What Is The Function Of A Cell Membrane In An Animal Cell
Cell Membrane
Definition, Structure/Function
Diagram, Creature/Constitute Cell
Vs Plasma Membrane
Definition
Essentially, a cell membrane is the outermost barrier that separates the internal contents of a cell in the cytoplasm from the external environment (e.g. separates the internal environs of the cell from the extracellular matrix or forms the boundary between neighboring cells). It'due south thin and fragile, ranging from v to 10nm in thickness depending on the type of cell.
In all living organisms, the jail cell membrane serves both morphological and functional roles varying from one blazon of cell to some other. For case, in amoebas, the cell membrane plays an important office in the development of pseudopodia that are involved in feeding and locomotion.
Some of the other functions of the cell membrane include:
- Transport of molecules and ions in and out of the cell
- Communication between neighboring cells
- Signal receptor
- Secretion
Structure
The prison cell membrane is a complex structure that consists of a phospholipid bilayer. As such, it consists of lipids in the form of phospholipids. They may as well contain cholesterol and glycolipids.
Autonomously from these lipids, the membrane also consists of a number of other components (east.grand. glycoproteins, proteins, and ions, etc) that serve a variety of functions. Here, the manner in which prison cell membrane components are arranged is associated with their respective functions.
For the majority of cells, the cell membrane consists of three master components. These include glycerol, two fat acid chains as well as a phosphate grouping. Therefore, for a cell membrane with glycerol every bit the backbone, this complex is known equally glycerophospholipids (or phosphoglycerides).
Here, the glycerol, which is the courage of the membrane, consists of three carbons, fiver hydrogen, as well equally 3 hydroxyl groups. Attachment/linkage of the fatty acid chains (two fatty acid bondage) to the glycerol occurs through a procedure known equally esterification - the first and second carbons of the glycerol react (esterification) with the carboxyl groups of the fatty acid chains to form an ester bond.
In addition, some other ester bail is formed between the hydroxyl group located at the third carbon of the glycerol and phosphoric acrid. These reactions result in the production of diacylglycerol three-phosphate (phosphatidate) which is the simplest form or precursor of the phosphoglyceride.
* The phosphoglycerides are produced through the formation of an ester bond between the phosphate group of the precursor (phosphatidate) and the hydroxyl group of given alcohols (e.g. choline, ethanolamine, and inositol among others).
While the prison cell membrane of eukaryotes and most bacteria consist of phospholipids, the membrane of archaeans (single-celled prokaryotes) consists of ether lipids. Hither, the non-polar chains have been shown to be linked to the glycerol through ether bonds.
This type of link is peculiarly of import for archaeans given that it's more resistant to hydrolysis. It allows these cells to survive in hostile habitats. In add-on to the ether links, the membrane of these organisms consists of branched alkyl chains.
Unlike ether linkages, these bondage tend to be highly resistant to oxidation and thus withstand such harsh environmental weather equally low pH, loftier salinity, and farthermost temperatures.
* In some organisms, lipids are in the form of glycolipids (saccharide-containing lipid).
Some of the other components of the plasma membrane construction include:
Proteins - While they are not equally abundant every bit lipids, proteins are also an of import office of the cell membrane. In the majority of cells, the cell membrane consists of two types of proteins namely, integral and peripheral proteins.
Integral membranes are embedded in the membrane (integrated into the cell membrane). While some of these proteins extend along the entire width of the membrane known as transmembrane proteins, others only extend halfway.
The proteins have ane or several hydrophobic regions that ballast them to the hydrophobic part of the cell membrane in the hydrophobic tail.
Different integral proteins, peripheral proteins are either located inside or outside the surface of the jail cell membrane. They may be attached to the phospholipids of the membrane or to the integral proteins embedded in the membrane.
* The transmembrane that extends the entire width (thickness) of the membrane may consist of several hydrophobic amino acids. In this case, the amino acids are arranged in an alpha helix.
* Membrane proteins have been shown to brand up about 50 percent of the total membrane mass - While they are nowadays in smaller numbers compared to lipids, they have a large molecular mass.
