BLG 311 Lecture Notes - Lecture 11: Neuroglia, Symporter, Potassium Channel

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viridianmacaw215

8 Feb 2018

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Chapter 11: membrane transport of small molecules and the electrical properties of membranes. Do not form a continuous pore or hole across the membrane: think of a revolving door; binding of solute -> change -> release on other side of membrane, channels. In aqueous pores, continuous pores throughout the membrane: accepts only molecules of a specific size. Active transport: active transport has a primary and secondary class, primary class uses atp or light to function, secondary class uses a coupled transport, example: the plasma membrane na+-glucose symporter. Binding of na+ to the symporter causes a conformational change: this change in shape increases binding of glucose to outside of transporter, transport of glucose against its concentration gradient requires. Na+ electrochemical gradient: active, secondary transport (coupled, the na+-glucose symporter is found in the plasma membrane of epithelial cells in kidney and intestines. Purpose is to recover glucose from feces or urine. [na+] gradient is maintained by na+/k pump (primary active transport)

Related Questions

1 Which of the following statements is false?

(a) CO₂ and O₂ can diffuse freely across the cell membranes.

(b) The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.

(d) Cells expend energy in the form of ATP hydrolysis to maintain ion concentrations that differ from those found outside the cell.

2 Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell?

(a) Na⁺

(b) K⁺

(d) Cl^â

3 Pumps are transporters that are able to harness energy provided by other components in the cells and drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________.

(a) active transport.

(b) free diffusion.

(d) passive transport.

harlequinbuffalo618

1. The plasma membrane of liver cells contains a glucose uniportthat transports glucose by facilitated diffusion. When the[glucose] is higher inside the liver cell than the [glucose]outside the liver cell, the glucose uniport will

A. couple the transport of glucose out of the cell to thehydrolysis of ATP

B. couple the transport of glucose into the cell to thehydrolysis of ATP

C. switch to a closed conformation, allowing no transport ofglucose

D. transport glucose out of the cell by passive transport

E. transport glucose in of the cell by passive transport

2. Unlike the positive charged ion shown in the middle diagramof figure 11-4B, K+ is higher in concentration inside the cell. Howwill the membrane potential of a cell at rest (shown in both themiddle and right-hand diagrams of Figure 11-4B) affect theelectrochemical gradient for K+?

A. The membrane potential will increase the electrochemicalgradient

B. The membrane potential will decrease the electrochemicalgradient

C. The membrane potential will have no effect on theelectrochemical gradient

3. Which of the following proteins carries out activetransport?

A. gluclose symport

B. Bacteriorhodopsin

C. ABC transporter

D. NA K pump

E. All of the above

4. Aquaporin will not transport Na+ ions because

A. Two asparagine residues in the channel prevent the passage ofNa+ ions by binding the oxygen of each water molecule as it passesby

B. Na+ ions are repelled by the positive charges at the entranceto the channel

C. Na+ ions cannot make contact with the carbonyl (C=O) groupson all four sides of the channel

D. The passage of Na+ ions is energetically unfavorable becauseone side of the channel is hydrophobic in nature

5. The acetylcholine receptor is different from other channelproteins we have discussed, such as the K+ leak channel,because

A. The acetylcholine channel is composed of a single polypeptiderather than multiple subunits

B. The acetylcholine channel transports Na+ ions against theconcentration gradient for sodium

C. The acetylcholine channel has a much smaller diameter thanother channel proteins

D. The acetylcholine channel transports ions with theirassociated shell of water molecules

E. The acetylcholine channel is always open, and never switchesto a closed conformation

6. After opening briefly along the axon of a neuron,voltage-gated ion channels switch to an inactivated conformationthat slowly returns to the original closed conformation of theprotein. This slow change in conformation, requiring about amillisecond, is important because

A. all of the ions that were transported across the membranewhen the ion channels were open must be actively transported backto the other side of the membrane, restoring the originalconcentration gradient, before the ion channels can open again

B. ATP hydrolysis is necessary to drive this energeticallyunfavorable change in conformation

C. it prevents the action potential from reversing direction andtraveling back toward the cell body of the neuron

D. the channel protein must be dephosphorylated in order tocomplete the transport process and return to the originalnonphosphorylated conformation

limeelephant476

It's a pretty elementary concept, and when I first learned of itI don't think I had the foundations to even think of such aquestion, but I found myself the other day thinking about theamphipathic nature of the phospholipids in the plasma membrane andwhy it might be that lipid-soluble molecules don't stay in betweenthe layers (of the bilayer).

I know that simple diffusion is a response to a concentrationgradient, but consider a case where equilibrium is being restoredand lipid-soluble molecules are diffusing from whateverextracellular matrix through the membrane and into the cytosol.Towards the end of this process, when equilibrium is nearlyrestored and the last few molecules are making their way into thecell, the rate of diffusion for these last couple molecules will beslower than those that diffused when the concentration differencewas greater. Since the polar heads on the outside and inside of thebilayer are hydrophilic but the inner part, where the fatty acidtails are, is hydrophobic, what drives a molecule to leave thecozy, accepting, lipophilic environment of the middle (of thebilayer) to cross through the cytosolic-side rejecting polar headsand enter the cytosol?

I understand that initially these molecules were moving into thecell in response to a difference in intracellular vs extracellularconcentration, but I'm asking whether we would ever see a casewhere the gradient is nearly zero and a molecule in transit simplydecides to reside in between the layers instead of crossing all theway into the cell; as if moving through the cytosolic polar headside is not worth the effort to reduce a nearly-zero gradient tozero.

Please ask me if I can clarify my question in any way -- I'mfinding it difficult to phrase. I asked my professor (who has herdoctorate in toxicology & pharmacology) and she understood whatI was asking but didn't have an answer.

BLG 311 Lecture Notes - Lecture 11: Neuroglia, Symporter, Potassium Channel

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