BioChem Ch 10

Shown above is a schematic diagram of the E. coli leader peptidase (Lep) which has several basic amino acids in a cytoplasmic loop. Propose a mutant of Lep that would be a test of the "inside positive" rule for the orientation of proteins in membranes.

(+), (+), terminal, reversed

What is the contribution of Ca2+ to the membrane potential?

-92.2 mV

A. Facilitated diffusion is a type of _______. B. Structure A is a _____. C.Structure B is a _____.

A. passive transport B. solute C. transport protein

Hydrogenation of a monounsaturated fatty acid yields a saturated fatty acid. Oleic acid, CH3(CH2)7CH=CH(CH2)7CO2H is a monounsaturated fatty acid. Predict the product of its hydrogenation:

CH3(CH2)16COOH

Which of the following are sources of cholesterol for the body?

Eating meats and eggs Drinking milk Synthesis in the liver from carbohydrates Synthesis in the liver from fats

The amino alcohol is a polar part of a glycerophospholipid and, thus, a hydrophilic (water-loving) section of the molecule. What is the common name for the amino alcohol present in the glycerophospholipid shown in Part A?

Ethanolamine

Look again at the molecular model of the K+ channel KcsA from Streptomyces lividans. In what state are the K+ ions when they reside in the spacious 10-angstrom diameter cavity, prior to translocating through the selectivity pore?

Fully hydrated

The epidermal growth factor receptor has a single transmembrane helix. Find it in this partial sequence:...RGPKIPSIATGMVGALLLLVVALGIGILFMRRRH...

MVGALLLLVVALGIGILFM

Explain why αα-helices are most commonly observed in transmembrane protein sequences when the distance from one side of a membrane to the other can be spanned by significantly fewer amino acids in a β-strand conformation.

The helical conformation spanning the bilayer satisfies all the main-chain H-bond donors and acceptors within the helix, whereas the strand would be unable to form intramolecular H-bonds to satisfy it.

Sphingomyelin contains a fatty acid linked by an ________ bond and phosphocholine linked via the C-3 hydroxyl group of sphingosine.

amide

Suppose, however, that an action potential is artificially triggered at the point indicated by the red arrow. In what sequence would the action potential pass through points (a), (b), and (c)?

b,a,c

Review the mammalian voltage-dependent K+ channel of the Shaker family. Closing of the channel in response to membrane depolarization relies primarily on essential arginine residues located where?

in the extracellular voltage sensor domain

Which class of lipids does the following molecule belong to?

steriods

Conserved histidine, asparagine (blue), and cysteine (yellow) residues are present on the surface of the water channel. Which of the following is LEAST likely to hydrogen-bond with a water molecule?

the R group (side chain) of the cysteine

B. Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. C.Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers.

B. lipids, water, carbon dioxide, oxygen C. picture

A. A semipermeable membrane is placed between the following solutions.

Solution A: 1.4%

B. A semipermeable membrane is placed between the following solutions.

Solution D. 12.4%

Which side of the organelle membrane is positive, and which is negative?

The inside of the organelle is negative with respect to the outside.

Drag the labels onto the flowchart to show the sequence of events that occurs once the membrane potential reaches threshold. You may use a label once or not at all.

membrane potential reaches threshold --> many voltage gated Na+ channels open --> Na+ ions rush into the cell --> membrane potential rises (depolarizes) rapidly

Suggest a saturated fatty acid that should melt below 30

n-octanoic acid

Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply.

-The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane -The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane -The electrochemical gradient is larger for Na+ than for K+

Aquaporin-1 exists in the cell membrane as a tetramer. Each monomer is a water channel that can hold 4 molecules of water at a time. How many water molecules would be present in a complete aquaporin complex in the membrane of a red blood cell at one time?

16

Linolenic acid has cis double bonds with the formula CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH. Write out the abbreviated systematic numbering for this fatty acid.

18:3cdelta9,12,15

Calculate the minimum number of residues in an α-helix required to span this distance. (30 A thick)

30/1.5= 20 residues

Calculate the minimum number of residues in a β-strand required to span this distance.

30/3.3= 9 residues

How many H2 molecules are needed to completely hydrogenate the following triacylglycerol molecule?

