In this article we are focusing and giving explanation on the topic “13 Facts on Diffusion in Cell Membrane: Complete guide!”.
Diffusion is a process of membrane transport that takes place in a cell membrane to facilitate the internalization of carbon dioxide, oxygen, lipid soluble molecules. Molecules are diffused through the cell membrane via channels or with the assistance of carrier molecules.
There are so many factors that are involved in the diffusion process, such as; the temperature, area of interaction, the size of the particles and the concentration gradient. All these factors play a great role individually and together in altering the rate of diffusion and its extent.
There are many examples of diffusion that we encounter in our day-to-day life and some are occurring inside our body that we do not realize happening, some of them include; Respiration, Diffusion is happening continuously in our lungs for the exchange of gases, Oxygen and carbon dioxide. Oxygen is taken from the air in alveoli to the blood and carbon dioxide is moved from the blood to the air in the alveoli.
When we light incense sticks the smoke coming out of it gets rapidly diffused into the air and spreads throughout. A perfume or a room freshener diffused into the air rapidly and the Odor can be sensed in air in the entire space. A tea bag when dipped in hot water diffuses in the water and change its color. Diffusion in plants, water from the soil is taken up by the plants through their roots with the help of diffusion.
What is Diffusion in cell membrane?
Diffusion is a type of a Passive transport. It works in the absence of any kind of cellular energy. In general terms, diffusion is referred to a movement of solute or anything from a higher concentration region to a lower concentration space.
Process of Diffusion in Cell Membrane
Diffusion is a process by which molecules such as, ions, particles, molecules and solutions, move under a concentration gradient across the cell membrane in all living organisms. It is one of the necessary processes in living organisms that helps to maintain the normal homeostasis. In this process, molecules move in and out of the membrane from a region of higher concentration to a region of lower concentration and the process goes on till the concentration on both sides of the membranes are equal.
Where does diffusion occur in cell membrane?
Diffusion occurs at cell membrane interface between the extra cellular and intracellular space, through the lipid bilayer. It occurs nonstop and ubiquitously from nucleus to cytoplasm and vice versa, from inside to outside of the cell and vice versa. Diffusion occurs for the exchange of chemicals and gases in and out of the cells. In lungs diffusion occurs for the exchange of oxygen and carbon dioxide.
In kidneys diffusion is involved in the diffusion of salts, water and waste products. In intestines calcium and other nutrients like glucose and amino acids are diffused from the food to the cells.
When diffusion occurs in cell membrane?
Diffusion occurs when the particles move from a region of higher concentration to a region of lower concentration to maintain the equilibrium to both inside and outside of the cell. This movement is random and true for both liquids and gases molecules.
Function of diffusion in cell membrane
Major function of diffusion is to transport the nutrients, minerals, ions and solutes in and out of the cell membrane. Certain lipid soluble substances can easily pass through by the cell membrane without any assistance from membrane proteins such type of diffusion is known as simple diffusion whereas active diffusion comes into play when there is a need for energy expenditure for the transport of large polar molecules.
Types of diffusion in cell membrane
Diffusion is a kind of passive diffusion, which is further divided into subtypes; Simple diffusion, Channel Diffusion, Facilitated diffusion, Translational diffusion, Passive Diffusion.
Simple diffusion in cell membrane
It is a major type of diffusion where molecules pass through a semipermeable membrane from a higher concentration region to a lower concentration region without any assistance or energy requirement. It totally depends on the size of the particles and the concentration of the solute. Generally, simple diffusion is fueled by kinetic energy and concentration gradient which makes the movement of the molecules random.
The concentration gradient is the difference in concentration between the two sides of the semi-permeable membrane which forces the molecules to be transferred to a region of lower concentration from a higher concentration area to maintain the equilibrium. Examples of molecules that uses simple diffusion process are usually small, non-polar molecules such as Carbon dioxide, hydrogen ions, steroids and ethanol.
Facilitated diffusion in cell membrane
Facilitated diffusion as the name suggests is a passive diffusion process where the molecules need assistance which is provided by the membrane proteins for the entry and exit through the semi-permeable membrane, these proteins are called Channel proteins and Carrier proteins. Here, the diffusion is selective the membrane allows only certain particles to pass through, this type of diffusion is also known as the active transport.
