Uniporters and ion channels support facilitated transport across cellular membranes. Although both are examples of facilitated transport, the rates of ion movement via an ion channel are roughly 104- to 105-fold faster than the rates of molecule movement via a uniporter. What key mechanistic difference results in this large difference in transport rate? What contribution to free energy (ΔG) determines the direction of transport?
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Uniporters and ion channels support facilitated transport across cellular membranes. Although both are examples of facilitated transport, the rates of ion movement via an ion channel are roughly 104- to 105-fold faster than the rates of molecule movement via a uniporter. What key mechanistic difference results in this large difference in transport rate? What contribution to free energy (ΔG) determines the direction of transport?
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- Uniporters and ion channels support facilitated transport across cellular membranes. Although both are examples of facilitated transport, the rates of ion movement via an ion channel are roughly 104 - to 105 -fold faster than the rates of molecule movement via a uniporter. What key mechanisticdifference results in this large difference in transport rate?What contribution to free energy (ΔG) determines the direction of transport?Name the three classes of membrane transport proteins. Explain which one or ones of these classes is able to move glucose and which can move bicarbonate (HCO3 −) against an electrochemical gradient. In the case of bicarbonate, but not glucose, the ΔG of the transport process has two terms.What are these two terms, and why does the second not apply to glucose? Why are cotransporters often referred to as examples of secondary active transport?Name the three classes of membrane transport proteins. Explain which one or ones of these classes is able to move glucose and which can move bicarbonate (HCO3−) against an electrochemical gradient. In the case of bicarbonate, but not glucose, the ΔG of the transport process has two terms. What are these two terms, and why does the second not apply to glucose? Why are cotransporters often referred to as examples of secondary active transport?
- For each type of membrane transport, know the following:– Is a transporter protein required? If so, what type?– Is there an energy requirement, and if so, what is the energy source?– What is the relative rate of solute transport based on molecule type? On concentration gradient?– What are examples of the types of solutes transported by carriers and channels?In the following situations, what is the free energy change if 1 mole of Na+is transported across a membrane from a region where the concentration is1 μM to a region where it is 100 mM?(Assume T = 37 °C.) (a) In the absence of a membrane potential. (b) When the transport is opposed by a membrane potential of 70 mV. (c) 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 cytoplasmic concentrations: ATP = 4.60 mM, Pi = 5.10 mM, ADP = 310 μM?Cells transporting substances across their membranes is essential. Choose TWO of the following types of cellular transport. ๏osmosis ๏active transport ๏facilitated diffusion ๏endocytosis / exocytosis (a)For each type of transport you choose, describe the transport process. Explain how the organization of cell membrane plays a role the movement of specific molecules across membrane. (b)Using the same transport types, identify a specific cell that utilizes that type of transit (i.e. one cell for each transport type, or two different cell examples), and detail a substance that is transferred. (c)A typical human lymphocyte has a radius of about 10 μm, while a typical bacterium (e.g., S. pneumoniae) has a radius of about 1 μm. Assuming that both cell types are perfectly spherical, compare and contrastthe transport mechanisms for each of these cells.
- In the situations described below, what is the free energy change if 1 mole of Na* is transported across a membrane from a region where the concentra- tion is 1 µM to a region where it is 100 mM? (Assume T = 37 °C.) (a) In the absence of a membrane potential. (b) When the transport is opposed by a membrane potential of 70 mV. (c) In cach case, will hydrolysis of 1 mole of ATP suffice to drive the trans- port of 1 mole of ion, assuming pH 7.4 and the following cytoplamic concentrations: ATP= 4.60 mM, P = 5.10 mM, ADP = 310 µM?Distinguish between simple diffusion (SD), facilitated diffusion (FD), and active transport (AT) across a membrane for the following questions. (a) Which processes are energy dependent? (b) Which processes need some kind of carrier protein(s)? (c) Which processes can be saturated by substrate? (d) Which processes can establish a concentration gradient? (e) How much energy does it take to transport an uncharged substrate in, if its starting inside concentration is 10-fold greater than outside?Glucose transport across cell membranes varies depending upon blood glucose levels. When glucose levels are high, glucose transport is accomplished via membrane transporters. When glucose concentrations are low, the transport of glucose across the membrane is dependent upon the sodium ion concentration. What types of transport is observed for glucose? A)simple diffusion at high [glucose], secondary active transport at low [glucose] B)facilitated diffusion at high [glucose], secondary active transport at low [glucose] C)simple diffusion at high [glucose], primary active transport at low [glucose] D)facilitated diffusion at high [glucose], primary active transport at low [glucose]
- Below find the structures for ibogaine and cocaine. Ibogaine and cocaine inhibit the dopamine active transporter (DAT). This transporter is a secondary active transporter, and depends on the primary active transporter Na+/K+ ATPase. Ibogaine had a Kι = 2 μM, and cocaine a Kι = 0.64 μM respectively. (a) Define secondary active transport. (b) Is ibogaine an effective treatment for cocaine based on DAT binding?Liver cells are in contact with the blood and exchange a variety of substances with the blood plasma (the noncellular part of blood). The concentration of water is equal in the cytoplasm of liver cells and in the blood plasma. Explain this observation in terms of membrane permeability and transport mechanisms. Animal cells typically maintain a higher concentration of Na+ outside the cell and a higher concentration of K+ inside the cell via the Na+-K+ pump. The drug ouabain inhibits the activity of the Na+-K+ pump. A nerve cell is incubated in ouabain. Predict what will happen to the concentrations of Na+ and K+ inside and outside the nerve cell as a result.In Chapters 11 & 12, the following examples of membrane transport proteins are given. Fill out the table with the correct answer for that particular transport protein. Type of transport protein (channel or carrier/transporter?) K* leak channel glucose transporter bacteriorhodopsin Na-K pump glucose-Na symport Na-H exchanger Performs active or passive transport? Energy source for movement of solute(s) or ion(s) Direction of movement of solute(s) or ion(s) with respect to the electrochemical gradient Na K* Na glucose Na H' Direction of movement of solute(s) or ion(s) with respect to the membrane crossed Na K₁ Na' glucose Na H' Is the protein a uniport, symport, antiport, or none of the above?