Polvi lec #14 Flashcards
What is B-tubulin?
B-tubulin is a G protein that hydrolyzes GTP to GDP after a dimer is added
Why is B-tubulin important in microtubule assembly?
because it is what is required for the growth of the microtubule
How do microtubules grow?
In a growing microtubule B-Tubulin-GTP dimers are added for growth, then when GTP is hydrolyzed the tube is closed because the GTP-tubulin becomes GDP tubulin.
What causes strain on a growing microtubule? What happens as an outcome of this strain?
Since GDP-tubulin has a different confirmation is causes mechanical strain on the growing microtubule, this causes the protofilaments in the growing microtubule to curl outward and undergo shrinkage in the absence of stabilization
What mediates the strain on the growing microtubule?
MAPs
What stabalizes the the catastrophe that occurs on a growing microtubule? How?
+TIPs, these bind to the positive end of the microtubule regulate the rate of growth or shrinkage and mediates the attachment to other subcellular structures
How does the forming of microtubules influence the movement of material within a cell?
They can shrink or grow which pulls material that their attached to or pushes it
What three things do microtubules do the for the structure of the cell?
They provide mechanical support- are stiff enough to resist compression/bending forces
Help determine the shape of the cell
Maintains intracellular location of organelles
How do microtubules move things around the cell?
They can transport membrane vesicles from one membrane compartment to another
they can transport stuff that isn’t bound by a membrane (like RNA, ribosomes, cytoskeletal elements)
What do microtubule motorproteins do?
They utilize ATP hydrolysis to generate mechanical forces that move themselves and the stuff (cargo) they carry along the cytoskeleton
What are examples of what microtubule motor proteins might move?
Membranous vesicles
ribosomes, rna
Organelles
Chromosomes
Other cytoskeleton filaments
What are the two types of microtubule motor proteins?
Kinesins, dyneins
What is the structure of Kinesin?
It has a tetramer structure, it has two heavy chains and two light chains.
It has a globular head that binds to microtubules and does ATP hydrolysis and conserves it’s amino acid sequences
It has a tail which binds to cargo and can have varying amino acid sequences depending on the cargo it binds too
How does Kinesin move?
It moves towards the positive end, it does this by having one of it’s heads (the leading head) bind one ATP, hydrolyze it, and that causes a power stroke that pushes the trailing head forward 1 tubulin dimer. At least one of the heads is attached to to the microtubule at all times, and the proteins movement is very processive- can move long distances, it’s speed depends on the amnt of ATP there is
How does the Kinesin tail carry the cargo?
it uses an adaptor (can be an integral membrane protein) to attach cargo to tail
