W5 Membrane II Flashcards
GLUT1 + GLUT3
In all mammalian tissues
Kt = 1 mM
Basal glucose uptake
GLUT2
Liver and pancreatic beta cells
Kt = 15-20 mM
Pancreas = plays a role in regulation of insulin Liver = removes excess glucose from the blood
GLUT4
Muscle and fat cells (recruited to cell surface)
Kt = 5 mM
Amount in muscle plasma membrane increases w/endurance training
Stimulated by insulin
GLUT5
Small intestine
Kt = —
Primarily a fructose transporter
Simple glucose transporter function
12 transmembrane domain
Asparagine 45 on TM 1+2
NH3+ at TM 1
COO- at TM12
Membrane transport -facilitated diffusion
Conformational changes result in transport
Driven by concentration gradient
Bidirectional transport
Gradient maintained by phosphorylation
Glucose to G6P so no need for a transporter + maintains [] gradient for glucose
Foxglove
Digitalis
Cardiotonic steroid
Inhibits the Na+/K+pump
So intracellular [Na+] increases
Thus slower removal of Ca2+ by Na+/Ca2+ exchanger thus insreased contraction of heart muscle (Ca2+ for contraction)
Sodium dependent glucose transporters SGLUT-1 and 2
In blood
Use Na+ gradient to draw across glucose
Does not require energy however for it to continue does require energy
Cellular asymmetry
Glucose drawn out of cell by simple diffusion due to [] gradient - to maintain transport process
Na+ is also removed
Na+/K+ ATPase on basal surface of cell
To maintain asymmetry we have junctions which prevent movement of membrane associated proteins
Re-hydration therapy
Na+/glucose co-transported into the body
Due to their osmotic effect they draw in water by osmosis
Chloride channel and cystic fibrosis
Chloride channel mutation causes cystic fibrosis (single mutation in AA)
Maybe also related to the protein involved in multi drug resistance pumps out small molecules
Compartmentalization
Separates reactions
Enables the local environment to be regulated for instance pH
Brings reactants together
Proteins have signal sequences which target them to specific organelles
A disease of misdirection (storage disease)
The enzyme (a phosphotransferase) in golgi lacks ability/unable to add M6P tag Thus products taken by lysosomes accumulate
Membrane carbohydrates in cell recognition
Endothelial cells express particular membrane protein = lectins (glycoproteins)
Selectins - recognised by circulating neutrophils and they grab hold of neutrophil + allow them to pass through endothelial
Blood group dependent on one difference in the glycoproteins on the RBC = the expression or not of a specific glycosyltransferases
