cell junctions

Question 1

what are junctions and connections between cell required for

Answer 1

cell communication between cells
cell memory to ensure cell stability

Question 2

what is selective cell adhesion

Answer 2

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

Question 3

what are tight junctions

Answer 3

• they create sealed barriers by protein networks and strands

Question 4

what are tight junctions formed from

Answer 4

small integral membrane proteins mainly, along the cells

Question 5

what is an example of a tight junction

Answer 5

epithelial lining of the intestine

Question 6

what is the function of tight junctions

Answer 6

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

Question 7

what disorders are linked to tight juncltions

Answer 7

coeliac - caused by increase permeability to gladin

Question 8

what is nephrocalcinosis

Answer 8

calcium deposition within the kidney

Question 9

what is hypomagnesemia

Answer 9

electrolyte disturbance due to low Mg in blood

Question 10

what is hypercalciuria and what is it caused by

Answer 10

excess calcium in the blood stream and urine
- impaired paracellular transport

Question 11

what is impaired paracellular transport caused by

Answer 11

caused by a genetic defect of claudin 16 or 19

Question 12

what are gap junctions

Answer 12

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

Question 13

what is the role of connexons

Answer 13

they form water filled channels to allow inorganic ions and water soluble molecules to move from one cell cytosol to the other

Question 14

what are plasmodesmata

Answer 14

• 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

Question 15

what is the functions of gap junctions and plasmodesmata

Answer 15

• 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

Question 16

what is an example of gap junctions and plasmodesmata junctions

Answer 16

the connection between cardiac muscles to allow electrical impulses to travel

Question 17

what disorders are linked to gap junction malfunctions

Answer 17

chronic liver disease
hepatic failure
Charcot-Marie-tooth disease (CMT)

Question 18

what causes chronic liver disease

Answer 18

– connexin CX32 lost from hepatocyte membrane by apoptosis

Question 19

what causes hepatic failure

Answer 19

– CX32 and CX40 linked to paracetamol-induced liver injury

Question 20

what causes Charcot-Marie-Tooth disease (CMT)

Answer 20

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

Question 21

what are desmosomes and what do they do

Answer 21

• 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

Question 22

what do hemidesmosomes bind epithelial cells to

Answer 22

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

Question 23

what is the structure of adherens

Answer 23

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

Question 24

what is the function of desmosomes, hemidesmosomes, adherens

Answer 24

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)

Question 25

disorders linked to desmosome, hemidesmosome and adheren junction malfunctions

Answer 25

-Desmosome abnormality and poor intracellular cohesion in epidermal cells
-Defect in skin integrity and skin fragility
-Alopecia – non scaring hair loss

Question 26

where do cells et together to form tissue

Answer 26

the extra cellular matrix

Question 27

what is the extracellular matrix

Answer 27

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

Question 28

where is the extra cellular matrix located

Answer 28

it s a component of bones tendons and skin
- varied amount dependant on the person
-bursa and fluid filled areas contain higher polysaccarides

Question 29

what is the extra cellular matrix formed of

Answer 29

collagen - which is a protein
- it forms a triple helix > fibrils > fibres to give strength

Question 30

what is the function of the extra cellular matrix

Answer 30

to provide structure and support to tissues
aids in binding cells together (in addition to junctions)
influence tissue development
regulate molecule movement

Question 31

what disorders are linked to faulty extra cellular matrix’s

Answer 31

• 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

Question 32

what is tumorigenesis

Answer 32

the process for the transformation of normal cells to cancer cells

Question 33

what changes occur to the ECM once undergoing tumorigenesis

Answer 33

increase in ECM stiffness
decrease in ECM elasticity
increase in ECM remodelling

Question 34

what does a loss of any of the ECM components cause

Answer 34

a lack of homeostasis - which promotes the tumour phenotype

Question 35

what are the 5 stages of biofilm formation

Answer 35

attachment - growth - maturation - detachment - redevelopment

Question 36

what happens in the attachment stage of the biofilm formation

Answer 36

bacteria attaches to a variety of surfaces (from metal to skin) using tail like structures

Question 37

what happens in the growth stage of the biofilm formation

Answer 37

cells grow and divide forming a matrixed structure
- cannot be seen, too thin

Question 38

what happens in the maturation stage of the biofilm formation

Answer 38

when there are enough bacteria in the film the bacteria secrete a slimy ECM of proteins and polysaccarides

Question 39

what happens in the detachment stage of the biofilm formation

Answer 39

the slime protects the bacteria from harsh environments, along with many chemicals and the immune system

Question 40

what happens in the re-development stage of the biofilm formation

Answer 40

the colonies mature and the structures created weaken casting off bacteria to look for new places to grow and multiply