Human Physiology Exam 1

This is an equilibrium ligand binding curve, where [L] is given in mM. Estimate kd

0.5 mM

Which number represents the mass of one water molecule in grams?

18/(6*10^23)

The smallest size that is clearly visible under an optical microscope is close to

250nm

The diameter of a round cell A is 3 times larger than that of another round cell B.

3^3 = 27

Estimate the fraction of occupied receptors if kd = 0.83 mM and [L] = 0.71 mM. Take a reasonable guess (no calculator needed).

40%

The arrows point to a lipid bilayer membrane. What could possible be the length of the scale bar (in the bottom right)?

50nm

Estimate the quantitative relationship between the two curves

?

Reproduce the calculation of the resting daily energy need

?

By how much is the volume of A larger than the volume of B?

Chemical concentrations of >100 M (let alone 100,000 M) are impossible.

What condition does the GHK equation represent?

Constancy of membrane potential in time.

Reproduce the energy diagram from memory, with all the main quantities labeled.

DeltaE

How would the membrane potential be affected if permeability for Ca2+ increased? (Assume the typical distribution of Ca2+).

Depolarization

Two atoms have the same numbers of electrons but different numbers of protons. What can you say about them?

Different elements, at least one of them is ionized

These curves show kinetics (time course) of ligand-receptor dissociation for two different ligands, A and B.

Dissociation rate constant koff for ligand B is higher than for ligand A

What is the difference between potential difference and field strength?

Field strength is the force acting on a charge; it is equal to potential difference divided by the distance over which it develops.

This is an image of a cultured cell. What type of image is it? (black image that looks like a bunny).

Fluorescence

This is an image of an adipose tissue section. What microscopic technique was most likely used to obtain this image? (black and white image of this)

Fluorescence (characteristic dark background)

0.1 mole of a substance contains 6*10x molecules. What is x?

For 1 mole, x = 23; for 0.1 mole, x = 22

How would you classify uncharged hydrogen atom H?

Free radical

Why do denatured proteins become less water-soluble?

From exposure of normally buried hydrophobic residues

What is the main functional difference between tight junctions and gap junctions?

Gap junctions allow passage of small molecules, most tight junctions do not.

How would you expect glucose import via the sodium-glucose cotransporter to be affected by membrane hyperpolarization (making it more negative)?

Glucose transport will increase

Give an example of monosaccharide, disaccharide, polysaccharide.

Glucose, sucrose, glycogen.

The reason water has a high boiling temperature is

Hydrogen bonds

Which of these molecules should be able to pass through a gap junction?

Potassium ion Glucose

What is the significance of the absolute refractory period?

Prevents backward travel of AP

What is the requirement for a ligand-receptor equilibrium binding that is responsive to ligand concentration? (As in the case of insulin).

Quantities expressed in different units cannot be compared.

What medical procedures make use of free radical reactions?

Radiation therapy, photodynamic therapy, sterilization by hydrogen peroxide

What effect does an increase in Ea have on reaction rate?

Reaction becomes slower

What type of transport is responsible for cholesterol uptake?

Receptor-mediated endocytosis

How can you explain the repulsion between a hydrophobic solvent and a hydrophilic solute?

Reduction in energy upon separation

Unidirectional propagation of the action potential is explained by

Refractory period

Give a few additional examples of transformations between mechanical work, mechanical energy, non-mechanical energy, and heat

Rubbing (mechanical work) → Heat Chemical process → electricity in an electric eel Chemical energy of food → walking (mechanical work) Nuclear energy → Heat (nuclear plant) Heat → Thunder (mechanical energy of a sound)

Two atoms have the same numbers of protons but different numbers of electrons. What can you say about them?

Same element, at least one of them is ionized

Why does not every graded potential in neuron produce an action potential?

Sodium channels begin to open when the membrane potential reaches > -55 mV. That requires sufficient stimulation. At the same time, leakage of ions through the membrane continuously opposes accumulation of charge (VHP).

One advantage of electrical synapses over chemical is ...

Speed

What type of tests are commonly used to see if cells are alive?