4

A. Which of these is NOT a lipid? B. This figure is an example of a(n) _____. C. Which of these is a phospholipid? D. Which of these is rich in unsaturated fats? E. A function of cholesterol that does not harm health is its role _____.

A. RNA B. saturated fat C. picture D. Olive Oil E. as a component of animal cell membranes

A.) A neuron's nucleus is located in its _____. B.) A nerve impulse moves toward a neuron's cell body along _____. C.) A nerve impulse moves away from a neuron's cell body along _____. D.) An impulse relayed along a myelinated axon "jumps" from _____ to _____. E.) Axons insulated by a(n) _____ are able to conduct impulses faster that those not so insulated. F.) What type of cell makes up the myelin sheath of a motor neuron? G.) What part of a neuron relays signals from one neuron to another neuron or to an effector?

A. cell body B. dendrites C. axons D. node of Ranvier.... node of Ranvier E. myelin sheath F. Schwann cells G. synaptic terminal

A.) Which term describes the difference in electrical charge across a membrane? B.) Resting neurons are most permeable to which of the following ions? C.) True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane. D.) Which channel is mainly responsible for the resting potential of a neuron? E.) Which term describes an electrical signal generated by neurons? F.) Which channel maintains the concentration gradients of ions across a neuronal membrane? G.) What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?

A. membrane potential B. K+ C. False D. Potassium leak channel E. action potential F. The sodium-potassium pump moving Na+ ions out and K+ ions in. G. The sodium channel opens, and Na+ ions flow in.

A. What is the function of Structure E? B. Identify Structure D. C. Identify Structure A.

A. stabilization of the phospholipids B. phospholipid bilayer of membrane C. glycoprotein

A. Structure A is a(n) _____. B. Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?

A. transport protein B. B,C, and D

A.) In the absence of a membrane potential. B.) When the transport is opposed by a membrane potential of 70 mV.

A.) 29.7 kJ/mol B.) 36.4 kJ/mol

An action potential moves along an axon due to the sequential opening of voltage-gated Na+ channels. The diagram below shows voltage-gated Na+ channels separated by a short distance in the plasma membrane of an axon. Initially (left panel), only channel (a) is open. Within a very short time (right panel), channel (b) also opens.

After the first channel opens, the movement of many types of ions (both inside and outside the cell) alters the distribution of charges near the second channel, causing it to open.

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes.

crenation: A, D, E hemolysis: C, B

In eukaryotic nerve cells, K+ concentrations at rest are __________.

higher inside the cell than outside the cell

The strength of a stimulus (for example, whether you feel a slight pain versus an intense pain) determines the number of action potentials sent along an axon. As the graphs show, a strong stimulus produces more action potentials spaced more closely together than a weak stimulus.

how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential

View the side groups in the model, with attention to the water channel. What do the numerous aromatic rings on the surface of the channel suggest about the chemical properties of the channel?

the channel will have significant hydrophobic properties

Aquaporins allow water to pass through the channel but prevent other solutes and ions from also crossing the membrane. Protons can move with water using the same hydrogen bonding facillitated movement. What PREVENTS protons from passing through the water channel?

the chemical properties of the amine groups of the two conserved asparagines in the channel.

What best explains how Na+ ions are excluded while K+ ions are allowed to pass through the selectivity channel?

the higher stability of teh hydrated form of Na+ compared with teh dehyrated form of Na+ within the selectivity channel

List two differences you would expect to see in the composition of lipids in the E. coli membrane when the cells are incubated at 25 ∘C compared to incubation at 37 ∘C.

the membranes of cells grown at 25 degrees would have shorter fatty acids with a greater number of cis-double bonds compared to the membranes of cells grown at 37 degrees.

What prevents glycerol from passing through the water channel?

the narrow diameter (~2.8 A) of teh selectivity channel

Examine the molecular model of the K+ channel KcsA from Streptomyces lividans. Regions with charged amino acids can be found primarily in all of the following locations, EXCEPT in __________.

the transmembrane region

In each case, will hydrolysis of 1 mole of ATP suffice to drive the transport of 1 mole of ion, assuming pH = 7.4 and the following cytoplamic concentrations: ATP = 4.6 mM, Pi = 5.10 mM, ADP = 310 μM?

yes, for both cases