Module 8

Question 1

Three Developmental Germ Layers

Answer 1

1) Endoderm
2) Ectoderm
3) Mesoderm

Question 2

Describe the 1907 study that demonstrated the ability of cells to recognize and adhere to one another?

Answer 2

a) H.V. Wilson (1907)
b) Used cells from two species of sponges
c) Mixed them together
d) Result - cells from the same species associated together

Question 3

Describe the 1950s study that demonstrated the ability of cells to recognize and adhere to one another?

Answer 3

a) Johannes Holtfreter (1950s)
b) Used cells from two different germ layers from a frog embryo
c) Mixed them together
d) Result - cells from the same germ layer associated together

Question 4

T or F: Cells can associate together due to a collection of transmembrane proteins called cell adhesion molecules (CAMs), which aggregate to form specialized cell junctions

Answer 4

True

Question 5

T or F: Cell junctions allow epithelial cells to connect together to form the epithelial lining of the digestive system

Answer 5

True

Question 6

Epithelial Cell Junctions [5]

Answer 6

1) Tight Junctions
2) Adherens Junctions
3) Desmosomes
4) Gap Junctions
5) Hemidesmosomes

Question 7

Hemidesmosomes [def]

Answer 7

[def] adhesion complexes that connect cells to the extracellular matrix at the basal region of the cell

NOTE: all the other junctions connect cells to cells but hemidesmosomes connect cells to the extracellular matrix

Question 8

Tight Junction [functions]

Answer 8

a) Connect adjacent cells just below the apical surface (pinching)
b) Prevents fluid from moving across layers
b) Restricts the diffusion of small molecules
c) Prevents leakage of digestive enzymes

Question 9

What two proteins are found in tight junctions in linear arrays

Answer 9

Occludin and Claudin

Question 10

T or F: In an experiment with tight junctions, a small electron-dense molecule called lanthanum hydroxide diffuses in the ECM but cannot move further towards the apical surface

Answer 10

True

Question 11

What is the function of gap junctions?

Answer 11

To link the cytosol of adjacent cells and allow exchange of ions and small molecules

Question 12

What type of molecules pass through gap junctions?

Answer 12

Small molecules like cAMP and calcium (Ca²⁺), up to ~1 kDa in size.

Question 13

What is the structure of a gap junction?

Answer 13

Formed by two aligned connexon hemichannels, each made of 6 connexin subunits.

Question 14

What is the diameter of a gap junction channel?

Answer 14

1.5 to 2.0 nanometers

Question 15

What types of signalling molecules can diffuse through gap junctions?

Answer 15

Ions, cAMP, and calcium (Ca²⁺)

Question 16

What is one experimental method used to visualize gap junction communication?

Answer 16

Injecting a fluorescent dye into one cell and observing its spread to adjacent cells.

Question 17

What physiological processes rely on gap junction-mediated coordination?

Answer 17

Cardiac muscle contraction and uterine muscle contractions.

Question 18

What are plasmodesmata?

Answer 18

Channels between plant cells that allow direct communication and transport

Question 19

Which animal structure are plasmodesmata similar to?

Answer 19

Gap junctions

Question 20

What plant tissue depends on plasmodesmata?

Answer 20

The phloem, which transports nutrients

Question 21

What do plasmodesmata connect in the phloem?

Answer 21

Sieve-tube elements to companion cells

Question 22

What do companion cells provide through plasmodesmata?

Answer 22

ATP, proteins, and nutrients

Question 23

What structural feature do plasmodesmata span that gap junctions don’t?

Answer 23

The plant cell wall.

Question 24

What types of informational macromolecules travel through plasmodesmata?

Answer 24

Transcription factors, mRNA, and small RNAs

Question 25

T or F: Viral pathogens cannot pass through plasmodesmata.

Answer 25

False – viruses can exploit plasmodesmata to spread between plant cells.

Question 26

What are the types of anchoring junctions?

Answer 26

1) Adherens junctions 2) Desmosomes 3) Hemidesmosomes

Question 27

What distinguishes anchoring junctions from other junctions?

Answer 27

Their association with the cytoskeleton, in particular actin filaments.

Question 28

What does each anchoring junction link?

Answer 28

[desmosomes] two cells [hemidesmosomes] cell and extracellular matrix [adherens junctions] actin cytoskeleton between neighbouring cells.

Question 29

What are the four major families of CAMs?

Answer 29

1) Cadherins 2) Ig-superfamily 3) Integrins 4) Selectins

Question 30

Which CAMs form homophilic interactions?

Answer 30

Cadherins and Ig-superfamily CAMs

Question 31

Which CAMs form heterophilic interactions?

Answer 31

Integrins and selectins

Question 32

What's the difference between homophilic and heterophilic binding?

Answer 32

[homophilic] association of similar cells [heterophilic] connection of different cells together

Question 33

What junctions do cadherins help support?

Answer 33

Adherens junctions

Question 34

What is required for cadherins to mediate adhesion?

Answer 34

Calcium

Question 35

What are the three major classes of classical cadherins?

Answer 35

1) E-cadherin (epithelial) 2) N-cadherin (neural) 3) P-cadherin (placental)

Question 36

What anchors cadherins to the actin cytoskeleton?

Answer 36

Cytosolic cofactors called catenins

Question 37

What happens to epithelial cells in culture when E-cadherin transgene is introduced? Is there a difference if calcium is present or not?

Answer 37

They aggregate into epithelial-like clumps ONLY if cadherin transgene AND calcium is present

Question 38

What is neutrophil extravasation?

