IIIC Cell Junctions

1. What the two types of occluding junctions

Tight junctions ( vertebrates only ) and Septate Junctions ( invertebrates )

2. What are the three types of communication junctions

gap junctions, chemical synapses, plasmodesmata

3. What are the two types of anchoring junctions

actin filaments ( adherens junction and focal adhesion) IF ( desmosomes and hemi desmosomes )

4. Another name for tight junctions

zonulae occludens

5. anastomosing network of protein strands connecting the outer leaflets of the two interacting PM

tight junctions

6. What are the proteins involved in tight junctions

occludin, claudin, Zonulae occludens proteins, Cingulin, Junctional Adhesion Molecules, cadherins

7. Functions of tight junctions

(1) Seal neighboring cells together so that water-soluble molecules cannot leak between the cells (2) confine transport proteins to their appropriate membrane domains

8. Explain the role of tight junctions in the transcellular transport of glucose

apical domain Na+ driven glucose symport, basolateral domain facilitated passive diffusion. The main purpose if for the directional transport of glucose since Na+ - glucose symport must not be allowed to migrate to the basolateral surface of the cell. If this were to happen, blood would be absorbed by the body inefficiently and would require more energy. Tight junctions confine transport proteins to their appropriate membrane domains

9. What is the difference between septate junctions and tight junctions

septate junctions are arranged in parallel roles with regular periodicity

10. These are the main occluding junction in invertebrate tissues

septate junctions

11. Septate junctions can co exist with another junction that serves as sites attachment for actin filaments called

adhesion belts

12. These occluding junctions form continuous band around the apical borders of epithelial cells

septate junctions

13. These are paracellular diffusion barriers

tight junctions ( vertebrates ) and septate junctions ( invertebrates )

14. This is the most widespread type of communicating junction

gap junctions

15. True or false: gap junctions are higher in number in animals cells

true

16. How great is the gap in gap junction

2-4 nm

17. What does the gap junctions have in between the pm

open channel proteins

18. What are the protein subunits that make up the channel in gap junctions

connexins

19. Describe the formation of the channels found in the gap junction

6 connexins > 2 connexons > channel

20. Types of open channel proteins in gap junctions

heteromeric, homomeric (isang kayer lang this, connexons lang) them homotypic and heterotypic ( open channel )

21. When will the open channel proteins located in the cell junction close

↑ [Ca2+] and ↓ pH of the cytosol

22. These proteins protrude from the cell surface holding the interacting plasma membrane at a fixed distance

connexons

23. Pore diameter of gap junctions

1.5 mm

24. Size of molecules that can enter the open channel proteins

< 1000 daltons (small molecules, inorganic ions, sugars, amino acids)

25. Functions of the gap junction

(1) cell to cell communication and (2) electrical and chemical coupling between cells in contact (3) coordination of individual cells. (4) passageway of intracellular mediators. (5) role in embryogenesis

26. What junctions facilitate spread action potentials in nerve cells and how

gap junctions as it maintains Electrical and chemical coupling between cells in contact

27. What junction facilitate the synchronize contraction of heart and smooth muscles and how

gap junctions as it maintains Electrical and chemical coupling between cells in contact

28. What junction facilitate the in peristaltic movement of the intestine

gap junctions as it maintains Electrical and chemical coupling between cells in contact

29. What junction facilitate the beating of the cilia in the epithelial cell sheet

gap junctions as it plays a role in Coordination of activities of individual cells

30. What is the role of gap junctions in embryogenesis

Early vertebrate embryo (late 8-cell stage) → cells are electrically coupled to one another. Upon differentiation → cells become uncoupled

