Question 1

A protein is found to extend all the way through the membrane of a cell. Describe this protein in terms of the location of particular types of amino acid side chains in its structure and its ability to move within the membrane.

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Question 2

Glycosphingolipids and cholesterol cluster together in membrane regions known as "_____." These microdomains are more _____ than the surrounding phospholipid-rich membrane due to a high content of _____ fatty acids. These regions are rich in proteins that are anchored to the membrane by covalently attached _____ and _____ groups and also those anchored by GPI linkage. Proteins aggregated in this fashion are often functionally related. Examples are (1) _____ proteins and (2) _____ proteins.

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Question 3

Describe two different ways a plant can adjust the components of its cell membranes to keep them as fluid as possible on a cold winter morning.

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Question 4

You are trying to isolate an enzyme that catalyzes the conversion of A $\rightarrow$ B, and you have a sensitive assay for this enzyme. After lysing open the cells, you find that the activity is associated with the membrane fraction, not the soluble fraction (which you throw away). You then follow the procedure shown below. Explain the sudden re-occurrence of activity at the end of your protocol.

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Question 5

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why?
Histidine ($\mu$M)
Transport ($\mu$M/min)
2.5
42.5
7
119
16
240
31
490
72
1,000

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Question 6

What are the similarities and differences between integrins, cadherins, and selectins?

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Question 7

(a) What kinds of forces or bonds anchor an integral membrane protein in a biological membrane? (b) What forces hold a peripheral membrane protein to the membrane? (c) What might one do to solubilize each of the two types of membrane proteins?

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Question 8

What is the major difference between gated and nongated ion channels? Give an example of two different gating signals.

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Question 9

Explain why nonpolar compounds are generally able to diffuse across biological membranes without the aid of a specific transport system.

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Question 10

What are three differences between ion channels and ion transporters?

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Question 11

a) What is meant by the transition temperature of a membrane? List the two characteristics of the fatty acids in a biological membrane that affect the transition temperature. Using $\downarrow$ or $\downarrow$, show in which direction an increase in these characteristics would change the transition temperature.

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Question 12

Describe a hydropathy plot for a hypothetical integral membrane protein with 3 transmembrane segments and containing 190 amino acids.

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Question 13

If the hydrophobic interior of a membrane were about 3 nm thick, what would be the minimum number of amino acids in a stretch of transmembrane $\alpha$ helix?

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Question 14

The bacterium E. coli can grow at 20 °C or at 40 °C. At which growth temperature would you expect the membrane phospholipids to have a higher ratio of saturated to unsaturated fatty acids, and why?

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Question 15

Compare and contrast symport and antiport. Which term best describes the transport system mediated by the Na⁺K⁺ ATPase?

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Question 16

Compare the structure and activity of a membrane transport protein that transports a polar substance across a membrane with a typical soluble enzyme. How are transporter and enzyme similar? How are they different?

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Question 17

Distinguish between simple diffusion (SD), facilitated diffusion (FD), and active transport (AT) across a membrane for the following questions. (More than one may be true.)
(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?

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Question 18

Explain the differences between integral and peripheral membrane proteins.

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Question 19

A plant breeder has developed a new frost-resistant variety of tomato that contains higher levels of unsaturated fatty acids in membrane lipids than those found in standard tomato varieties. However, when temperatures climb above 95 °F, this frost-resistant variety dies, whereas the standard variety continues to grow. Provide a likely explanation of the biochemical basis of increased tolerance to cold and increased susceptibility to heat of this new tomato variety.

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Question 20

Reagents A and B both react covalently with primary amino groups such as those of phosphatidylethanolamine. Reagent A permeates erythrocytes, but reagent B is impermeant. Both A and B are available in radioisotopically labeled form. Describe a simple experiment by which you might determine whether the phosphatidylethanolamine of erythrocyte membranes is located in the outside face of the lipid bilayer, the inside face, or in both.