Answer 38

The process by which neutrophils (white blood cells) exit blood vessels to respond to infection or injury

Question 39

What types of cells form the walls of blood vessels?

Answer 39

Endothelial cells, a specialized type of epithelial cell

Question 40

What prevents circulating blood cells from leaking out of blood vessels under normal conditions?

Answer 40

Adhesion between endothelial cells in the vessel wall

Question 41

T or F: Leukocytes normally move freely through tissues outside of blood vessels

Answer 41

False – they move within blood vessels and require extravasation to enter tissues.

Question 42

Why must leukocytes form temporary connections with endothelial cells?

Answer 42

To stop their movement in the bloodstream and migrate into tissues at the site of infection or injury.

Question 43

What are the three families of leukocytes?

Answer 43

1) Granulocytes (neutrophils, eosinophils, basophils) 2) Monocytes 3) Lymphocytes (NK, T, and B cells)

Question 44

Which granulocyte is most numerous and undergoes extravasation?

Answer 44

Neutrophils

Question 45

What do monocytes differentiate into, and what is their role?

Answer 45

Macrophages - they engulf bacteria and dead cells by phagocytosis

Question 46

What are the roles of lymphocytes? [2]

Answer 46

1) NK cells destroy virally infected or tumour cells 2) T and B cells are involved in antibody production and immune response.

Question 47

Which specific leukocytes are capable of extravasation?

Answer 47

1) Neutrophils (not eosinophils or basophils) 2) Monocytes (as macrophages) 3) Lymphocytes

Question 48

What initiates neutrophil extravasation?

Answer 48

A signal generated by an infection

Question 49

What are the five steps of neutrophil extravasation in order?

Answer 49

Capture, rolling, slow rolling, firm adhesion, and transmigration.

Question 50

What happens during the "capture" step?

Answer 50

A transient association forms between the neutrophil and the apical surface of an endothelial cell.

Question 51

What occurs after capture as neutrophils are pushed by blood flow?

Answer 51

They roll along the surface of the endothelial cells, forming and breaking weak interactions.

Question 52

What leads to firm adhesion in extravasation?

Answer 52

Strong attachment between neutrophils and endothelial cells, followed by structural changes that enable migration.

Question 53

What is transmigration?

Answer 53

The movement of neutrophils between endothelial cells into surrounding tissue at the site of infection.

Question 54

What contributes to swelling at infection sites?

Answer 54

Escape of blood plasma and the accumulation of leukocytes in surrounding tissue.

Question 55

What triggers neutrophil capture at the site of infection?

Answer 55

Cytokines released at the site of infection, such as TNF-alpha

Question 56

How do cytokines affect endothelial cells?

Answer 56

They change the behaviour of endothelial cells, leading to the presentation of selectins on the apical surface

Question 57

What specific molecule appears on the apical surface of endothelial cells during capture? What does that molecule interact with on neutrophils?

Answer 57

P-selectin interacts with a selectin-specific glycoprotein ligand on the neutrophil surface

Question 58

T or F: P-selectin is constantly present on the surface of endothelial cells.

Answer 58

False – it is stored in secretory vesicles and appears after cytokine signalling.

Question 59

What causes neutrophils to begin rolling along the vessel wall?

Answer 59

Weak interactions between P-selectin and its ligand (PSGL-1) slow the neutrophil's movement.

Question 60

What causes neutrophils to transition from rolling to slow rolling?

Answer 60

An increase in the density of selectins (both P- and E-selectin) at the site of infection.

Question 61

What is the significance of slow rolling?

Answer 61

It increases contact time, allowing neutrophils to receive additional signals for further activation

Question 62

What cytokine is displayed on endothelial cells during slow rolling?

Answer 62

Platelet Activating Factor (PAF)

Question 63

What does PAF bind to on the neutrophil surface?

Answer 63

The PAF receptor, a transmembrane GPCR

Question 64

What happens inside the neutrophil after PAF receptor activation?

Answer 64

A signal transduction pathway is initiated, leading to changes in gene expression and activation of integrins

Question 65

What do activated integrins on neutrophils bind to on endothelial cells?

Answer 65

ICAMs (Intercellular Adhesion Molecules)

Question 66

What is the result of integrin binding to ICAMs?

Answer 66

Firm adhesion, also known as tight binding, which arrests neutrophil movement

Question 67

T or F: PAF signalling only occurs during capture.

Answer 67

It occurs during slow rolling

Question 68

What domains of integrins form the ligand-binding site?

Answer 68

The propeller and beta-A domains

Question 69

What is the inactive conformation of integrin?

Answer 69

The ligand-binding domains are folded down and cannot interact with ICAMs

Question 70

What causes integrins to switch to their active conformation?

Answer 70

PAF signalling via the PAF receptor on neutrophils

Question 71

What additional cellular change does integrin activation cause in neutrophils?

Answer 71

Reorganization of the actin cytoskeleton to allow cell migration

Question 72

T or F: Integrin–ICAM interactions are weaker than selectin interactions

Answer 72

False – they are stronger and more stable

Question 73

What happens during the final step of extravasation, transmigration?

Answer 73

The neutrophil stops moving and migrates by crawling between endothelial cells

Question 74

How do neutrophils break connections between endothelial cells during transmigration?

Answer 74

They produce (protease) enzymes that degrade the junctions between endothelial cells

Question 75

What does confocal microscopy show during transmigration?

Answer 75

A single neutrophil changing shape as it crosses the endothelial layer

Question 76

T or F: Neutrophils pass directly through endothelial cells during transmigration

Answer 76

False – they migrate between them

Question 77

What is the order of CAM involvement during neutrophil extravasation?

Answer 77

Selectins → Integrins