cell adhesion 3

what are the types of cell-cell junctions?

• tight junctions

• adherens junctions

• demosomes

• hemidesmosomes

• gap junctions

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 basal lamina

What are adherens junctions?

• cadherins are key components
• calcium dependent adherence proteins
• provide mechanical strength by linking cytoskeletons of adjoining cells
• can identify the proteins by adding green fluorescent proteins
• cadherins relocate to positions of cell-cell contact
• leads to formation of adherens junctions

what are adhesion belts?

• adherence junctions are usually located near the apical cell surface

what occurs during bending of epithelial sheets?

• connections between adherens junctions and the cytoskeleton allow sheets of epithelial cells to change shape
• apical bundles of actin filaments can contract causing epithelial cells to narrow at their apex
• epithelium rolls up into a tube or invaginates to form a vesicle

what is spina bifida?

occurs when the neural tube fails to close or form

what occurs when there is failure in epithelial tube closure?

• can cause spina bifida
• abnormalities of the spinal chord
• often leads to neurological deficits

what is the role of desmosomes?

• connect keratin filaments in neighbouring epithelial cells
• keratin makes up a type of intermediate filament
• desmosomes contain cadherins (different to those in adherens junctions)
• desmosomes found mainly in tough exposed epithelia

what is the role of hemidesmosomes?

• how epithelial cells connect to the basal lamina
• interns in the epithelial cell membrane connect keratin filaments in the cell to the basal laminate
  -integrins bind laminin in the basal lamina

what are the new treatments for skin diseases?

• uses cell adhesion
• epidermolysis bullosa (EB) is a genetic skin disorder resulting in blisters and lesions
• gene therapy can be used to correct defect in mutant gene

what are gap junctions?

• small regions of plasma membrane where 2 cells are very closely apossed in parallel
• allow small

what is the gap junction physiology?

• molecular flow creates electrical and mechanical coupling between cells
• gap junctions between cardiac muscle cells provides electrical coupling
• allows waves of electrical stimulation to spread synchronously through heart
• triggers coordinated contraction of cardiac cells that produces each heart beat

what is the gap junction permeability?

• they are gated
• permeability can be regulated by extracellular signals
• in retinal neurone they close in response to dopamine

what is the role of gap junction permeability in retinal neurones?

• they close in response to dopamine
• increased light triggers dopamine release which switches retina from using rod to cone photoreceptors

what are plasmodesmata?

• plants lack any of the types of junctions
• structural role is carried out by cell wall
• in plants

how is stress transmitted?

• mechanical stress is transmitted from cell to cell by cytoskeletal filaments anchored. to cell- ECM and cell-cell adhesion sites
• ECM directly bears mechanical stresses of tension and compression