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Tuesday, March 19, 2019

Active Transport - Definition, Types and Examples

Hey! Do you want to know about what is  Active Transport its Types and Examples? Before drive in, we will first go through the insights of this article.

Active transport definition

Active transport is a process in which polar or charged solutes are transported across the membrane against the concentration gradient by using energy.

These solutes are unable to cross the membrane by any form of passive transport as they need to move against the concentration gradient, so they take the path of active transport.

The active transport due to its energy requiring factor for a carrier protein to move solutes against the concentration gradient it is considered an active process.

Sources of energy and their use
  •  1. The energy released in the hydrolysis of ATP is used in the primary active transport.
  • 2. The energy present in the ion concentration gradient is used in secondary active transport.

Primary active transport

Energy in the form of ATP is directly used in the transport of molecules across the membrane against the concentration gradient.

Example Na+/K+ pump.

Secondary active transport

Energy in other forms than ATP is used to transport molecules across the cell membrane. The energy stored in the ion concentration gradient is used in secondary active transport.

Example Na+/glucose co-transporters.

The two processes viz. endocytosis and exocytosis accomplish the process of active transport.

In exocytosis, the materials are moved out of the cell by fusing them with the plasma membrane of vesicles inside the cell.

In exocytosis opposite of the endocytosis takes place as the materials are moved into the cell.

Types of active transport

Antiport pumps

Antiport pumps are used in the transport of two or more different molecules in the opposite direction.

Due to the use of only one ATP in doing these two separate tasks the antiport pumps are considered as extremely efficient pumps.

The important example of the antiport pump is the
 Sodium-potassium pump, which we will discuss in detail under the headline Examples of Active transport.

Symport pumps

In symport pumps, the molecules are transported via diffusion gradient from the areas of higher concentration to the areas of lower concentration.

In the symport pump, the molecules or substances that move from an area of higher concentration to an area of lower concentration also carries another substance or molecule with it against the concentration gradient.

The important example of symport pump is the sodium glucose transport protein that is described in detail under headline examples of active transport.

Endocytosis

The endocytosis is that type of active transport in which large substances or we can say a large amount of ECF or extracellular fluid is drawn into the cell.

The process of endocytosis is of three types
  • Receptor-mediated endocytosis
  • Phagocytosis
  • Bulk-phase endocytosis

Receptor-mediated endocytosis

Being the highly selective type of endocytosis this process is used by the cell in taking up of specific ligands.

The specific ligands that are transported via receptor-mediated endocytosis include LDLs, transferrin, some vitamins, antibodies, and certain hormones.

Phagocytosis

Is that type of endocytosis in which cell engulfs large solid particles such as worn-out cells, whole bacteria or viruses

The cells called phagocytes are only cells in the body that have the ability to perform the process phagocytosis.

Examples of phagocytic cells in the body are neutrophils and macrophages.

Bulk phase endocytosis

It is also known as pinocytosis in this type of endocytosis the tiny droplets of extracellular fluid are taken up.
The process of bulk-phase endocytosis takes especially in the cells involved in the process of absorption example absorptive cells of kidney and liver.

Exocytosis

This process being opposite to endocytosis is used to carry materials out of the cell by the formation of vesicles inside the cell.

The cell uses exocytosis to transport substances like hormones, antibodies, and enzymes formed within the cells to the sites in the body where these substances are needed.

The proteins formed in the endoplasmic reticulum are ultimately moved into the Golgi complex of the cell. The Golgi complex consists of various sac-like structures called cisternae that give it a cup-like shape.

The Golgi complex packages and processes the products and fuses with the cell membrane. As the vesicles become part of the cell membrane they pour the processed products into the extracellular space.

EXAMPLES OF ACTIVE TRANSPORT

Sodium-potassium pump

The sodium-potassium pump is an important active transport pump that is used to move sodium and potassium in the opposite direction against their concentration gradient into and out of the cell.

This task of moving ions in and out of the cells seems to be a very simple task but it consumes about 20-25% of energy generated from the food.

The nerve cells generate nerve impulses due to the concentration difference between inside and outside of the nerve cell.

In addition to this, the ion concentration gradient is involved in doing various physiological activities such as muscle contraction, sensations and even contraction of heart muscle etc.

Sodium-Glucose transport protein

Sodium-glucose transport protein is an important example of a symport pump which binds to 2 Na+ ions and 1 glucose ion. The former wants to move into the cell while as latter wants to stay outside of the cell.

In this way, the glucose is carried into the cell without the expenditure of ATP. However, ATP is utilized by the sodium-potassium pump in keeping up the sodium gradient so that the sodium glucose transport protein can function properly.

White blood cells attacking bacteria

The white blood cells or leucocytes engulfing pathogens in the body is an important example of endocytosis.

The white blood cells have the ability to recognize the foreign harmful bodies that are usually not present in the body which may be bacteria, after recognizing the foreign body it is bounded and then taken into the cytoplasm.

After entering into the cytoplasm is then subjected to lysosome which contains powerful chemicals and enzymes to digest and breakdown the organic matter. In this way, the white blood cells digest the foreign invader.

This was all about  Active Transport - Definition, Types and Examples from myself. I hope you will like this article and don't forget to share it !...

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