BIO 327 Lecture Notes - Lecture 13: Cytosol

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brownfly906

18 May 2016

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Na+ most plentiful outside the cell, k+ most abundant inside: the high of na+ outside the cell is electrically balanced chiefly by extracellular cl, high concentration of k+ inside is balanced by negatively charged organic/inorganic ions. Two main classes of membrane transport proteins: transporters || transfers only those molecules/ions that fit into specific binding sites. After a meal, glucose is plentiful and it binds to the transporter"s external binding sites to change protein conformation. When hungry, hormone glucagon stimulates liver cells to produce large amounts of glucose by breakdown of glycogen: channels || only based on size and electric charge. Electrical changes are mediated by alterations in the permeability of membrane to ions: in resting stage, the negativity of the cell is balanced by k, membrane contains a set of k+ leak channels. When these are open, k+ flows out creates voltage difference.

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

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

BIO 327 Lecture Notes - Lecture 13: Cytosol

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