CBG29 Flashcards
Where are chemical junctions/synapses found?
exclusively in the NS
- one of the best understood occurs at neuromuscular junctions.
What happens at neuromuscular junctions?
- Neurotransmitters are synthesized in the termial and stored in small synaptic vesicals
- vesicles released into synaptic cleft at specific points (active zones)
- liberated neurotransmitters bind to specific receptors proteins on post synpatic membrane and open ion channels
vesicles = 50nm
cleft = 20-30nm
10^5 vesicles.
What is a gap junction?
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
What is evoluationarily older in the animal kingdom,
electrical or chemical synapse?
electrical
- chemical pathway is much more specialised.
What can happen if something goes wrong in a gap junction?
can cause pathology in: development deafness skin disorders cardiac arrythmia charcot marie tooth disease - leads to deformation and lameness.
What are semiphorins?
class of secreted membrane bound proteins primarily act as short range inhibitory signals.. receptors are plexins and neuropilins
What do all semaphorins and plexins have?
an amino terminal sema domain of about 400 amino acids
How many known mammalian semaphorins are there?
20 grouped into 5 classes. class 3 = transmembrane secreted proteins class 4-6 = membrane associated proteins class 7 = membrane associated proteins.
How many mammalian plexins are there?
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
What do some semaphorins needs to bind and activate plexins?
class 3 semaphorins. the plexin to be associated with a neuropilin 1 or 2 co rececptor.
How many known mammalian semaphorins are there?
20
grouped into 5 classes.
What are semaphorins important in?
cancer
bone formation/turnover
macrovascular influence
alot of auto immune diseases
What is the apoplastic and symplastic pathways?
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
What does callose do in symplastic pathway?
pools at the neck of the cyoplasmic sleeve, quanitity effects permeability.
more=smaller pores = less permeable
What are tight junctions?
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
What does a tight junction do?
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.
In which group of organisms are tight junctions found?
vertebrates
similar septate junction in invertebrates
Give an example of a tight junction
zo-1 located on the intracellular side of the plasma membrane which anchor strands to actin component of cytoskeleton.
What is an Adherans junction?
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
What are desmosomes/macula adherans?
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.
What happens if there is mutation in desmosome?
it is the main cause of arrhymogenic right ventricular cardiomyopathy blistering disease antibodies target desmogene 381 desmogene breakdown fluid through epitherlium.