Tests for impermeability of the plasma membrane to hydrophilic molecules

Why do cells need facilitated diffusion?

To transport membrane-impermeant molecules

What are the relationships between the initial segment, the trigger zone, and the hillock?

Trigger zone is the general term for the site of AP generation.

What could be the units of Vmax?

nmol/(ml*s) for example

What could be the units of Km?

nmol/ml for example

How is neurotransmitter removed from the synaptic cleft?

(1) diffuse away from the synaptic cleft, (2) taken up by the presynaptic neuron for reuse, (3) enzymatically degraded. (Neurotransmitters in the brain are also removed by glial cells)

The pH of a solution can be expressed as (a question from MCAT):

-log10 [H+]

A muscle has been producing a stationary tension (without moving) of 20 N for 10 seconds. How much mechanical work has it produced?

0

Are there any limits to kon and koff?

0.01

This is a figure from a slide. Which curve corresponds to the highest affinity?

0.01

How much sucrose (in moles) must be added to 1 L of water to make it isosmolar to 0.1 M NaCl?

0.2 mol

4 micrograms in 1 mL = 4 milligrams in ... what?

1 L

The mass of 1 ml of water is

1 g

Same question, only [L] = 1 mM 5. If koff = 0.01 s-1, what is the probability of complex dissociation in 1 second?

1 mM = 10-3 M; 1/(10-3·107) = 1/104 = 10-4 s = 0.1 ms

If the energy of water hydrogen bonds is 5 kcal/mol, what would it be per gram?

1 mol of water = 18 g, 5 kcal/mol = 5 kcal/18g = 0.28 kcal/g

1% concentration corresponds to how many g/L? (Enter the number without units, such as 0.015)

1% = 1 g/0.1 L = 10 g/L

Find the amount of energy released from hydrolysis of one molecule of ATP

1.17x10-20 cal 7 kcal/mol = 7/(6*1023) kcal/molecule = 1.17*10-23 kcal = 1.17*10-20 cal

[L] = 10-8 M, kon = 107 1/M*s. Roughly estimate the time needed to achieve substantial receptor occupancy.

1/(10-8·107) = 1/10-1 = 10 s

Express a 0.1 g/L concentration in terms of percent

10-2 M = 10 mM 4. 0.1 g/L = 0.01 g/0.1 L = 0.01%

What are the typical intracellular (cytosolic) and extracellular calcium concentrations?

10-7 M and 10-3 M, respectively.

Compare the concentrations of hydrogen ions at pH1 and pH4

1000 times larger at pH1

If [H+] = 1 nM then pH = ? 35. pH difference by 3 units correspond to [H+] difference by ... ?

1000-fold

Calculate the equilibrium potential for a positive monovalent ion, Cin= 0.1 uM, Cout = 10 uM.

120 mV

Using the formula E = 1.4log(C2/C1) calculate the energy stored in a gradient when the concentration is 105 times higher on one side than on the other. (The molecule is uncharged. It's not specified on which side the concentration is higher, so the sign doesn't matter)

7kcal/mol

Calculate the mechanical power required to lift 1 kg by 2 m in 0.2 seconds.

9. 10 N∙2 m/0.2 s = 100 W

What is temperature?

A form of energy resulting in a temperature change

What is heat?

A measure of kinetic energy of molecules

What the smallest size that can be clearly visible under an optical microscope?

A quarter of a micron

Would a very hydrophobic substance easily cross a lipid bilayer?

A very hydrophobic substance would dissolve in a lipid layer but may not be able to cross it and to enter the aqueous phase that is beyond the lipid.

A ligand-receptor complex at initial concentration 10 mM starts dissociating with Koff = 1.0 (1/s). Roughly estimate how long it will take before its concentration becomes 5 mM.

About 1 s

"The turnover numbers can range from single digits to millions per second". What do you think it depends on?

Activation energy

Show that the units of kon (1/M*s) make sense.

After 100 s, its concentration will become 3.68 mM, so it will reach 5 mM a little sooner (in fact, after 69 s)

What are amyloids?

Aggregates of misfolded protein

How do the authors conclude that the cells in B and D failed to reseal?

