Lecture 1 Membrane Structure and Transport Flashcards
What is the role of glucosamine-phosphatidylinositol (GPI) anchors in immunity, specifically in the host defense mechanism?
GPI-anchored proteins are involved in the recognition of microorganisms, and in the insertion of mycobacteria and trypanosomes into phagosomes
In an artificial membrane, the low lipid solubility of water would predict that it has low permeability. Is that true in biological membranes?
No, because water is transported through the membrane via aquaporins, a channel protein in the membrane through which water diffuses.
There are thirteen mammalian aquaporin isoforms. Where in the kidney are AQP-2, 3 and 4 located and what is a key difference in their physiology?
AQP-2 is vasopressin (AVP)-sensitive, found in the tubular lumen, and AQP-3 and 4 channels are found on the basolateral membranes and are not AVP-senstive
Describe the structure of the bovine urea transporter.
bUT consists of 3 subunits with 12 transmembrane alpha-helical domains each
What is the difference between primary and secondary active transport?
In primary active transport, molecules are “pumped” again an electrochemical gradient at the expense of energy (ATP), a direct use of energy, whereas secondary active transport is driven by the energy stored in the electrochemical gradient of another molecule, an indirect use of energy
Describe glucose transport in the intestine.
Glucose is absorbed in the GI via SGLT1/2 (secondary active co-transport). Na+/K+-ATPase (primary active transport) on basolateral membrane maintains Na+ gradient. Glucose is transported to bloodstream via GLUT2 (facilitated transport).
Gq-coupled receptors activate phospholipase C which cleaves _______ into ______ and _________.
Gq-coupled receptors activate phospholipase C which cleaves phosphatidylinositol 4,5-bisphosphate into 1,4,5-inositol triphosphate (IP3) and sn-1,2-diacylglycerol (DAG).
The Ca2+ ATPase take place where? What does it maintain?
Takes place in the sarcoplasmic reticulum.
Maintains low cytosolic Ca2+ concentration.
Which symporter is critical for pH balance?
Na+ HCO3 symporter
What are the main functions of the Na+/K+ ATPase?
1) Maintains electrochemical gradients for electrical signaling
2) Osmotic balance
3) Target of cardiac glycosides
Where do you find H+ ATPases?
In the parietal cells of gastric glands for HCl secretion and intercalated cells of distal renal tubules for H+ secretion from blood to urine
What do Cardiac Glycosides inhibit and what does this inhibition result in?
Cardiac glycodsides inhibit Na+-K+ ATPase and results in:
1) Increased Intracellular Na+
2) Increased contractile force (inotropy)
3) Increased Intracellular Ca2+
4) Decreased Na+/Ca2+ Exchanger (antiporter)
Name the heart failure drug from Foxglove plant that is a poison, but has been used as a herbal remedy for centuries. Name the what category does it belong to?
Digoxin and its a type of cardiac glycoside
Which antiporter is found in most cells?
Na+/Ca2+ Exchanger
Which antiporter is found in the PROXIMAL kidney tubules?
Na+/H+ Exchanger
Which antiporter is found in most cells and red blood cells, specifically band 3?
Na+/Cl- Exchanger
Which antiporter is found in the DISTAL kidney tubules?
Na+/HCO3 Exchanger
Describe the glucose transport in the kidney.
In the proximal tubule SGLT-2 reabsorbs about 90% of glucose from urine against a 100 fold gradient.
Distal kidney tubules express an SGLT-2 isoform, which transports glucose against a higher gradient.
GLUT2 transports glucose into blood by facilitated diffusion.
Na+ gradient maintained by Na+/K+ ATPase.
What is the extracellular fluid and intracellular concentrations of Na+?
[Intracellular]: 10 mEq/L
What is the extracellular fluid and intracellular concentrations of K+?
[Intracellular]: 140 mEq/L
What is the extracellular fluid and intracellular concentrations of Ca2+?
[Intracellular]: 0.0001 mEq/L
What is the extracellular fluid and intracellular concentrations of Cl-?
[Intracellular]: 4 mEq/L
What are the factors that affect net diffusion?
- Concentration gradient
- Electrical potential (EMF)
- Hydrostatic Pressure Difference
What does it mean when the concentration gradient is a factor that affects net diffusion?
