Question

what is secondary active transport? can you also give an example?

Answer 1

In Cells Transportation occurs by two ways
1) Passive Transportation, and
2) Active Transportation
In passive transportation membranes moves across the cell without any utilization of energy.
Whereas in Active Transportation movement of substances across cell membrane occurs from lower concentration region to higher concentration region against the concentration gradient, hence requires cellular energy.
Active transport is of two types

1. Primary active transport: It uses ATP (Adenosine tri phosphate) as energy.
2. Secondary Active transport: Its uses Electrochemical gradient.

SECONDARY ACTIVE TRANSPORT

• Secondary active transport is also known as coupled transport or cotransport.
• It relies on electrochemical potential difference created by pumping ions in/out of the cell.
• Hydrogen pumps are also used to create an electrochemical gradient.
• In secondary active transport substances transport along with other in same direction of opposite direction
  Symporters: Both are transported in same direction.It uses the downhill movement of one solute species from high to low concentration to move another molecule uphill from low concentration to high concentration (against its concentration gradient)
  Antiporters: Both ions or solutes are pumped in opposite directions across a membrane.One of these ion or solute is allowed to flow from high to low concentration which yields the entropic energy to drive the transport of the other solute from a low concentration region to a high one.

Examples
1)  Sodium-calcium transport: Exchanger or antiporter, allows three sodium ions into the cell to transport one calcium out.This antiporter mechanism is important within the membranes of cardiac muscle cells which keep the calcium concentration in the cytoplasm low. The exchanger comes into service when the calcium concentration rises steeply or "spikes" and enables rapid recovery.

2)  Glucose - Sodium Transport: symporter SGLT1, co-transports one glucose (or galactose) molecule into the cell for every two sodium ions it imports into the cell. This symporter is located in the small intestines,heart,brain, and S3 segment of the proximal tubule in each nephron in the kidneys.