Answer: leaky cells are expected to show persistent calcium elevation and possibly the leakage of fura-2. Calcium levels are given by the upper traces, and the concentration of the dye by the lower traces. In the cells that have been successfully repaired (A and C), calcium has returned to nearly initial levels or just slightly elevated; the intracellular fura-2 remained at a stable level in A and was partly lost in the cell C but has stabilized afterwards. In the cells B and D, calcium either kept rising or remained at a much higher level, and the internal dye kept leaking, as would be expected in a damaged cell. A separate question is why some cells have repaired successfully while other have not. As the authors claim, an increase in calcium is required for membrane repair. Indeed, urchin embryos in a low-calcium solution (B) did not respond to membrane damage with a calcium spike as did the cells in high calcium (A). An initial calcium spike in 3T3 fibroblasts, which were kept in low calcium (D), did occur but was only half of that in high calcium (C), and this difference may have accounted for their failure to reseal.

Does binding of any ligand to a receptor produce a biological response?

Antagonists are ligands that do not elicit a response.

Think of an everyday analogy to excitatory synaptic integration

Any kind of decision influenced by multiple pro- (excitatory) and con- (inhibitory) considerations. There are many such analogies in life. For example: I don't want to read a physiology lecture today because it is boring (inhibitory #1), I am having a headache after yesterday's party (inhibitory #2), and Helen invited me to play a game (inhibitory #3). On the other hand, I want to do well on a test next week (excitatory #1) and John asked me to help him understand the action potential (excitatory #2). So, I better study after all (a digital decision resulting from multiple analogue outputs).

Slide 12 shows a hydrostatic pressure preventing further migration of water to the left compartment. What other factor can terminate water accumulation there?

As water moves to the left compartment, it dilutes the osmolytes on the left side and concentrates them on the right side. That reduces the osmotic gradient.

In myelinated axons, action potentials are only generated in the nodes of Ranvier. Estimate whether the refractory period is long enough to prevent backward signal propagation in myelinated axons.

Assume that the distance between the nodes of Ranvier is 1 mm and the speed of action potential is 10 m/s. It would take (10-3 m)/(10 m/s) = 10-4 s to cross the distance between the two nodes. The refractory period lasts longer (~103 s) and would prevent backward travel of impulses within myelinated axons.

The graph shows the distribution of membrane potential along the nerve at two time points. Which potential was recorded first: A before B or B before A?

B before A

Do liquids with higher surface tension tend to bead or to spread?

Bead

Why could blood transfusion be ineffective for cobra bite?

Because of the slow dissociation rate, lowering its concentration in the blood will not wash off the toxin.

Find the molar concentration of a 5% solution if molecular weight of the solute is 100. Put a number in M without units (for example, 18.7)

Between 0.5 and 0.5 Step 1: 5% = 5 g/0.1 L = 50 g/L Step 2: 100 g/L = 1 M (by definition); 50 g/L = x; x = 0.5 M

Calculate the mechanical power (in W) required to lift 1 kg by 2 m in 0.2 seconds.

Between 95 and 105, I said 100

Explain how soap works

By providing connection between hydrophobic dirt and water

How is the mitochondrial potential formed?

By removal of protons from the matrix

What is the main difference between a pore and a channel?

Channels are more selective

What are the leak channels?

Channels that are open at all times

One characteristic of diffusion (A) depends on another characteristic (B) as a square root: 𝐴∝√𝐵. What are A and B? Why is it important?

Distance ∝ (Time)1/2. Because of that, diffusion spreads rapidly over short distances but slowly over long distances. The question allows an alternative answer: Distance ∝ (Diffusion coefficient)1/2

Explain the meaning of Ea

Ea and T

If kd for compound A is smaller than kd for compound B, what (if anything) can be said about their association and dissociation rates?

Each subsequent bound ligand decreases the affinity of the remaining unoccupied sites.

What are the other important conditions for log-term cell stability?

Electric neutrality, osmotic equilibrium, stable concentrations for each ion species.

