Part 1.2 Flashcards
Transporter proteins types and rates
Gated channels: voltage and ion
Rate: 10^9 ions
Ex. Voltage gated Na+ channels
Transporters: uniport, symport, antiport
Rate: 10^4 ions/s
Ex. CACT is an antiporter, aquaporin is a uniporter, GLUT are uniport
ATP-powered pumps move solutes against their concentration gradient
Rate: 10^2 ions/s
Facilitated diffusion definition
Protein-mediated transport of one solute down its concentration gradient - AKA uniport
Function like an enzyme - creates higher rate than simple diffusion
Partition coefficient is irrelevant but displays Km and Vmax
Selective, specific and reversible (depending on concentration gradient)
ATP Powered Pumps About Function and Structure
P type
Example
AKA ATPases, primary active transport
Use energy from ATP to transport solutes against concentration gradient
P type autophosphorylate alpha-subunit (phosphoprotein) - makes it move in a way that is essential to its activity
Ex. Na+/K+ ATPase in basolateral membrane of small intestine
Symporter and Antiporters functions and examples
AKA secondary active transport
Both use favorable concentration gradient to power movement of a solute against its concentration gradient
Symporter - both solutes move in the same direction
Ex. Na+/glucose SGLT1
Antiporter - solutes move opposite directions
Ex. 3 Na+/2 Ca2+ transporter
Lysine example of transport protein coordination
Lysine is pos charged - cannot cross membrane
1) Na-Lysine symporter ECM to cytoplasm (Na down [ ])
2) Na+/K+ ATPase transports Na+ back into ECM
3) K+ channel re-establishes [ ] in ECM
All to ensure lysine can enter cells
Acidification of the stomach example of transporter collab
1) CO2 + OH- (from H2O) —> HCO3 via carbonic anhydrase
2) H+ (from H2O) and K+ (from lumen) pumped via antiport ATPase across apical membrane
3) Re-establish [K+] across apical membrane in lumen with uniport channel
4) Remove HCO3 from cytosol (blood) with Cl- (cytosol) antiport basolateral membrane
5) Re-establish [Cl-] in cytosol across apical membrane (lumen)
All to maintain stomach pH of ~1
Absorption of dietary glucose transporter collab
1) SGLT secondary active symport of glucose and Na into cytoplasm against [glucose] across apical membrane
2) GLUT2 uniport glucose into blood down [glucose] across basolateral membrane
3) Na/K antiport across basolateral membrane to re-establish [Na]
4) K uniport channel re-establish [K] across basolateral membrane
Different glucose transporter isozymes and sugars they transport
SGLT1 from lumen into enterocyte cytoplasm
- Glucose, galactose and Na
GLUT2 across basolateral membrane into blood
- glucose, galactose, fructose
GLUT5 from lumen into enterocyte
- fructose
*cancer cells utilize to increase fructose uptake
Where is GLUT2 found
What does it require to be active?
What does it mean if a GLUT transporter has a low Km?
Kidney tubules and SI epithelium, pancreatic beta cells and hepatocytes
High Km so high [glucose] required to be active, aka has low affinity for glucose
A low Km means the GLUT has a high affinity for glucose and can be active with low [glucose] and reach Vmax faster
GLUT1, 2, and 3 where they are found, their Km and sugars they transport
GLUT1: most cells except kidney and SI epithelium
- Low Km = high affinity
- glucose and galactose transport
GLUT2: Basolateral kidney and SI epithelium and pancreas B cells and hepatocytes
- high Km = low sugar affinity
- glucose, galactose and fructose
GLUT3: brain, placenta and testes
- low Km = high affinity
- glucose and galactose
How the GLUT transporter works/moves
1) When not bound to glucose, GLUT displays outward open/inward closed conformation
2) Binding site is deep in protein (hydrophilic pocket), glucose binds
3) GLUT1 binds glucose and forms closed conformation
4) Then conformational change to inward open conformation and loses affinity for glucose (releasing it)
Role of Na/Glc symporters in pancreatic, hepatocytes, enterocytes and erythrocytes?
Energy used?
Transport is thermodynamically unfavorable requiring active transport (cytosolic [glucose] is higher)
Na ion and electrical potential gradient used (form of ∆G) to power Glc transport
- maintained by Na/K ATP pumps
- Nernst equation: ∆G = RT ln [Na in]/[Na out]
How to Na/Glc Symporters work?
1) Presence of Na potentiates the binding of Na which increases affinity for glucose binding
2) Transporter closes upon glucose binding
3) Closing to extracellular environment (lumen in this case) causes it to open to the intracellular (cytoplasm)
4) As it opens to cytoplasm it loses affinity for Na and then glucose loses affinity
5) Empty hydrophilic binding pocket signals to return to close config
Why we use glucose to identify cancer
Solid tumors increase rate of glycolysis even in the presence of O2
Warburg effect - aerobic glycolysis
This leads to increased glucose uptake into cancer cells which can be tracked using FDG in PET scans
How PET scans work
1) FDG instead used as a fluorescent component to track
- Lack of OH on C2 prevents entry to glycolysis
2) More accumulation of FDG increases radiation presence
- Brain, kidneys, bladder, heart all light up
3) PET CT relies on symmetry in the body to identify abnormalities which are asymmetrical with the axis with the body
*2-deoxyglucose used to turn off glycolysis as a control in experiments
