Question

Briefly describe the different forms of transport across a cell membrane ie; how a molecule moves across the membrane, and give examples. What is the sodium-potassium pump and why is it important? What is the difference between primary and secondary active transport? What is a secondary messenger and give an example?

Answer 1

different forms of transport across a cell membrane are-

1.Passive Transport.

a.Simple Diffusion

b.Facilitated Diffusion

2.Active Transport.

a.Primary Active transport

b.Secondary active transport.

Simple diffusion and Facilitated diffusion are passive transports in which ATP is not used.

Simple diffusion-diffusion of substances through a membrane without requiring any help from other substances.

Facilitated Diffusion-Requires helps of Tranmembrane Proteins For Transport(But not ATP)

primary active transport & secondary active transport requires energy for the Transport of substances(Active Transport)

Primary active transport- processes draws energy directly from the hydrolysis of ATP.For Example-Na+−K+ pump driven by ATP hydrolysis

Secondary active transport- transport of molecules across the cell membrane utilizing energy in forms other than ATP-By using an Symport or Antiport

(Symport- 2 compounds move simultaneously across a membrane in same direction

Antiport-2 compounds move simultaneously across a membrane in opposite direction)

.For example Transport of Glucose in PCT(SGLUT transporters move glucose, along with 2 Na +ions )

**sodium potassium pump is a is a protein pump found in the cell membrane of neurons ( type of Primary Active Transport of Na+ and K+ by use of ATP.)

Na + K + Pump Pumps 3 Na+ Outside of cell & for 2 K + Inside of cell.

This is Important as This create a gradient between Na and K ions. This Gradient is Responsible for the Occurance of Depolarisation and Repolarisation(Action Potential) in a Neuron.

Na+ K+ Pump Helps in -

1.Nerve cell signaling

2.Heart contractions

3.Kidney functions

**Secondary messenger: these are the molecules that relay signals received at the receptors on the cell surface( Signals-protein hormones, growth factors)to target molecules inside the cell (cytosol or nucleus)

Examples:

1.Cyclic AMP

2.Cyclic GMP

3.Inositol trisphosphate

4.Diacylglycerol

5.Calcium