Carbohydrates - Similar peripheral proteins, carbohydrates are commonly institute on the surface of the prison cell. Unlike proteins, carbohydrates are on the extracellular side of the cell membrane. Here, carbohydrates, consisting of between ii and 60 monosaccharides, may be linked to proteins thus forming glycoproteins or bound to lipids to form glycolipids. For the majority of cells, sugars are jump to betwixt 2 and x percent of lipids
Water and ions - H2o is an integral component for all molecules found in living matter. As such, it can also be found in the cell membrane where information technology's integrated into the polar ends of the membrane (the hydrophilic ends).
Apart from water, ions have also been shown to exist associated with the membranes in a number of means. For instance, they may be present equally they laissez passer through the ion channels/pumps or having adhered to the surface of the membrane
A jail cell membrane consists of a large number of phospholipids. As mentioned, these phospholipids consist of two singled-out parts including the hydrophilic head, the part that contains the phosphate and glycerol, and the hydrophobic tail consisting of the fatty acids.
In an environment with water, the hydrophilic part interacts with water while the hydrophobic tails cluster together as they avoid interacting with water.
As a result, both the inner and outer surfaces of the membrane volition consist of the hydrophilic heads that readily collaborate with water while the inner/fundamental part of the membrane will consist of the hydrophobic tails that avoid interacting with water. Therefore, the cell membrane will generally appear as the diagram beneath
* Because of the environment in which a cell resides (consisting of h2o) and the nature of the cell membrane (with hydrophobic and hydrophilic parts) a hollow sphere represents the virtually stable structure of the membrane.
* The hydrophobic part (C-tail) consists of saturated (straight tails) and unsaturated (with a bend/kink). Whereas the saturated phospholipids tend to pack tightly, unsaturated phospholipids permit the construction to be more fluid-like by introducing spaces.
Cytoskeleton and Structural Support
While the very nature of phospholipids causes them to pack tightly in a membrane, structural back up is required in order to maintain the shape of the cell as also prevents the bilayer from being damaged.
This support is provided past the cytoskeleton which is located beneath the membrane. It consists of actin filaments that form a mesh-like framework on which the membrane lies.
While the cytoskeleton is located beneath the membrane, it has been shown to collaborate with some of the integral membrane proteins. This not just limits the diffusion of these proteins but also enhances structural support to the membrane.
Fluid Mosaic Model of the Cell Membrane
Proposed in 1972 past South. Jonathan Singer and Garth Nicolson from the University of California, the fluid mosaic model of the cell membrane is the model used to describe the basic construction and behavior of the membrane (of many cells).
With this model, the prison cell membrane consists of a number of components/molecules, together make up a mosaic, that motility freely in a fluid fashion. Movement of these components/molecules (proteins, cholesterol, etc) motility in a manner resembling that of icebergs in the ocean.
According to studies, a number of factors influence fluidity of the cell membrane.
These include:
Temperature - Every bit is the case with other molecules in nature (due east.g. gases and liquids) an increment in temperature causes the phospholipids to grow apart and become more than flexible. In the case of low temperature, the phospholipids come closer together causing the structure to become more rigid
Cholesterol - In the cell membrane, cholesterol molecules are appropriately distributed in a manner that holds phospholipids together. An increment or decrease of these molecules affects the structural integrity of the membrane also every bit the power of the membrane to control the motility of molecules and ions in and out of the cell.
Fatty acids - As already mentioned, the cell membrane consists of both saturated and unsaturated fatty acids. Because of the single bonds betwixt the carbon atoms of saturated fat acids, they take been shown to be straight bondage that tend to pack tightly.
As a outcome, a membrane that only consists of these fatty acids would exist solid at normal body temperature which would in plough interfere with the movement of molecules and ions in and out of the cells.
However, the presence of unsaturated fatty acids (with a double membrane betwixt some of the carbon atoms and thus a curve/kink) creates spaces in the membrane thereby preventing the structure from existence tightly packed.
By creating spaces in the membrane, unsaturated fatty acids increase fluidity of the structure and also let some of the molecules to laissez passer without much difficulty.
Functions
The cell membrane is a continuous sheet that separates the inner part of the jail cell from the external environment. As such, information technology serves a number of important roles that allow the cell to function normally.
These include:
Morphological/Compartmentalization - The prison cell membrane confines diverse subcellular organelles thereby separating them from the external environment. Being a continuous sheet, the membrane allows normal intracellular processes to continue without interruptions from the external environment.
