[Campbell Biology P.186] Which of the following statements accurately describes a step in th... | Practice Question
Which of the following statements accurately describes a step in the sodium-potassium pump cycle as illustrated in Figure 7.16?
A: At step 2, 2 K+ ions bind to the pump, stimulating phosphorylation.
B: At step 3, phosphorylation reduces the pump's affinity for Na+, leading to their release, and simultaneously increases its affinity for K+.
C: At step 4, the pump gains a high affinity for K+ and binds 2 K+ ions from the extracellular side.
D: At step 5, the pump releases the phosphate group, which increases its affinity for K+.
Explanation
Figure 7.16, step 4 explicitly states: 'The new shape has a high affinity for K+; 2 K+ bind on the extracellular side, triggering release of the phosphate group.' This directly matches option C.