chapter 12 - for merginggg

1. What are motor proteins?

Proteins that bind to a cytoskeletal filament and use energy from ATP
hydrolysis to move along it.

2. What direction do myosin motor proteins move along F-actin?

Towards the barbed
(+) end

3. What are the two classes of myosin?

Conventional myosin (e.g., Myosin II) and unconventional

myosins (at least 17 classes, e.g., Myosin V).

4. What is the structure of myosin motor proteins?

Composed of one pair of heavy chains and
two pairs of light chains.

5. What is the function of the head domain of myosin?

It contains the ATP-hydrolysis domain
for power generation and the actin binding region.

6. What happens to myosin heads in the resting state?

They are bent backwards and
sterically interfere with each other, resulting in inactivity.

7. How does myosin generate force?

Through coupled ATP hydrolysis and conformational changes
during each cycle of binding, hydrolysis, and release.

8. What is a sarcomere?

The contractile unit of muscle, consisting of an array of ordered thick and thin
filaments.

9. What are the components of a sarcomere?

Thin filaments (actin) and thick filaments (myosin
II) with overlapping regions.

10. What occurs during sarcomere contraction?

Actin and myosin slide past each other without
shortening.

11. What role does tropomyosin play in muscle contraction?

It interferes with actin
binding to myosin heads.

12. What triggers muscle contraction?

An increase in cytosolic Ca2+ concentrations.

13. What is the role of troponin in muscle contraction?

It is a Ca2+ binding protein that, when
bound to Ca2+, changes tropomyosin's conformation to allow myosin heads to contact actin.

14. What is the function of myosin II in non-muscle cells?

It is required for cell motility and
cytokinesis during cell division.

15. What distinguishes unconventional myosin proteins?

They have either one head or two
and are involved in intracellular transport.

16. What is unique about Myosin V?

It has two heads and a long neck region, allowing it to take long
strides on actin without letting go.

17. What is the role of microfilaments in cell motility?

Essential for embryo development,
blood vessel formation, wound healing, and movement of immune cells.

18. What is the cell cortex?

A specialized, thin layer of cytoplasm just under the plasma membrane.

19. What are filopodia?

Thin, spike-like protrusions with an actin filament core.

20. What is the function of titin in the sarcomere?

It positions thick filaments midway between
Z-discs and acts like a spring during contraction and relaxation.

21. What is the M line in a sarcomere?

The location of proteins linking adjacent Myosin II proteins.

22. What happens to the I-band and H-zone during muscle contraction?

They are
greatly reduced in size.

23. What is the role of capping proteins like CapZ in the Z disc?

They stabilize and cap
the actin filaments.

24. How does ATP binding affect the myosin head?

It releases the myosin head from the actin
filament.

25. What is the significance of the 'power stroke' in myosin activity?

It generates force
and restores the myosin head to its original conformation.

26. What is the function of the bare zone in a bipolar filament?

It is free of myosin head
domains, allowing for efficient sliding of actin filaments.

27. What are lamellipodia?

Flattened, sheet-like protrusions supported by a meshwork of actin filaments
that drive forward movement of migrating cells.

28. What are pseudopodia?

3D protrusions that are thicker than lamellipodia.

29. What is blebbing?

A 3D protrusion where the plasma membrane detaches from actin, and cytoplasm
pushes the membrane forward.

30. What drives the forward pulling forces in cell motility?

Actin polymerization generates
the protrusion and forward pulling forces.

31. What is the role of Myosin II in cell motility?

Myosin II generates retraction forces at the rear
of the cell.

32. What activates WASP proteins in cell motility?

Stimulus received on one end of the cell
activates a family of proteins in the cytosol.

33. What is the function of the Arp2/3 complex in actin filament formation?

Activated Arp2/3 proteins serve as a nucleating site for new actin filaments.

34. What happens to older actin filaments as new ones form?

Older filaments are
disassembled by proteins like Cofilin

35. How do Rho-GTP proteins contribute to cell motility?

Rho-GTP activates Formin proteins
to create actin bundles and inactivate destabilizing proteins.

36. What is the role of Dynein in microtubule transport?

Dynein moves towards the negative
end of microtubules, facilitating retrograde transport.

37. What is Kinesin's direction of movement?

Kinesin moves towards the positive end of microtubules, facilitating anterograde transport.

38. What is the structure of Dynein?

Dynein is composed of two heavy chains and several intermediate
and light chains.