A sodium-phosphate transporter moves three Na+ along with one HPO42-. Would it likely be a symport or antiport? Electroneutral or electrogenic?

Electrogenic. It is likely to be a cotransporter because otherwise a rapid accumulation of electric charge would result.

What is the mechanism of cholesterol transport?

Endocytosis

In the table from slide b4, the energy of photons is given in kcal/mol. But photons are not molecules; what does this unit mean?

Energy per 6*10^23 photons

Calcium binds troponin and initiates muscle contraction. Why does the removal of free calcium from the cytosol terminate muscle contraction?

Equilibrium between free and troponin-bound calcium shifts towards dissociation

If postsynaptic receptors were calcium-specific, would they be excitatory or inhibitory?

Excitatory (calcium influx causes depolarization)

Surface tension of liquid 1 is likely to be higher than that of liquid 2

False

The curve shows the viability of a virus treated with two drugs.

False

Compare bacteria placed in water with mammalian cells placed in 50 mM NaCl. Where would the mechanical pressure be smaller?

In mammalian cells

Doesn't the effect of the tetanus toxin seem counterintuitive?

Indeed, as an inhibitor of ACh release, tetanus toxin would be expected to weaken the muscles and not to increase their tension and rigidity. "The reason for this paradoxical enhancement of muscle action is that the greatest effect of these toxins is to inhibit synaptic transmission by inhibitory neurons in the spinal cord, neurons that would normally inhibit muscle contraction. The result is hyperstimulation of skeletal muscle contraction" (E.G. Moczydlowski. In: Boron and Boulpaep, Medical Physiology, 3rd ed.)

In what direction would Na+ be flowing through a large pore in a cell membrane?

Inside

Equilibrium potential for Mg2+ is 10 mV, the membrane potential is -10 mV. This situation favors magnesium transfer to ...

Inward

What does enzymatic energy coupling achieve?

It ensures that the energy released from ATP hydrolysis is not wasted in heat but used to drive the needed reaction.

Facilitated diffusion moves organic molecules down their chemical or electrochemical gradients. Why "or"?

It is electrochemical gradient if the molecules are charged, and chemical gradient if they are neutral.

What can you say about equilibrium potential for urea?

It is not defined because electric potential has no effect on uncharged urea.

Change the Figure on Slide 6 for Br-.

It will be the same curve, only the signs of will be positive

Change the Figure on Slide 6 for Ca2+.

It will be the same curve, only the values of will be halved.

Why do you think the graded potential is called so?

Its magnitude can change in small increments

Why do kon and koff have different units?

Kon[A][H+] expresses the rate of accumulation of AH and has to be in M/s. Therefore, the units of kon have to be (M/s)/(M*M) = 1/(M*s). The product koff[AH+] expresses the rate of decomposition of AH, which also has to be measured in M/s. Therefore, the units of koff are (M/s)/M = 1/s.

The protein NaV1.9 shown in this picture is embedded in a structure called...

Lipid draft

9. What is the difference between liposomes and micelles?

Liposomes have an interior lipid-free volume, micelles don't.

How would you interpret n < 1 in a Hill equation?

Logarithmic curves never cross zero. They are also symmetric around kd.

Why does the loss of ATP cause glutamate release?

Maintenance of a negative membrane potential requires energy.

Why is it called volume regulation and not osmolarity regulation?

Mammalian cells have no means of regulating their osmolarity: it is always the same as that of the environment (except during rapid transitions).

Photobleaching Discussion

Many native proteins are capable of rapid diffusion, and proteins from the photobleached area quickly disperse throughout the cell. In addition, fluorescent proteins that had not been exposed to light rapidly move into the photobleached area. The result is a rapid reestablishment of uniform fluorescence throughout the cell; it is less bright than in the beginning because the photobleached area was relatively large, and a significant fraction of all CFSE-labeled proteins became nonfluorescent. No fluorescence recovery was observed in the cell exposed to free radicals. The most likely explanation to this observation (which was confirmed by other experiments not shown here) is that free radicals caused alteration of protein structure and denaturation. Denatured proteins are less soluble and form large clumps and aggregates (as discussed in the lecture). And large aggregates diffuse much more slowly: firstly, because all large particles always diffuse slower and, secondly, because in the dense intracellular environment they may get caught on organelles and cytoskeletal filaments. Therefore, the photobleached spot persists for a much longer time. There seems to have been some confusion about protein "activity". By activity we usually mean the ability of a protein to perform the biological task it is designed for. The loss of activity is not necessarily identical to the loss of solubility and the slowing down of diffusion. Although denatured and aggregated proteins are most likely biologically inactive, the opposite is not necessarily true, and in any case, we cannot say anything about protein activity from this experiment.

