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exam 4- extracellular matrix + cell adhesion
Terms in this set (20)
-Interaction between cells and the extracellular matrix (ECM)-
Collagens, proteoglycans, fibronectin and laminin are proteins found in the ECM that are recognized by cell surface proteins. Cellular adhesion complexes that interact with the ECM proteins include transmembrane integrins of focal adhesions and hemidesmosomes.
-Interactions between cells-
Cells interact with each other through cell adhesion complexes including adherens junctions, desmosomes and tight junctions
There are many interactions happening in this figure.
Figure 16.8- GO OVER
Collagen is secreted by fibroblasts. Fibroblasts that secrete collagen have an extensive endoplasmic reticulum due to the amount of
collagen that is produced
Collagen consists of three protein chains that form non-covalent interactions (dotted red lines between polypeptides on the left) as they coil around each other to form a triple helical structure
Having glycine at every third position allows for tight coiling of the triple helix because glycine is the smallest amino acid
Mutations in collagen genes (COL1A1 and COL1A2) underlie the vast majority of osteogenesis imperfecta cases.
Mutations that convert glycine codons to those of larger amino acids interfere with formation of the collagen triple helix, and weaken collagen fibers
The triple helix domain of collagen contains a repetitive amino acid sequence Gly-X-Y, frequently having
proline (Pro) in the X position and hydroxyproline (Hyp) in the Y position. A partial amino acid sequence of collagen is shown in (B)
Collagen is modified and processed as it passes through the secretory pathway of a fibroblast, so collagen triple helices can't crosslink to each other until after
they are secreted
Nonhelical sequences within Type IV collagen interrupt the rigid molecular structure to allow formation of collagen networks
(compare the electron micrograph on the right with the rigid structure of collagen in the electron micrograph shown in the previous slide)
Fibronectin is a component of the ECM. It has specific amino acid sequences that interact with other molecules
For example, fibronectin can bind to other ECM molecules such as collagen and proteoglycans. Cell attach to fibronectin via integrins in focal adhesion complexes
Recognition of fibronectin's integrin binding domain sequence RGD (Arg-Gly-Asp) by integrin heterodimers is one example for
how cells bind to extracellular matrix proteins
Laminins contain three polypeptide chains, and they are a major component of the basal lamina. Laminins assemble into extensive networks as shown in (B). Specific sequences in the laminins are recognized by
cell surface proteins as cells attach to the basal lamina
Integrins are heterodimers of a-integrin and b-integrin
integrins have -three domains-, including an intracellular domain, a transmembrane domain and an extracellular domain
Integrin activity is dependent upon all three of these domains
•Binding of divalent cations such as Mg2+ to specific regions of the extracellular domain is required, so in absence of divalent cations, cells can't attach to a matrix.
•The transmembrane domain is recognized during translation such that the integrins are synthesized at the ER and subsequently undergo vesicle trafficking to the plasma membrane
.•The intracellular domain binds to other proteins of the focal adhesion complex (or alternatively, the hemidesmosome complex) to anchor cytoskeleton to integrins
Cell adhesion complexes are critical for adhesion of cells to the matrix. On the left is a focal adhesion complex, which serves as a link between actin cytoskeleton and the ECM proteins. On the right is a hemidesmosome that serves as a link between intermediate filaments and the basal lamina
Integrins and cadherins are the transmembrane molecules used to form the most stable
junctions in cells. Other adhesion molecules provide more temporary or weaker adhesion/interaction
As a first step in binding, oligosaccharides on the surface receptors of endothelial cells are specifically recognized by selectins on leukocytes, followed by integrin interactions with intracellular adhesion molecules (ICAMs). Multiple connections along the membrane give
additive strength in attachment
(AJs) mediate attachment between actin filaments and the junction complex
The extracellular domain of cadherins interacts in a homotypic fashion with the extracellular domain of the same type of cadherin on the adjacent cell. The divalent cation calcium (Ca2+) is required for this interaction.
The intracellular domain of cadherins attaches to cytoplasmic proteins including the catenins and vinculin. This complex attaches to actin filaments
mediate attachment between intermediate filaments and the junction complex
The extracellular domain of desmosomal cadherins interacts in a homotypic fashion with the extracellular domain of the same type of cadherin on the adjacent cell. The divalent cation calcium (Ca2+) is required for this interaction.
The intracellular domain of cadherins attaches to a cytoplasmic plaque proteins including plakoglobin and desmoplakin. This complex attaches to intermediate filaments
Junctional complexes mediate strong attachment among polarized epithelial cells, indirectly linking the actin and intermediate filament cytoskeleton throughout an entire sheet of cells. Transmission electron microscopy shows the different substructure of each type of junction labeled in part A. Note in part B that tight junctions provide such a tight seal that nothing can pass between the cells at that poin
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