Lecture 12

Question 1

What method is used to visualize the microtubules in the lecture image (Slide 1)?

Answer 1

A fluorescent antibody that labels the tubulin

Question 2

: Are microtubules branched or unbranched structures?

Answer 2

They are unbranched (they just go straight).

Question 3

What nucleotide do both alpha and beta tubulin bind to?

Answer 3

GTP

Question 4

How does the GTP hydrolysis speed compare between alpha and beta tubulin?

Answer 4

Alpha tubulin does not hydrolyze GTP very fast (stays as GTP); Beta tubulin hydrolyzes GTP to GDP pretty fast.

Question 5

What is a “protofilament”?

Answer 5

A vertical line of alpha-beta tubulin dimers

Question 6

Which end of the microtubule is the primary site for growth?

Answer 6

The Plus (+) end (where Beta tubulin is exposed).

Question 7

What typically happens to the Minus (-) end of a microtubule in the cell?

Answer 7

It is normally capped at the centrosome.

Question 8

What defines the “polarity” of a microtubule?

Answer 8

The fact that the two ends are different: alpha tubulin is exposed at one end (-), and beta tubulin is exposed at the other (+)

Question 9

What is the defining characteristic of “Dynamic Instability”?

Answer 9

Microtubules are never stable; they must essentially always be either growing or shrinking.

Question 10

Which form of tubulin makes the microtubule stable?

Answer 10

GTP-tubulin (tubulin bound to GTP).

Question 11

Which form of tubulin makes the microtubule unstable and prone to collapse?

Answer 11

GDP-tubulin (tubulin bound to GDP).

Question 12

What is the “GTP cap”?

Answer 12

A section of newly added GTP-tubulin dimers at the tip of the microtubule that prevents it from shrinking.

Question 13

What chemical change occurs to the tubulin shortly after it adds to the microtubule?

Answer 13

It hydrolyzes its GTP (3 phosphates) into GDP (2 phosphates).

Question 14

What is “Catastrophe”?

Answer 14

The rapid, random loss of the GTP cap which causes the microtubule to switch from growing to shrinking.

Question 15

What is “Rescue”?

Answer 15

The process where a shrinking microtubule regains a GTP cap and begins growing again.

Question 16

Describe the structural shape difference between GTP-tubulin and GDP-tubulin.

Answer 16

GTP-tubulin is straight; GDP-tubulin is kinked or curled outwards.

Question 17

Why does a microtubule fall apart during a catastrophe?

Answer 17

Without the straight GTP cap to hold them in place, the GDP-tubulin dimers curl outwards and the protofilaments peel away.

Question 18

How can you tell if a microtubule is shrinking by looking at an electron microscope image?

Answer 18

The ends will look curled outwards (kinked), whereas growing ends look straight.

Question 19

If a microtubule stops growing (stops adding new dimers), what happens to the cap?

Answer 19

The GTP in the cap is hydrolyzed to GDP, the cap disappears, and catastrophe (shrinkage) begins.

Question 20

What is the structural composition of Kinesin-1 (how many chains)?

Answer 20

It is a tetramer composed of 2 Heavy Chains and 2 Light Chains.

Question 21

What are the four main domains of the Kinesin Heavy Chain?

Answer 21

Head, Neck, Stalk, and Tail.

Question 22

What is the specific function of the Kinesin Head?

Answer 22

Head splits ATP and converts the energy into motion

Question 23

What is the specific function of the Kinesin Tail?

Answer 23

It binds to the cargo (e.g., vesicles, organelles).

Question 24

How many tubulin monomers does a single Kinesin step cover?

Answer 24

4 tubulin monomers.

Question 25

What is the function of the Light Chains?

Answer 25

What is the function of the Light Chains?

Question 26

Based on microtubule polarity, what is the direction of Kinesin transport within the cell?

Answer 26

From the center (centrosome) outward to the plasma membrane.

Question 27

What is the energy cost for Kinesin to take a step?

Answer 27

Hydrolysis of ATP (ATP to ADP + Pi)

Question 28

What is the physical distance of one Kinesin step?

Answer 28

16 nm.

Question 29

Describe the regularity of Kinesin movement.

Answer 29

It is homogeneous and progressive (steps are always the same size).

Question 30

What is the "attachment rule" for Kinesin heads during movement?

Answer 30

At least one of the heads is always attached to the microtubule (it doesn't float away).

Question 31

The movement of kinesin molecules is for what

Answer 31

long-range

Question 32

What is the primary purpose of an in-vitro motility assay?

Answer 32

To visualize motor protein dynamics and measure the speed of movement outside of a cell.

Question 33

In the described motility assay, which component is fixed to the coverslip?

Answer 33

The Kinesin motors (specifically, their tails are glued to the glass via a chemical reaction).