This is Slide 13 from the lecture. I forgot to add a more detailed description for the traces labeled Na+ and K+: they are obviously not the membrane potential, which is a cumulative characteristic not applicable to individual ions. What characteristics of Na+ and K+ could these lines possibly represent?

Membrane permeabilities (or currents); the vertical scale for these curves is not shown

Which of the following structures are surrounded by a membrane: ribosomes, mitochondria, nuclei, nucleoli, cytoskeleton, lysosomes?

Mitochondria, nuclei, lysosomes.

Suppose you have the same mass per volume concentrations of small molecules X and of large molecules Y. What can you say about their molar concentrations?

Molar concentration of X is larger

What is the origin of surface tension?

Molecules on the surface have a higher energy than when surrounded by similar molecules

What channels are responsible for the regulatory volume decrease (RVD)?

Potassium and chloride

Why, in discussing brain edema, do we emphasize the effect of Na+ on the volume and not of H+; in other words, should not export of H+ shrink the cell and cancel the swelling resulting from import of Na+?

Most of intracellular H+ is bound to cellular proteins, whereas Na+ remains free and makes a greater contribution to osmolarity.

What type of ion channels must be activated to produce RVI? Same question for RVD.

Na and Cl in RVI; K or Cl in RVI.

What types of channels are responsible for postsynaptic activation?

Na+ or nonspecific cation channels

Which of these transporters and electrogenic?

Na+/glucose

What is the typical mechanism of the end-product inhibition?

Negative allosteric regulation

Does the equilibrium potential depend on permeability?

No

Strong acids bind hydrogen more strongly than do weak acids: is that correct?

No

What is 6x10-23?

No physical meaning, just a number (the Avogadro number is 6x10+23)

Would you expect the volume of a neuron to change significantly during an action potential?

No, because the relative changes in ion concentrations that accompany depolarization and repolarization are very small. The accumulation of sodium mentioned in the lecture must be accompanied by the loss of potassium, which gets dispersed in the extracellular fluid.

Would hydrophobic molecules form micelles?

No, only amphiphilic

Would a very hydrophilic substance easily cross a lipid layer?

No; It would not be able to enter a lipid layer.

Explain the origin of the relative refractory period.

Non-synchronous recovery of Na permeability

Make sure you can obtain the values for equilibrium dissociation constants and the characteristic binding/dissociation rates for the examples in slides HP3a - 9 to 12

Nothing certain because a lower kd (for example) may result from higher kon or lower koff

What types of cells produce myelin?

Oligodendrocytes in the brain and Schwann cells in the PNS

What type of molecule is Tyr-Gly-Gly-Phe-Leu?

Oligopeptide

Where is acetylcholinesterase located?

On postsynaptic membranes

If the membrane potential is -30 mV and the equilibrium potential for a negative ion is -10 mV, which way would the ion move passively?

Out of the cell

Equilibrium potential for bicarbonate is -15 mV, the membrane potential is -20 mV. This situation favors bicarbonate transfer to ... 9

Outward

How can a partial sodium flux across the membrane be measured?

Partial flux could be measured by adding a radioactive isotope of sodium to the medium and measuring its accumulation in the cell.

in discussions of osmosis, the word "semipermeable membrane" is often used. What does it mean?

Permeable for solvent, impermeable for at least some of the solutes

What are the two special effects observed in the cytosol?

Phase separation, macromolecular crowding

This graph is taken from Wikipedia (contributed apparently by a student). There is something very strange about it... What is it?