39. What mechanism does Dynein use for movement?

Dynein uses a 'linker-swing,
dynein-winch' mechanism for movement along microtubules.

40. What are the four features of Kinesins?

Head (ATPase and binds MTs), Neck (direction of
movement), Stalk (flexibility/movement), Tail (binds cargo).

41. What is the Axoneme?

The inner core of cilia or flagella that bends to produce movement, consisting
of 9 doublets of microtubules and a central pair.

42. How do Dyneins cause bending in cilia and flagella?

Dyneins move along adjacent
doublets of microtubules, causing them to bend relative to each other.

43. What is the extracellular matrix (ECM)?

A complex network of proteins and polysaccharide
chains that cells secrete.

44. How do cells interact in multicellular structures?

Cells can be linked by direct interactions,
such as binding of integral membrane proteins, to form tissues and organs.

45. What role do adaptor proteins play in Dynein and Kinesin function?

Adaptor
proteins mediate binding to cargo for both Dynein and Kinesin.

46. What is the function of the WAVE proteins in cell motility?

WAVE proteins stimulate
Arp2/3 proteins to nucleate branched actin filaments and drive protrusion of the leading edge.

47. What is the significance of the cdc42 proteins in cell motility?

Cdc42 proteins help
establish polarity in the cell, influencing directionality of movement.

48. What is the role of actin tails in bacterial motility?

Some pathogens like Listeria monocytogenes use actin tails for propulsion by activating Arp2/3 to polymerize actin.

49. How do connective tissues relate to the ECM?

Connective tissues, like bone or tendon, are
formed from ECM and have very few cells that bear mechanical stress.

50. What is the basal lamina?

A thin mat-like structure that is part of the ECM, acting as a basement
membrane.

51. What are the three surfaces of epithelial cells?

Apical surface (exposed to lumen), basal
surface (attached to basal lamina), and lateral surfaces (where junctions occur).

52. What role do transmembrane adhesion proteins play?

They mediate cell-cell interactions and link the cytoskeleton to extracellular structures.

53. Name three types of transmembrane adhesion proteins.

Integrins, selectins, and
cadherins.

54. What are cadherins?

Glycoproteins that join cells together and have a modular construction of extracellular domains with calcium ions.

55. How do cadherins function in cell-cell interactions?

They act like 'Velcro' to mediate strong
cell-cell interactions.

56. What distinguishes classical cadherins from nonclassical cadherins?

Classical
cadherins are closely related in sequence, while nonclassical cadherins are more distantly related.

57. What are selectins?

Carbohydrate-binding proteins that bind specific oligosaccharides on cell surfaces.

58. What are integrins composed of?

Two noncovalently attached glycoprotein subunits (alpha and
beta).

59. What is the function of integrins?

They associate with ECM proteins or proteins on other cells and
interact with actin through adaptor proteins.

60. What are adherens junctions?

Protein complexes made up of cadherins that link two epithelial cells.

61. How do adherens junctions respond to mechanical stress?

They respond to tension
inside and outside of cells, facilitating mechanotransduction.

62. What is the role of catenins in adherens junctions?

Catenins link cadherins to the
cytoskeleton and inhibit actin-myosin fiber formation.

63. What are desmosomes?

Structures that provide strength in tissues subjected to mechanical stress by
linking cells with cadherins.

64. What types of cadherins are found in desmosomes?

Nonclassical cadherins, specifically
Desmoglein and Desmocollin.

65. What are tight junctions?

Structures that seal adjacent cells to prevent the movement of molecules
between them.

66. What proteins are involved in tight junctions?

Transmembrane proteins called Claudins and
Occludins.

67. What is the function of gap junctions?

To facilitate intercellular communication by forming
channels that allow small molecules to pass between cells.

68. What are connexons?

Channels composed of six four-pass transmembrane connexin proteins that form
gap junctions.

69. What is plasmodesmata?

Channels in plant cells that act like gap junctions for cell-to-cell communication.

70. What is the significance of the blood-brain barrier in relation to tight junctions?

Tight junctions form the blood-brain barrier, preventing unwanted substances from passing into the brain.

71. What is mechanotransduction?

The process by which cells convert mechanical stimuli into biochemical signals.

72. What is the role of keratins in desmosomes?

Keratins are intermediate filaments that provide
structural support and connect to the basal lamina via hemidesmosomes.