Question 34

In the motility assay, which component is observed moving?

Answer 34

The fluorescently labeled microtubules glide across the carpet of stationary kinesin heads.

Question 35

Motor activity of the kinesins

Answer 35

causes the microtubules to glide kinesins

Question 36

hat is the "common element" shared by all proteins in the Kinesin Superfamily?

Answer 36

The motor domain of the heavy chain.

Question 37

How are kinesins grouped into families (e.g., Kinesin-1, Kinesin-3)?

Answer 37

By phylogenetic clustering (building an evolutionary tree based on sequence similarity), similar to how biological species are grouped.

Question 38

Which family does the "classic" or "conventional" kinesin belong to

Answer 38

Kinesin-1 (often labeled KHC for Kinesin Heavy Chain).

Question 39

Describe the structure of Heterotrimeric Kinesin-2 mentioned in the lecture

Answer 39

It has a shorter stalk than Kinesin-1 and uses a different regulatory setup (e.g., a single accessory protein called KAP).

Question 40

What is the unique structural feature of Kinesin-3 (KIF1/Unc104) described in the lecture?

Answer 40

It is structurally very different and can switch between working as a monomer and a dimer

Question 41

: What is the primary function of Kinesin-13?

Answer 41

It is a microtubule depolymerase (it breaks down microtubules rather than walking on them).

Question 42

Does Kinesin-13 "walk" along the microtubule?

Answer 42

No, it binds to the ends to depolymerize them.

Question 43

mechanistically, how does Kinesin-13 cause the microtubule to fall apart?

Answer 43

It uses ATP hydrolysis to force the protofilaments to bend/curl outwards.

Question 44

Can Kinesin-13 disassemble a microtubule even if it has a stable GTP cap?

Answer 44

Yes

Question 45

Kinesin-13 proteins

Answer 45

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

Question 46

In which direction does Kinesin-14 move?

Answer 46

Towards the Minus (-) end in motility assays

Question 47

How is the movement of Kinesin-14 different from Kinesin-1?

Answer 47

It moves in the opposite direction (Kinesin-1 moves to the Plus end).

Question 48

The tail of kinesin-14 can bind what

Answer 48

microtubules and allows it to organize microtubule bundles

Question 49

Because Kinesin-14 binds microtubules at both ends (head and tail), what is its major function?

Answer 49

It crosslinks microtubules and can cause them to slide against each other or cluster.

Question 50

If Kinesin-14 acts on two antiparallel microtubules (oriented in opposite directions), what is the result?

Answer 50

Robust sliding.

Question 51

What is the primary function of Cytoplasmic Dynein regarding transport direction?

Answer 51

It brings cargo (like vesicles) back toward the centrosome (Minus end)

Question 52

How does the size of Dynein compare to Kinesin?

Answer 52

Dynein is approximately 4 times bigger and much more complex than Kinesin

Question 53

t: What are the large "AAA" domains found in the Dynein head structure?

Answer 53

They are ATPase domains where ATP hydrolysis occurs

Question 54

: How does the location of ATP hydrolysis differ between Kinesin and Dynein?

Answer 54

Kinesin hydrolyzes ATP in the head (near the microtubule); Dynein hydrolyzes ATP in the AAA ring, which is far away from the microtubule-binding site.

Question 55

What is unique about Dynein's ATP consumption compared to Kinesin?

Answer 55

Dynein has multiple hydrolysis sites (AAA1-AAA6) and hydrolyzes way more ATP per step than Kinesin

Question 56

Which specific part of the Dynein molecule physically contacts the microtubule?

Answer 56

The Microtubule-binding Domain located at the tip of the Stalk

Question 57

Which part of the Dynein molecule binds to the cargo (vesicle)?

Answer 57

The Tail

Question 58

What happens to Dynein's structure when ATP binds?

Answer 58

It changes conformation to dissociate (release) from the microtubule.

Question 59

: Compare the "stepping" movement of Kinesin vs. Dynein.

Answer 59

Kinesin takes regular, progressive steps; Dynein takes irregular, "weird" movements.

Question 60

Size of Kinesin vs. Dynein?

Answer 60

Kinesin is small; Dynein is big

Question 61

Which motor protein transports vesicles from the Golgi complex to the plasma membrane?

Answer 61

Kinesin.

Question 62

Which motor protein transports vesicles from the plasma membrane back to the Golgi/cell center?

Answer 62

Dynein.

Question 63

How are microtubules oriented between the Golgi and the plasma membrane?

Answer 63

Minus (-) ends are at the Golgi (center); Plus (+) ends are at the plasma membrane.

Question 64

After Kinesin transports a vesicle to the plasma membrane, how is the motor itself recycled/returned to the cell center?

Answer 64

It is transported back by Dynein.