The curve indicated by the circles appears to be shifted to 100 times higher values along the horizontal axis.

How would the binding curve be affected if the receptors were upregulated?

The curve would not change if plotted as q against [L]. It would stretch vertically if plotted as the total amount of bound ligand against [L]

The sodium-calcium exchanger replaces three sodium ions for one calcium ion. Explain the reason for the 3:1 ratio.

The energy released by transporting a single Na+ ion into the cell is not large enough to move one calcium ion against its own, much steeper, electrochemical gradient. Three Na+ ions are needed.

Sketch the binding curve for kd = 50 nM in linear coordinates

The energy that must be added to the molecule for reaction to occur

During the relative refractory period, "stimulation has to be stronger" to produce an action potential. What does it mean exactly, a stronger stimulation?

The graded depolarization must reach higher (less negative) values.

If concentration of epinephrine in the blood is steadily rising, which organ will be affected first: the heart or the blood vessels?

The heart, because it responds to lower concentrations of the hormone

What terminates the Na+ current during an action potential?

The inactivation gate

A complex at an initial concentration 10 mM starts dissociating with Koff = 0.01 1/s. Roughly estimate the time at which its concentration will become 5 mM.

The product of kon[L][R] must represent the rate of accumulation of C. The latter is measured in M/s. Indeed, by substituting just the units into the formula, we obtain: 1M∙s∙M∙M= Ms, which is correct.

Heat in an animal with size d is produced throughout the body at a rate proportional to volume, Ad3. It is lost at a rate proportional to its surface area, Bd2. Thus, the body temperature will remain constant if Ad3 = Bd2. What can we conclude from it?

The rate of heat production (A) must be higher in a small animal (given the same B)

What triggers the outward potassium current during the action potential?

The rising of membrane potential

What is the significance of the initial segment? What biochemical feature enables it to perform its task?

The site where AP is initiated due to a high density of voltage-gated channels

What are the two main molecular parameters that determine reaction rates?

The slowest one in a chain of reactions

Why does myelin speed up signal propagation?

The time-consuming process of action potential generation occurs only at specific points along the axon.

If d is the length of crab's chela, 19.8*d3 could express:

The volume of its propodus

Why do we usually disregard hydrogen ions when calculating osmolarity?

Their free concentration is low

As with any binding site, the bound ligand ... is in equilibrium with the unbound form" (p. 160 VHP). Does this agree with what we learned in Unit 3?

This probably depends on the neurotransmitter and on the receptor. Equilibrium is achieved only after a certain time, which depends on kon and koff; and if the unbound neurotransmitter is continuously being removed, equilibrium may never be reached.

What is the stoichiometry of the Na,K ATPase?

Three Na+ out, two K+ in, one ATP hydrolyzed

What makes a molecule or an atom free radical?

Unfilled outer shell of electrons

Does RVI or RVD require activation of water channels?

Usually not. Swelling or shrinkage that precede RVD or RVI are possible because the membrane is already permeable to water. But aquaporins may accelerate volume recovery.

A semipermeable membrane separates compartment A containing pure water from compartment B containing a 1 M solution of KCl. Fill in the blanks in the following sentence: To prevent the diffusion of ______ from ______, a pressure of atm must be applied to compartment ________.

Water A to B 50 B

Under what conditions does an osmotic pressure difference generate mechanical pressure?

When the membrane is water-permeable and stiff

Is acetylcholinesterase involved in signaling by muscarinic receptors?

Yes

Do visible photons carry enough energy to produce ATP from ADP?

Yes (plants do that): 57 kcal/mol > 7 kcal/mol 4.

Can a non-catalyzed reaction be faster than a catalyzed one?

Yes, because at high concentrations of reagents, enzymatic rates level off but noncatalyzed reaction rates continue to increase.

Estimate the travel time of acetylcholine across a 20 nm-wide synaptic cleft using information from Unit 4. Compare it to the number given in VHP for the delay between the arrival of action potential and membrane potential changes in the postsynaptic cell.

