Cytoskeleton

Question 1

Describe the morphology and cellular location of each of the three major cytoskeletal proteins.

Answer 1

Actin - under cell membrane and some towards nucleus from membrane
Intermediate Filaments- throughout cytosol
Microtubules- eminate from centrosomes or basal bodies

Question 2

What is the function of actin in the cell?

Answer 2

To determine cell shape, control cell polarity, connect adherens junctions and focal contacts, enable phagocytosis, enable muscle contraction, and allow the cell to migrate

Question 3

Describe the subunits that make up the actin microfilaments.

Answer 3

Globular monomers of actin

Question 4

Understand and describe the kinetics of actin filament assembly.

Answer 4

Arp nucleates minus end at a 70 degree angle.
ATP binding allows polymerization.
Plus end is more dynamic.
Accessory proteins mediate growth

Cofilin is an actin depolymerization factor. Cap Z covers plus end to stop growth and protect strand.

Question 5

Describe the importance of nucleotide (ATP) hydrolysis in actin filament dynamics and treadmilling.

Answer 5

ATP hydrolysis=shrinkage of actin filaments
Addition of ATP on plus end allows it to grow.
Same rate of degradation and growth=Cc=treadmilling

Question 6

Describe the global cytoskeletal rearrangements regulated by Rho family proteins.

Answer 6

Rho proteins allow for bundling and polymerization.

Cdc 42 = microspikes, filopodia - tight, parallel networks
Rac 1 = lamellipodia - gel-like network
Rho = stress fibers/focal contacts - loose, antiparallel networks

Question 7

Describe the basis for the toxic physiological effect of actin-specific drugs.

Answer 7

Phalloidin - Binds and stabilizes filaments; blocks depolymerization
Cytochalasin - Caps filament plus ends; blocks polymerization
Latrunculin - Binds subunits and prevents their polymerization

Question 8

Describe the overall structure of Myosin II in the bipolar thick filament found in muscle.

Answer 8

Two heavy chains attached to four light chains. The four light chains form two heads.

Question 9

Describe the subunits that make up microtubule filaments.

Answer 9

Alpha-tubulin = minus end, buried in centrosome
Beta-tubulin = plus end

Both can bind GTP, but beta’s GTP can be hydrolyzed

Question 10

Understand and describe the kinetics of microtubule assembly.

Answer 10

GTP end allows for growth.

Question 11

Describe the importance of nucleotide (GTP) hydrolysis in microtubule filament dynamics and dynamic instability.

Answer 11

GTP hydrolysis results in shrinkage (catastrophe). Adding a GTP = rescue

Question 12

Explain why some microtubule specific drugs are useful for cancer chemotherapy.

Answer 12

Microtubules are involved in mitotic spindle formation. Interfering with them may stop cells from dividing.

Question 13

Describe the structural composition and function of microtubule-based astral arrays, cilia and flagella.

Answer 13

Cilia and flagella are organized into an axoneme configuration (2 central and 9 surrounding) and are anchored by basal bodies. Cilia line respiratory epithelium, and flagella propel sperm and protozoa.

Astral arrays are organized by centrosomal MTOCs

Question 14

Describe the molecular characteristics of microtubule-based molecular motors.

Answer 14

Kinesin- move toward positive
Dynein - move toward negative

The motors bind microtubules and use ATP binding propels the other head forward, hand over hand.

Question 15

Compare and contrast the functions of actin and microtubule motor proteins.

Answer 15

Actin motor proteins serve to enable muscle contractions and cell movement

Microtubule motor proteins serve to transport vesicles, etc.

Question 16

Describe the subunits that make up intermediate filaments.

Answer 16

Acidic and basic coils wrapped around each other. They associate with each other via lateral interactions in a staggered manner.

Question 17

Describe how the structure of intermediate filaments provides high tensile strength.

Answer 17

The structure described above allows for a rope-like tensile strength.

Question 18

Describe why the tissue specific expression pattern of intermediate filaments is useful in tumor diagnosis.

Answer 18

Intermediate filaments are tissue specific, and this can be helpful in tumor diagnosis.

Question 19

When would a cell migrate?

Answer 19

During development, wound healing, as part of the immune system and during metastasis.

Question 20

What is the function of the microtubule system?

Answer 20

To position organelles, esp. the ER and Golgi
To transport vesicles
Cell motility via flagella and cilia
Mitotic spindles

Question 21

What is the function of the intermediate filament system?

Answer 21

Provides strength to the cell and tissues.

Promotes cell-cell adhesion at the desmosome and hemidesmosome

Provides axonal diameter and strength

Nuclear lamins contribute to the mechanical integrity of the nucleus

Question 22

Describe the role of ATP In actin-based motors

Answer 22

Binds ATP - myosin released
ATP hydrolyzed - myosin head cocked forward
Phosphate released - myosin lands on ATP
ADP released - power stroke (change in myosin orientation)