lecture 4 Flashcards
what are muscle cells like?
long skinny tubes which have ability to contract into short fat tubes
true or false, all cells are the same
false, cells come in many shapes
how do cells have different shapes, even though all have same genes inside of them?
cause they are building themselves a particular skeleton
in intestinal cells, what do the projections allow for?
projections allow to increase surface area, for better nutrient import
what are the characteristics of cells?
-cells come in many shapes
-cells are internally organized (ex: projections)
-cells import and export cargo (ex: some cells specialize in secretion)
-cells move
what carries cargo through cytoplasm?
motor protein
give an example of the movement of cells
cells migrate into wounds:
in zebrafish, neutrophils move from blood stream to the wound
what is the cytoskeleton?
internal skeleton of the cell
what filaments is the cytoskeleton composed of?
-microfilaments (actin)
-microtubules (tubulin)
-intermediate filaments
what is the leading edge?
place where microfilaments are enriched in the direction of movement of the cell
what mediates the mvoement of the cell?
cytoskeleton
what do the intermediate filaments do?
forms cage around nucleus
what are the roles of the cytoskeleton?
-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)
what are the intermediate filaments made of?
-made of various different molecules, forms spaghetti network spanning the cell
what are microfilaments made of?
2 stranded actin polymer winded together like a rope
what are microtubules made of?
-polymer of tubular
-thick hallow tubes
-ab-tubulin dimer
what type of structure is the cytoskeleton?
tensegrity structure
what can we compare the 3 type of filaments to?
-microtubules= poles (stiff, resistant to compression)
-actin filaments=wires (high tensile strength, flexible)
-intermediate filaments=ropes (elastic and flexible)
what is a tensegrity structure
structure maintained by tension and not compression (being pulled equally in different directions)
what is actin?
ATPase that drives cell motility
what does actin polymerize into?
two stranded helical filament
in which cells is actin a major component of?
muscle cells
how are actin filaments organized in different cells? what are the different functions?
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
what do cells control about actin filaments?
-length
-number
-angle
-bundling
-orientation
what do microvili and stress fibers have in common?
they contain bundles of actin filaments
what type of actin filaments does the leading edge contain?
branched (dendritic actin filaments)
true or false, actin filaments drive cell movement?
true
how do cells move?
actin filaments extend the lamellipodium and pull the cell forward
how do the leading edge and the stress fibers work together to move the cell?
The Leading Edge pushes forward and Stress Fibers pull up the rear
what does ATP do to actin?
makes it competent for polymerization
what is G-actin?
globular actin, diffuses in solution
what are the phases that actin polymerization occurs in?
what do we call the + and the - end of the actin filament?
+ end: barbed end
- end: pointed end
what is the difference between the 2 ends of the actin filament?
Plus end: This is where actin filaments grow faster.
Minus end: This is where growth is slower and more prone to depolymerization.
why is the critical concentration at the + end lower than for the - end?
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.
what do critical concentrations refer to?
concentration at which polymerization is equal to depolymerization at this specific end
each end of the actin polymer has an “on” and “off” rate, which one depends on the concentration?
the “on” rate. the exact rate is gotten by multiplying the number with the concentration of actin in the solution
between which two concentrations does the treadmilling concentration occur?
at concentration between the critical concentration of both ends
what are the different actin regulators? what do they do?
-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
what molecules control actin regulators? what do they do?
-Cdc42
-Rac
-Rho
they activate actin regulators in response to extracellular signals
