Flashcards in membrane structure + function II Deck (23):
what are the major functions of the plasma membrane?
what are the major functions of the inner and outer membranes of the mitochondria?
→INNER: energy transduction
→ OUTER: barrier
what are the functions of the rough and smooth endoplasmic reticulum?
→ protein processing
→ synthesis of complex lipids
what is the major function of the Golgi Apparatus?
→ processing for secretion
what is the major function of the nuclear membranes?
→ attachment of chromatin
what is the major function of the lysosomal membrane?
→contain in hydrolytic enzymes
what is the major function of the peroxisomal membrane?
→fatty acid oxidation
what kinds of molecules can get through the membrane by simple diffusion?
→hydrophobic molecules, such as N2 or O2
→small, uncharged, polar molecules, such as H2O, CO2, urea and glycerol
what kinds of molecules cannot get through the membrane by simple diffusion?
→ large, uncharged, polar molecules, such as glucose
→ions, such as H+, Na+, K+, HCO3-, Ca2+, Cl-, Mg2+
what are the two different ways in which membrane transport occurs?
→Membrane transport can be passive (no energy required) or active (energy required)
→It can also be non-mediated (i.e. molecules just move through, always passive) or it can be carrier-mediated (could be passive or active).
what are the two kinds of cotransport and what is it used for?
→Cotransport is when a transporter moves two molecules at the same time.
→This can be an antiporter (moving molecules in opposite directions) or a symporter (moving them in the same direction).
→This would be used to generally get one target molecule through using the concentration gradient of another.
why is glucose transport carrier-mediated?
→glucose transport is carrier-mediated; it cannot get through quick enough by simple diffusion.
→It can be passive (by facilitated diffusion) or active (by sodium symporter).
→ if there was no carrier, glucose transport would be incredibly slow.
→The carrier-mediated facilitated diffusion speeds up the rate of glucose transport greatly.
what does KT tell us about glucose transporters
→There is a family of glucose transporters called GLUT transporters.
→These each have their own tissue locations and a Kt value (same as Km), which tells us the affinity of the transporter for glucose.
→The higher the affinity (lower Kt value) the more readily it’ll bind to glucose, meaning it'll get saturated at low levels of glucose.
what are the 5 glucose transporters?
→ found in all mammalian tissue
→ responsible for basal glucose uptake
→found in liver and pancreatic β cells
→ in the pancreas, plays a role in regulation of insulin
→ in the liver, removes excess glucose from the blood
→found in all mammalian tissue
→responsible for basal glucose uptake
→found in muscle and fat cells
→the amount in muscle plasma membranes increases with endurance training
→found in the small intestine
→primarily a fructose transporter
how do glucose transporters work?
→The transporter binds to glucose and undergoes a conformational change.
→opens the inner portion to the cytoplasm and the glucose diffuses in.
→Because the transport of glucose is driven by the concentration gradient of glucose, the cell maintains this gradient by phosphorylating the glucose as it enters the transporter.
what kind of kinetics do glucose transporters show?
→ similar to enzyme kinetics.
→They exhibit saturation-type kinetics (ie. starts to plateau) and can be regulated.
→The kinetics are also specific to the molecules they transport.
how can glucose uptake be increased in cells using insulin?
→When there is no insulin present, the transporters are brought inside the cell via a vesicle (ie. away from the membrane).
→This stops the transporters from functioning.
→When insulin is present, the vesicle with the transporters fuses with the membrane to express them on the membrane.
→This allows the transporters to function.
what is an example of active transport?
→The concentration of Na+ outside cells (around 140mM) is higher than inside the cells (around 15mM), but there is no free movement as they cannot get through the membrane.
→Like facilitative transport, active transport is selective and requires an integral membrane protein.
→Sodium is linked to an antiport system with potassium; the protein involved is a Na+/K+ ATPase.
→ requires energy in the form of ATP to work.
→pumps 3 Na+ out for every 2K+ in, establishing the concentration gradient inside and out.
how does foxglove affect the Na+/K+ pump?
→Foxglove contains the chemical Digitalis.
→Digitalis is a cardiotonic steroid which inhibits the Na+/K+ pump.
→ increases the force of contraction of the heart, so it's the treatment of choice for congestive heart disease.
→the reason it does this is that the inhibition of the pump leads to increased intracellular Na+.
→ This leads to slower removal of Ca2+ by the Na+/Ca2+ exchanger, resulting in an increased ability of the muscle to contract using the excess Ca2+.
how do sodium dependent glucose transporters work?
→Sodium-dependent glucose transporters are SGLUT-1 and 2.
→These are symporters which will only work if you have both Na+ and glucose bound; once both are bound, both will be transported into the cell.
→This is a passive process.
→The glucose gets phosphorylated while Na+ is pumped actively out by the Na+/K+ ATPase in order to maintain the Na+ concentration gradient.
→because of this, the SGLUT-1 and 2 would be said to be indirectly active processes because they rely on this concentration gradient brought about by an active process.
where is the SGLUT-1 found?
→The SGLUT-1 is a Na+ driven glucose symporter. Present on the gut lumen side of the enterocyte, this transports glucose from area of lower concentration to an area of higher concentration using the concentration gradient of Na+.
where is the SGLUT-2 found?
→On the other side of the cell (facing the extracellular fluid, the basal domain) is the GLUT -2 which transports glucose down its concentration gradient (from higher in the cell to lower in ECF). The Na+/K+ ATPase pump also works down here.