Of The Following Functions, Which Is Most Important For The Glycoproteins Of Animal Cell Membranes?

Introduction

Cells are the bones units of life that are capable of carrying out all the processes of life. They are the building blocks of all organisms. Some living organisms are made upward of merely ane cell and are called unicellular, while the remainder are made upwards of many cells called multicellular organisms. In both unicellular and multicellular organisms, the cells are kept separated from each other and surroundings by a bulwark called plasma membrane or cell membrane.

Cell membrane, too called the plasma membrane, is a physical bulwark between a jail cell and the surrounding environment. It is the outermost part of the jail cell in animals. Yet, in plants, bacteria, and fungi, it is surrounded by a thick cell wall. Everything that is contained within the cell is not immune to exit it unless allowed past the plasma membrane. Similarly, nothing tin can enter the jail cell unless it is permeable through the prison cell membrane.

In this article, nosotros will discuss the structure and composition of the prison cell membrane as well every bit its functions.

Fluid Mosaic Model

The structure of the jail cell membrane is described by the fluid mosaic model, a universally accustomed model of the plasma membrane. According to this model, the jail cell membrane is considered as a liquid having two surfaces. It is composed of a lipid bilayer with proteins embedded in it. Allow u.s. study the detailed composition of this lipid bilayer and other substances found in the cell membrane.

Lipid Bilayer

The lipid bilayer is made up of two layers of phospholipids that are amphipathic compounds. Remember that a phospholipid molecule has a polar head and ii nonpolar tails. The phospholipid molecules are arranged into two layers form a lipid bilayer. They are organized in such a way that the tails of the molecules in two layers face each other, while their heads are directed opposite. The heads are in contact with the water in the cytoplasm besides as in the extracellular fluid.

Certain hydrophobic interactions develop among the tails of phospholipids, forming a spherical hydrophobic bulwark around the cell. As a result, water and other dissolved substances in the cytoplasm or the extracellular fluid cannot enter or leave the cell. However, lipid-soluble compounds can easily cantankerous this lipid bilayer. It is also impermeable to polar equally well as charged compounds.

Other lipids

In addition to the phospholipids, two other types of lipids are also nowadays in the cell membrane. These are cholesterol and glycolipids. The percentage of these lipids in the cell membrane varies from jail cell to cell.

Cholesterol

Information technology is abundantly present in the prison cell membranes of animal cells. Cholesterol molecules are nowadays in the spaces amidst the hydrophobic tails of phospholipids in the lipid bilayer.

The office of cholesterol is to regulate the fluidity of the jail cell membrane. According to the fluid mosaic model, the cell membrane is but like a fluid in which the individual components can movement freely. Cholesterol molecules in the lipid bilayer bank check this mobility. The office of cholesterol is temperature-dependent. At high temperatures, it decreases the mobility of phospholipid molecules while at a lower temperature, it promotes their mobility.

Glycolipids

The amount of glycolipids also varies from cell to cell. They are mostly seen in the membranes of nerve cells. The hydrophobic chains of such lipids have an even number of fat acids. The fatty acid chains are cached inside the lipid bilayer while the sugar component is present either on the cellular or extracellular face of the membrane.

The glycolipids serve to stabilize the prison cell membrane. They are too responsible for cell to cell interactions. Some glycolipids in the membrane too serve as cell surface receptors. The blood antigens are also glycolipids in nature, present on the cell membrane of red blood cells. The carbohydrate role of glycolipid is antigenic.

Proteins

Proteins are the second-largest component of prison cell membranes. They brand around 50% of the total cell membrane. They can be divided into two types;

Integral proteins
Lipid anchored proteins
Peripheral proteins

Integral Proteins

These are the integral components of the cell membrane. Integral proteins are those that span throughout the width of the cell membrane. Therefore, they are also called transmembrane proteins.