The molecules that can pass through are ions, small molecules, proteins and some other solutes which are hydrophobic and non-polar. In this diffusion certain factor are involved that affects the movement, these are as follows:
- Temperature: With an increase in temperature the movement of molecules also increases.
- Concentration: The molecules move from a higher concentration region to a lower one.
- Diffusion distance: It mainly affects the diffusion rates. Smaller diffusion distance causes an increase in the diffusion rates than larger distance, for instance; diffusion of gases is much faster through thin walls than thick walls.
- Size: The size of the molecules determines the diffusion rates; smaller and lighter molecules diffuse faster than larger molecules.
Transporters used in Facilitated diffusion
Facilitated diffusion is of great significance for the transfer of certain substances that can not pass through by themselves these substances include; Glucose, Sodium, Potassium, Calcium, Amino acids and nucleic acids. Glucose transporters are further of two types; Sodium glucose transporters and Facilitative glucose transporters, the former functions in the small intestines for the transport of glucose against a concentration gradient, and the later is involved in bidirectional glucose molecule transfer.
There are certain Ion channels that are type of transmembrane proteins which helps in the selective diffusion of ions and other solutes through the membrane. Protein involved in Facilitated diffusion are called transmembrane proteins or integral proteins that facilitates the diffusion of selective molecules through the cell membrane. Two types of proteins involved in this process are;
- Channel proteins: These proteins make the passage for the substances for their movement inside and outside of the cell membrane. The are further of two types; Open Channel proteins which allow the charged molecules to pass through by making pores in the cell membranes and Gated Channel proteins that can be open or closed regulating the inside and outside movement of the substances.
- Carrier Proteins: These proteins are present on the membrane of the cells which helps in carrying the molecules, changing their conformations and transferring them to the either side of the membranes.
Translational diffusion in cell membrane
Translational diffusion is of great significance for the transfer of electrons, in visual transduction and receptor mediated processes. It has been reported that diffusion coefficients are created at translational diffusion in monolayers at the air-water interface much lager than in lipid bilayers and this diffusion coefficient is not affected by the transition of phospholipid monolayer from fluid to crystalline phase.
The translational diffusion can be measured by fluorescence micro photolysis or photobleaching technique. Translational diffusion and phase transition studies has been parallelly to study molecular mobility of cell membrane components.
Passive diffusion in cell membrane
Passive diffusion is the general mechanism that is used by the molecules for their movement across the plasma membrane. During this process the molecules easily passes through the bilayer by dissolving and diffusing through it and then after being transferred to the outside of the cells it again dissolves in the external aqueous environment.
Osmosis is a perfect standard example of the passive diffusion. It refers to the movement from the lower concentration of the solute to the higher concentration of the solute through the semi-permeable membrane. It refers to a movement along a concentration gradient. Simple diffusion and Facilitated diffusion or active diffusion are other examples for the passive transport.
What is Lateral diffusion in cell membrane?
It is mainly the movement of proteins and lipids laterally in the membrane, as they are not restricted by any interactions and can move freely in a lateral motion quickly and spontaneously in the membrane fluidity. This type of diffusion is shown by lateral and peripheral membrane proteins and is important for regulating the proper function and dynamics of the cells.
Process of lateral diffusion in cell membrane
Lateral diffusion occurs rapidly in each leaflet of the lipid bilayer because of the fluid present in the membrane. This movement can be measured by a technique known as FRAP (Fluorescence recovery after photobleaching) and FLIP. Using these techniques diffusion coefficient is calculated from the bleached proteins.
Diffusion of water in cell membrane
The process of diffusion of water through the cell membrane is termed as Osmosis. It is defined as the movement of water from a lower concentration of solute region towards a higher region of solute concentration through a semi-permeable membrane. It is a spontaneous process that does not require any energy or other molecules for the movement and is solely based on the random kinetic movement.
This process of diffusion goes on until the both sides of the membrane come to an equilibrium concentration state, with a uniform distribution of the particles on each side. Osmosis is a regular process occurring at constant rates within a living cell across a semi permeable lipid bilayer called a plasma membrane. There are certain gated channels that facilitates the entry and exit of water across the membrane, these are called Aquaporins.
To summarize the article, we can say that diffusion is the prime and most predominant process happening continuously within living cells and any mutation or misleading of the process could be fatal and lead to diseases.