Chapter 9 Flashcards
How are microtubules arranged?
Hollow, cylindrical structures. They are a set of globular proteins arranged in longitudinal rows called protofilaments.
Microtubules contained _____ non-covalenty bonded protoflaments. Describe the structure of these
13.
Composed of dimers of alpha and beta tubulin subunits assembled into tubules with plus/minus ends
Why is there a plus and minus end of the microtubule?
Top molecules is beta tubulin (plus end) and bottom is alpha tubulin (minus end), alternating along microtubule, and because heterodimer structure is asymmetric the ends must be different.
What is the most significant difference between alpha and beta tubulin and why?
Beta tubulin has GDP in it whereas alpha tubulin has GTP. The GTP in alpha is not hydrolyzable, whereas the GDP in beta is
What does “MAPs” stand for? Why are they so important?
Microtubule-associated proteins. The structural integrity of microtubules is dependent on MAPs, which attach one domain to a microtubule while the other projects outward. They have been seen connecting microtubules to each other to maintian parallel alignment.
What do MAPs do and how are they regulated?
They attach to the surface of microtubules and increase stability and promote assembly. The binding activity of MAPs is regulated by phosphorylation of specific amino acid residues
_____ is a MAP protein found at Neurofibrillary Tangles in neurons. How do neurofibrillary tangles form?
Tau.
The tangles form when Tau protein is hyperphosphorylated (unable to bind to microtubules) and arranges itself in clumps - which happens in Alzheimers cases
How are microtubules related to axonal function?
Function in axonal transport, and axonal growth during embryogenesis
How do microtubules provide ultimate support to the plant cell? How are they arranged in relation to the long axis of the cell?
Help maintain cell shape by influencing formation of cell wall during interphase, influencing cellulose orientation (which is in the same places as microtubules). They are arranged perpendicularly to the long axis of the cell.
How do microtubules help with intracellular motility, especially in neurons?
A single axon can stretch much farther than the average cell (from spinal cord to finger for example). The cell body portion of the neuron is in the spinal cord and that is where proteins are produced. The axon is full of parallel microtubules for transport membrane bound cargo (vesicles, organelles) and non-membrane bound cargo (ribosomes, RNA), and mediate tracks for motor proteins.
What do motor proteins do?
Convert energy from ATP to mechanical energy. Move unidirectionally along their cytoskeletal track in a stepwise manner.
What are the three categories of molecular motors and what types of cytoskeletal elements do they move along?
Kinesin, dynein move along microtubules and myosin moves along microfilaments.
Describe the structure of kinesin-1
Kinesins are tetramers consisting of two identical heavy chains and two identical light chains. Each kinesin includes a pair of globular heads (bind to microtubule and act as HTP-hydrolyzing engine) connected to a neck, a rod-like stalk, and finally a tail that binds the cargo.
Describe the Dynein motor protein structure
Huge proteins composed of two heavy chains, as well as a variety of intermediate and light chains. Each heavy chain has a globular, force-generating head and a elongated stalk. Each stalk has a microtubule binding site. A longer projection (stem) comes off of the heads and connects to the intermediate and light chains
Requires an adapter (dynactin) to interact with membrane-bounded cargo.
Describe the Myosin motor proteins
Move along microfilament
Kinesins are members of a superfamily called ______. In which direction do they move?
Kinesin-related proteins. Anterograde, most move toward plus end of microtubule. Kinesin 13 does not move and Kinesin 14 moves toward the minus end of microtubule.
How would one prove experimentally that the only difference between kinesin 14 (which is retrograde) and the anterograde kinesins is in the head. What happened when this was done in the lab?
Swap the heads! Scientists did this in the lab and there was no change. They realized that it was actually the neck that caused the difference in movement
How do kinesins move?
Move along a single protofilament at a velocity proportional to ATP concentration. Protein moves a long distance without falling off.
Deynein is responsible for the movement of ____ and ____
Cilia, flagella
Distinguish between “DYNAMIN”, “DYNACTIN”, and “DYNEIN”
Dynamin - a collar protein found on vesicles
Dynactin - adapter protein
Dynein - motor protein (retrograde)
Microtubules running from ER to golgi are arranged in such a way that the ____ end is along the golgi complex
Minus
What are MTOCs?
Microtubule-organizing centers: Specialized structures for the nucleation/synthesis of microtubules
_____ microtubules are arranged in triplets around 1 centriole
9
______ are structures where outer microtubules (those in cilia and flagella) are created
Basal bodies