You can easily find online the diffusion coefficient of acetylcholine (4x10-6 cm2/s). Then, using the diffusion time calculator, we find the time needed to travel a 20 nm distance: ~0.5 s. That is 400 times faster than the synaptic delay (p. 160), which tells us that other processes (receptor binding, channel activation) occur much slower and are rate-limiting.

A muscle has been producing a stationary tension (without moving) of 20 N for 10 seconds. How much mechanical work has it produced?

Zero (because no movement has been produced)

Which of the following would be legitimate units for kd: mole, g/L, M?

[L] axis is logarithmic and has no zero point

Sketch the binding curve for kd = 50 nM in semilogarithmic coordinates

[L] scale is linear and may start with [C] = 0

a) Estimate the concentration of norepinephrine at which the response reaches 50% (disregard that there are two curves). Express this concentration in M. (b) What is the concentration at the arrow level? Assume it is half a unit on the given horizontal scale. Express the concentration in nM. Solution

a) 10-6 = 1 M; 10-7 = 0.1 M; 0.13 units to the left would be 10-0.13 ~ 0.74 of that value, or 0.74*0.1 M = 0.074 M. b). Half a unit on a log scale corresponds to a 100.5 = 3.16-fold difference, so the concentration at the arrow is 3.16 times smaller than 0.1 M = 100 nM, which is 32 nM.

The curve A is for protein-ligand alone. A certain treatment has caused the curve to shift from A to B. This treatment could have been:

addition of an allosteric activator

What is the reason that free amino acids often have a larger impact on cell volume than do proteins?

amino acids are small

Reproduce the graph showing the action potential as (x) from memory

ch. 5

What tissue is it?

connective

Solute A has a larger reflection coefficient than solute B. That means that the membrane is more permeable to A than to B

false

How would you tell whether a binding curve represents cooperative binding or is drawn on a logarithmic scale?

g/L and M (they are the units of concentration)

Does acetylcholinesterase get on the way of acetylcholine receptor activation? (See Side 3.11a)

in theory, yes; however, the amount of acetylcholine in the cleft is initially so high, that it probably does not matter.

What property of ligand-receptor binding is most important in ensuring a maximal response every time ligand is present?

kd << [L]

What is the requirement for a ligand-receptor equilibrium binding that is supposed to achieve maximum response every time? (As in the case of acetylcholine).

kd must be higher than the typical [L]

What is the main molecular parameter that determines equilibrium concentrations?

kon can be limited to about 109 1/M*s by frequency of molecular collisions. There is no such limit for koff because dissociation does not require collisions.

Evaluate log(1/10) without a calculator

log(1/10) = -log(10) = -1

If protons were distributed passively, would you expect a higher, lower, or equal pH in the cytosol compared to that of the extracellular fluid? Assume that the membrane potential is negative.

lower

What is the concentration of [H+] at pH 2? pH 3? pH 2.5 (estimate)?

pH 9

What is the concentration of free protons in lemon juice?

pH = 2;

Summary for kinetics

q (receptor saturation) = L/(kd + L) kd = L at which half-saturation (q = 0.5) is achieved at equilibrium. • Small kd → tight binding, high affinity • Also, kd = koff/kon This makes sense because: large koff → fast dissociation, low affinity large kon → fast binding, high affinity • Time required for 50% complexes to dissociate is ≈ 1/koff • Time required for 50% complexes to form is ≈ 1/kon[L]

One atom has 37 protons, 37 electrons, and 85 neutrons. Another atom has 37 protons, 37 electrons, and 87 neutrons. They are:

same elements, different isotopes

What type of transport is symport?

secondary active

Which of these would form micelles in water?

soap

Both permeant and impermeant solutes contribute to osmolarity

true

What could the graph represent?

y - surface tension of water; x - amount of added detergent

This seems like a small voltage compared to the 110 V in the wall outlet, but it is applied to a very thin membrane" ... How thin? Estimate the field strength in the membrane and, for comparison, try to find some numbers for electric field strength in thunder clouds.

~50 mV/5 nm = 10 MV/m. For thunderclouds, I found the numbers around 1 MV/m. Sparks would fly through dry air at 3 MV/m.