BIOL 3P34 Lecture Notes - Lecture 7: Nernst Equation, Farad, Membrane Potential

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coffeealpaca216

10 Oct 2016

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No ion species is distributed evenly across the membrane. Na+ and cl- is more concentrated on the outside. K+ and organic anions are more concentrated on the inside. Consider a glial cell (and next a neuron: glial cell: has non-gated channels selective only for k+ Driving force on the ion is both from the electrical and concentration gradient (called the electrochemical driving force) The electric gradient pushes k+ back into the cell. Outward movement of k+ leaves inside surface more . K+ moves along its concentration gradient out of the cell. Diffusion of k+ continues until the electric gradient has an effect equal but opposite to the concentration gradient. **this is known as the equilibrium potential for k+ There is no net flow of k+ at ek. For a cell permeable to only k+ (glial cell) the resting membrane potential settles at the equilibrium potential.

Related Questions

1) Look up the structures of the following molecules. For each carbon atom, indicate its oxidation state. Calculate the average oxidation state of the carbon atoms in each.

Glucose

Pyruvic acid

Citric acid

Oxaloacetic acid

Carbon dioxide

2) Consider the following hypothetical cell. Initially, the cell has an equal number of positive and negative charges (cations and anions) on either side of its plasma membrane (extracellular, intracellular). There are equal concentrations of Na+, K+, and Cl- on either side of the plasma membrane. Consider the effects of the following events, in sequence, upon the ion concentrations and charge distributions (membrane electrical potential).

A. NKA proteins are activated in the plasma membrane. How does this affect the ions and the membrane electrical properties?

B. A small number of K+ channels open in the plasma membrane. How does this affect the ions and the membrane electrical properties?

C. An even larger number of Na+ channels open in the plasma membrane.

D. The Na+ and K+ channels close. Cl- channels open.

3) Pancreatic juice contains approximately 150 mM Na+. How do these Na+ ions contribute to the absorption of amino acids and sugars? Explain how 100% of an amino acid can be absorbed from the small intestines. HINT: intestinal epithelial cells have NKA, numerous cotransporters (symporters) and facilitated diffusion proteins.

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

Cellular biology answer check. please check if my answers arecorrect or not.

1) The concentration of ions inside a cell is the same as theirconcentration outside of the cell. True or false? (i chose falsesince having equilibrium inside a cell is bad)

2) Membrane transport proteins...

a)...transport membrane potentials between cells

b)	...transport membranes from the ER to the Golgi

c)	...are made up of phospholipids

d)	...transport molecules across membranes

i chose d

3)The electrochemical gradienttakes into account:

a)	The concentration of solutes on either side of themembrane.

b)	The overall charge on either side of the membrane.

c)	Both of these.

i chose C. (although i am sure that overall charge matters, Iwasn't sure if concentration of solutes are taken account.)

4) If no energywere expended by an animal cell:

a)	Both gradients would be depleted

b)The K+ gradient would maintain itself.

c)	None of these

d)	The Na+ gradient would maintain itself.

I chose d) mainly because I think Na+ gradient exist in animalcell and not K+ gradient.

5) Which of the following is a true statement aboutactin?

a)	Once actin has polymerized, it never depolymerizes.

b)	Actin is a transmembrane protein.

c)	Actin can form branched networks.

d)	Actin filaments are organized into hollow tubes.

I chose c. can't explain why.

6)Ion channels:

a)	Form a hydrophobic channel through the membrane

b)	Have filters that let sugars through

c)	Are selective for particular ions (only the

taupeshark376

BIOL 3P34 Lecture Notes - Lecture 7: Nernst Equation, Farad, Membrane Potential

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