Lecture 5: CAMs And Junctional Complexes Flashcards Preview

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Describe the basement membrane, including it's purpose, components, and approximate size.

Basement Membrane consists of the Epithelial Basal Lamina, and the connective Reticular Lamina, which form together to separate epithelial tissue from connective tissue. It is approximately 50-80 nm thick.


What are some of the components that make up the basal lamina, and the reticular lamina

Reticular Lamina - Type III collagen (aka Reticular Fibers)

Basal Lamina - Laminin, Fibronectin, Type IV collagen, Heparan Sulfate Proteoglycans, and Nidogen (also called entactin)
See Fig 1-21 for tissue sample of basement membrane


Briefly describe Type IV collagen

Does Not form fibrils, and is produced by epithelial cells, which seems to be the main thing that sets it apart from other collagen


Briefly describe laminins

Primary "Unit" of the basal lamina; has 3 chains: Alpha, Beta, and Gamma
Laminin has binding sites for three other components of the basal lamina (Proteoglycans, Type IV collagen, and entactin) as well as Integrin


Briefly Describe Fibronectin

Fibronectin is made of 2 Polypeptide Chains, connected by Disulfide Bonds. Fibronectin has 2 potential forms: Cellular (Produced by fibroblasts), and Plasma (Secreted into blood by hepatocytes)

Fibronectin has binding sites for integrin, heparin, collagen, and fibrin.


List the 4 main types of Calcium Adhesion Mollecules, whether or not they're calcium dependent, what types of ligands they bind to, and their Junction Types

1. Cadherins - Yes - Other Cadherins - Occludens and Desmosomes
2. Selectins - Yes - Carbohydrates - None
3. Integrins - No - Extracellular Matrix Molecules - Hemidesmosomes
4. Ig Superfamily - No - Integrins - None


Describe Cadherins, including their 3 Classical Types, and nonclassical cadherins.

-Type of adheren reliant on calcium usually found in cis/trans homophilic dimers. This includes E-Cadherins (Found in Epithelial Cells), N-Cadherins (in Nerve Cells), and P-Cadherins (Placenta)
- Nonclassical Cadherins include desmocollins, desmogleins, and are found in desmosomes (macular adherens)


Describe E-Cadherins

- Epithelial Cadherins are the most common types of cadherins. - They form HVA dimers for binding faces (amino acid chain combination) at the tips of the extracellular end of their molecules and facilitate cis-homophilic dimers with calcium ions.
- Loss of E-Cadherins is associated with invasive tumor cells


Describe the proteins that are known to bond the cytoplasmic end of cadherins with the cell's cytoplasmic actin

Catenins: There are 3 known components of catenin:
- Beta and plakoglobin catenins: Attach to the cytoplasmic end of cadherins. The beta catenin is also known to be a transcription cofactor and binds to the alpha catenin.
- Alpha Catenins - bind directly to the cytoplasmic actin.


Figure 1-8 Quiz:
1. What forms when two cadherin dimers join?
2. How many domains are there in the extracellular portion of cadherin for calcium?
3. What are the three actin binding proteins used alongside catenin?

1. 2 cis-homophilic dimers join to form a trans-homophilic interaction
2. 4
3. Fibrin-1, Vinculin, and Alpha-Actinin


Briefly describe the function of selectin

1. Binds to carbohydrate molecules (things that do this are lectins)
2. The binding site for selectin is called a CRD (carb receptor domain) and is calcium-dependent
3. Involved in the movement of leukocytes from blood to tissues


Describe the 3 types of selectins and their relation to immunological inflammation

1. L-Selectins - Carried by LYMPHocytes to sulfated carbohydrates
2. E-Selectins - Expressed by ENDOthelial cells
3. P-Selectins - Expressed by PLATELETS AND activated endothelial cells.
Selectins and Integrins are play a significant role in Homing Lymphocytes to Inflamed Areas


Describe Integrins

While adherins are responsible for cell-cell adhesing, integrins are responsible for bonding cells to extracellular related materials, such as fibronectin and laminin.
- Extends from the cytoskeleton into the extracellular matrix
- Consists of 17 possible alpha subunits, and 8 possible beta subunits


1. What is the amino sequence used to bind integrin with fibronectin and laminin?
2. What does the laminin and fibronectin in the basement membrane usually bind to?
3. What are integrin's role in hemidesmosomes?

1. RGD (Arginine, Glycine, Aspartic Acid)
2. Type IV Collagen, Entactin, and proteoglycans
3. In hemidesmosomes, integrins link the basal domain of cells to the extracellular matrix through intracellular tonofilaments (Such as keratin)


What are the 3 binding proteins associated with binding actin with integrins in the cytoplasm?

Talin, vinculin, and alpha-actinin


Briefly describe the process of a lymphocyte/neutrophil homing in on inflamed sites (specifying the roles of selectins and integrins)

1. Lymphocytes travel through vascular endothelium by "rolling" along the cell walls.
2. Selectins along the epithelial cells lining bind to lymphocyte carbohydrate ligands, slowing the roll. If activated, it also triggers chemical mediators (ICAMs) that activate more ligands, and helps Integrin further bind to the lymphocyte.
3. The integrin works with actins to interact with the ligands on the cell, mediating the cell to be "pushed" through the endothelial lining.


Describe the characteristics of the Immunoglobulin superfamily

- Members of this family possess an extracellular segment with one or more domains characteristic of Immunoglobulins.
- 2 (3) types of this family include N-CAMs, which mediates homophilic and heterophilic interactions.
And ICAMs (Types I and II), which facilitate transendothelial migrations of leukocytes.