Lecture 22: Motors, Actin, Cell Motility

Question 1

Microtubules (MT) types

Answer 1

Axonemal MT - highly organized, stable, part of structures involved in cell movement
Cytoplasmic MT - loosely organized, very dynamic, located in cytosol

Question 2

About microtubules (MT)

Answer 2

• largest cytoskeletal element
• polymer of two different proteins (monomers): alpha tubulin and beta tubulin

Question 3

What is a heterodimer?

Answer 3

Alpha and beta particles together which forms long protofilaments

Question 4

How many protofilaments make a microtubule?

Answer 4

13 protofilaments in longitudinal array

Question 5

A microtubule is _______

Answer 5

Hollow

Question 6

Orientation of microtubules?

Answer 6

• polarity present
• fast-growing plus end - more dynamic, not a positive charge just the name
• slow-growing minus end

Question 7

Microtubule organizing center (MTOC)

Answer 7

Central site of MT assembly, only in eukaryotic cells, microtubule grows away from MTOC, therefore the plus end is always the farther part of the MT from the MTOC, and the negative end is closest to MTOC

Question 8

What binds the MT’s?

Answer 8

Microtubule associated proteins: which modulate assembly and function and mediate interactions with other structures
- Non-motor proteins
- Motor proteins

Question 9

MT-associate non-motor proteins functions

Answer 9

• control MT organization in cytosol (Tau, and MAP2)
• stabilizes MT band stimulates assembly

Question 10

Defective Tau protein consequences?

Answer 10

• neurofibrillary tangles -> Alzheimer’s disease

Question 11

MT-associated motor proteins functions

Answer 11

• use ATP to generate force
• can move material along MT track
• can generate sliding force between MTs
• kinesin: plus end directed
• dynein: minus end directed

Kinesin receptor attaches Motor protein to vesicle

Question 12

Zebra fish Kinesin and dynein

Answer 12

Kinesin: darkly coloured
Dynein: lightly coloured

Question 13

Microfilaments functions

Answer 13

• maintenance of cell shape
• cell movement
• vesicle transport
• muscle contraction
• cytokinesis

Question 14

Microfilaments

Answer 14

• 8nm
• polymer of actin protein
• plus and minus end

Question 15

Microfilaments (MF) monomers and polymers

Answer 15

• Monomer - G-actin: four subdomains
• Polymer - F-actin: 28 subunits of G-actin make up this unit, two strands of G-actin monomers

Question 16

MTs plus and minus end

Answer 16

Plus end is fast growing
Minus end is slow
They are polar

Question 17

Phalloidin and actin?

Answer 17

Once binded to actin, you can track actin using fluorescent phalloidin, come from mushrooms

Question 18

proteins in microfilaments?

Answer 18

Actin-binding proteins help to organize microfilaments

Question 19

Which two ways can microfilaments be assembled?

Answer 19

microfilaments can be arranged in loose network OR in tight bundles

Question 20

F-actin microfilaments are associated with _________

Answer 20

Motor proteins

Question 21

What are myosin’s in microfilaments?

Answer 21

Motor proteins associated with microfilaments, there are two types:
1. Conventional myosin’s: Type II, primary motors for muscle contraction
2. Unconventional myosins: type I and III-XVII, organelle and vesicle movement

Question 22

Myosins move towards ______ end of microfilaments

Answer 22

Plus

Question 23

MT and MF based motors cooperate in ______

Answer 23

Intracellular transport (e.g. movement of pigment to PM)

Question 24

Intermediate filaments (IF) functions

Answer 24

• 10 nm diameter
• exclusive to multicellular animal cells
• provide structural support and mechanical strength
• stable in comparison to MT and MF
• arrangement of fibrous alpha helical proteins
• NOT POLAR

Question 25

Types of intermediate filaments

Answer 25

Keratins - in cytosol
Lamins - in nucleus

Question 26

In axons of neurons, IF’s….

Answer 26

Arranged in stacks