Cell Junctions

Question 1

What are the four types of cellular junctions?

Answer 1

Tight (or occluding) junctions
Cell-Cell Anchoring junctions
Gap (or communicating) junctions
Cell-Matrix Anchoring junctions

Question 2

What is the general function of tight junctions?

Answer 2

Keep things out of the cell.

Form a permeability barrier.

Question 3

What is the purpose of tight junctions in the blood epithelium and intestinal lumen?

Answer 3

Blood vessel epithelium, esp. in the brain. - to prevent substances in blood from leaking out

Intestinal lumen - to prevent water from outside the intestines from leaking in

Question 4

What is the importance of transcellular transport across cells linked by tight junctions?

Answer 4

Transcellular transport enables the cell to move nutrients through the cell, establishing a gradient. Otherwise, cell couldn’t absorb anything.

Question 5

Explain the process of paracellular transport.

Answer 5

Substances cannot cross the apical or basolateral membrane. Instead, they are passed through intercellular space between the cells.

Question 6

What are the two general functions of anchoring junctions?

Answer 6

To attach cells and their cytoskeletons either to other cells or to the cell matrix.

To stabilize the cell against mechanical stress.

Question 7

What are the different types of anchoring junctions?

Answer 7

Desmosomes
Adherens junctions

Actin-linked cell-matrix junction
Hemidesmosomes

Question 8

What is the transmembrane protein found in adherens junctions

A) Nonclassical cadherins
B) Classical cadherins
C) Integrin
D) alpha-beta-integrin, type 17 collagen

Answer 8

B

Question 9

What is the transmembrane protein found in desmosomes?

A) alpha-beta-integrin, type 17 collagen
B) Classical cadherins
C) Nonclassical cadherins
D) Integrin

Answer 9

C

Question 10

What is the transmembrane protein found in actin-linked cell-matrix junctions?

A) Nonclassical cadherins
B) Classical cadherins
C) alpha-beta-integrin, type 17 collagen
D) Integrin

Answer 10

D

Question 11

What is the transmembrane protein found in hemidesmosomes?

A) Nonclassical cadherins
B) alpha-beta-integrin, type 17 collagen
C) Integrin
D) Classical cadherins

Answer 11

B

Question 12

What cytoskelelal element do desmosomes and hemidesmosomes bind?

A) Actin
B) Myosin
C) Intermediate filaments
D) Microtubules

Answer 12

C

Question 13

What cytoskelelal element do adherens and actin-linked cell matrix junctions bind?

A) Actin
B) Myosin
C) Intermediate filaments
D) Microtubules

Answer 13

A

Question 14

What role do selectins play in the interaction between white blood cells and endothelial cells?

Answer 14

WBC rolls along blood vessel. When its selectin contacts a specific sugar signal, it is allowed to leave the blood vessel.

Question 15

Explain the relationship between desmosomes and pemphigus?

Answer 15

Antibodies against desmosomal cadherin are produced. Cells lose cell-cell adhesion, resulting in blistering.

Question 16

What is the general function of gap junctions?

Answer 16

To allow small molecules and electric signals to pass through interacting cells

Question 17

What are the transmembrane proteins that form gap junctions?

Answer 17

Connexins
4 transmembrane proteins
6 together make a pore

Question 18

What are the 2 types of transmembrane proteins that form tight junctions?

Answer 18

Claudin and occludin

Question 19

What can pass through connexons?

Answer 19

Molecules less that 1000 Da in size

Question 20

Explain the relationship of GAGs to proteoglycans.

Answer 20

Proteoglycans are GAGs covalently attached to a protein. They are synth. on core proteins and have sugars attached to then in the Golgi.

Question 21

Describe the characteristics of glycosaminoglycans (GAGs).

Answer 21

One sulfated sugar, one uronic acid.
Pattern is repeated in a chain.
Absorbs lots of water to occupy space

Question 22

Which cells secrete the most matrix molecules of connective tissue?

Answer 22

Fibroblasts, chondroblasts (cartilage), osteoblasts (bone) and epithelium (basal lamina)

Question 23

What are the major components of the extracellular matrix

Answer 23

Glycoaminoglycans, proteoglycans, fibrous proteins

Question 24

Purpose of proteoglycans

Answer 24

Form specialized gel. Bind growth factors, protease + protease inhibitors.

Question 25

What are the special features of collagens that provide strength to the matrix?

Answer 25

Long stiff triple helix alpha chains Gly- smallest aa, hydrophobic ixns Hydroxyproline+hydroxyserine interchain bonds stabilize the triple helix

Question 26

What are three principal types of collagens?

Answer 26

Collagen I Collagen II Collagen V

Question 27

Explain how a deficiency in vitamin C reduces the stability of the triple helix and the stability of collagen.

Answer 27

A lack of vitamin C inhibits the hydroxylation of serines and prolines, destabilizing the collagen triple helices

Question 28

Identify the characteristic of elastin fibers that gives them their elasticity.

Answer 28

Kinked and cross-linked nature of fibers

Question 29

Explain the consequences of a mutation of the fibrillin gene, i.e. Marfan’s syndrome

Answer 29

Excessive growth of long bones Tall stature Weakened blood vessels, heart valves Aortic dilation and rupture Malformed cartilage and ligaments Skeletal abnormalities

Question 30

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

Answer 30

Arg-Gly-Asp (RGD) sequence binds integrins.

Question 31

Identify the major glycoprotein and proteoglycan components of basal lamina.

Answer 31

Laminin is a major adhesive protein that binds cells to the basal lamina Type IV collagen, Perlecan, Nigoden, Heparin Sulfate are also abundant

Question 32

Describe the functions of the basal lamina.

Answer 32

a. Molecular filter: Kidney glomerulus b. Barrier for cell migration: Cancer c. Cell migration: Neuromuscular Junction d. Cell orientation is reciprocally regulated by fibronectin fibrils and cytoskeleton e. Cell survival: Anchorage Dependence is mediated by integrins

Question 33

Describe the basic structure of integrins.

Answer 33

Transmembrane heterodimer of alpha- and beta- glycoproteins (24 types, 9 types). Ligand binding is Ca2+ or Mg2+-dependent. Focal contact.

Question 34

Identify the intracellular proteins to which integrins attach and predict their importance to the strength of the association.

Answer 34

Fibronectin Laminin Important, as these are the most abundant proteins in the ECM. These allow the cells to remain attached to ECM

Question 35

Distinguish between inside-out signaling and outside-in signaling

Answer 35

Inside-Out Signaling Inactive integrins are activated by the cells a. Platelets activate 3 integrin to bind fibrinogen and cause aggregation b. T lymphocytes active 2 integrins to bind antigen presenting cells Outside-In Signaling a. Clustering of integrins at ECM contact sites activates signaling b. Focal Adhesion Kinase (FAK) is recruited and activated. c. Similar to conventional growth factor receptors