U2-L4 Cytoskeleton

Question 1

function of cytoskeleton:

Answer 1

• Cell shape
• Internal organization
• Cell movement
• Mechanical strength

Question 2

Cells are filled with 3 types of filament that form part of the cytoskeleton:

Answer 2

1. actin microfilaments
2. intermediate filaments
3. microtubules

(all protein filaments)

Question 3

actin microfilaments
* purpose
* size (thinnest, thickest)
* how concentrated and where (shape)
* how do they increase/decrease in size

Answer 3

• structure and support in the cell
• 7 nm (thinnest)
• Highly concentrated in the cortex, beneath the plasma membrane (shape)
• Monomers of g-actin assemble into a helix shaped threat called F-actin
• Monomers can attach (+ end) or detach (- end) from the polymer
• Only need energy to increase size - release energy to decrease in size

Question 4

microfilaments in non muscles

Answer 4

• It gives cell shape - platelet activation
• Microvilli - allow cell to increase area of absorption
• Cytokinesis contractile ring
• Actin cytoskeleton from adjacent cells bind through adherens belts

Question 5

microfilaments in muscle cells (muscle contraction) - 2

Answer 5

• Actin filaments are part of the sarcomere
• Actin filaments move over other filaments (myosin), producing muscle contractions

Question 6

intermediate filaments:
* purpose in the cytoplasm
* size (thickest, thinnest)
* structure
* energy requiered for polymerization
* function - 3
* type of protein depending on cell - 3

Answer 6

• form an elaborate network in the cytoplasm of most cells, extending from a ring surrounding the nucleus to the plasma membrane
• 8-10 nm (middle in size)
• Ropelike fibers of long strands of proteins twisted together
• No energy is required for polymerization
  Function:
• Very stable
• Resistant to temperature changes
• Provide mechanical strength
  Strands of different proteins (depending on the cell):
• Epithelial cells: keratin –> Hair and nails - filled with keratin
• Muscle cells: desmin
• Neurons: neurofilaments –> Allow to hold the shape of the nerve axons

Question 7

microtubules
* size
* shape
* subunits
* protofilaments - 2

Answer 7

• 25 nm - biggest in size
• Hollow tube shaped
• Subunits: dimers of a-tubulin + b-tubulin
• Binding of dimers → protofilament
• There is 13 protofilaments → microtubule

Question 8

microtubules
* structure
* function

Answer 8

MT emerge from the MTOC (MT organizing center) (- end) and grow towards the cell membrane (+ end)

1. Vesicles and organelles transport
   * ATP needed
   –> motor proteins:
   Kinesin: towards + end → towards plasma membrane
   Dynein: towards - end → towards MTOC
2. Mitotic spindle:
   * Mother cell divides into two daughter cell → the mitotic spindle made of microtubules has to be split everything equally into two
3. Movement of cilia and flagella
   * Its mobile because of the presence of microtubules

Question 9

junctional complex
* what it is
* components
* 2 things about each component - attach to what, bound to what

Answer 9

• structure formed between 2 adjacent cells
• consists of 3 components: tight junction + adherens junction + desmosome