Lecture 12

Question 1

What are the 3 filamentous structures that compose the Cytoskeleton?

Answer 1

Microtubules, actin filaments, intermediate filaments

Question 2

List the 5 functions of the cytoskeleton

Answer 2

Structure support
Positioning of cell organelles
directing of material movement
generating movement
cell division

Question 3

what are properties of microtubules, what protein are they made from, what are they called when organized into longitudinal rows?

Answer 3

they’re hollow, rigid and tubular
Made of the protein tubulin
called protofilaments when arranged

Question 4

what are the building blocks of protofilaments? what are their properties?

Answer 4

Made of Alpha & Beta-Tubulin subunits
the subunits fit tightly together, organized in a linear array, asymmetric and polar

Question 5

What is the function of microtubules?

Answer 5

Provides mechanical support (resist compression), determines cell shape, directs movement within the cell

Question 6

how do microtubules move objects in cells?

Answer 6

serves as a track for motor proteins that generate force
motor proteins are kinesin and dynein

Question 7

what are some properties of Kinesin motor proteins? what do they bind to in order to move and what do they use?

Answer 7

Smallest motor protein, made of 2 identical heavy & light chains
binds to microtubules and uses ATP for force generation

Question 8

True for false?
the movement of Kinesin motor proteins is proportional to ATP concentration

Answer 8

True

Question 9

towards what to kinesin tend to move vesicles and organelles to?

Answer 9

an outwards direction towards the cell’s plasma membrane

Question 10

What is some properties of the Cytoplasmic Dynein motor protein?

Answer 10

Huge protein, made of 2 identical heavy chains, variety of medium and light chains, moves towards the negative end of microtubules (opposite of Kinesin)

Question 11

What are some functions of Cytoplasmic Dynein motor protein?

Answer 11

Positions spindle and moves chromosomes during mitosis
positions centrosome and Golgi complex
moves organelles, vesicles and particles through cytoplasm

Question 12

what does microtubule-organizing centers control?

Answer 12

Number & polarity of microtubules, number of protofilaments and time/location of assembly

Question 13

what do Centrosomes contain? What is it a major site of?

Answer 13

Contains 2 centrioles surrounded by electron dense pericentriolar material
is a major site of microtubules initiation and is the center of the microtubule network

Question 14

what is a Basal body another type of? where does it form? How does it compare to centrioles?

Answer 14

another type of microtubule-organizing center that forms at cilium or flagellum (movement locations)

identical in structure to centrioles
centrioles and basal bodies can each turn into one another

Question 15

what do Microtubule-organizing centers have in common and what does it do?

Answer 15

contain Gamma-Tubulin, critical for microtubule nucleation

Question 16

What are some of the dynamic properties of microtubules?

Answer 16

can shorten, lengthen, disassemble and reassembleq

Question 17

what are some things that can initiate microtubules to disassemble?

Answer 17

Modifications, temperature, pressure, High Ca2+ conc., chemicals

Question 18

what are the interactions between GTP and Beta-Tubulin?

Answer 18

GTP binds to Beta-tubulin during assembly. GTP becomes GDP and stays bound

When being disassembled, GDP is replaced by a new GTP

Question 19

What do microtubules depend on for growth or shrinking?

Answer 19

They depend on the tubulin dimers at the positive end

Question 20

What is Dynamic instability and what does it explain?

Answer 20

phenomenon that explains microtubule behavior

Explains:
Growth and shrinkage can coexist in the same region of a cell
A microtubule can switch back and forth unpredictably between growing and shortening

Question 21

What end is Dynamic instability important for?

Answer 21

Important for the positive end of the microtubule where subunits are added for growth and lost for shrinkage

Question 22

What are the 2 types of Cilia

Answer 22

motile cilia - occurs in large numbers on a cell’s surface. moves fluid and particulate material

nonmotile cilia - acts as a sensory organelle to monitor mechanical and chemical properties of the ECF

Question 23

What is the Axoneme?

Answer 23

core of the cilium containing an array of microtubules running longitudinally
made of a 9 + 2 array (9 peripheral and a central pair)

Question 24

What do the Central tubules in anoxeme connect to and with what??

Answer 24

the A tubules with radial spokes

Question 25

What process transports materials to the cilium / flagella?

Answer 25

the intraflagellar transport

Question 26

What is the process of intraflagellar transport?

Answer 26

proteins assemble into a complex called IFT particle
particles line up to form a linear array (IFT trains)
IFT particles carry cargo proteins

Question 27

How does motion for the cilia and flagella occur?

Answer 27

Dynein undergoes a conformation change after binding from the B tubule to the A tubule
A stroke occurs, the dynein then detach from B and cycle continues

Question 28

True or false?
At any given time, the dynein arms on both sides of the axoneme can be active or inactive

Answer 28

False, only 1 side is active while the other is inactive

Question 29

Describe the components and major functions of the cytoskeleton.
▪ Describe the structure and the functions of microtubules.
▪ Explain how kinesins and dyneins function as motor proteins within
a cell.
▪ Explain the activities that occur at microtubule-organizing centers
(MTOCs) and the underlying basis of microtubule dynamics.
▪ Explain how the movement of cilia and flagella relates to their
structure.