Channel proteins’ passive transport system is one of the most important membrane transport systems in cells. Here we are going to discuss all possible aspects of channel proteins passive transport.
Channel proteins passive transport is a special kind of membrane protein transport system.It doesn’t require energy to transport molecules. A special kind of membrane proteins called channel proteins are involved in this. By opening pore or channel these proteins stimulates molecular transportation across cytoplasmic membrane.
Instead of using ATP molecules for transportation, it allows molecules to flow according to their concentration gradient.
Channel proteins passive transport from Wikimedia commons
What Are Passive Transport Channels?
Passive transport channels are the fundamental pillars of the membrane transport system which completes faster rate of transportation across the plasma membrane.
Passive transport channels are the special kind of hydrophilic passageway, opened by membrane channel proteins. These channels are used to transport cellular substances such as water and polar ions across the cell membrane. The molecules which need to be transported are diffused through these channels down to their concentration gradient.
Though the transportation rate via facilitated diffusion process highly depends on the permeability of cell membrane. The passive transport channels can transport millions of molecules ( water and polar ions) in a second. The channel proteins passive transport is highly molecule specific, it only allows a specific molecule or similar molecules to diffuse through it. The polar ions repelled by the hydrophobic areas of cell membrane while crossing through it . The passive transport channels inhibit the interaction between polar ions and hydrophobic areas of the plasma membrane, thus providing a faster rate of transportation without any kind of hindrance.
Integral membrane proteins from Wikimedia Commons
How Are Channel Proteins Involved In Passive Transport?
The channel proteins only follow the passive transport mechanism for molecular transportation processes across the plasma membrane.
The channel proteins involved in passive transport directly. When a channel protein is activated for transportation of some specific molecules, it opens a pore or hydrophilic passageway. Then the molecules cross the cytoplasmic membrane by passive transport via these channels or passageways.
The channel protein does not consume energy for transportation. It allows molecules to cross the membrane by the facilitated diffusion process.
What Are The Three Types Of Passive Transport?
In membrane transport systems when transportation of molecules does not consume energy, it is called the passive transport. It can be generally classified into three types such as-
Diffusion
The word Diffusion comes from diffundere, a Latin word. It means “to spread out”.
It is an important transportation process within all living cells. Through diffusion process molecules flow down to their concentration gradient without consuming any energy. There are two different kind of diffusion process is present, such as-
Simple Diffusion
When cellular molecules move without consuming energy or without taking any help from others down to their concentration gradient, this type of passive transportation process is known as simple Diffusion. In this process the water molecules and solutes form hydrogen bonds between them, which helps them to spread properly.
In bacterial cells, water substances, gasses, and nutrients are transported from one place to another via the simple diffusion process.
Facilitated Diffusion
Facilitated Diffusion is a transportation process in which molecules move down to their concentration gradient with the help of some integral membrane proteins (channel proteins or carrier proteins). The mechanism of facilitated diffusion varies slightly in channel proteins and carrier proteins. Incase of channel proteins, the facilitated diffusion is the only process to transport molecules across the plasma membrane. This process also doesn’t consume energy to transport molecules.
The facilitated diffusion process relies on different factors, such as temperature, concentration of that molecule, diffusion distance and size of the molecules. With the increasing temperature the transportation rate also increases gradually. The whole concept of facilitated diffusion process stands on the concentration of that molecule, as it moves from higher concentration area to lower concentration zone. The smaller diffusion distance indicates the faster transportation rate. The larger molecules transport much more slowly than the smaller ones.
Most of the water substances and polar ions transport across the cytoplasmic membrane via facilitated diffusion processes with the help of channel proteins. Aquaporins,ion channels are most common examples which transport molecules via facilitated diffusion processes.
Ion channels Facilitated Diffusion from Wikimedia Commons
Filtration
Filtration is a passive transport system, in which water and solute molecules move across the cell membrane through membrane pores. This process is regulated by the hydrostatic pressure generated by the body. The filtration process is generally described as a physical separation process in which water or the solute molecules are being separated through a filter medium; it is also an example of the passive transport system.
As an example, the Bowman’s capsule in the kidney separates albumin or other proteins via filtration process only.
Osmosis
Osmosis is a passive transport system in which the solvent molecules pass from the lower concentration area to higher concentration area across the selectively permeable membrane. The osmosis process influences the nutrients transportation, maintains the balance between extracellular fluid and intracellular water and also controls the diffusion process.
There are three types of osmotic solutions found in nature, such as-
Isotonic solution
In an isotonic solution the cell has the same concentration of solute in both outside and inside the cell. Hence molecular transportation occurs from both directions following the same transportation rate.
Hypertonic solution
In hypertonic solution, the outer solute concentration is higher than the intracellular solute concentration of the cell. Hence the water molecules move outside the cell causing the cell to shrink.
Hypotonic solution
When the intracellular solute concentration is higher than the outer solute concentration of the cell it is called hypotonic solution. Hence the water molecules move towards the intracellular environment, causing cell swelling.
In plant cells water absorption and transportation mostly depends on the osmosis process.
To know more about cells read our articles Do Humans Have Animal Cells: Interesting FACTS
Do Channel Proteins Use Energy?
Channel protein passive transport system is an energy independent passive transportation process.
Channel proteins do not consume energy for molecular transportation. When channel protein triggers it opens a pore or channel for some highly specific molecules and allows them to diffuse through it. In case of gated channel proteins, after receiving some biological signal it activates, opens the channel but does not use energy.
Channel proteins only transport molecules by facilitated diffusion process which is an energy independent process. It follows Flick’s first law to transport molecules across the plasma membrane, that means the water substances or polar ions which are to be transported, flow down to their concentration gradient without consuming energy.
To know more about eukaryotic cells read our article on Eukaryotic Cells Examples: Detailed Insights
Do Protein Channels Use ATP?
ATP or Adenosine triphosphate molecules are one of the basic energy storage and transferring molecules in cells. When energy is needed, ATP molecules break their phosphate bonds and release energy.
Protein channels do not use ATP molecules for consuming energy to stimulate the molecular transportation process. ATP hydrolysis is not necessary in channel proteins’ passive transport systems. Protein channels (Aquaporins, ion channels) only allow facilitated diffusion processes for molecular transportation.
ATP molecules are only needed in an active transport mechanism, where the carrier proteins of a cell move molecules across the cell membrane in opposite to its concentration gradient. Only the carrier proteins undergo ATP hydrolysis process, converting ATP into ADP molecules and consume energy for transport molecules.
To know about cells read our article on Do humans have plant cells: Interesting Facts
As a whole channel proteins passive transport is one of the most significant membrane transport systems of cells. In this system water substances and polar ions are transported across the membrane only by facilitated diffusion processes. Here we discuss different kinds of passive transport systems in cells. We also know about the energy requirement factor during the membrane transport process. Hope it will be informative to you.
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Hello, I am Piyali Das, pursuing my Post Graduation in Zoology from Calcutta University. I am very passionate on Academic Article writing. My aim is to explain complex things in simple way through my writings for the readers.
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