31. Explain the transmission of signals in neurons

oki

32. This cell junction in plants causes direct cell-cell communication as it connects cytoplasm of adjacent cells

plasmodesmata

33. narrow cylindrical tube that runs through the center of channel that is also continuous with sER elements

desmotubule

34. Molecules that are allowed to travel across plasmodedmata

passage of molecules with MW < 800 daltons

35. Diameter of plasmodesmata or the cytoplasmic channels that runs thru intervening cell walls

20-40 nm diameter

36. These types of junctions connect cytoskeleton of a cell to those of its neighboring cells or to the ECM

anchoring junctions

37. These types of junctions enable group of cells to function as robust structural units

anchoring junctions

38. True or false: anchoring junctions are abundant in tissues that are subjected to severe mechanical stress

true

39. Actin filaments attachment sites

adherens junctions

40. What are the two types of adherens junctions

Cell-cell adherens junctions ( adhesion belts ) and Cell-matrix adherens junctions ( focal contacts )

41. Two types of Intermediate filaments attachment sites

Desmosomes (cell-cell) and Hemidesmosomes (cell-matrix)

42. Two classes of proteins and their difference

intracellular attachment proteins ( loob) and transmembrane linker proteins ( with domains )

43. These are proteins that have distinct plaque on cytoplasmic side of the PM that connect functional complex to AF or IF

intracellular attachment proteins

44. What are the two domains of transmembrane linker proteins

cytoplasmic domain and extracellular domain

45. True or false: transmembrane linker proteins can bind to intracellular attachment proteins

true

46. Another name for adhesion belts

zonula adherens

47. What type of anchor junctions are present in epithelial cells of small intestine

cell-cell adherens junctions, form a continuous adhesion belt or zonula adherens

48. intracellular attachment proteins that are attached to cadherins

α, β, and γ catenins, vinculin, α-actinin and plakoglobin

49. Role of adhesion belts in invagination.

an organized tightening along the adhesion belts in the epithelial sheet causes invagination

50. These type of anchor junctions resemble desmosomes morphologically but is chemically and functionally distinct

Hemidesmosomes or half-desmosomes

51. True or false: Hemidesmosomes or half-desmosomes connect the basal surface of epithelial cells to the basal lamina (a specialized material of ECM)

true

52. Example of transmembrane linker protein

integrin

53. Desmosomes are composed of

intracellular attachment proteins ( plakoglobin, desmoplakin ) and transmembrane linker proteins → cadherins

54. IF type depends on the cell type, determine the type of cells used for epithelial and muscle cells

keratin and desmin filaments

55. connect bundles of intermediate filaments from cell to cell or from cell to ECM

Intermediate filament attachment sites

56. What junctions does cultured fibroblast exhibit

cell-matrix adherens junctions

57. Another name for focal contacts

adhesion plaques

58. What is the transmembrane linker protein in focal contacts

intgrin

59. What is the Intracellular attachment proteins of integrins

talin, α-actinin, vinculin

60. Difference between adherens junction and focal adhesion in transmembrane adhesion protein

cadherin ( e- cadherin ) and integrin

61. Difference between adherens junction and focal adhesion in extracellular ligand

cadherin in neighboring cell and extracellular matrix proteins

62. Difference between adherens junction and focal adhesion in INTRACELLULAR CYTOSKELETAL ATTACHMENT

af both

63. Difference between adherens junction and focal adhesion in INTRACELLULAR ANCHOR PROTEINS

(1) α- and β-catenins, vinculin, α-actinin, plakoglobin (γ- catenin) (2) talin, vinculin, α-actinin, filamin

64. Difference between Desmosomes and hemidesmosomes in TRANSMEMBRANE ADHESION PROTEIN

cadherin ( desmoglein, desmocollin) and integrin α6β4, BP180

65. Difference between Desmosomes and hemidesmosomes in EXTRACELLULAR LIGAND

desmogleins and desmocollins in neighboring cell and extracellular matrix proteins

66. Difference between Desmosomes and hemidesmosomes in INTRACELLULAR CYTOSKELETAL ATTACHMENT

both if

67. Difference between Desmosomes and hemidesmosomes in INTRACELLULAR ANCHOR PROTEINS

desmoplakins,

68. plakoglobin (γ- catenin) and plectin, BP230