Without this membrane, for instance, communication required for given molecules to be synthesized is affected thereby changing diverse cellular processes. In addition, the human relationship between neighboring organelles (e.g. between the nucleus and ribosome) is altered.
Control the movement of material/substances in and out of the cell - Being the barrier between the prison cell and the external environment, the jail cell membrane is involved in regulating the motility/transport of various molecules and ions in and out of the jail cell.
Here, the send/motility of these substances may occur through a number of mechanisms that include:
Diffusion
Substantially, diffusion involves the movement of substances from an area with loftier concentration to an area of low concentration. As such, this manner of movement is largely dependent on an imbalance in concentration inside and outside the cell. With regards to the movement of substances, diffusion may take three forms.
These include:
Passive or simple diffusion - As the name suggests, this type of diffusion is simple and involves the movement of molecules from where they are highly concentrated to the area of low concentration.
For the about part, these molecules are small and nonpolar. A skillful example of this is the improvidence of gases (eastward.g. oxygen) in and out of the prison cell.
Some of the other molecules that pass through the cell membrane are water molecules, which have a niggling charge, and carbon dioxide.
Facilitated diffusion - Unlike simple diffusion, facilitated diffusion is a process in which molecules accept to be assisted to pass through the membrane. While it is also dependent on a concentration gradient, this mode of send is likewise dependent on such channels as the poly peptide channels, (due east.g. aquaporins that transport h2o molecules).
Molecules that depend on this mode of transport tend to exist larger and have polarity (e.g. sodium and potassium articles). Also, facilitated diffusion may occur through carrier proteins.
Here, the molecules attach to the carrier proteins which crusade it to change shape in a way that allows the molecules to be transported in or out of the prison cell.
In this style of send, the carrier proteins may only bind to a given type of molecule (specific) - Ion channels may also be included in this category. These channels are often gated and thus only allow a given type of ion.
Active transport
Unlike improvidence, agile transport is the blazon of transport where molecules have to be transported confronting their gradient. As such, information technology's non dependent on the concentration slope.
Given that agile send involves moving molecules against a concentration gradient, it too requires free energy to do so.
In that location are ii master types of active ship that include:
Principal active send - A good example of primary active transport is the sodium/potassium pump (Na+/K+ pump). Here, the transporter (protein) is embedded into the membrane and extends the unabridged length of the membrane.
Typically, the extracellular side of this transporter is closed while the intracellular side is open up. The intracellular side is associated with ATP - a source of free energy. In this state, the transporter has a high affinity for sodium ions located in the prison cell.
These ions enter and attach to the transporter which in plow causes the ATP to transfer phosphate to the transporter. This provides the transporter with the energy that is required to close the open intracellular side and open the extracellular finish.
As a result, an affinity for sodium ions reduces assuasive them to exist released to the extracellular environment. Once these ions are released, the transporter increases its affinity for potassium which causes potassium ions to enter and adhere to the transporter. This is followed past the closing of the extracellular end while the phosphate at the intracellular end is released.
Therefore, a new ATP binds to this site causing the intracellular end to open and release the potassium into the prison cell. This style of transport uses a pregnant amount of energy. For this reason, these transporters are few.
Secondary active transport - While secondary active transport also relies on membrane proteins, the free energy used here is derived from ions electrochemical gradient rather than APT. Ane of the proteins involved in this fashion of transportation is the sodium-glucose co-transporter 1.
Initially, the side of this protein that is in contact with the cytoplasm is closed while the extracellular end is open up. In this state, two negatively charged sodium ion bounden sites are exposed and attract two sodium ions (sodium anions).
As the ions move downwards the electrochemical gradient, energy is released, causing the protein transporter to change shape. In plough, this increases its infinity for glucose molecules located outside the prison cell. Glucose in this environment is in depression concentration.
An increase in affinity for glucose causes glucose molecules to attach to the transporter resulting in the closing of the extracellular end of the protein as the cytoplasm stop opens. With the release of sodium ions into the cell, affinity for glucose by the protein decreases assuasive the glucose to be released into the cell.
Vesicle transport - The third blazon of transport is known as vesicle transport and involves the germination of membrane-leap vesicles. This involves such processes as endocytosis and pinocytosis where a molecule is internalized having come in contact with the cell membrane.
