Cell Junctions, Cell Adhesion, and Extracellular Matrix

Question 1

List the four major classes of cellular junctions

Answer 1

Anchoring junctions, Occluding junctions (tight junctions), Channel-forming junctions (gap junctions), and signal-relaying Junctions

Question 2

Anchoring Junctions

Answer 2

Stabilizes the cell against mechanical stress. Attaches the cell and their cytoplasm to a neighboring cell or to the extracellular matrix.

Question 3

Occluding (Tight) Junctions

Answer 3

Creates a permeability barrier to seal off the cells from the outside environment. It allows some cells to leak through via paracellular transport. This barrier prevents the mixing of the proteins/solutes. Claudins are the major type of tight junction proteins followed by Occludin.

Question 4

Channel-forming (Gap) Junctions

Answer 4

Electrically connect cells. Provides a passageway for small molecules and ions to pass from cell to cell.

Question 5

Signal-relaying Junctions

Answer 5

Transmission of information between cells. It is a very complicated junction and it typically involves proteins mediating signal transduction.

Question 6

Different types of Anchoring Junctions

Answer 6

Adherens junctions, actin-linked cell-matrix junction, desmosomes, and hemidesmosomes.

Question 7

Adherens Junction

Answer 7

Transmembrane protein- calcium-based cadherins

Cytoskeletal protein- actin filaments

Question 8

Desmosomes

Answer 8

Transmembrane protein- non-classical cadherins

Cytoskeletal protein- intermediate filaments

Question 9

Actin-linked cell-matrix Junction

Answer 9

Transmembrane protein- integrin

Cytoskeletal protein- actin filaments

Question 10

Hemidesmosomes

Answer 10

Transmembrane protein- alpha & beta integrin and type 11 collagen
Cytoskeletal protein- intermediate fillaments

Question 11

Explain the role of selectins with the interaction of WBC

Answer 11

Selectins works with integrin to move WBC out into the tissues. Selectin assists with the rolling of the WBC because it has a weak interaction while integrin assists with the emigration of the WBC out through its strong adhesion.

Question 12

Identify the transmembrane proteins that form gap junctions.

Answer 12

They are formed through connexins that are tissue specific. Six connexins come together to form a connexon which is a functional pore that the cell can open and close to allow the passage of small molecules/ions.

Question 13

Identify the cells the secrete most of the matrix molecules of connective tissues

Answer 13

Secreted by fibroblasts, chondroblasts (produces collagen), osteoblasts (bone), and epithelium.

Question 14

Major types of components that comprise the ECM

Answer 14

Glycosaminoglycans, proteoglycans, and fibrous proteins.

Question 15

Characteristics of GAGs

Answer 15

Repeated polysaccharide. 
Negatively charged (because it is sulfated) and therefore it interacts with water and sodium.
Absorbs a large amount of water and serves to occupy space.
Hyaluronan is a common type of GAG but is not sulfated.

Question 16

Proteoglycans

Answer 16

GAGs attached to protein. Serves as a space filler but also is involved in regulating movement by serving as a platform for cells to migrate along.

Question 17

Features of collagen

Answer 17

Triple Helix.
1000 amino acids long.
Gly-Pro-Hydroxyproline serves to provide the tight wounded interaction and the OH-Pro, OH-Lys provides interchain hydrogen bonding for a more stable conformation.

Question 18

Identify the tripeptide sequence in the fibronectin repeat that serves as a binding site to integrins.

Answer 18

Arg-Gly-Asp is the integrin binding site.

Question 19

Major glycoprotein and proteoglycan components of the basal lamina

Answer 19

Nidogen (glycoprotein) and Perlecan (proteoglycan).

Question 20

Describe the basic structure of integrins

Answer 20

Heterodimers of alpha and beta glycoproteins with cytoplasmic tails of the beta subunit linking to the cytoskeleton.

Question 21

Inside-out signaling

Answer 21

You have an integrin on the cell surface but is unable to bind. The inactive integrin has something inside the cell that activates it and then the integrin is able to bind to the ligand.

Question 22

Outside-in signaling

Answer 22

The integrin just needs the ligand, once it binds to the ligand it sends a signal to the cell which undergoes a signal transduction pathway.