Active transport pump

Facilitated diffusion (channel), molecule moves down its electrochemical gradient. Active transport (pump) molecule moves up its electrochemical gradient (requires energy input). Pumps use energy (usually ATP hydrolysis). Na+ high outside/K+ high inside. 

C. Neurotransmitter synaptic reuptake—an example of molecular transport using an active transport pump... 

Chemical neurotransmission can be described more completely as a team of molecular players. The neurotransmitter may be the captain of the team, but it is only one key player. Other molecular players on the synaptic transmission team include the specific ions (Fig. 2—8), that interact with the ion channels (e.g., Fig. 2—6), various enzymes (Fig 2—9), transport carriers (Fig. 2—10), active transport pumps (Fig. 2—11), second messengers (Fig. 2—12), receptors (Fig. 2—13), transcription factors (Fig. 2—14), genes (Fig. 2—15), and gene products (Fig. 2—16). 

FIGURE 2—11. If a transport carrier is coupled with an energy-providing enzyme such as ATPase, it is called an active transport pump. 

One example of molecular transport requiring energy is the reuptake of neurotransmitter into its presynaptic neuron, as already mentioned above. In this case, the energy comes from linkage to an enzyme known as sodium-potassium ATPase (Fig. 2—9). An active transport pump is the term for this type of organization of two neurotransmitters, namely a transport carrier and an energy-providing system, which function as a team to accomplish transport of a molecule into the cell (Fig. 2—11). 

Neurotransmitter Synaptic Reuptake—an Example of Molecular Transport Using an Active Transport Pump... 

The chapter has specifically reviewed how receptors and enzymes are the targets of drag actions in psychopharmacology. We have explored the components of individual receptors and discussed how receptors function as members of a synaptic neurotransmission team, which has the neurotransmitter as captain and receptors as major team players interacting with other players on the team including ions, ion channels, transport carriers, active transport pumps, second-messenger systems, and... 

Noradrenergic neurons. The noradrenergic neuron uses NE for its neurotransmitter. Monoamine neurotransmitters are synthesized by means of enzymes, which assemble neurotransmitters in the cell body or nerve terminal. For the noradrenergic neuron, this process starts with tyrosine, the amino acid precursor of NE, which is transported into the nervous system from the blood by means of an active transport pump (Fig. 5 — 17). Once inside the neuron, the tyrosine is acted on by three enzymes in sequence, the first of which is tyrosine hydroxylase (TOH), the rate-limiting and most important enzyme in the regulation of NE synthesis. Tyrosine hydroxylase converts the amino acid tyrosine into dihydroxyphenylalanine (DOPA). The second enzyme DOPA decarboxylase (DDC), then acts, converting DOPA into dopamine (DA), which itself is a neurotransmitter in some neurons. However, for NE neurons, DA is just a precursor of NE. In fact, the third and final NE synthetic enzyme, dopamine beta-hydroxylase (DBH), converts DA into NE. The NE is then stored in synaptic packages called vesicles until released by a nerve impulse (Fig. 5—17). 

FIGURE 5—31. Dopamine (DA) is produced in dopaminergic neurons from the precursor tyrosine (tyr), which is transported into the neuron by an active transport pump, called the tyrosine transporter, and then converted into DA by two of the same three enzymes that also synthesize norepinephrine (Fig. 5-17). The DA-synthesizing enzymes are tyrosine hydroxylase (TOH), which produces DOPA, and DOPA decarboxylase (DDC), which produces DA. 

To gain familiarity with ion channels, transport carriers and active transport pumps. 

An active transport pump is a type of transport carrier which is linked to an energy utilizing system. True or False. 

Because the driving force for diffusion is a concentration gradient, active transport pumps, such as the sodium-potassium pump, create gradients of these two ions that are continually (though slowly) degraded by diffusion. Note in Table 10.6 that sodium and potassium ions do not have facilitated transport systems, so their permeability constants are very low. 

The striking compartmentalization of potassium in intracellular fluid, and of sodium in extracellular fluid, is a condition which is established and maintained by active transport across all plasma membranes. In the absence of active transport pumps, cotransporters and conductance channels, a directional, selective, rapid and regulated movement of potassium (or sodium) through the cell membranes would be impossible. The major molecular pathways of potassium permeation through plasma membranes are Na, K- ATPase, H-K-ATPase, Na-2C1-K-transporter, and potassium conductance channels (Peterson 1997). 

Fig. 15. Diagram of an active transport pump model based on a dissipative functional structure. The necessary dissipation to create this structure is here the diffusion of an acid and its gradient this creates inverse allotopic activation or inhibition on face 1 and face 2 of the two enzymes of different...

Fig. 16. Diagram of an active transport pump model with permanent functional structure. The local pH difference between faces 1 and 2 is due to different fixed chares (Allotopia due to regulation...

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