cell to

the basal lamina

what is epidermolysis bullosa

a genetic skin disorder resulting in blisters and lesions

what are gap junctions

small regions of plasma membrane where two cells are very closely apposed in parallel

what do gap junctions allow

direct communication between two cells, small intracellular water soluble molecules to move from cell to cell

what is the role of connexon protein complexes in gap junctions

connexon protein complexes in the plasma membrane of each cell line up to form a water filled channel between the two adjacent cells

give an outline of what gap junctions allow in the cardiac muscle

molecular flow creates an electrical and mechanical coupling between cells, this allows waves of electrical stimulation to spread synchronously throughout the heart, triggering coordinated contraction of cardiac cells that produces each heartbeat, when action potential reaches cell, calcium channels open and initiation of actin myosin contraction can occur, this can occur almost simultaneously as gap junctions allow the flow of ions

are gap junctions gated or ungated

gated

how can the permeability of gap junctions be regulated

by extracellular signals

in retinal neurones, what do gap junctions close in response to

dopamine

give an outline of how gap junctions respond to increased light

increased light triggers dopamine release, which switches retina from using rod to cone photoreceptors

what type of junctions do plants lack

tight junctions, adherens junctions, demosomes and hemidesmosomes

what carries out the function of gap junctions in plants

plasmodesmata

are plasmodesmata gated or ungated

gated

what helps regulate the permeability of plasmodesmata

deposition of cellulose

give an overview of tight junctions

seal neighbouring cells together in an epithelial cell sheet to prevent leakage of extracellular molecules between them, helps polarise cells

give an overview of adherens junctions

joins an actin bundle in one cell to a similar bundle in a neighbouring cell

give an overview of desmosomes

join the intermediate filaments in one cell to those in another

give an overview of gap junctions

forms channels that allow small, intracellular, water soluble molecules, including inorganic ions and metabolites, to pass from cell to cell

give an overview of hemidesmosomes

anchors intermediate filaments in a cell to the basal lamina