BRS: I. CELL PHYSIOLOGY Flashcards
THESE ARE PROTEINS THAT ARE NOT IMBEDDED IN THE CELL MEMBRANE, NOT COVALENTLY BOUND TO MEMBRANE COMPONENTS AND ARE LOOSELY ATTACHED TO THE CELL MEMBRANE BY ELECTROSTATIC INTERACTIONS.
PERIPHERAL PROTEINS
PROTEINS THAT ARE ANCHORED TO, AND IMBEDDED IN, THE CELL MEMBRANE THROUGH HYDROPHOBIC INTERACTIONS AND MAY SPAN THE CELL MEMBRANE.
INTEGRAL PROTEINS
EXAMPLES OF INTEGRAL PROTEINS
ION CHANNELS
TRANSPORT PROTEINS
RECEPTORS
GUANOSINE 5′-TRIPHOSPHATE (GTP)–BINDING PROTEINS (G PROTEINS)
CELL MEMBRANES ARE COMPOSED PRIMARILY OF PHOSPHOLIPIDS AND PROTEINS. PHOSPHOLIPIDS HAVE A __________ BACKBONE, WHICH IS THE HYDROPHILIC (WATER SOLUBLE) HEAD, AND TWO ________, WHICH ARE HYDROPHOBIC (WATER INSOLUBLE). THE HYDROPHOBIC TAILS FACE EACH OTHER AND FORM A BILAYER.
GLYCEROL; FATTY ACID TAILS
THESE ARE THE ATTACHMENTS BETWEEN CELLS (OFTEN EPITHELIAL CELLS AND MAY BE AN INTERCELLULAR PATHWAY FOR SOLUTES, DEPENDING ON THE SIZE, CHARGE, AND CHARACTERISTICS.
TIGHT JUNCTIONS
OTHER NAME FOR TIGHT JUNCTIONS
ZONULA OCCLUDENS
EXAMPLE OF AN IMPERMEABLE TIGHT JUNCTION
RENAL DISTAL TUBULE
EXAMPLE OF A “LEAKY” OR PERMEABLE TIGHT JUNCTION
RENAL PROXIMAL TUBULE
GALLBLADDER
THESE ARE THE ATTACHMENTS BETWEEN CELLS THAT PERMIT INTERCELLULAR COMMUNICATION; FOR EXAMPLE, PERMIT CURRENT FLOW AND ELECTRICAL COUPLING BETWEEN MYOCARDIAL CELLS.
GAP JUNCTIONS
THIS IS THE ONLY FORM OF TRANSPORT THAT IS NOT CARRIER MEDIATED, OCCURS DOWN AN ELECTROCHEMICAL GRADIENT (“DOWNHILL”) AND DOES NOT REQUIRE METABOLIC ENERGY AND THEREFORE IS PASSIVE.
SIMPLE DIFFUSION
DIFFUSION CAN BE MEASURED USING THE FOLLOWING EQUATION:
J = − PA(C1 − C2)
J = FLUX (FLOW) (MMOL/SEC)
P = PERMEABILITY (CM/SEC)
A = AREA (CM2)
C1 = CONCENTRATION1 (MMOL/L)
C2 = CONCENTRATION2 (MMOL/L)
WHAT ARE THE FACTORS THAT INCREASE PERMEABILITY
↑ OIL/WATER PARTITION COEFFICIENT OF THE SOLUTE INCREASES SOLUBILITY IN THE LIPID OF THE MEMBRANE.
↓ RADIUS (SIZE) OF THE SOLUTE INCREASES THE DIFFUSION COEFFICIENT AND SPEED OF DIFFUSION.
↓ MEMBRANE THICKNESS DECREASES THE DIFFUSION DISTANCE.
CHARACTERISTICS OF CARRIER-MEDIATED TRANSPORT
STEREOSPECIFICITY
SATURATION
COMPETITION
ANALOGOUS TO THE MAXIMUM VELOCITY (VMAX) IN ENZYME KINETICS
TRANSPORT MAXIMUM (TM)
THIS OCCURS DOWN AN ELECTROCHEMICAL GRADIENT (“DOWNHILL”), DOES NOT REQUIRE METABOLIC ENERGY AND THEREFORE IS PASSIVE, IS MORE RAPID THAN SIMPLE DIFFUSION AND IS CARRIER MEDIATED AND THEREFORE EXHIBITS STEREOSPECIFICITY, SATURATION, AND COMPETITION.
FACILITATED DIFFUSION
THIS OCCURS AGAINST AN ELECTROCHEMICAL GRADIENT (“UPHILL”), REQUIRES DIRECT INPUT OF METABOLIC ENERGY IN THE FORM OF ADENOSINE TRIPHOSPHATE (ATP) AND THEREFORE IS ACTIVE, IS CARRIER MEDIATED AND THEREFORE EXHIBITS STEREOSPECIFICITY, SATURATION, AND COMPETITION.
PRIMARY ACTIVE TRANSPORT
EXAMPLES OF PRIMARY ACTIVE TRANSPORT
NA+, K+-ATPASE (OR NA+–K+ PUMP)
CA2+-ATPASE (OR CA2+ PUMP)
H+, K+-ATPASE (OR PROTON PUMP)
THE TRANSPORT OF TWO OR MORE SOLUTES IS COUPLED. ONE OF THE SOLUTES (USUALLY NA+) IS TRANSPORTED “DOWNHILL” AND PROVIDES ENERGY FOR THE “UPHILL” TRANSPORT OF THE OTHER SOLUTE(S). METABOLIC ENERGY IS NOT PROVIDED DIRECTLY BUT INDIRECTLY FROM THE NA+ GRADIENT THAT IS MAINTAINED ACROSS CELL MEMBRANES.
SECONDARY ACTIVE TRANSPORT
IF THE SOLUTES MOVE IN THE SAME DIRECTION ACROSS THE CELL MEMBRANE, IT IS CALLED
COTRANSPORT OR SYMPORT
EXAMPLE OF COTRANSPORT OR SYMPORT
NA+-GLUCOSE COTRANSPORT IN THE SMALL INTESTINE AND RENAL EARLY PROXIMAL TUBULE
NA+–K+–2CL– COTRANSPORT IN THE RENAL THICK ASCENDING LIMB
IF THE SOLUTES MOVE IN OPPOSITE DIRECTIONS ACROSS THE CELL MEMBRANES, IT IS CALLED
COUNTERTRANSPORT, EXCHANGE, OR ANTIPORT
EXAMPLE OF COUNTERTRANSPORT, EXCHANGE, OR ANTIPORT
NA+-CA2+ EXCHANGE
NA+–H+ EXCHANGE
