Microtubules

Question 1

Main function of Microtubules

Answer 1

The organizer of the Cell
-Transport: Create tracks that vesicles, organelles, and other cellular components move along
-anchor organelles
-form mitotic spindles for chromosome segregation
-form Cilia and flagella structures.

Question 2

Microtubule Structure:

Answer 2

Built from dimer subunits of alpha and beta tubulin proteins
-tubulin stacks together by non-covalent bonding to form protofilaments

Question 3

Protofilaments

Answer 3

tube structure composed of 13 protofilamets lined up side by side

Question 4

do microtubules have polarity?

Answer 4

Yes.
Beta tubulin is positive
Alpha tubulin is negative

Question 5

Where do microtubules originate?

Answer 5

Centrosome
-this is where the tubulin units polymerize from nucleation sites

Question 6

Nucleation Sites

Answer 6

Starting point of microtubulin growth
- Alpha/Beta tubulin dimers are added to the positive end of the y tubulin
**mins end is anchored

Question 7

Dynamic Instability

Answer 7

Microtubules Grow and Shrink

Question 8

How does the Growth of Microtubules occur?

Answer 8

Controlled by the rate of GTP Hydrolysis
- each free tubulin dimer is bound to GTP and is added to the growing microtubule
-GTP and eventually hydrolyzed to GDP
-GTP bound tubulin is binded tightly compared to GDP

Question 9

When is the Polymerization of Microtubules rapid?

Answer 9

dimers are added to the plus end of beta-tubulin at a faster rate resulting in a GTP CAP where the microtubule continues to grow

Question 10

What is microtubule growth controlled by?

Answer 10

The Rate of GTP hydrolysis

Question 11

Microtubule Stabilizing Protein

Answer 11

MAPS: Tau Proteins bind to hetero-dimers for stabilization
-binds to GDP

Question 12

Review Slides 8-14 Part 1

Answer 12

8-14

Question 13

Microtubule Function

Answer 13

Guide Transport
-have transport proteins

Question 14

Transport Proteins contain…

Answer 14

2 Globular Heads
-that bind to the microtubule
bind to ATP and Hydrolyze if to provide energy for conformational changes which allows the motor proteins to move along the microtubule

A Tail
-binds to either a vesicle of an organelle, determines cargo for motor protein

Question 15

Kinesin

Answer 15

Motor Protein that moves away from the centrosome and towards the plasma membrane
-moves to the positive end

Question 16

Dynein

Answer 16

Motor Protein that moves toward the nucleus
-move toward the negative end

Question 17

the Tail of Motor Proteins

Answer 17

transports different cargos, tail region has specificity for a variety of cargo.

Question 18

Microtubules and Motor Proteins Function:

Answer 18

-Microtubule Transport
-Position Organelles
-Help form Cilia and Flagella (no motor protein)

Question 19

Flagella

Answer 19

propel a cell through fluid using repetitive wave-like motion
-propel sperm and protozoa

Question 20

Cilia and Flagella Structure

Answer 20

9+2 Arrangement
-9 doublet microtubules in a ring around a pair of 2 single microtubules in the center.

Question 21

What causes the flagellum to bend?

Answer 21

Dynein Motor Protein
-generates bending motion
-Doublets are tied to each other by flexible protein links that allow bending NOT sliding