9.3 Cell Junctions

Question 1

Tight junctions

Answer 1

(occludens junctions) Found at the top of a polarized cell. They restrict the movement of extracellular fluid past the cell. They also restrict the movement of membrane components from one cell compartment to another.

Question 2

Anchoring junctions

Answer 2

Physical structures that attach cells to each other or to their surroundings and the extracellular matrix.

There are 3 types:

• Adherence junctions
• Desmosome
• Hemidesmosome

Question 3

Communication junctions

Answer 3

Allow movement of small ions and other signals between cells. Communication junctions are not physically strong and lack attachment to the cytoskeleton.

Question 4

In invertebrates, the cell junction that would be similar to tight junctions in vertebrates is called _______ .

Answer 4

Septate junction.

Question 5

What types of cell junctions do you find actin filaments associated with?

Answer 5

Adherence junctions (type of anchoring junction)

Question 6

Tight junctions are formed by the transmembrane proteins _____ and _____.

Answer 6

Claudin and occludin

Question 7

Occludin

Answer 7

(light green) Transmembrane protein that forms sealing strands in tight junctions

Question 8

Claudin

Answer 8

(darker green) Transmembrane protein that forms sealing strands in tight junctions

Question 9

The protein that forms septate junctions in invertebrates is called _________ .

Answer 9

Discs-large

Question 10

Anchoring junctions have both ______ anchor proteins and _____ adhesion proteins.

Answer 10

intracellular/transmembrane

Question 11

What are the 2 classes of Anchoring Junctions?

Answer 11

1. Cell-to-cell

2. Cell-matrix

Question 12

Integrins

Answer 12

calcium-dependent cell-matrix adhesion molecules with cytoskeletal support. Integrins are heterodimers, with an alpha and beta subunit.

Question 13

Desmosomes

Answer 13

Form strong connections between cells. Most common in mechanically stressed tissues.

Question 14

Desmosomes and Hemidesmosomes are stronger than _______.

Answer 14

Actin supported junctions (adherens junctions)

Question 15

Communication junctions

Answer 15

Lack supporting cytoskeletal elements and are thought of as a specialized transmembrane pore that is formed between 2 neighboring cells.

Question 16

In animals, communication junctions are called _______.

Answer 16

Gap junctions

Question 17

Connexon

Answer 17

A communication junction channel is formed by a hexagonal group of 6 proteins created by cells called connexons. 2 connexon channel structures form a communication channel.

Question 18

Connexins

Answer 18

The proteins that make up connexons

Question 19

What is the function of a communication junction?

Answer 19

Allows electrical signals and small but not large molecules to move between cells

Question 20

What is the general structure of an Anchoring junction?

Answer 20

Every anchoring junction has intracellular anchor proteins and transmembrane adhesion proteins.

Question 21

Focal adhesions are found at the ends of ____________ .

Answer 21

Actin filament bundles.

Question 22

Focal Adhesion

Answer 22

Cell to matrix junctions and are supported by actin filaments. They have Integrin instead of Cadherin as their transmembrane protein and Vinculin, alpha actinin and filamin as intracellular coupling proteins.

Question 23

Plasmodesmata

Answer 23

Channels of cytoplasm that join neighboring plant cells through small holes in the cell wall.

Question 24

Desmotubules

Answer 24

ER derived membrane tubes found in the center of plasmodesmata.

Question 25

What is the role of calcium in the formation of cell junctions (what junctions require it and what does it do?)

Answer 25

Both Integrin and Cadherins are calcium dependent adhesion proteins. Both classes of proteins require calcium to maintain the correct shape necessary to allow them to bind to their target proteins.

Question 26

What junction would form fluid barriers in vertebrates? And the molecules/proteins involved

Answer 26

Tight junction. The proteins involved are occludin and claudin.