Cmcb Microtubules And Microtubule Motor Protein

Front 1

What are microtubules used for?

Back 1

Used for trafficking of membrane bound organelles, movement of cilia and flagella, movement of chromosomes during mitosis.

Front 2

What is the structure of microtubule?

Does it have polarity?

Back 2

one subunit of microtubule is heterodimer of one alpha tubulin and one beta tubulin.

The alpha tubulin permanently has GTP binding site. Beta tubulin ATP gets hydrolyzed.

There are 13 protofilaments in one big microtubule

Yes it has intrinsic polarity. + end is faster growing than -end. similar to actin

Front 3

What conditions favor microtubule assembly?

Back 3

Subunits
low calcium
GTP (or GDP)-not GTP hydrolysis
warm temperature

Front 4

Describe treadmilling for microtrubules.

Back 4

It is rarely observed in microtubules because of dynamic instability. Sometimes the - ends are capped and can't participate in treadmilling.

Front 5

What is dynamic instability? What does GTP capping have to do with this?

What are hte structural differences between GTP bound and GDP bound?

Back 5

Dynamic instability occurs on the plus end. Sometimes there is rapid disassembly (catastrophe) and then it is rescued to start growing again.

- when assembly is fast due to high concentration of GtP bound dimers, + end outpaces hydrolysis. A GTP cap is put on to furthur stabilize it and to allow further assembly.

-when assembly is slow due to low concentration of GTP bound dimers, hydrolysis catches up and there is instability and rapid shortening.

*GTP bound is straight
*GDP bound has kinks in it.

Front 6

What are MTOCs?
What do the centrioles do and what is their structure?
What experiment revealed MTOC's function?

Back 6

They are microtubule organizing centers (centrosome) that cap the -ends of microtubles, decreasing the dynamics of the - end.

In the center there are pair centrioles. They have 9 triplet MTs around hollow core. They act as nucleating centers in vitro

Colchcine wash out experiment. After drug was washed out, you could see reassembly of microtubules at MTOC.

Front 7

Where is MTOC located? What else does it hold besides centrioles?

Back 7

It is located in the cytoplasm of the cell.
It holds gamma tubulin which is different from alpha and beta. The gamma creates a ring complex y-TuRc which binds to the - ends to grow. They are present in all cells (cells with or without centrioles)

Front 8

What are MAPS? What do they do? what are catastrophe factors? Eb1?

Back 8

They are microtubule assisting proteins. They stabilize, promote assembly of microtubules, cross bridging and mediating interaction between microtubules. Very heat stable.

Map can bind to + ends of MTs to assemble or disassemble. Catastrophe factors bind to + ends to disassemble

Eb1 only binds to GTP cap.

Tau is only found in axons of neurons--seen in alzheimers.

MAP2 is found in cell bodies of neurons.

Front 9

What are Taxol, colchicine, vinblastine, nocodazole?

Back 9

They are all microtubule specific drugs.
Taxol binds and stabilizes microtubules.
Colchine, vinblastine, nocodazole all bind and prevent polymerization.

Front 10

What are three microtubule based motility systems? and what motors do they use?

Back 10

1. cilia and flagella - axonemal
2. membrane/organelle traffic - cystolic motors
3. mitotic spindle - spindle motors

Front 11

Explain cilia and flagella motion.

What does Axonemes have to do with it? Are axonemes connected to anything?

Why is dyenin important and what are two types of dyenin?

Back 11

Both have same core structures except flagella has longer tail.

There is a power stroke and recovery stroke. Cilia is whip like and flagella is more sinsuidoial action.

They have a core of MT that are responsible for their motility called Axoneme. It has 9 outer doublets MTs and 2 singlet MTs in center (9+2). They have dyenin motor arm that walks toward -end. Axonemes are connected to basal bodies that have 9T arrangement. BB is a nucleating center for ciliary and flagella.

1. axonemal ciliary dyenins - 3 heavy chains, 3 motor heads withATP binding site for B microtubule

2. cytoplasmic dyenin - heavy chain homodimers, two heads

Front 12

What is the mecanism of ciliary motility?

Back 12

Microtubule sliding. When ATP is added, dyenin arms walk towards the - end. Proteins cross link to prevent sliding apart which leads to bending motion. without aTP, dyein is locked.

Front 13

What is kartagener syndrome?

Back 13

Mutations in the dyenin complex lead to defective cilia. tract diseases, reversed heart, etc.

Front 14

What are two microtubule based cystolic motors for organelle transport?

What two examples are given for microtubule transport system?

Back 14

Kinesins and cystolic dyenins transport membrane bound organelles (small vesicles, ER, etc)

Kinesin= + end directed-exocytosis, secrete stuff out of cell

cytoplasmic dyenin= - end directed endocytosis (towards cell center)

**fast membrane bound organelles occur on microtubules.

-melanophores- transport of pigment granules
- + end directed transport of ER.
- -end directed transport of golgi body.

Front 15

describe kinesin structure and movement

Back 15

Kinesin 1 - two head domains that are atpase motors at n terminal. they bind to the microtubules.
c-terminal associate with light chains and bind cargo.

*if two heads on microtubule, walk towards the + end.
*if kinesin - c terminal is bound on the glass surface, can still slide microtubule with minus ends leading.

**processive hand over hand stepping along hte MT.
-need atp hydrolysis to move

Front 16

Describe Cytoplasmic dyenins structure and movement

Back 16

Have two heavy chains-->two heads that have atphase activity

Have dynactin complex- bunch of acessory proteins. This dynactin complex is the receptor to the vesicles that dyenins carry.

-end directed movement.

Front 17

What works on the -end of microtubules?

What works on the +end of microtubules?

Back 17

-end: gamma tubulin, dyenin, MTOC

+end: kinesin, catastrophe factors