Cell junctions and cytoskeleton

microtubules made of what protein, how organized, 

tubulin

heterodimer that polymerises into protofilaments (13 protofilaments form one microtubule)

contains GTP that can be freed in B complex

polarity of alpha and beta complexes

GTP to GDP can occur by hydrolysis

GDP form more readily depolymerizes 

allows dynamic instability

What modulates MT dynamics?

MT binding proteins such as MAP and Tau

Tau involved in Alzheimer’s

How is tubulin formed?

pair of centrioles, with surrounding gamma tubulin ring complexes from with MT grow

What are the apical and basolateral membranes of a polarized cell?  Does MT’s polarity vary by cell?

apical —> facing the lumen

basolateral —> facing the basal membrane

intestinal epithelial —> more positive end faces basolateral membrane

in neuronal cell positive end at terminal end of axon and negative end at dendrites

What does a tight junction do? What is made of? What assay shows tightness of seal?

• molecular seal - separating apical and basolatral cell surface

• contains Claudins and occludins

that seal two membranes laterally together

Dextran tracer assay

What does an adheren junction do?

anchoring junction - connect actin cytoskeleton between cells

encode cell surface identity and mediate mechanotransducers

cadherins bind to actin via catenins

form adhesion belts

What are desmosomes?

belong to anchoring junctions - connect intermediate filament cytoskeleton between cells

• provide mechanostability

• made of non-classical cadherins

What are Hemidesmosomes?

anchoring junction - connect cytoskeleton

connect intermediate filaments to the extracellular matrix

What are gap junctions?

formed by connexin

continuous aqueous channels

can vary In size and are in continuous turnover

What other functions do MTs carry out?

• mitotic spindle for separating sister chromatids

• cilia contractile movement - axoneme (structure core of cilia)

• growing plus ends can pull membranes along

What are the motor proteins on MT’s

Kinesis plus end directed movement —> anterograde transport

Dynein minus end directed movement —>retrograde transport

both have ATPase motor domain

What are actin filaments?

helical polymers of protein actin

form F-actin

flexible polar filaments

fast growing plus end (barbed) and slow growing minus end (pointed)

ATP to ADP —> polymerase vs depolymerase

accessory proteins determine characteristics

What allows cell migration using actin?

fast growing + end form protrusions

What end does the motor protein myosin move towards on the actin filament?

positive end

Experimental evidence for motor activity of myosin

purified myosin heads

F-actin

ATP

myosin moves towards the + ends and the filament moves towards the negative end

What is an example of an intermediate filament and what’re their general features?

monomers wrapped around each other

non-polar

Keratin or lamina are intermediate filaments int he nucleus

lamin A and C = rigidity and B - flexibility

lamina A mutation leads to progeria - pre-mature aging

nucleus shape and flexibility

What are neurofilament types and disease?

Three types of Neurofilaments NF-L, NF, M and NF-H form hetero polymers in neurons to stabilize the axons.
The neurodegeneratice disease Lou Gehrigs disease of amyotrophic lateral sclerosis (ALS) is often associated with
abnormal assembly of NFs leading to axonal transport defects.

What are the different protein coats in vesicle trafficking?

COP11, COP1, clathrin

Coat Protein Complex I and Coat Protein Complex II, respectively.

What is COPII used for?

RER to Golgi apparatus

What is COPI used for?

Golgi to RER

What is clathrin used for?

Internalization (endocytosis) & transport from TGN to endosomes