cell junctions Flashcards
what are junctions and connections between cell required for
cell communication between cells
cell memory to ensure cell stability
what is selective cell adhesion
Cells have different adhesion and junction molecules within their plasma membrane so need to ensure selective binding to other cells of the same type to prevent mixing
what are tight junctions
- they create sealed barriers by protein networks and strands
what are tight junctions formed from
small integral membrane proteins mainly, along the cells
what is an example of a tight junction
epithelial lining of the intestine
what is the function of tight junctions
they provide a tight seal between cells to prevent molecule leakage
- prevents water soluble molecules passing between cells
- provides strong mechanical attachments
- maintain polarity by preventing diffusion of proteins
- provide close chemical communication
what disorders are linked to tight juncltions
coeliac - caused by increase permeability to gladin
what is nephrocalcinosis
calcium deposition within the kidney
what is hypomagnesemia
electrolyte disturbance due to low Mg in blood
what is hypercalciuria and what is it caused by
excess calcium in the blood stream and urine
- impaired paracellular transport
what is impaired paracellular transport caused by
caused by a genetic defect of claudin 16 or 19
what are gap junctions
cell membranes of 2 cells that lie close together
- with a gap between 2-4mm
- the gap contains transmembrane proteins called connexins
- multiple connexin subunits form one connexon
what is the role of connexons
they form water filled channels to allow inorganic ions and water soluble molecules to move from one cell cytosol to the other
what are plasmodesmata
- only found in plant and algae cells
- similar to gap junctions
- have channels called plasmodesma
- cells held together by a shared cell wall but they have their own plasma membrane but continuous shared cytoplasm
what is the functions of gap junctions and plasmodesmata
- they form channels between cells
- they allow inorganic ions and water soluble molecules to move from one cell cytosol to the other
- changes in permeability to open or close channels to effect junction communication
- are gated junctions and highly regulated
what is an example of gap junctions and plasmodesmata junctions
the connection between cardiac muscles to allow electrical impulses to travel
what disorders are linked to gap junction malfunctions
chronic liver disease
hepatic failure
Charcot-Marie-tooth disease (CMT)
what causes chronic liver disease
– connexin CX32 lost from hepatocyte membrane by apoptosis
what causes hepatic failure
– CX32 and CX40 linked to paracetamol-induced liver injury
what causes Charcot-Marie-Tooth disease (CMT)
mutation in GJB1 (Gap junction protein beta 1) gene encoding CX32, codes for protein located in myelin sheath
-X-linked inherited demyelinating neuropathy of peripheral nerves
-Progressive muscle weakness
what are desmosomes and what do they do
- they bind epithelial cells to each other
- Proteins span the plasma membrane and linked inside the cells to cytoskeletal filaments
- Built from desmosomal cadherin family of proteins
- Identical cadherin proteins within each cell bind to each other
- Cadherin also bind to keratin filament giving greater strength and support
what do hemidesmosomes bind epithelial cells to
the underlying basement membranes of cells (basal lamina)
- integrin transmembrane proteins span the cellular space
- also bind to cytoplasmic keratin intermediate filaments
stud-like structures
what is the structure of adherens
similar to desmosomes
-bind one epithelial cell to another
forms a continuous belt around cells
-linked to actin filaments so they’re involved in contraction allowing flexibility in shape
what is the function of desmosomes, hemidesmosomes, adherens
provide mechanical strength
- joins the intermediate filaments of one cell to a neighbouring cell or to the basal lamina
e.g. tissues requiring high tensile strength (bladder epithelium and gastrointestinal mucosa)
disorders linked to desmosome, hemidesmosome and adheren junction malfunctions
-Desmosome abnormality and poor intracellular cohesion in epidermal cells
-Defect in skin integrity and skin fragility
-Alopecia – non scaring hair loss
where do cells et together to form tissue
the extra cellular matrix
what is the extracellular matrix
a structural component of all tissues
- secreted by cells to surround them
- its made up of a complex network of polysaccharides and proteins
- fluid and dynamic non cellular structure
-external to the cell - functions like the internal cytoskeleton
where is the extra cellular matrix located
it s a component of bones tendons and skin
- varied amount dependant on the person
-bursa and fluid filled areas contain higher polysaccarides
what is the extra cellular matrix formed of
collagen - which is a protein
- it forms a triple helix > fibrils > fibres to give strength
what is the function of the extra cellular matrix
to provide structure and support to tissues
aids in binding cells together (in addition to junctions)
influence tissue development
regulate molecule movement
what disorders are linked to faulty extra cellular matrix’s
- defect in collagen assembly leads to extra stretchy skin - hypertensible
- lack of integrins in ECM of blood platelets can lead to blood clotting disorders (as platelets cannot bind to the necessary clotting factor in the ECM
what is tumorigenesis
the process for the transformation of normal cells to cancer cells
what changes occur to the ECM once undergoing tumorigenesis
increase in ECM stiffness
decrease in ECM elasticity
increase in ECM remodelling
what does a loss of any of the ECM components cause
a lack of homeostasis - which promotes the tumour phenotype
what are the 5 stages of biofilm formation
attachment - growth - maturation - detachment - redevelopment
what happens in the attachment stage of the biofilm formation
bacteria attaches to a variety of surfaces (from metal to skin) using tail like structures
what happens in the growth stage of the biofilm formation
cells grow and divide forming a matrixed structure
- cannot be seen, too thin
what happens in the maturation stage of the biofilm formation
when there are enough bacteria in the film the bacteria secrete a slimy ECM of proteins and polysaccarides
what happens in the detachment stage of the biofilm formation
the slime protects the bacteria from harsh environments, along with many chemicals and the immune system
what happens in the re-development stage of the biofilm formation
the colonies mature and the structures created weaken casting off bacteria to look for new places to grow and multiply
