lecture 4

Question 1

what are muscle cells like?

Answer 1

long skinny tubes which have ability to contract into short fat tubes

Question 2

true or false, all cells are the same

Answer 2

false, cells come in many shapes

Question 3

how do cells have different shapes, even though all have same genes inside of them?

Answer 3

cause they are building themselves a particular skeleton

Question 4

in intestinal cells, what do the projections allow for?

Answer 4

projections allow to increase surface area, for better nutrient import

Question 5

what are the characteristics of cells?

Answer 5

-cells come in many shapes
-cells are internally organized (ex: projections)
-cells import and export cargo (ex: some cells specialize in secretion)
-cells move

Question 6

what carries cargo through cytoplasm?

Answer 6

motor protein

Question 7

give an example of the movement of cells

Answer 7

cells migrate into wounds:
in zebrafish, neutrophils move from blood stream to the wound

Question 8

what is the cytoskeleton?

Answer 8

internal skeleton of the cell

Question 9

what filaments is the cytoskeleton composed of?

Answer 9

-microfilaments (actin)
-microtubules (tubulin)
-intermediate filaments

Question 10

what is the leading edge?

Answer 10

place where microfilaments are enriched in the direction of movement of the cell

Question 11

what mediates the mvoement of the cell?

Answer 11

cytoskeleton

Question 12

what do the intermediate filaments do?

Answer 12

forms cage around nucleus

Question 13

what are the roles of the cytoskeleton?

Answer 13

-shape structure and stability
-intracellular transport (microtubules form roadway for transport of cargo)
-spatial organization (forms compartments)
-contraction and motility (basis of muscle cells and muscle contractions)

Question 14

what are the intermediate filaments made of?

Answer 14

-made of various different molecules, forms spaghetti network spanning the cell

Question 15

what are microfilaments made of?

Answer 15

2 stranded actin polymer winded together like a rope

Question 16

what are microtubules made of?

Answer 16

-polymer of tubular
-thick hallow tubes
-ab-tubulin dimer

Question 17

what type of structure is the cytoskeleton?

Answer 17

tensegrity structure

Question 18

what can we compare the 3 type of filaments to?

Answer 18

-microtubules= poles (stiff, resistant to compression)
-actin filaments=wires (high tensile strength, flexible)
-intermediate filaments=ropes (elastic and flexible)

Question 19

what is a tensegrity structure

Answer 19

structure maintained by tension and not compression (being pulled equally in different directions)

Question 20

what is actin?

Answer 20

ATPase that drives cell motility

Question 21

what does actin polymerize into?

Answer 21

two stranded helical filament

Question 22

in which cells is actin a major component of?

Answer 22

muscle cells

Question 23

how are actin filaments organized in different cells? what are the different functions?

Answer 23

they can be organized in different ways for different functions:
-thin portrusions packed with actin filaments
-cell cortex (cage-like structure to maintain plasma membrane)
-adherens (thick bundle forming seal to prevent fluids from sneaking out)
-filopodia (slender portrusions)
-lamellipodium (leading edge)
-stress fibers
-phagocytosis
-moving endocytic vesicles
-contractile ring

Question 24

what do cells control about actin filaments?

Answer 24

-length
-number
-angle
-bundling
-orientation

Question 25

what do microvili and stress fibers have in common?

Answer 25

they contain bundles of actin filaments

Question 26

what type of actin filaments does the leading edge contain?

Answer 26

branched (dendritic actin filaments)

Question 27

true or false, actin filaments drive cell movement?

Answer 27

true

Question 28

how do cells move?

Answer 28

actin filaments extend the lamellipodium and pull the cell forward

Question 29

how do the leading edge and the stress fibers work together to move the cell?

Answer 29

The Leading Edge pushes forward and Stress Fibers pull up the rear

Question 30

what does ATP do to actin?

Answer 30

makes it competent for polymerization

Question 31

what is G-actin?

Answer 31

globular actin, diffuses in solution

Question 32

what are the phases that actin polymerization occurs in?

Answer 32

Question 33

Answer 33

Question 34

what do we call the + and the - end of the actin filament?

Answer 34

+ end: barbed end - end: pointed end

Question 35

what is the difference between the 2 ends of the actin filament?

Answer 35

Plus end: This is where actin filaments grow faster. Minus end: This is where growth is slower and more prone to depolymerization.

Question 36

why is the critical concentration at the + end lower than for the - end?

Answer 36

Lower Critical Concentration: Since ATP-actin has a higher affinity for the filament, polymerization at the plus end can occur at lower concentrations of G-actin.

Question 37

what do critical concentrations refer to?

Answer 37

concentration at which polymerization is equal to depolymerization at this specific end

Question 38

each end of the actin polymer has an "on" and "off" rate, which one depends on the concentration?

Answer 38

the "on" rate. the exact rate is gotten by multiplying the number with the concentration of actin in the solution

Question 39

between which two concentrations does the treadmilling concentration occur?

Answer 39

at concentration between the critical concentration of both ends

Question 40

what are the different actin regulators? what do they do?

Answer 40

-formins: grow the filament -ADF/Cofilin: cut the filament -cap the filament: capping protein -make branched filament: Arp2/3 complex -bundle the filaments: alpha actinin

Question 41

what molecules control actin regulators? what do they do?

Answer 41

-Cdc42 -Rac -Rho they activate actin regulators in response to extracellular signals