During endocytosis (receptor-mediated endocytosis), for example, the substance (e.thou. low-density lipoproteins) start comes in contact with the specific receptors located on the cell membrane. This stimulates the formation of vesicles on the membrane through inward bending of the membrane.
In the procedure, the molecule is enclosed in the vesicle and transported into the cell. Similar processes are important for the transport of molecules required by the jail cell, phagocytosis too as feeding past such organisms as amoebae – This method is usually used to transport larger molecules.
See page on Passive Diffusion Vs Active Ship
See Endocytosis Vs Exocytosis
Jail cell signaling
As mentioned, the cell membrane consists of a variety of molecules. Some of these molecules are protein receptors that demark to specific types of molecules.
Adept examples of these receptors are insulin receptors that bind insulin. By binding to given point molecules in the extracellular environment, these receptors (transmembrane proteins) permit the cell to answer appropriately to the stimuli - Information from the stimuli is transmitted across the cell membrane and into the jail cell through such pathways equally signal transduction cascades.
Creature Cells and Plant Cells
Both plants and animals are eukaryotes and thus take cells with membrane-leap organelles. Like creature cells, institute cells as well incorporate diverse of import organelles including the nucleus, mitochondria, the Golgi apparatus, and ribosomes amid others. However, plant cells contain a number of extracellular components not plant in fauna cells. These include the chloroplast, a large central vacuole as well as the prison cell wall.
In plants, the cell membrane is located betwixt the prison cell cytoplasm and the cell wall. Every bit is the example with animal cells, the cell membrane in plants is a lipid bilayer. It'southward made up of phospholipids and too contains poly peptide and carbohydrate molecules. Here, the cell membrane is involved in a number of functions including containing cell organelles, transportation of molecules in and out of the cell as well as jail cell communication.
The cell wall is a harder layer that surrounds the cell membrane. Different the cell membrane, the cell wall of plant cells is primarily made upwardly of cellulose. It also consists of pectin among several other components. By surrounding the cell membrane, the cell wall serves to provide tensile strength while also protecting the cell against various ecology stresses.
In addition, information technology also contributes to tissue rigidity by withstanding turgor pressure - internal cell pressure that pushes the cell membrane in plant cells confronting the cell wall. As such, information technology plays an of import role in limiting water loss (and thus the loss of turgor pressure) that would otherwise cause wilting.
Jail cell Membrane Vs Plasma Membrane
The words cell membrane and plasma membrane are oftentimes interchanged to mean the same affair. However, plasma membrane refers to the type of membrane that surrounds cell organelles while the cell membrane is the membrane that surrounds the cell as a whole. The plasma membrane is commonly constitute in eukaryotic cells that contain membrane-bound organelles.
In these cells, this membrane forms the barrier between the cell organelles (e.grand. nucleus and mitochondria) and the external surroundings (external to the organelles). Like the cell membrane, nonetheless, the plasma membrane is likewise fabricated up of phospholipids and besides consists of proteins and carbohydrates.
In addition to existence a barrier that separates the organelles from the cellular environment, the membrane is as well involved in communication between cells and cell components as well equally regulating the move of molecules in and out of the organelles.
* Some of the organelles contain a double membrane (e.yard. mitochondria and nucleus) while others only have a single membrane (e.g. vacuole, Golgi apparatus, and lysosome etc).
See also: What are the Functions of Lipids, Proteins and Lipopolysaccharides on the Jail cell Membrane?
Return to Prison cell Biology main page
Return from Cell Membrane to MicroscopeMaster dwelling
References
David E. Sadava. (1993). Jail cell Biology: Organelle Structure and Office.
Jeremy G Berg, John Fifty Tymoczko, and Lubert Stryer. (2002). Biochemistry, 5th edition.
Natalie Gugala, Stephana Cherak, and Raymond J. Turner. (2016). The Membrane.
Valerica Raicu and Aurel Popescu. (2008) Prison cell Membrane: Construction and Concrete Properties. In: Integrated Molecular and Cellular Biophysics.
Links
https://world wide web.sciencedirect.com/topics/medicine-and-dentistry/jail cell-membrane
https://opentextbc.ca/biology2eopenstax/chapter/lipids/
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