Lecture 12

Question 1

Microtubules are made up of what dimers?

Answer 1

Microtubules are made up of alpha and beta tubulin heterodimers.

Question 2

Microtubules have _______?

Answer 2

Microtubules have polarity.

Question 3

what end of microtubules grows?

Answer 3

The B-tubulin (plus) end is where most of the growth occurs.

Question 4

What end is where the centrosome is?

Answer 4

The a-tubulin end is where the centrosomes are located. This is also the minus end.

Question 5

Catastrophe?

Answer 5

A catastrophe is when there is a change from growth to shrinkage.

Question 6

What is a rescue?

Answer 6

The change from shrinkage to growth is called a rescue.

Question 7

What is dynamic instability?

Answer 7

Microtubules undergo a process called dynamic instability, where individual microtubules alternate between cycles of growth and shrinkage.

Question 8

Difference structurally between shrinking and growing?

Answer 8

Growing microtubules have a GTP cap where shrinking microtubules have no GTP cap and only have GDP.

Question 9

What are kinesins?

Answer 9

Classic kinesins are motors that move towards the plus ends of microtubules.

Question 10

What types of chains do kinesins have?

Answer 10

Kinesins have two light chains and two heavy chains.

Question 11

What does the stepping of kinesins require?

Answer 11

Each stepping of the kinesins requires ATP hydrolysis.

Question 12

Kinesins are what kind of proteins?

Answer 12

Kinesin is a tetrameric protein

Question 13

What are some structural features of kinesin?

Answer 13

• They have two heavy chains and two light chains
• The heavy chain has many domains
• The head splits ATP and converts the energy into motion
• The tail is the cargo-binding portion.

Question 14

What is the movement of kinesin for?

Answer 14

The movement of kinesin molecules is for long range movement

Question 15

What is the size of a kinesin step?

Answer 15

Kinesin steps are the size of 4 tubulin monomers
- This is also the same a 16nm

Question 16

Are all thr steps of kinesin the same?

Answer 16

Yes, kinesin has progressive steps - they are all the same size.

Question 17

Heads of kinesin are always ____?

Answer 17

At least ONE of the heads is always attached to the microtubule.

Question 18

How can we see kinesin dynamics?

Answer 18

We can see kinesin dynamics by a kinesin in-vitro motility assay.
- Occurs in a tube

Question 19

How do we perform a kinesin in-vitro motility assay?

Answer 19

• Kinesins are deposited onto a coverslip
• microtubules are labelled with a fluorescent marker
• Moto activity of the kinesins causes the microtubules to glide.

Question 20

What molecules are needed for an in-vitro motility assay?

Answer 20

We need dimers, GDP and ATP

Question 21

Kinesin family similarities of heavy chain?

Answer 21

Kinesins are a large superfamily in which the motor domain of the heavy chain is the common element.

Question 22

What is the role of kinesin-13 proteins?

Answer 22

Kinesin-13 proteins (microtubule depolymerases) induce depolymerization uniquely from both ends of the microtubule.

Question 23

What are the roles of kinesin-13 proteins?

Answer 23

They are incapable of movement. They regulate microtubule dynamics to control spindle assembly.

Question 24

What also are kinesin-13 proteins called?

Answer 24

Kinesin-13 proteins are also called catastrophe factors because they are involved in inducing catastrophe (depolymerization of microtubules)

Question 25

What is the role of kinesin-14?

Answer 25

Kinesin-14 (Ncd) is unusual as it moves from microtubule plus ends towards the minus ends in motility assays.

Question 26

What is unique about the tail of kinesin-14?

Answer 26

The tail of kinesin-14 can bind microtubules an allows it to organize microtubule bundles.

Question 27

What are some forms that microtubule bundles can take?

Answer 27

- Parallel microtubules - Clustering microtubules - Overlap microtubules (3 diff arrangements) - Antiparallel microtubules

Question 28

What is dynein?

Answer 28

Cytoplasmic Dynein is another microtubule motor protein.

Question 29

Feature of Dynein size?

Answer 29

Dynein is ~4 times bigger and more comp[lex than kinesin.

Question 30

What does Dynein head do?

Answer 30

- Its head is in charge of the force generating motor (AAA=ATPase domain) - A = ATP hydrolysis domain

Question 31

What is the stalk of Dynein's job?

Answer 31

The dynein stalk contains the microtubule-binding site at its tip

Question 32

Where does Dynein bind cargo?

Answer 32

Dynein cargo binds at the tail

Question 33

ATP role in Dynein?

Answer 33

ATP changes the conformational structure to dissociate microtubule binding.

Question 34

Dyenein steps how?

Answer 34

Dynein steps are large but irregular and it moves toward the minus ends of a microtubule

Question 35

Dynein moves which direction?

Answer 35

Cytoplasmic Dynein moves toward the minus ends

Question 36

Classical Kinesin overview?

Answer 36

- Small - Towards plus end - ATP driven - Regular steps

Question 37

Cytoplasmic Dynein overview?

Answer 37

- Large - Towards minus ends - ATP driven - Irregular movements

Question 38

Microtubule involvement in secretory pathway?

Answer 38

Microtubule motors move vesicles in the secretory pathway - Secretory pathway is the kinesin-mediated and dynein-mediated transport of vesicles, vesicluar-tubular clusters and organelles.

Question 39

Evidence of kinesin transport of organelles?

Answer 39

Kinesins transport mitochondria and other organelles to the periphery - We can see this when we observe the difference between cells with and without kinesins and how they arrange themselves

Question 40

What is involved in melanosome movement?

Answer 40

The rapid movement of melanosomes is mediated by dynamin and microtubules.

Question 41

What does a melanosome do?

Answer 41

The melanosome is an organelle that synthesizes and stores melanin.

Question 42

How is melanosome movement coordinated?

Answer 42

They have coordinated movement because microtubules are uniformly polarized.

Question 43

Axonal transport of organelles?

Answer 43

Neurons transport vesicles with neurotransmitters to the synapse - The vesicle contains both types of motor proteins - Motor proteins can be inactivated to get the back

Question 44

How do we accomplish minus end transport?

Answer 44

Kinesin must be inhibited for minus-end transport to occur.

Question 45

What prevents kinesin binding?

Answer 45

Kinesin-binding protein prevents kinesin-microtubule binding

Question 46

Speed of organelle transport?

Answer 46

Organelle transport goes a long way! Synaptic vesicle speed = 5 micrometers/second or 0.4 m/day

Question 47

What are cilia and flagella?

Answer 47

Both cilia and flagella are hairlike cell appendages that have a bundle of microtubules at their core.

Question 48

Flagella motion and location?

Answer 48

Flagella are found on sperm and many protozoa and have an undulating motion - This is like a propellor motion

Question 49

Cilia motion?

Answer 49

Cilia beat with a whiplike motion - back and forth beating

Question 50

Name of the core of the cilium and flagellum?

Answer 50

The core of the cilium and flagellum is called the axoneme, which is composed of microtubules and their associated proteins

Question 51

Axonemal dynein?

Answer 51

Anonemal dyne bends the axosome which move the cilium and flagellum.