BIOL211 L8

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  • Created by: Katherine
  • Created on: 24-04-17 10:12
What does valinomycin do?
It depolarises cells
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What is the structure of Valinomycin?
A ring structure from 12 residues. Potassium is bound. It has a n aqueosu pocket which holds K+ (hydrophilic). K+ binds by carbonyl oxygens. The outer perimeter of ring is lipophilic - diffuse free in membrane. It is highly selective for K+ over Na+
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Why is valincomycin highly selective for potassium over sodium?
K has a lower free energy of dehydration
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What is the mechanism of transport across alinomycin?
A high potassium concentration on the outside, it goes into the valinomycin and the ion dehydration occurs. The ion is rehydrated once it passes across the membrane.
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What are the kinetic properties of carriers?
Binding of substrate from outside and formation of carrier substrate complex. Re-orientation of CS to align binding site to the inside. Release of substrate. Empty carrier re-orientates to align binding site to outside.
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Carrier mediated transport can be described with michaelis menten kinetics, wht is this equation?
E + S = ES = E + P, C + S0 = S0 = C + S1
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What is the Vmax value?
Transport rate independent of substrate - it reflects the rate of carrier re-orientation
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What is the Km value?
Transport rate dependent on the substrate availability - reflects binding and release of solute
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What do kinetic constants do?
Give insight into physiological role of carrier
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In summary, what does valinomycin do?
Diffuses across the membrane and as a result exposes the ion binding site alternatively to each side of the membrane.
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What is GLUT1?
A glucose facilitator
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What is the proposed model of uniport transport by GLUT1?
The glucose binding site is facing toards the outside and poised to bind glucose, binding of glucose, GLUT1 undergoes a conformational change to orientate the binding site to face inward. Gucose is released and GLUT1 re-orientaates to outside
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How does NSSs work? What is it?
Neurotransmitter sodium symporters - Major route for neurotransmitter clearance. Require Na+ and Cl- to drive uphill transport of neurotransmitters. Dysregulation of NSS function associaed with many debilitating disorders (e.g depressiong, epilepsy)>
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What is the structure of neurotransmitter sodium symporters?
6TMS (form the structural part of the protein), 2 Hairpin loops and 2 more TMS
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What do the hair pin loops act as?
The two gates which expose the substrate bindng site
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What is required for the NSS to work?
Neurotransmitter binding is Na+ dependent - Na+ binding increases affinity of binding site for neurotransmitter. Hence in high (Extracellular) Na+, neurotransmitter is bound and in low (intracellular Na+ neurotransmitter is released.
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What is the ICH?
Intracellular helical bundle is unique to the GLUT1 transporter - it is 4 short a helices that connect the N and C termini.
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Including ICH, what is the process of GLUT1 action? 1,2
Preferred state in absence of substrate (affinity between N and C termini on cytosolic side is greatest and depends on ICH region. Substrate binding (high glucose)induces extra contact on extracellular side - closes access to binding site (occluded).
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Including ICH, what is the process of GLUT1 action? 3, 4
Extra contact induces higher affinity between TMS 7 nd 1 on extracellular side which surpasses that of the ICH region. Switches to inward open configuration, exposes substrate binding site to cytosolic side, substrate dissociate. ICH affinity dominat
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The ICH domain is key to...
The rocking motion of GLUT1
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What are some physiologically important carriers? Facilitators
GLUT 2 (Transporter of glucose between liver and blood and glucose absorbance from gut. GLUT1 (main transporter of glucose to brain (across blood brain barrier). Loss of functions mutations in GLUT1: GLUT1 deficiency syndrome characterised by epileps
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What does it mean is GLUT1 is over expressed?
Prognostic indicator for cancer
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Alot of cancer cells upregulate GLUT1, why?
Because they use it as an energy source
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Why is yeast different to other fungi in terms of glucose?
They use facilitators to transport glucose, whereas other fungi require active transport using a proton gradient. - This is due to the low conc of glucose in soil.
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What is a secondary active transporter?
Secondary active transport is a form of active transport across a biological membrane in which a transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or
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Give an example of Na+ coupled sugar transport in mammalian cells
Glucose uptake from the intestinal lumen into the blood
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Why shouldn't you look at any of the transporters in isolation?
They form a transport strategy
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Where is the Na+ Ca+ antiporter found?
In cardiac muscle cell plasma membrane
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In the Na+ Ca+ antiporter, how many Na+ are associated with the movement of 1 Ca2+
3
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Why are 3Na+ assocaited with the movement of 1 Ca2+?
Because the calclium concentration gradient is huge
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What does the Na+ Ca+ antiporter do?
Maintains a low cytosolic Ca2+ which allows relaxation of heart muscle following contraction
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What maintains a Na+ gradient?
Na+/K ATPase maintains a Na+ gradient enabling Ca2+ efflux via the antiporter
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What is used to treat heart failure?
Oubain widely used as treatment to inhibit Na+/K+ ATPase, elevating cytosolic Ca2+ and increasing the force of the heart muscle contractions
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What is the job of the plant vacuole?
To store nutrients and toxins, nd keep the cytosol maintained
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What are the transporters on the plant vacuole?
Proton antiport proteins and H+ pumping proteins
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What is the symport responsible for in plant roots?
Protons (H+)
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Other cards in this set

Card 2

Front

What is the structure of Valinomycin?

Back

A ring structure from 12 residues. Potassium is bound. It has a n aqueosu pocket which holds K+ (hydrophilic). K+ binds by carbonyl oxygens. The outer perimeter of ring is lipophilic - diffuse free in membrane. It is highly selective for K+ over Na+

Card 3

Front

Why is valincomycin highly selective for potassium over sodium?

Back

Preview of the front of card 3

Card 4

Front

What is the mechanism of transport across alinomycin?

Back

Preview of the front of card 4

Card 5

Front

What are the kinetic properties of carriers?

Back

Preview of the front of card 5
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