Comprehension - L14-L15

Question 1

What is it called when there is an absence of stabilization in microtubules?

Answer 1

Protofilaments curl outward and undergo catastrophic shrinkage

Question 2

What do +TIPS do?

Answer 2

• Bind to +ve end of microtubule and regulate the rate of growth or shrinkage
• Mediate attachement to subcellular structure
• Microtubule polymerization/disassembly can push and pull material within the cell

Question 3

What is the purpose of microtubules?

Answer 3

• Provide mechanical support: are stiff enough to resist compression or bending forces
  -Determine the shape of a cell
• Maintains intracellular location of organelles

Question 4

What do motor proteins do?

Answer 4

Utilize ATP hydrolysis to generate mechanical forces that move the motor protein and attached cargo along the cytoskeleton

Question 5

What are examples of cargo that are transported on microtubules?

Answer 5

• Membraneous vesicles
• Non membrane bound ribos, RNA
• Organelles (lysosomes, mitos)
• Chromosomes
• Other cytoskeletal filaments

Question 6

What are the three types of motor proteins?

Answer 6

• Microtubule motor proteins (kinesins and dyneins)
• Actin motor proteins (myosins)

Question 7

In kinesin, what are part of the globular head?

Answer 7

• Binds microtubules
• ATP hydrolysis
• Conserved sequences

Question 8

In kinesin, what is part of the tail?

Answer 8

• Binds to cargo
• Diverse sequences

Question 9

Which direction does kinesin move?

Answer 9

Towards the positive end

Question 10

How does kinesin move?

Answer 10

Leading head binds 1 ATP: hydrolysis and release of ADP + Pi = power stroke that swings the trailing head forward

Question 11

How does dynein bind to cargo?

Answer 11

Via an adaptor protein, called dynactin

Question 12

Which direction does dynein move?

Answer 12

Towards the negative end

Question 13

What does dynein do?

Answer 13

• Positioning the spindle and moving chromosomes during mitosis
• Positioning organelles and moving vesicles

Question 14

What is the axonome?

Answer 14

Core contains microtubules oriented longitudinally

Question 15

How are all microtubules oriented?

Answer 15

+ at the distal end
- at the basal body

Question 16

In the axoneme, how many doublets are there and how are they connected to each other?

Answer 16

There are 9 peripheral doublets and they are connected to each other via nexin

Question 17

Describe the 4 steps of the movement of flagella

Answer 17

1. dynein tails attached to the A tubule and dynein stalks bind to B tubules
2. Power stroke
3. Dynein stalks detach
4. Dynein stalks reattach

Question 18

What does actin do?

Answer 18

Involved in cellular motile processes
- movement of vesicles
- Phagocytosis
- Cytokinesis
Provides structure support

Question 19

Actin filaments have polarity. The positive and negative ends are…

Answer 19

+: barbed
-: pointed

Question 20

Is ATP actin added to just the positive end of the filament?

Answer 20

No. IT is added to both ends, but there is faster addition at the barbed end

Question 21

What is the critical concentration?

Answer 21

• Minimal concentration of available ATP-actin required to elongate
• critical concentration of the barbed end is lower

Question 22

What are the steps of actin filament and disassembly?

Answer 22

1. Preformed actin seed in presence of ATP-actin
2. at high [ ] its added to both ends
3. [ ] reaches critical [ ] of the pointed end; addition stops at pointed end
4. loss of subunits at the pointed end but addition continues at barbed end (steady state)
   5.relative position of subunits is continually moving (treadmilling)

Question 23

Which way does myosin move?

Answer 23

all myosin move towards the + barbed end

Question 24

What are the 3 components of Conventional Myosin Type 2?

Answer 24

Motor: binds actin filament, binds and hydrolyzes ATP, conserved sequences

Neck: lever arm, moves during power stroke

Tail: Intertwining of 2 heavy chains, allows the formation of filaments of myosin

Question 25

What does Unconventional Myosin Type V do?

Answer 25

Moves processively along actin filament
Moves hand over hand
Long necks act as swinging arms
Can take very large steps\

Question 26

What is the adaptor called that binds Myosin type V to a vesicle?

Answer 26

Rab 27a

Question 27

Movement over long distances occurs mostly on:
Movement locally in the outskirts of the cell occurs on:

Answer 27

Microtubules
Actin filaments