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Quiz 11: Biological Membranes and Transport

A protein is found to extend all the way through the membrane of a cell. Describe this protein in terms of the location of particular types of amino acid side chains in its structure and its ability to move within the membrane.

Describe two different ways a plant can adjust the components of its cell membranes to keep them as fluid as possible on a cold winter morning.

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why? Histidine ( $\mu$ M) Transport ( $\mu$ M/min) 2.5 42.5 7 119 16 240 31 490 72 1,000

What are the similarities and differences between integrins, cadherins, and selectins?

(a) What kinds of forces or bonds anchor an integral membrane protein in a biological membrane? (b) What forces hold a peripheral membrane protein to the membrane? (c) What might one do to solubilize each of the two types of membrane proteins?

What is the major difference between gated and nongated ion channels? Give an example of two different gating signals.

Explain why nonpolar compounds are generally able to diffuse across biological membranes without the aid of a specific transport system.

What are three differences between ion channels and ion transporters?

Describe a hydropathy plot for a hypothetical integral membrane protein with 3 transmembrane segments and containing 190 amino acids.

If the hydrophobic interior of a membrane were about 3 nm thick, what would be the minimum number of amino acids in a stretch of transmembrane $\alpha$ helix?

The bacterium E. coli can grow at 20 °C or at 40 °C. At which growth temperature would you expect the membrane phospholipids to have a higher ratio of saturated to unsaturated fatty acids, and why?

Compare and contrast symport and antiport. Which term best describes the transport system mediated by the Na⁺K⁺ ATPase?

Compare the structure and activity of a membrane transport protein that transports a polar substance across a membrane with a typical soluble enzyme. How are transporter and enzyme similar? How are they different?

Explain the differences between integral and peripheral membrane proteins.

Quiz 11: Biological Membranes and Transport

A protein is found to extend all the way through the membrane of a cell. Describe this protein in terms of the location of particular types of amino acid side chains in its structure and its ability to move within the membrane.

Describe two different ways a plant can adjust the components of its cell membranes to keep them as fluid as possible on a cold winter morning.

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why? Histidine ( μ\muμ M) Transport ( μ\muμ M/min) 2.5 42.5 7 119 16 240 31 490 72 1,000

What are the similarities and differences between integrins, cadherins, and selectins?

(a) What kinds of forces or bonds anchor an integral membrane protein in a biological membrane? (b) What forces hold a peripheral membrane protein to the membrane? (c) What might one do to solubilize each of the two types of membrane proteins?

What is the major difference between gated and nongated ion channels? Give an example of two different gating signals.

Explain why nonpolar compounds are generally able to diffuse across biological membranes without the aid of a specific transport system.

What are three differences between ion channels and ion transporters?

Describe a hydropathy plot for a hypothetical integral membrane protein with 3 transmembrane segments and containing 190 amino acids.

If the hydrophobic interior of a membrane were about 3 nm thick, what would be the minimum number of amino acids in a stretch of transmembrane α\alphaα helix?

The bacterium E. coli can grow at 20 °C or at 40 °C. At which growth temperature would you expect the membrane phospholipids to have a higher ratio of saturated to unsaturated fatty acids, and why?

Compare and contrast symport and antiport. Which term best describes the transport system mediated by the Na+K+ ATPase?

Compare the structure and activity of a membrane transport protein that transports a polar substance across a membrane with a typical soluble enzyme. How are transporter and enzyme similar? How are they different?

Explain the differences between integral and peripheral membrane proteins.

Transport of histidine into a bacterial cell was measured at several different histidine concentrations. Does histidine uptake operate by passive or facilitated transport, and why? Histidine ( $\mu$ M) Transport ( $\mu$ M/min) 2.5 42.5 7 119 16 240 31 490 72 1,000

If the hydrophobic interior of a membrane were about 3 nm thick, what would be the minimum number of amino acids in a stretch of transmembrane $\alpha$ helix?

Compare and contrast symport and antiport. Which term best describes the transport system mediated by the Na⁺K⁺ ATPase?