9.3 Cell Junctions

Define Integrins

Transmembrane proteins that facilitate cell-extracellular matrix adhesion

Define Plectin

intracellular protein Involved in connecting intermediate filaments with other cell components

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

-Adherens Junctions and Focal Adhesions are supported by actin filaments while desmosomes and hemidesmosomes are support by intermediate filaments. -Adherens Junctions exist as Cell-Cell junctions. The transmembrane proteins found in Adherens Junctions are Cadherins, more specifically E-Cadherins (Epithelial Cadherins). The Intracellular Proteins are Vinculin and Alpha Actinin -Focal Adhesions are Cell-Matrix Junctions and have Integrins as Transmembrane Proteins and Vinculin, Alpha Actinin and Filamin as intracellular proteins

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

-Adherens Junctions and Focal Adhesions are supported by actin filaments while desmosomes and hemidesmosomes are supported by intermediate filaments. -Desmosomes are Cell-Cell Junctions and have Cadherins (Desmoglein and desmocollins) as Transmembrane Proteins and desmoplakin and desmoglobin as intracellular proteins -Hemidesmosomes are Cell-Matrix Junctions and have Integrins as Transmembrane Proteins and Plectins as intracellular proteins

What is the general structure of an anchoring junction?

-All anchoring junctions have intracellular anchor proteins and transmembrane adhesion proteins. Anchoring Junctions are physical structures which attach cells to each other or to their surrounding. There are Cell to Cell as well as Cell to Matrix Anchoring Junctions. -All anchoring junctions will have proteins that interact with partners on the adjacent cell or attach to extracellular matrix components. The anchoring junctions have a complex which includes transmembrane adhesion proteins which are attached to the plasma membrane. Intracellular anchor proteins are attached to these adhesion proteins in the membrane and on the other side are also cytoskeletal filaments.

Describe the role(s) of calcium in the formation of cell junctions (what sorts of junctions require calcium and what does it do in each case)?

-Cadherins are calcium dependent adhesion proteins and are present in Adherens Junctions as well as Desmosomes. Cadherins are made up of a number of globular domains and molecular calcium binds to each of these domains and causes them to protrude from the cell's surface. Protruding cadherins from opposite cells join together and the interacting domains at the end of cadherins also require calcium in order to generate attachments. -Integrins are also calcium dependent cell-matrix adhesion molecules with cytoskeletal support. The calcium helps to maintain to correct shape and allow them to bind to target proteins. Integrins are present in Focal Adhesions and Hemidesmosomes

What cell junctions are primarily used to form stable, mechanically strong connections, and what are the molecular specializations allowing them to perform this function?

-Hemidesmosomes are supported with intermediate filaments rather than actin filaments so they are stronger and more stable. They are generally found in non-motile cells but in specialized situations with strong and stable attachments are needed such as in the cells lining the tooth cavity to a tooth.

What are occludens junctions found in invertebrates known as and what protein is involved in their formation?

-In vertebrates Occludens Junctions are known as Tight Junctions, in invertebrates they are known as Septate Junctions -These are found closest to the top layer of cells and the function is to separate the top membrane from the membrane found in the lateral and basal regions of the cell. These junctions help to regulate passive movement of fluid across the cell layer and their permeability can be regulated. -In invertebrates Septate Junctions are more regularly arranged and have a protein called "discs-large" which are related to occludins. A key feature of Septate Junctions is the absence of cytoskeletal filaments in the surrounding cytoplasm.

What are occludens junctions found in vertebrates known as and what protein is involved in their formation?

-In vertebrates Occludens Junctions are known as Tight Junctions, in invertebrates they are known as Septate Junctions -These are found closest to the top layer of cells and the function is to separate the top membrane from the membrane found in the lateral and basal regions of the cell. These junctions help to regulate passive movement of fluid across the cell layer and their permeability can be regulated. -Tight junctions are formed by a branched network of contacts between plasma membranes of two cells called Sealing Strands and by transmembrane proteins called Claudin and Occludin. These demonstrate homotypic interactions that attach the membranes to each other.

Name and describe the organization of junctions forming fluid barriers in vertebrates, list the molecules/proteins involved.

-In vertebrates Occludens Junctions are known as Tight Junctions. In invertebrates Occludens Junctions are known as Septate Junctions -These are found closest to the top layer of cells and the function is to separate the top membrane from the membrane found in the lateral and basal regions of the cell. These junctions help to regulate passive movement of fluid across the cell layer and their permeability can be regulated. -Tight junctions are formed by a branched network of contacts between plasma membranes of two cells called Sealing Strands and by transmembrane proteins called Claudin and Occludin. These demonstrate homotypic interactions that attach the membranes to each other.

What types of cell junctions include integrins?

-Integrins are also calcium dependent cell-matrix adhesion molecules with cytoskeletal support. The calcium helps to maintain to correct shape and allow them to bind to target proteins. Integrins are present in Focal Adhesions and Hemidesmosomes

Define Desmo

-Intracellular protein which is a critical component of desmosome structures in cardiac muscle and epidermal cells which function to maintain structural integrity at adjacent cell contacts

Define Desmocollins

-Member of the cadherin superfamily, mediates adhesion at desmosomal junctions. -The extracellular domains mediate cell adhesions while the cytoplasmic tails associate with desmosomal plaque proteins.

What types of cell junctions would you expect to find produced by motile fibroblasts, and what type would you expect to be formed by dermal epithelial cells?

-Motile fibroblasts are cells of mesenchymal origins generally have Vimentin components in their Intermediate Filaments similar to those in Blood, bone and muscle I expect to find communication junctions to allows the rapid movement of signaling molecules -Occludens or Tight Junctions allow regulation for the movement of fluid across epithelial cell barriers. E- Cadherin Proteins which are present in Adherens Junctions will attach more epithelial cells.

Define Cadherins

-Named for calcium dependent adhesion. -A type of cell adhesion molecule (CAM) that is important in the formation of adherens junctions to bind cells with each other. -Cadherins are calcium-dependent transmembrane proteins that constitute the major intercellular link at adherens junctions and bind to catenins and other proteins intracellularly to link to the actin cytoskeleton.

Describe the structures of communicating junctions in plant and animal cells.

-Specialized junctions to facilitate the transfer of information between adjacent cells. Communication junctions are not physically strong and they lack attachment to the cytoskeleton -These structures lack supporting cytoskeletal elements and can be thought of as a specialized transmembrane pore but are formed by the cooperation of two neighboring cells. -Each channel is formed by hexagonal group of six proteins created by an individual cell called a connexon. Two connexons, one from each cell, will fuse to form a channel, the proteins that make up are called connexins and there are a number different connexin proteins and they can be grouped together in different ways to create connexons

Define Desmoglein

-family of desmosomal cadherins, also known as a plaque protein, that plays a role in the formation of desmosomes that join cells to one another. -Adhesion molecule which function to maintain tissue integrity and facilitate cell-cell communication

Which types of cell junctions include intermediate filaments?

Adherens Junctions and Focal Adhesions are supported by actin filaments while desmosomes and hemidesmosomes are support by intermediate filaments.

What are two critical function of occludins junctions?

These junctions help to regulate passive movement of fluid across the cell layer and their permeability can be regulated