Epithelia & Junctions

Question 1

What are the four major tissue types in the body?

Answer 1

Connective, Epithelial, Nervous, Muscular

Question 2

What are epithelial cells organized into?

Answer 2

Sheets

These cover an external surface or line an internal body cavity

Question 3

What are the two main types of junctions in epithelial cells?

Answer 3

Cell-cell junctions and cell-extracellular matrix (ECM) junctions

Question 4

What is the primary function of tight junctions?

Answer 4

Stops diffusion across the epithelial sheet

Question 5

Which proteins form tight junctions?

Answer 5

Occludin and claudin

Question 6

What is the significance of functional polarization in epithelia?

Answer 6

Allows apical and basolateral membranes to have different functions and compositions

Epithelia are functionally polarised

Question 7

What type of transport do tight junctions enable in epithelial cells?

Answer 7

Polarized transport of nutrients

Question 8

What do hemidesmosomes link to in epithelial cells?

Answer 8

Basal lamina (ECM)

Question 9

What proteins are used in adherens junctions?

Answer 9

Cadherins

Question 10

What is the role of cadherins in epithelial cells?

Answer 10

• transmembrane proteins in the plasma membrane
• bind to an identical cadherin in the next cell
• interaction needs calcium (in absence of Ca2+ they will come apart)

Question 11

What do desmosomes link together in epithelial cells?

Answer 11

Intermediate filaments

Question 12

What is the function of desmosomes in tissues?

Answer 12

Provide tensile strength

Abundant in tissues under high shear stress such as heart muscle and in tough, exposed epithelia

Question 13

What are integrins in hemi-desmosomes responsible for?

Answer 13

Linking to keratin intermediate filaments

Question 14

What is the primary role of cell-cell interactions in tissues?

Answer 14

Help define tissues and allow cells to communicate directly

Question 15

What are gap junctions and where are they found?

Answer 15

Channels allowing transfer of ions and small molecules, found in most epithelia

Question 16

What is the plant equivalent of gap junctions?

Answer 16

Plasmodesmata

Large molecules such as proteins and regulatory mRNAs can pass through these

Question 17

Which cadherin is expressed in epithelial cells?

Answer 17

E-cadherin

Question 18

Which cadherin is expressed in muscle cells?

Answer 18

N-cadherin

Question 19

True or False: Cancer cells often continue to express the specific cadherins that keep them in place.

Answer 19

False

Question 20

What type of molecules can pass through gap junctions?

Answer 20

Inorganic ions and small water-soluble molecules (<1000 daltons)

Question 21

What do cadherins help cells to do?

Answer 21

Recognize each other and assemble into tissues

Question 22

Fill in the blank: Epithelia must connect to the underlying tissue via _______.

Answer 22

Hemi-desmosomes

Question 23

What happens to cancer cells regarding cadherin expression?

Answer 23

They may express N-cadherin instead of E-cadherin, making them highly motile.

Question 24

What is the composition of the extracellular matrix (ECM)?

Answer 24

A network providing structural and biochemical support to surrounding cells

Question 25

What is the primary role of the extracellular matrix in connective tissues?

Answer 25

Provides strength

Question 26

What is transcytosis?

Answer 26

Polarized transport of proteins from one side of the epithelium to the other

Question 27

What is the importance of cell-cell interactions in the context of cancer?

Answer 27

They help keep cells in the right place and prevent metastasis

Question 28

Tissue structure in the gut

Answer 28

- epithelial, muscle and nervous tissues - have little ECM - intermediate filaments and cell-cell junctions provide strength - connective tissues with few cells & lots of ECM that provides strength

Question 29

Role of adherens junctions

Answer 29

Joins an actin bundle in one cell to a similar bundle in a neighbouring cell

Question 30

Characteristics of tight junctions

Answer 30

- found in vertebrates - formed of strands of occludin and Claudin proteins - these complexes allow lipids in the plasma membrane to diffuse freely but not membrane proteins - protein composition of the apical and basal membranes can be different

Question 31

Which epithelia have secretion from the apical surface?

Answer 31

- airways - stomach - intestine - mammary gland

Question 32

Importance of the epithelia being functionally polarised

Answer 32

Allows polarised transport of nutrients E.g. glucose and amino acids in the intestine

Question 33

Role of adherens junctions and desmosomes

Answer 33

Link the cytoskeleton of epithelial cells to their neighbours Using Cadherins

Question 34

Role of hemidesmosomes

Answer 34

Link the cytoskeleton of epithelial cells to the basal lamina Using integrins

Question 35

Cadherin in adherens junctions

Answer 35

- cadherins link to actin filaments - adhesion belt = continuous band of adherens junctions - forms an actin network across the epithelium - can be contractile due to the presence of myosin II

Question 36

Movement of epithelial cell sheets

Answer 36

Contractility across the epithelium allows epithelial sheets to move E.g. neurulation —> generates the neural tube in development

Question 37

Effect of desmin mutations

Answer 37

- desmosomes in adjacent muscle cells are linked to desmin IFs - desmin is expressed in cardiac, skeletal and smooth muscle - desmin mutations cause muscular dystrophy and cardiac myopathy

Question 38

Key characteristic of hemi-desmosomes

Answer 38

Look superficially like half a desmosome but the membrane proteins are integrins

Question 39

What do integrins in the basal plasma membrane bind to?

Answer 39

- Laminin in the basal lamina - IFs inside the cell via linker proteins

Question 40

What are integrins in focal adhesions responsible for?

Answer 40

Link to actin filaments

Question 41

What is the role of cadherins in cell-cell interactions

Answer 41

- specific cadherins help cells recognise each other - help keep cells in the correct place - cancer cells often no longer express specific cadherins that would normally keep a cell in its correct place - expressing N-cadherin instead of E-cadherin makes cells highly motile - cancer cells may secrete more matrix proteases (these digest the ECM) than normal, helping them escape through the basal lamina

Question 42

What percentage of cancer starts in epithelial tissues?

Answer 42

85% These are carcinomas

Question 43

What are connexon channels?

Answer 43

Allow direct transfer of inorganic ions and small waste soluble molecules between cells E.g. IP3 and calcium ions This results in electrical coupling & gives a regular heartbeat