Lecture 2: 07/09

Question 1

What are 3 polymers that form the cytoskeleton :—)

Answer 1

Vimentin (intermediate filaments), Tubulin (microtubules), F-Actin (microfilaments)

Question 2

Purpose of cytoskeleton?

Answer 2

provides cells with mechanical
strength and the ability to generate active forces
- Regulates shape and structure
- sets mechanical moduli and integrity
- Generates movement (internal, external)

Question 3

Structure and function of microtubules (tubulin polymers)

Answer 3

Structure: hollow tubes, wall consists of 13 columns of tubulin molecules
Function: maintain cell shape (compression resisting) , cell motility, chromosome movements in cell division, organelle movements

Question 4

Structure and function of microfilaments (actin filaments)

Answer 4

Structure: two intertwined strands of actin, each a polymer of actin subunits
Function: Main cell shape (tension bearing elements), changes in cell shape, cytoplasmic streaming, cell motility, cell division (cleavage furrow formation)

Question 5

Structure and function of intermediate filaments

Answer 5

structure: fibrous proteins supervoiled into thicker cables
Function: main cell shape (tension bearing), anchorage of nucleus and certain other organelles, formation of nuclear lamina

Question 6

What is critical concentration in regards to polymerization kinetics?

Answer 6

Concentration that determines if polymerization or depolymerization will be favoured.
Ccrit = Koff/Kon = 1/Kequilibrium

Question 7

What is treadmilling?

Answer 7

When monomer addition and removal occur at equal rates, thus filaments will be continuously refreshed but stay at the same length.
About 1/3 of our biochemical energy goes into treadmilling.

Question 8

What is needed to determine the force create through polymerization?

Answer 8

boltzmann constant * temperature (kbT), monomer diameter (delta), concentration of monomers, Kon (binding rate), Koff (dissociation rate)

Question 9

Do intermediate filaments generate force? why?

Answer 9

Intermediate filaments do no hydrolyze phosphate, thus do not consume energy in polymerization and thus CANNOT generate force

Question 10

Filament stability and KbT: If the binding energy (Eb) is (greater than, equal to, less than) KbT, what type of binding occurs?

Answer 10

Eb &laquo_space;KbT : no binding
Eb ~ KbT: reversible binding
Eb&raquo_space; KbT: “permanent” binding

Question 11

What process is essential in order for a cytoskeletal polymer to perform work?

Answer 11

Polymerization/depolymerization processes that hydrolyze phosphate can perform mechanical work

Question 12

What does passive mean? What is an example of a passive structural biopolymer?

Answer 12

Passive: no energy input or generation
Example: Intermediate filaments (i.e., vimentin, keratin)

Question 13

What is the forces generated by polymerization used for?

Answer 13

• Motor for amoeba & other protozoa
• Many bacteria
• Leading edge of many mammalian cells