A transmembrane poly peptide has the following structures;

A hydrophilic domain that is present on the cytosolic side of the membrane. This domain interacts with the molecules present in the cytoplasm of the cells.
A hydrophobic domain that spans the width of the lipid bilayer. Information technology is responsible for anchoring the protein in the cell membrane.
Some other hydrophilic domain that is present on the extracellular side of the membrane. It interacts with the molecules in the surrounding environment of the cell.

Examples of integral proteins are transport channel proteins like glucose transporter, potassium channels, etc.

Anchored Proteins

Such proteins are not in contact with the cell membrane. They are attached to a lipid residue that is inserted into the lipid bilayer of the prison cell membrane. The protein is present either in the cytoplasm or in the extracellular fluid.

Examples of anchored proteins include alkaline phosphatase enzyme on the extracellular surface and Thou-proteins coupled to receptors on the cytoplasmic side of the membrane.

Peripheral Proteins

These are the proteins that are present merely on one side of the cell membrane. They are present in association with the integral proteins or with the peripheral parts of the lipid bilayer.

These are the temporary proteins and lose their association with the cell membrane as soon every bit they take performed their role. Examples of such proteins include hormones attached to receptor proteins, etc.

Carbohydrates

Carbohydrates are also nowadays in the cell membranes. Even so, they are e'er present in conjugation with lipids or proteins. They are involved in prison cell to cell recognition and other inter-cellular interactions.

Glycocalyx is formed by glycoproteins and glycolipids around some eukaryotic and prokaryotic cells. It is responsible for prison cell to cell adhesions. It is by and large seen in the instance of the epithelial cells and bacterial cells.

Membrane Polarity

An important concept that must be understood in the context of cell membranes is membrane polarity. It means that the charges on the 2 sides of the cell membrane are not equal.

In a resting cell, the cytoplasm has more negative charges as compared to the extracellular fluid. It is due to the presence of organic anions in the cytoplasm. Too, potassium ions keep diffusing exterior the jail cell down the concentration slope. This further makes the cytoplasm negative as compared to the extracellular fluid.

On the other hand, extracellular fluid is rich in cations, the major cations being the sodium ions. Due to this difference of charges on both sides, the jail cell membrane is never neutral. Rather, it shows electrical polarity. The cytoplasmic side carries a negative charge while the extracellular side carries a positive charge with respect to each other.

Functions

In this section, we volition discuss the several functions performed by prison cell membrane concerning a jail cell.

Jail cell membrane acts as Barrier

This is the near of import part performed by the cell membrane. Information technology acts as a barrier that controls the movements of substances across the cell. It is a selectively permeable membrane that allows only limited substances to pass through it.

Different substances can cross the prison cell membrane via one of the post-obit processes.

Passive Diffusion

Information technology is the move of substances downwardly their concentration gradient without using free energy or any carrier protein. Prison cell membrane allows elementary improvidence of merely lipid-soluble substances. The hydrophobic compounds similar steroid hormones tin easily cantankerous the cell membranes via simple improvidence. As well, gases like CO₂ and O₂ can too freely diffuse across the cell membranes.

However, polar substances similar water every bit well equally charged compounds cannot just diffuse through the cell membranes. They need some type of channel proteins to cross them.

Facilitated Diffusion

This type of diffusion is facilitated by some channel proteins. It is the process by which substances movement downward the concentration gradient by passing through a channel proteins. Polar and charged compounds use specialized transmembrane proteins chosen channel proteins to cantankerous the prison cell membranes.

Examples of such protein channels are potassium channels that allow the improvidence of potassium ions, and aquaporins that allow the diffusion of h2o molecules across the membranes.

Nutrients such equally sugars and amino acids also enter or leave the prison cell via specialized ship channels.

Agile Transport

It's the movements of substances against the concentration slope using free energy in the course of ATP. It takes place via specialized transmembrane proteins that have an integral ATPase activity and so the they can breakdown the ATP and use the energy that is released.

Jail cell membrane is necessary for Jail cell Signalling

Jail cell signalling is the process by which various metabolic processes taking place in the cell are controlled and regulated to maintain homeostasis. It is necessary for the overall coordination of the body.