Question 65

Microtubules motors move vesicles in what

Answer 65

The secretory pathway

Question 66

How are mitochondria distributed in a normal cell?

Answer 66

They are dispersed throughout the cytoplasm (extending to the periphery).

Question 67

How are mitochondria distributed in a Kinesin mutant cell?

Answer 67

They are aggregated (clumped) at the center of the cell.

Question 68

What does the Kinesin mutant experiment prove about mitochondrial transport?

Answer 68

Kinesin is required to transport mitochondria outward to the cell periphery.

Question 69

Does removing Kinesin significantly change the structure of the microtubule network itself?

Answer 69

No, the microtubules remain relatively well-organized; only the organelle distribution changes.

Question 70

What are melanosomes?

Answer 70

synthesizes and stores melanin

Question 71

The rapid movement of melanosomes is mediated by

Answer 71

dynamin and microtubules

Question 72

Which motor protein is responsible for dispersing melanosomes throughout the cell?

Answer 72

Kinesin (moving towards the plus ends/periphery).

Question 73

Which motor protein is responsible for aggregating melanosomes in the center of the cell?

Answer 73

Dynein (moving towards the minus ends/center).

Question 74

If an animal (like a frog) is on a light background, what happens to the melanosomes?

Answer 74

They aggregate in the center (making the animal look lighter to blend in).

Question 75

If an animal is on a dark background, what happens to the melanosomes?

Answer 75

They disperse throughout the cell (making the animal look darker to blend in).

Question 76

Coordinated movement because what

Answer 76

microtubules are uniformly polarized

Question 77

a vesicle contains what

Answer 77

both types of motor proteins

Question 78

sIn a neuron, which motor protein transports vesicles from the cell body to the synapse?

Answer 78

Kinesin (Anterograde transport).

Question 79

In a neuron, which motor protein transports cargo from the synapse back to the cell body?

Answer 79

Dynein (Retrograde transport).

Question 80

Why can't Kinesin and Dynein be active on the same vesicle at the same time

Answer 80

They would pull in opposite directions, resulting in no net movement (a tug-of-war).

Question 81

What is the specific protein mentioned that inhibits Kinesin?

Answer 81

Kinesin-binding protein (KBP).

Question 82

How does Kinesin-binding protein (KBP) function mechanism-wise?

Answer 82

It binds to the kinesin heads and prevents them from binding to the microtubule.

Question 83

When the cell wants to move cargo back to the center (retrograde), what must happen to Kinesin?

Answer 83

It must be inhibited (e.g., by KBP Kinesin-binding protein) so Dynein can take over.

Question 84

What is the speed at which synaptic vesicles move along an axon?

Answer 84

5 µm/second (or approximately 0.4 meters/day)

Question 85

In the example of the fruit fly larva, where do the motor neuron axons originate and end?

Answer 85

They originate in the brain and extend all the way to the muscles.

Question 86

What specific human nerve is cited as an example of extremely long-range transport?

Answer 86

The Sciatic nerve

Question 87

hat does the lecture emphasize about the continuity of these axons?

Answer 87

That a single cell spans the entire distance (it is not a chain of multiple cells).

Question 88

What are cilia and flagella?

Answer 88

Hairlike cell appendages containing a bundle of microtubules used for movementat their core

Question 89

What is the difference in motion between Flagella and Cilia?

Answer 89

Flagella have an undulating or propeller-like motion (e.g., sperm); Cilia have a back-and-forth beating or whiplike motion.

Question 90

What embryonic development process is determined by beating cilia?

Answer 90

The determination of the left and right axis (e.g., heart position).

Question 91

What is the specific name for the microtubule core of a cilium or flagellum?

Answer 91

The Axoneme

Question 92

The Axoneme

Answer 92

composed of microtubules and their associated proteins,

Question 93

Describe the specific microtubule arrangement of the Axoneme

Answer 93

The "9+2" arrangement: 9 outer doublets surrounding 2 central singlet microtubules.

Question 94

What is an "outer doublet" composed of?

Answer 94

Two fused microtubules: The A microtubule and the B microtubule.

Question 95

Axonemal dynein

Answer 95

bends the axoneme which move the cilium and flagellum

Question 96

How does Axonemal Dynein generate movement in the flagellum?

Answer 96

It tries to slide the microtubules past each other, but because they are linked, this force causes the structure to bend.

Question 97

How is the direction of bending controlled?

Answer 97

By coordinating the activation of dyneins on one side while relaxing the dyneins on the opposite side

Question 98

In the structural diagram, what are the "radial spokes"?

Answer 98

Protein structures connecting the outer doublets to the central sheath/singlets.

Question 99

In the structural diagram, what is "nexin"?

Answer 99

A linking protein that connects adjacent outer doublets (preventing them from sliding apart completely).