Cell Membrane Flashcards
junctional complexes
peripheral proteins in the plasma membrane that attach adjacent epithelial cells on their lateral surfaces
terminal bar
unresolved (can’t be visualized) group of junctional complexes. using light microscopy, looks like a little bar or spot where the lateral surfaces of epithelial cells meets the apical surface
terminal web
a filamentous structure found at the apical surface of epithelial cells, possesses microvilli (between the epithelial cells and the microvilli)
describe the glycocalyx
- extracellular domain of the plasma membrane that is glycosylated by CHO portions of glycolipids and transmembrane glycoproteins (“sugar shell”)
- in the electron micrograph, it shows up as an enzyme layer on top of the microvilli
functions of the glycocalyx
- protection and lubrication
- contains enzymes
- cell-cell interaction
homing
a type of cell-cell interaction in which leukocytes are allowed to leave blood vessels and mediate inflammatory responses. this is allowed by the glycocalyx (and the transmembrane proteins that it possesses?)
passive transport
movement of molecules or ions across the membrane down their concentration or electrochemical gradient; no energy required
active transport
protein-mediated movement of molecules or ions across the membrane against their concentration or electrochemical gradient; energy required
primary active transport
transport of a substance across the membrane directly coupled to ATP hydrolysis
secondary active transport
simultaneous movement of two substances across the membrane indirectly coupled to ATP hydrolysis
- cotransport (symport): both substances in the same direction
- countertransport (antiport): substances move in opposite directions
example of cotransport
- remember, this is secondary active transport in which ions move in the same direction
- Na+-glucose transporter in small intestinal epithelial cells (move both glucose and sodium into cells)
example of countertransport
- remember, this is secondary active transport in which ions move in opposite directions
- Na+-Ca2+ transporter in heart muscle cells (calcium out of the cell, sodium in)
non-carrier-mediated transport
small hydrophobic molecules and small uncharged polar molecules can pass through the membrane with no carrier
carrier-mediated transport
transport proteins have a high level of specificity for the transported molecule or ion, undergo conformational changes during the transport process (can include facilitated diffusion or active transport, anything that requires a carrier)
examples of active transport in the myocardium
- Ca2+ pump (primary, uses ATP to pump Ca2+ out of the cell
- Na+/Ca2+ exchanger (3:1, secondary active transport, uses Na+ gradient to push Ca2+ out of the cell)
- Na+/K+ ATPase (primary, 3:2)
how is the Na+/Ca2+ exchanger related to membrane potential?
- when the membrane potential is negative (resting cells), Ca2+ goes out as Na+ enters the cell down its gradient
- when the cell is depolarized and has a positive membrane potential, the exchanger works in the opposite direction, so Na+ leaves the cell as Ca2+ enters
what is the Na/Ca exchanger constantly doing under resting conditions
moves 3 Na+ ions out of the cell and 2 K+ ions in, maintaining their gradient (this pump is only slightly electrogenic!)