4.2 The Tissue Level Of Organization: Cell Junctions

Front 1

What are the four basic types of body tissues?

Back 1

Epithelial Tissue

Connective Tissue

Muscular Tissue

Nervous Tissue

Front 2

What are cell junctions?

Back 2

Point of contact between plasma membranes of tissue cells.

Front 3

What are the five most important types of cell junctions?

Back 3

Tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.

Front 4

Which type of cell junction functions in communication between adjacent cells?

Back 4

Gap junctions allow cellular communication via passage of electrical and chemical signals between adjacent cells.

Front 5

What do tight junctions consist of?

Back 5

Weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells.

Front 6

Cells of epithelial tissue that lines the __________, __________, and _________ have many tight junctions. (3 organs)

Back 6

Stomach

Intestines

Urinary Bladder

Front 7

Tight junctions prevent what?

Back 7

Inhibit the passage of substances between cells and prevent the contents of these organs from leaking into the blood or surrounding tissues.

Front 8

Adherens junctions contain what? What is it?

Back 8

Plaque: a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton.

Front 9

Transmembrane glycoproteins called __________ join the cells in adherents junctions.

Back 9

Transmembrane glycoproteins called cadherins join the cells.

Front 10

In epithelial cells, adherens junctions often form extensive zones called ____________ because they encircle the cell.

Back 10

In epithelial cells, adherens junctions often form extensive zones called adhesion belts because they encircle the cell.

Front 11

Like adherens junctions, desmosomes have what two things?

Back 11

Contain plaque and have transmembrane glycoproteins (cadherins).

Front 12

What is different about desmosomes compared to adherens junctions?

Back 12

The plaque of desmosomes does not attach to microfilaments - attaches to intermediate filaments, which consist of the protein keratin.

Front 13

Desmosomes are common in what parts of the body?

Back 13

Epidermis and cardiac muscle cells.

Front 14

What do desmosomes prevent?

Back 14

Prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction.

Front 15

Although hemidesmosomes resemble desmosomes, they do not ______.

Back 15

Do not link adjacent cells.

Front 16

Rather than cadherins, hemidesmosomes have what?

Back 16

Integrins.

Front 17

Where do integrins attach?

Back 17

On inside: attach to intermediate filaments made of the protein keratin.

On outside: attach to the protein laminin, which is present in the basement membrane.

Front 18

Hemidesmosomes anchor cells to what?

Back 18

To the basement membrane, not to each other.

Front 19

At gap junctions, membrane proteins called _________________ form tiny fluid-filled tunnels called ___________ that connect neighbouring cells.

Back 19

At gap junctions, membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighbouring cells.

Front 20

What can diffuse through the cytosol in gap junctions? What cannot?

Back 20

Ions and small molecules can diffuse.

Passage of large molecules such as vital intracellular proteins is prevented.

Front 21

The transfer of nutrients, and perhaps wastes, takes place through gap junctions where?

Back 21

In avascular tissues such as the lens and cornea of the eye.

Front 22

What are the functions of gap junctions?

Back 22

1. Transfer of nutrients and waste

2. Communication

3. Enable spread of nerve impulses