In the figure below is depicted a membrane and an integral membrane protein called a Na+-K+ ATPase.
In the figure are two triangles that indicate concentration gradients of Na+ and K+ across the membrane.
The Na+-K+ ATPase will transport Na+ ions against its concentration gradient and K+ ions against its concentration gradient.
The series of steps depicted below are as follows:
The figure below represents a sequence of events that occur with the same protein over a period of time
Step 1
3
Na+ ions bind to the ATPase under conditons of low Na+ concentrations because
ATP andthe transport
protein has a high affinity for Na+. This
means the protein will bind Na+ ions even when the Na+ concentration is low
Mg++ bind to the protein . These are exergonic
reactions
The
transport protein cleaves ATP into ADP and Phosphate ion.The
phosphate ion becomes covalently bonded to the protein.The phosphorylation
of the protein causes it to become energetically unstable and the protein
changes conformation.The shift in conformation of the protein in some manner
causes the Na+ to travel across the protein and they are released from the
protein on the other side of the membrane because the protein now has a
low affinity for Na+ .These are exergonic processes
K+
ions bind to the protein even it there is a low K+ concentration because in
this conformation the protein has a high affinity for
K+ ions.The covalently bound phosphate group is cleaved from the
protein which causes the protein to undergo another conformational shift.
This
conformational shift causes the K+ to be in some manner transported across
the protein and released on the other side of the membrane. The
K+ ion is released because now the protein has a low affinity
for K+ ions. The protein is restored to the ordinal conformation
of the protein and the process starts again .
