CBG29

Question 1

Where are chemical junctions/synapses found?

Answer 1

exclusively in the NS

- one of the best understood occurs at neuromuscular junctions.

Question 2

What happens at neuromuscular junctions?

Answer 2

1. Neurotransmitters are synthesized in the termial and stored in small synaptic vesicals
2. vesicles released into synaptic cleft at specific points (active zones)
3. liberated neurotransmitters bind to specific receptors proteins on post synpatic membrane and open ion channels
   vesicles = 50nm
   cleft = 20-30nm
   10^5 vesicles.

Question 3

What is a gap junction?

Answer 3

an electrical junction
specialised intercellular connections between a variety of animal cell types.
-hexamer, with 6 connexins on each part of the cell=1 connexon. approx 39kDa
2 together is a connexon complex. = gap junction
1.5nm pore forms in the centre which allows sugars t pass through but not DNA/RNA- nothing greater than 1000Da

Question 4

What is evoluationarily older in the animal kingdom,

electrical or chemical synapse?

Answer 4

electrical

- chemical pathway is much more specialised.

Question 5

What can happen if something goes wrong in a gap junction?

Answer 5

can cause pathology in:
development
deafness
skin disorders
cardiac arrythmia
charcot marie tooth disease - leads to deformation and lameness.

Question 6

What are semiphorins?

Answer 6

class of secreted membrane bound proteins
primarily act as short range inhibitory signals.. 
receptors are plexins and neuropilins

Question 7

What do all semaphorins and plexins have?

Answer 7

an amino terminal sema domain of about 400 amino acids

Question 8

How many known mammalian semaphorins are there?

Answer 8

20
grouped into 5 classes. 
class 3 = transmembrane secreted proteins
class 4-6 = membrane associated proteins
class 7 = membrane associated proteins.

Question 9

How many mammalian plexins are there?

Answer 9

4 classes
A-D
intracellular part of all plexins contains a GTPase activating a GAP domain
which is separated into 2 segments by a rhoGTPase binding domain RBD

Question 10

What do some semaphorins needs to bind and activate plexins?

Answer 10

class 3 semaphorins.
the plexin to be associated with a neuropilin 1 or 2 co rececptor.

Question 11

How many known mammalian semaphorins are there?

Answer 11

20

grouped into 5 classes.

Question 12

What are semaphorins important in?

Answer 12

cancer
bone formation/turnover
macrovascular influence
alot of auto immune diseases

Question 13

What is the apoplastic and symplastic pathways?

Answer 13

plant cell-cell pathways
apoplast = through cell walls,which are permeable to small soluble proteins and other solutes
symplastic - direct refulated intracellular transport of substances through plasmodesmata

Question 14

What does callose do in symplastic pathway?

Answer 14

pools at the neck of the cyoplasmic sleeve, quanitity effects permeability.
more=smaller pores = less permeable

Question 15

What are tight junctions?

Answer 15

non communicating
closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid
- majority of proteins involved are claudins. 20-27 kda
occludin -65kda 522 AA - human integral plasma membrane protein

Question 16

What does a tight junction do?

Answer 16

control permeability across cell membrane
holds cell together
affect cell polarity
prevent seepage of solutes
blood brain barrier
- loss of tight junctions in eg. distal convoluted tubule.

Question 17

In which group of organisms are tight junctions found?

Answer 17

vertebrates

similar septate junction in invertebrates

Question 18

Give an example of a tight junction

Answer 18

zo-1 located on the intracellular side of the plasma membrane which anchor strands to actin component of cytoskeleton.

Question 19

What is an Adherans junction?

Answer 19

protein complexes that occur at cell–cell junctions in epithelial and endothelial tissues
cell junction whose cytoplasmic face is linked to the actin cytoskeleton
important in morphogenesis and remodelling tissues and organs
major proteins = cadherins - lambda catenin. or plakoglobin- alpha catenin
more basal than tight junctions
phsycially links cells
regulate cell cell contact

Question 20

What are desmosomes/macula adherans?

Answer 20

a cell structure specialised for cell to cell adhesion
role = resist shearing forces
major proteins = desmoglein and desmocollin- members of the caherin family of cell adhesion molecules.
desmocollin and desmoglein form the extracellular domain
desmoplakin is on the cytoplasmic side.

Question 21

What happens if there is mutation in desmosome?

Answer 21

it is the main cause of arrhymogenic right ventricular cardiomyopathy
blistering disease
antibodies target desmogene 381 
desmogene breakdown 
fluid through epitherlium.