L18 Questions
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Publicado: 15 de febrero de 2013
REVIEW QUESTIONS FOR TOPICS COVERED IN LECTURE 18
1. In comparing proteins modified with palmitoyl (16:0 fatty acid), myristoyl (14:0 fatty acid), orprenylgroups (methylated fatty acids), which preferentially partition to lipid rafts? Outside of lipid rafts?
What is the relationship between fatty acid length and strengthof membrane binding?
2. In studying the primary sequence of a newly discovered membrane protein, you note two hydrophobic
regions in which a stretch ofhydrophobic amino acids is interrupted by a single asparagine residue.
This protein functions to transfer polar molecules across the membrane. What do you think the role ofthe two asparagines are? How could you test this hypothesis?
3. Why is the double reciprocal plot a popular way to graph transporter activity when determiningwhether
a patient might have a protein mutation leading to decreased transport?
4. At pH 7, tryptophan crosses a lipid bilayer at about one-thousandth the rate ofindole (shown), a closely related compound. Suggest an explanation for this
observation.
5. How might you determine whether a lipid flippase is a primary activetransporter or a secondary active
transporter based on either a) its protein sequence or b) comparing its activity in isolated membranes vs.
intact cells?
6. Youare studying the uptake of L-leucine by epithelial cells of the mouse intestine. Measurements of the
rate of uptake of L-leucine and several of its analogs, withand without Na+ in the assay buffer, yield the
results given in the table. What can you conclude about the properties and mechanism of the leucine
transporter?
1. In comparing proteins modified with palmitoyl (16:0 fatty acid), myristoyl (14:0 fatty acid), orprenylgroups (methylated fatty acids), which preferentially partition to lipid rafts? Outside of lipid rafts?
What is the relationship between fatty acid length and strengthof membrane binding?
2. In studying the primary sequence of a newly discovered membrane protein, you note two hydrophobic
regions in which a stretch ofhydrophobic amino acids is interrupted by a single asparagine residue.
This protein functions to transfer polar molecules across the membrane. What do you think the role ofthe two asparagines are? How could you test this hypothesis?
3. Why is the double reciprocal plot a popular way to graph transporter activity when determiningwhether
a patient might have a protein mutation leading to decreased transport?
4. At pH 7, tryptophan crosses a lipid bilayer at about one-thousandth the rate ofindole (shown), a closely related compound. Suggest an explanation for this
observation.
5. How might you determine whether a lipid flippase is a primary activetransporter or a secondary active
transporter based on either a) its protein sequence or b) comparing its activity in isolated membranes vs.
intact cells?
6. Youare studying the uptake of L-leucine by epithelial cells of the mouse intestine. Measurements of the
rate of uptake of L-leucine and several of its analogs, withand without Na+ in the assay buffer, yield the
results given in the table. What can you conclude about the properties and mechanism of the leucine
transporter?
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