Cells respond to the signals when a ligand binds to the prison cell surface receptors. These receptors are generally proteins present in the prison cell membrane. This is true for all types of signalling molecules except the steroid hormones that are lipid-soluble.

Cell membrane anchors the Cytoskeleton

The cytoskeletal framework of the cell is necessary for the maintenance of its shape and structure. Information technology provides structural and mechanical back up to the jail cell. Cytoskeleton is anchored to the cell membrane via linker proteins such every bit integrin. The microfilaments and other components of the cytoskeleton are kept anchored to the cell membrane via these anchoring proteins.

The anchoring of the cytoskeleton is necessary for its function. If the framework is not anchored, it volition not be able to provide mechanical support to the cell.

Cell membrane is Involved in Cell to Cell recognition

This function is performed by glycolipids and glycoproteins present on the outer surface of cell membranes. Cells belonging to the same tissue have a particular arrangement of glycolipid and glycoproteins on the membrane that can be recognized by partner cells only non by the cells of the other tissues.

Endocytosis and Exocytosis

These are the methods of transporting bulk substances across the jail cell membranes. In endocytoses, the membrane of the cell extends around the large substance to form an endocytic vesicle. This vesicle is later taken in by the cell every bit it breaks from the prison cell membrane. During exocytosis, the preformed vesicles fuse the cytoplasmic surface of the cell membrane. The vesicle becomes a office of the membrane while the substance is dumped into the extracellular fluid.

Summary

Cell membrane is the barrier that separates a cell from the surrounding cells and the extracellular environment.

It is the outermost role of the cell except in the example of cells having a cell wall.

The structure of the cell membrane is described by the fluid mosaic model which states that the cell membrane is a fluid-structure made up of a lipid bilayer along with the proteins floating in information technology.

The lipid bilayer is fabricated of phospholipids that are arranged in 2 layers with their tails facing each other.

Other lipids present in the membrane are;

Cholesterol, information technology regulates the fluidity of membrane
Glycolipids, they stabilize the membrane

Three types of proteins are present in the cell membrane;

Integral proteins, that span the entire width of membranes
Anchored proteins, that are kept anchored to the membrane via lipids
Peripheral proteins, they are temporarily attached to the membrane on either side

The cell membrane has a polarity with a net negative accuse on the inner surface of the membrane in the resting land.

Cell membrane performs the following functions;

It acts equally a filter, only assuasive selective substances to laissez passer through it
It is necessary for jail cell signaling
It is required for anchoring the cytoskeletal framework of the cell
It is involved in jail cell to cell recognition
Endocytosis and exocytosis takes place through the prison cell membrane

References

Tom Herrmann1; Sandeep Sharma2. (March 2, 2019). "Physiology, Membrane" . StatPearls. 1 SIU School of Medicine 2 Baptist Regional Medical Center. PMID 30855799 .
Alberts B, Johnson A, Lewis J, et al. (2002). Molecular Biology of the Cell (4th ed.). New York: Garland Science. ISBN 978-0-8153-3218-3 . Archived from the original on 2017-12-20.
Gorter Due east, Grendel F (March 1925). "On Bimolecular Layers of Lipoids on the Chromocytes of the Claret" . The Periodical of Experimental Medicine. 41 (iv): 439–43. doi : 10.1084/jem.41.4.439 . PMC 2130960 . PMID 19868999 .
Due south J Singer and G L Nicolson."The fluid mosaic model of the structure of cell membranes." Scientific discipline. (1972) 175. 720-731.
Sharp, Fifty. Westward. (1921). Introduction To Cytology . New York: McGraw Hill, p. 42.
Kleinzeller, A. 1999. Charles Ernest Overton'southward concept of a cell membrane. In: Membrane permeability: 100 years since Ernest Overton (ed. Deamer D.Westward., Kleinzeller A., Fambrough D.M.), pp. ane–18, Bookish Press, San Diego,.

Source: https://alevelbiology.co.uk/notes/cell-membranes/

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