Solutes will go from a higher solute concentration to an area of lower solute concentration
net diffusion ~ (Co- Ci)
What does it mean when the electrical potential (EMF) is a factor that affects net diffusion?
EMF = electrical force that opposes the concentration force
Demonstrated by Nernst Equation:
EMF (mV) = ±61 log (Ci / Co)
Particles that are inside the membrane that are a charge (e.i. +) will pull charged particles of another charge (i.e. -) by electrical attraction.
When electrical force and chemical force equal, an equilibrium will occur.
What does it mean when the hydrostatic pressure difference is a factor that affects net diffusion?
High pressure increases energy available to drive net particle movement
Adding heat increases collision frequency, which increases flux and pressure is changed
What is osmotic pressure?
The amount of pressure required to oppose osmosis.
Water will go from a higher amount of water to a lesser amount of water.
What is Osmolality?
# of particles in a kg of water measured in mOsm = milliosmole
What is Osmolarity?
# of molecules in a Liter of solution measure in mM = millimolar
What is the molarity and milliequivalents (mEq) equation? What does this equation take into account?
mEq/L x Valence = mMolarity
-Takes into account the valence charge x particles per liter
1 milliequivalent (mEq) equals how much Molarity (M)?
1 milliequivalent = 1mM
How much molarity do you get when you have 1 mEq/L of a monovalent ion (H+, Na+, K+, and Cl-)?
1mEq/L x 1 = 1 mM
mEq and mM are equivalent
How much molarity do you get when you have 1 mEq/L of a divalent ion (Ca2+, Mg2+)?
1mEq/L x 2 = 2 mM
mEq is half of mM
What does tonicicity solely depend on?
The concentration of impermeant solute
What does it mean when a cell is hypotonic?
Low impermeant solute
Water goes into the cell
Cell swells
What does it mean when a cell is isotonic?
Equal solute concentration
No water movement
What does is mean when a cell is hypertonic?
High impermeant solute
Water out of cell
Cell shrinks
What does it mean when a cell is Hypo-osmotic?
Extracellular osmolarity less than normal (~288)
Water goes in
What does it mean when a cell is Iso-osmotic?
Equal osmolarity
What does it mean when a cell is Hyperosmotic?
Extracellular osmolarity is more than normal
Water goes out
What is the osmotic coefficient? What is it also known as.
It is the deviation of solutes, particularly ion, from their ideal behavior in solution due to molecular attraction. I is a constraint on random collisions.
The osmotic coefficient is also known as the van’t Hoff coefficient
What is the actual osmolality of NaCl at physiological concentrations (0.9% NaCl solution) when the osmotic coefficient is 93?
0.9% NaCl solution = 0.9g/100ml = 9g/1L NaCl molar mass = 58.44g/mol mol = mass/molar mass mol = (9g/L) / (58g/mol) mol in 1 L~ 0.154mol/L = 0.154 M = 154mM 154mM x 2 = 308 mOsm Osmotic Coefficient = 93--meaning NaCl only 93% dissociated 308mOsm x 0.93 = 286 mOsm (actual osmolality)
What is permeability most dependent on?
Most dependent on lipid solubility, but other factors are size and charge.
How soluble and permeable are gases like CO2, N2, O2 through a membrane?
Gases have high lipid solubility and high permeability through a membrane
Passes through the membrane
How soluble and permeable are small uncharged polar molecules like ethanol through a membrane?
Small uncharged polar molecules have high lipid solubility and have predictably high permeability due to being a small polar molecule.
Passes through the membrane
How soluble and permeable are molecules like water and urea through a membrane?
Molecules like water and urea have low lipid solubility and have predictably low permeability.
Can pass through the membrane sometimes
How soluble and permeable are large uncharged polar molecules like glucose through a membrane?
Large uncharged polar molecules like glucose have low lipid solubility and are impermeable due to their large size.
Do not pass through the membrane
How soluble and permeable are ions (i.e. K+, Mg2+, Ca2+, Cl-, HCO3-, HPO42-) through a membrane?
Ions are impermeable and do not pass through the membrane?
How soluble and permeable are charged polar molecules like amino acids, ATP, and G6P through a membrane?
Metabolites are impermeable due to their low lipid solubility, large size, and charge.
