BIO130H1 Lecture Notes - Lecture 22: Intermediate Filament, Axon Terminal, Endomembrane System

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22 Mar 2019
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BIO130 Lecture 22 21/03/2019
Nerve cells
These neurons in the arm can be a meter long
Problem:
o How does neurotransmitter synthesized in the ER get to the synapse?
o Neurotransmitters are secreted via vesicles to the axon terminal
o How do you move these vesicles a meter way from the cell body to the
axon terminal?
Axon vesicular transport
Types of motor proteins:
o Dynein movement
Towards cell body
Move towards the microtubule’s minus end
o Kinesin movement
Towards the axon terminus
Move towards the microtubule’s plus end
Kinesin and dynein use ATP
Movement of vesicles through the endomembrane system
Endomembrane system: ER, Golgi, Vesicles, lysosomes
Plus ends next to the cell membrane and the ER
Minus ends next to the Golgi
The Golgi apparatus is also a MTOC but it’s different
from the centrosome
Microfilaments / Actin filaments
Involved in:
o Cell motility (crawling)
o Contractile activity (muscles)
o Cytokinesis
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Made of:
o Actin monomers
o Flexible
o Inextensible not elastic
o Helical filaments
Mote protein:
o Myosin
The structure of actin filaments
Composed of a single type of globular protein:
o Actin monomers
o Two protofilaments twisted in a right-handed helix
Are acting filaments polar?
o Yes
o Due to the regular orientation of actin monomers in each protofilament
o Head to tail arrangement of actin monomers
Actin monomers
Free monomers are bound to ATP;
o ATP is bound in the center of the protein
Actin is an ATPase:
o Hydrolyses ATP
o ADP remains bound
ATP hydrolysis occurs more rapidly after actin monomers have been
incorporated into the filament
o ATP hydrolysis decreases the strength of binding between monomers in
the filament
Growth of the filament is:
o Faster at the plus end
o Actin filaments have an ATP cap
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