Cell Junctions, Cell Adhesion, and Extracellular Matrix Flashcards
List the four major classes of cellular junctions
Anchoring junctions, Occluding junctions (tight junctions), Channel-forming junctions (gap junctions), and signal-relaying Junctions
Anchoring Junctions
Stabilizes the cell against mechanical stress. Attaches the cell and their cytoplasm to a neighboring cell or to the extracellular matrix.
Occluding (Tight) Junctions
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.
Channel-forming (Gap) Junctions
Electrically connect cells. Provides a passageway for small molecules and ions to pass from cell to cell.
Signal-relaying Junctions
Transmission of information between cells. It is a very complicated junction and it typically involves proteins mediating signal transduction.
Different types of Anchoring Junctions
Adherens junctions, actin-linked cell-matrix junction, desmosomes, and hemidesmosomes.
Adherens Junction
Transmembrane protein- calcium-based cadherins
Cytoskeletal protein- actin filaments
Desmosomes
Transmembrane protein- non-classical cadherins
Cytoskeletal protein- intermediate filaments
Actin-linked cell-matrix Junction
Transmembrane protein- integrin
Cytoskeletal protein- actin filaments
Hemidesmosomes
Transmembrane protein- alpha & beta integrin and type 11 collagen
Cytoskeletal protein- intermediate fillaments
Explain the role of selectins with the interaction of WBC
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.
Identify the transmembrane proteins that form gap junctions.
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.
Identify the cells the secrete most of the matrix molecules of connective tissues
Secreted by fibroblasts, chondroblasts (produces collagen), osteoblasts (bone), and epithelium.
Major types of components that comprise the ECM
Glycosaminoglycans, proteoglycans, and fibrous proteins.
Characteristics of GAGs
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.
Proteoglycans
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.
Features of collagen
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.
Identify the tripeptide sequence in the fibronectin repeat that serves as a binding site to integrins.
Arg-Gly-Asp is the integrin binding site.
Major glycoprotein and proteoglycan components of the basal lamina
Nidogen (glycoprotein) and Perlecan (proteoglycan).
Describe the basic structure of integrins
Heterodimers of alpha and beta glycoproteins with cytoplasmic tails of the beta subunit linking to the cytoskeleton.
Inside-out signaling
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.
Outside-in signaling
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.