How is cholesterol involved with the plasma membrane?
Amphipathic molecules that inserts within the phospholipid bilayer of the cell membrane. It increases membrane stability and decreases fluidity and permeability.
Even though the composition of cell membrane vary depending on the specific tissue functions, what is the typical composition of a cell membrane?
Phospholipid 25% Protein 55% Cholesterol 13% Other lipids 3% Carbohydrate 4%
Phospholipids are ______ molecules because they have a polar part and a nonpolar part. What part of the phospholipid is polar and what part is nonpolar?
Phospholipids (PLs) are amphipathic or amphiphilic because they have a polar part and a nonpolar part. The polar part of the PLs is the phosphate, which is hydrophilic and the nonpolar part of the PLs is the fatty acid, which is hydrophobic.
What are the types of phospholipids in the cell plasma membrane?
- Phosphatidic Acid Derivatives
- Shingomyelins
- Glycolipids
What are the Phosphatidic Acid derivatives that help compose the cell plasma membrane?
Phosphatidylserine
Phosphatidylethanolamine
Phosphatidylcholine
Phosphatidylinositol
Which phosphatidic acid derivatives have a high percentage of composition within the plasma membrane?
Phosphatidylcholine
Phosphatidylehanolamine
Which phosphatidic acid derivatives have a low percentage of composition within the plasma membrane?Which one has the smallest?
Phosphatidylinositol –lowest
Phosphatidylserine
How are integral proteins related to the cell membranes?
Integral proteins span the membrane entirely. They have alpha helical coiling that is the transmembrane spanning domain. They also can contain sugars covalently attached. Specifically, integral proteins are difficult to extract since they span the membrane. They require detergent (harsh conditions) for extraction.
How are peripheral proteins related to the cell membranes?
Peripheral proteins are attached “loosely” to integral proteins and are often elements or activators of signal transduction pathways.
What are 4 types of integral proteins?
Ion channel proteins
Receptor proteins
Carrier proteins
Transporter proteins
What are 2 types of peripheral proteins and what makes them easily extractable?
Enzymes
Intracellular Signaling Molecules
Their ionic strength make them easily extractable.
What are membrane lipid rafts?
Signaling platforms stabilized by protein-protein, protein-lipid, and cholesterol interactions. They are signaling platforms where signal transduction occurs and can be involved in cell-cell recognition and cell adhesion.
What are the two types of carbohydrates involved with the cell membrane?
- Glycoproteins–sugars covalently bound that have negative charges that will attract positively charged target molecules. These are the basis of cell-cell recognition and adhesion molecules in the extracellular matrix.
- Glycolipids- Make up ~10% of sugars covalently bound to phospholipid. They are specific features of glycophophatidylinosiol anchors. They are also invovled in cell recognition.
What is Fick’s First Law of Diffusion?
Flux = -P (C2-C1)
Governing factor is the concentration gradient times the constant
P = permeability coefficient
C2-C1 = concentration gradient
What are the two types of ion channel electrophysiology measurement tools?
- 2-Electrode Voltage Clamp –Membrane voltage “clamped” at specific potentials. You place electrodes on the cell and they will anneal because of the glycoproteins. You get a lot of leakage.
- Single Electrode Patch Clamp–Whole cell or single channel that records electrical activity. Very fine level of recodings and won novel prize 1991
Ionophores and charge carriers are of bacterial origin and they do what and have what kind of defense mechanism? What are they slightly selective for?
They conduct ions through the membrane and have a cytotoxic defense mechanism. They are slightly selective for Na+.
Describe ionophores.
Ionophores form simple channels like gramiccidin and amphotericin B. They spontaneously insert into the membrane to form pores. They also participate in rapid transport and simple diffusion. These are very toxic.
Describe charge carriers.
Charge carriers are mobile ion carriers and are cage-like structures that shuttle ions. They partially span the membrane. They are hydrophobic out and hydrophilic in. Some examples are monesin and valinomycin.
What are 5 examples of simple diffusion?
Ion channels Aquaporins Urea Transport (UT-B) Lipid Soluble Molecules Ionophores
What are 3 examples of carrier proteins that are required for facilitated diffusion?
Glucose Transport protein
Amino acid Transport protein
Mobile charge carriers
