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Biological Sciences

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Plasma Membrane and Transport

Question
6 out of 7
 

A certain transmembrane protein has its amino terminus at the exterior of the cell, carboxy terminus in the cytoplasm and everything in between embedded in the membrane. Which of the following statements is true?

A The amino terminus must be hydrophobic.
B Much of the protein is hydrophobic.
C The protein probably transports sodium.
D The protein must have a neutral charge.
Ans. B

This is the best answer of the choices given. The amino terminus is probably not hydrophobic (choice A) as it is located extracellularly, where there is a great abundance of water. We are given no good reason to assume the protein transports sodium, so choice C is not the best. Transmembrane proteins do not necessarily carry any particular charge, and do not have to be neutral, so answer D is not correct. Answer B relies on your knowledge of the composition of the cell membrane, specifically the lipid component. For a protein to span the membrane, it must be compatible with the environment of the membrane, which is hydrophobic.


Plasma Membrane and Transport Flashcard List

7 flashcards
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The sodium-potassium (Na+/K+) pump is a critical element for many processes of the cell. For example, it is responsible for a neuron’s ability to transmit messages. The pump transports sodium out of the cell using energy from ATP (the extracellular matrix has a higher concentration of sodium than the intracellular space). The pump also imports potassium, which is more highly concentrated inside the cell than outside. The pump is an example of a cotransport system. Sodium binds to the transport protein and is exported. Once the sodium ion is released, a potassium ion binds and is transported into the cell (actually, for every three sodium ions pumped out of the cell, two potassium ions are pumped in). Thus, a sodium and potassium gradient are established and maintained across the membrane. Since the ions are being transported in opposite directions, this type of pump is called antiport. The sodium gradient established by the Na+/K+ pump can be used in many ways. Another cotransport system, the Na+/glucose pump, is active in human gut epithelial cells, and results in the uptake of glucose. Due to its concentration gradient, sodium diffuses into the cells through the Na+/glucose pump and transports glucose with it (this is called symport). The glucose is processed by the cells and can be used to generate energy. If a sodium gradient is formed, whereby there is a vast excess of sodium outside the cell, which is the most likely result?A An electrical gradient is also formed.B A magnetic gradient is also formed.C Other positively charged ions will enter the cell.D Negatively charged ions will enter the cell.
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The sodium-potassium (Na+/K+) pump is a critical element for many processes of the cell. For example, it is responsible for a neuron’s ability to transmit messages. The pump transports sodium out of the cell using energy from ATP (the extracellular matrix has a higher concentration of sodium than the intracellular space). The pump also imports potassium, which is more highly concentrated inside the cell than outside. The pump is an example of a cotransport system. Sodium binds to the transport protein and is exported. Once the sodium ion is released, a potassium ion binds and is transported into the cell (actually, for every three sodium ions pumped out of the cell, two potassium ions are pumped in). Thus, a sodium and potassium gradient are established and maintained across the membrane. Since the ions are being transported in opposite directions, this type of pump is called antiport. The sodium gradient established by the Na+/K+ pump can be used in many ways. Another cotransport system, the Na+/glucose pump, is active in human gut epithelial cells, and results in the uptake of glucose. Due to its concentration gradient, sodium diffuses into the cells through the Na+/glucose pump and transports glucose with it (this is called symport). The glucose is processed by the cells and can be used to generate energy. A poison was found that prevents binding of sodium to the Na+/K+ pump. What would be the most likely consequence of this poison? I. Potassium would not be pumped into the cell II. Glucose would not be pumped into the cell III. Nerve impulses would not be transmittedA I onlyB III onlyC I and IID I, II and III
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