CELL SHAPE IN THE EUKARYA

Question 1

what are the benefits of cytoskeletons?

Answer 1

1. structural support
   2.means for mitosis and meiosis
2. polarity to the cell
   4 motility to the cell
3. assistance in cell to cell interaction

Question 2

what are microfilaments?

Answer 2

• actin filaments in all eukarya
• many proteins associated to filaments.
• concentrate at the plasma membrane.
• serve as scaffolding and assist movement.
• associated to myosin in some cases.

Question 3

what are microtubules?

Answer 3

1. monomer is a heterodimer of α-tubulin and β-tubulin.
2. α-tubulin binds GTP and β-tubulin catalyses its hydrolysis into GDP and Pi.
3. grows from centromere
4. involved in chromosome segregation
5. associated to dynein and kinesin in some cases.

Question 4

what are intermediate filaments?

Answer 4

1. various heteropolymers.
2. lamins are found in the nucleus
3. structural and mechanical support

Question 5

what are the acti- binding proteins?

Answer 5

1. fibrin (68 kDa) – microvilli,
   adhesion plaques, stereocilia.
2. α-actinin (102 kDa) – filopodia,
   lamellipodia, stress fibres…
3. spectrin (245-280 kDa) – cortical
   networks.
4. dystrophin (427 kDa) – muscle
   cortical networks.
5. filamin (280 kDa) – same as αactinin.
6. • fascin (55 kDa) – ditto
7. villin (92 kDa) – microvilli in
   intestine and kidneys.

Question 6

what are microtubules?

Answer 6

1. α -tubulin and β -tubulin form a
   heterodimer (about 100 kDa)
2. the α -tubulin therein binds GTP and the β -tubulin therein hydrolyses it to GDP + Pi then swaps the GDP for GTP.
3. forms a helical structure microtubule.

Question 7

what are intermediate filaments?

Answer 7

• named as they are wider than actin and narrower than myosin
• vary in size
• some acidic/ basic keratin are intermediate filaments.

Question 8

what is myosin?

Answer 8

• motor proteins - involved in muscle contraction.
• bound to F-actin filaments and walks along them at expense of ATP hydrolysis.

Question 9

what is dynein?

Answer 9

body of the cell

Question 10

what are dynein and kinesin?

Answer 10

• walks along microtubules (not microfilaments) - ATP dependent.
• can carry things: molecules, organelles, vesicles.

Question 11

what is retrograde transport?

Answer 11

moves things towards minus end of microtubule and towards body of cell

Question 12

what is anteretrogade transport?

Answer 12

moves things towards plus end of cell towards the periphery of the cell

Question 13

what is cell migration?

Answer 13

1. cells have polarity
2. lamellopodia and filopodia interact with substratum.
3. polymerisation and depolymerisation of actin/ cytoskeleton.
4. can be coupled to following a signal - CHEMOTAXIS
5. An extension of this is phagocytosis using filopodia to pull items to the cell.