Active Transport Definition, Process, Types 1p

Active transport definition is the process by which energy is used to move substances in, out of, and between cells. In some cases, the movement of matter can be done by passive transport that does not consume energy. However, the cell often has to transport the materials against their concentration gradient. In these cases, active transport is required.

Process of Active Transport

In contrast to osmosis, active transport requires energy to move substances from a lower concentration of this substance to a higher concentration of this substance. Active transport is usually accomplished by a transport protein that undergoes a shape change when it connects to the cell’s “fuel” called adenosine triphosphate (ATP).

For example, some kind of active transport channel in the cell membrane would bind to the molecule to be transported – such as a sodium ion – and hold it in place until an ATP molecule comes by and binds to the protein. The energy stored in ATP then allows the channel to change shape so that sodium ions can escape on the opposite side of the cell membrane. This type of active transport uses ATP directly and is referred to as “primary” active transport.

Another type of active transport is “secondary” active transport. In this type of active transport, the protein pump itself does not use ATP, but the cell must use ATP to keep it functioning. This is explained in more detail in the section on Simport pumps below.

Finally, active transport can be achieved through processes known as endocytosis and exocytosis. In exocytosis, a cell moves a large amount of itself by wrapping it in a membrane called a vesicle and “spitting out” the vesicle. In endocytosis, a cell “eats” by wrapping and building its membrane around a substance or object.

Each type of active transport is explained in more detail below.

What are types of Active Transport?

Antiport Pumps

The antiport pump is a type of transmembrane co-transporter protein. They pump one substance in one direction while moving another substance in the opposite direction. These pumps are extremely efficient because many of them can use a single ATP molecule to perform these two different functions.

An important type of antiport pump is the sodium-potassium pump, which is discussed in more detail under “Examples of active transport”.

import pump
Simport pumps use diffusion gradients to move substances. The diffusion gradient is the difference in concentration that causes substances to naturally migrate from areas of higher concentration to areas of lower concentration.

In the case of a Simport pump, a substance that “will” is used to “carry” another substance down its concentration gradient from an area of ​​higher concentration to an area of ​​lower concentration.

An example of a symport pump – that of a sodium-glucose transport protein – is discussed below under “Examples of Active Transport”.

Endocytosis


In the third type of active transport, large objects or large amounts of extracellular fluid can be transported into the cell through the process of endocytosis.

In endocytosis, the cell uses proteins in its membrane to fold the membrane into a pocket shape. This pocket forms around the material that is absorbed into the cell. The pouch grows until closed, remodeling the cell membrane around it and locking the pouch and its contents within the cell. These membrane pockets that transport material in or between cells are called “vesicles”.

The folding of the cell membrane takes place in a mechanism similar to the antiport transport of potassium and sodium ions. ATP molecules bind to proteins in the cell membrane, causing them to change their shape. The conformational changes of several proteins simultaneously change the shape of the cell membrane until a vesicle forms.

In receptor-mediated endocytosis, a cell’s receptor can recognize a specific molecule that the cell “wants” and form a vesicle around the area where it recognizes the molecule. In other types of endocytosis, the cell relies on other signals to recognize and attach to a particular molecule.

Exocytosis


Exocytosis is the opposite of endocytosis. In exocytosis, the cell forms a vesicle that traps something inside the cell in order to transport it across the membrane outside the cell. This usually occurs when a cell wishes to “export” a vital product, such as cells that synthesize and export essential enzymes and hormones in the body.

In eukaryotic cells, protein products are formed in the endoplasmic reticulum. They are often packed into vesicles by the endoplasmic reticulum and sent to the Golgi apparatus.

The Golgi apparatus can be thought of as a cellular “post office”. It receives packets from the endoplasmic reticulum, processes them, and “addresses” them by adding molecules recognized by receptors on the cell membrane to take in the product.

The Golgi apparatus then packs the “addressed” products in their own vesicles. These vesicles move, dock, and attach to the cell membrane, making the vesicle membrane part of the cell membrane. The contents of the vesicle are then dripped into the extracellular space.

Examples of active transport


Sodium-Potassium Pump

One of the most important active transport proteins in animals is the sodium-potassium pump. Like animals, our nervous system works by maintaining differences in ion concentrations inside and outside of nerve cells.

It is this shield that allows our nerve cells to activate and cause muscle contractions, sensations, and even thoughts. Even our heart muscle relies on these ion gradients to contract!

The ability of the sodium-potassium pump to move potassium into cells while moving sodium out of cells is so important that some estimates suggest that it makes up 20-25% of all energy we get from food Function can be obtained from this alone. spend it! In neurons, much of the cell’s energy is used to power sodium-potassium pumps.

This may sound like a lot of energy, but it is an important and important task; It is the pump that enables us to move, think, pump blood through our bodies and see the world around us.

Sodium glucose transport protein


A well-known example of a symport pump is that of a sodium-glucose transport protein. This protein binds to two sodium ions, which are “searched for” in the cell, and a glucose molecule, which is “searched for” outside the cell. It is an important way of transporting sugar in the body, which is necessary to provide energy for cellular respiration.

The natural diffusion of sodium ions within the cell facilitates the transport of glucose into the cell. Glucose can be transported into the cell together with sodium without the transport proteins consuming ATP. However, ATP must be used by the sodium-potassium pump elsewhere in the cell to maintain the sodium gradient. Without the sodium gradient, the sodium-glucose transport could not function.

white blood cells destroy pathogens
An important example of endocytosis is the process by which white blood cells “eat” pathogens. When white blood cells detect a foreign body in the body, such as a bacterium, they move their cell membrane around it into their cytoplasm.

Then they fuse the vesicle that contains the invader with a lysosome – a vesicle that contains powerful chemicals and enzymes that can break down and digest organic matter. They essentially just created a cellular “stomach” to “digest” the intruder!

What is the difference between active transport and passive transport?


Active transport moves substances from an area of lower concentration to a higher concentration, i. This process requires energy because it does not take place naturally without active forces.

In contrast, passive transport occurs naturally, as substances move down a concentration gradient in the absence of energy. Therefore, the main difference between active and passive transport is energy requirements.

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Active Transport Definition, Process, Types 1p

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