Extracellular Matrix (Lec. 9) Flashcards
Describe the structure of bacterial cell walls
The principal component is a peptidoglycan, which consists of linear polysaccharide chains cross-linked by short peptides
Distinguish the organization of yeast and plant cell walls
Eukaryotic cell walls are composed principally of polysaccharides (chitin in fungi and cellulose in plants). In the plant cell wall, cellulose and hemicellulose fibers are embedded in a pectin matrix.
What do bacterial cell walls do?
Help determine cell shape (rod vs. spiral), protect against osmotic pressure. Made of peptidoglycan (linear polysaccharide chains cross-linked by peptides)
How does penicillin work?
It inhibits the enzyme responsible for making the cross-links in the bacterial cell wall, creating a faulty membrane
Describe plant cells walls
Made of cellulose (beta glucose monomers instead of the alpha glucose used in starch and glycogen); cellulose associates into microfibrils, which interact with other sugars and proteins to make the cell wall, which keeps the cell from swelling or shrinking
What does the basal lamina do?
Serves as a point of attachment for different cell types
What is the extracellular matrix made of?
Proteins in a gel-like polysaccharide ground substance (similar to cell walls)
What is the main family of proteins found in the ECM?
Collagens, which form a triple helix structure from amino acids secreted from the cell; further associate to form collagen fibers
What is the polysaccharide gel of the ECM made of?
Glycosaminoglycans or GAGs, which link to proteins to form proteoglycans
What do adhesion proteins do?
Link the components of the matrix together and link cells to the matrix
How are cells attached to the ECM?
Via integral proteins, especially integrin
Describe the structure of integrin, what it does, and what structures it’s present in
Made of two subunits; will recognize and bind to specific amino acid sequences found in different components of the matrix; present in focal adhesions and hemidesmosomes.
What is the difference between focal adhesions and hemidesmosomes?
Focal adhesions link actin filaments to the ECM, and hemidesmosomes link keratin filaments to the ECM
What are the proposed steps in locomotion?
- Protrusion: the leading edge extends and probes forward in search of a new substratum contact site
- Substrate adhesion: if/when the leading edge encounters an adhesive region of the substratum it will attach, stabilizing the forward extension.
- Traction/Cell Body Movement: a mechanism moves the bulk of the cell cytoplasm in the direction of the forward extension.
What are adhesion junctions?
Selective interaction between two cells; some interactions are transient and some are stable; goal is to anchor cells together
What do selectins do?
Mediate the adhesion of white blood cells to endothelial cells and platelets under flow
What do cadherins do?
Mediate cell-cell adhesion in animals; mediates contact inhibition (when cells touch each other they stop dividing); therefore if there’s some mutation or loss of cadherins, cancer becomes a thing that happens
What is a junctional complex?
A cluster of specialized cell-cell junctions that work together
What do tight junctions do?
Form seals that prevent molecules from passing in between epithelial cells
What are gap junctions?
Channels between two cells; allow these cells to exchange different molecules; made by joining two connexons (a connexon forms the pore for a gap junction, and each connexon is made of six subunits)
What are plasmodesmata?
When the plasma membranes of adjacent plant cells are continuous with each other (important in plant cell signaling); mediated by cell wall components instead of membrane proteins
