What Is Function Of The Cell Membrane – Definition: The outer membrane of the cell consists of two layers of phospholipids with embedded proteins and separates the contents of the cell from its external environment, as well as regulates what enters and exits the cell.

Just as every non-living body has a plastic or paper packaging material that keeps the contents of the body intact, in shape, protected and well preserved, cells have a protective outer layer called “cell membranes (CM)” or “plasma membrane ( PM)” or cytoplasmic membrane. Whether it is a prokaryotic cell or eukaryotic cell, the presence of a cell membrane has been noticed everywhere.

What Is Function Of The Cell Membrane

Basically, a cell membrane (or plasma membrane) is an ultrathin, plastic, dynamic, electrically charged and selectively-permeable membrane layer that separates the cytoplasm from the extracellular matrix and helps maintain cell structure and function. This should not be confused with the cell wall, which is an extra layer outside the cell membrane mainly in plants, bacteria and fungi.

Cell Membrane — Structure & Function

An animal cell membrane is an outermost layer while the plant cell membrane is the second layer after the plant cell wall. To be

, the cell membrane allows the movement of both solutes and some selected solutions. The movement is along the concentration gradient.

Semi-permeability means that a membrane allows the movement of solvent only from its higher concentration to a lower concentration; no solute movement is allowed.

See the cell membrane diagram below to have a basic idea of ​​its location in a cell.

Pdf) The Cell Membrane

Is a membrane that surrounds the cell and separates it from the outside environment. In animals, this membrane is the outermost covering of the cell, while in plants, fungi, and some bacteria it lies beneath the cell wall. Although some cells form another layer above the cell membrane (called the cell wall), other cells have the cell membrane as the only protective barrier between the cytoplasm and the outside of the cell.

Now that we know how to define cell membranes, let’s go ahead and understand how the idea of ​​membrane structure has evolved over the years.

There are several cell membrane models that help us develop further clarity about its structure, function, roles and purposes in a biological system.

Figure 3: Timeline of different cell membrane models proposed to better understand the structure of cell membrane. Image credit: Atlas of Plant and Animal Histology.

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Now we can hope that a better picture of the cell membrane must have developed in your mind. The various models help us understand how science and scientists interpret biological systems in varied ways and how the basic concept evolves with rational modeling over years…

To understand where the cell membrane is in both prokaryotic and eukaryotic cells, see the figure below.

Now let’s move on to the structure of the cell membrane and learn what the different components of a membrane are.

When talking about the structure of a cell membrane, the important thing to learn is the answer to this question,

Performing Specific Functions

The cell membrane consists of varying amounts of lipids, carbohydrates and proteins. Although lipids form the basic structure of the plasma membrane, proteins and carbohydrates play irreplaceable roles in the functioning of biological membranes.

They consist of hydrophilic polar heads and hydrophobic non-polar fatty acid tails. There are mainly 3 types of lipids present in the plasma membrane.

Figure 5: Cross-section of the cell membrane to understand the presence of the different components in the cell membrane. Source: OpenStax.

1) Phospholipids – Phospholipid molecules are amphipathic lipids with a phosphate group attached by a covalent bond. They are the most common form of lipids present in the cell membrane, often accounting for more than 50% of the total lipids. They are arranged in two layers with the hydrophilic ends in contact with the cytosol of the cell & with the extracellular environment. The hydrophobic ends of both layers form the core of the cell membrane. Some lipids are examples

Cell Membrane Google Slides

(major component) and sphingophospholipids (minor). So, when asked what a phospholipid is, we can say that it is a major type of lipid found in cell membranes.

Figure 6: Hydrophilic head and hydrophobic tails of phospholipid. Image source: OpenStax Anatomy and Physiology – Diagram, edited by Maria Victoria Gonzaga of Biology Online.

2) Glycolipids – They are lipids with carbohydrates linked by a glycoside bond. They are present in small amounts and constitute only about 2% of the total lipids of the cell membrane. However, they play a crucial role in maintaining cell membrane stability & in cellular recognition. It is interesting to note that the different blood groups in humans are determined by the oligosaccharide group of the glycolipids on the RBC membrane. Some common glycolipids are

3) Sterols – The rest of the remaining lipids are sterols. Cell membranes of plants usually contain sterols and those of animals contain cholesterol. They both serve the similar purpose of regulating the fluidity of the membrane at different temperatures.

Which Of The Following Is A Function Of The Cell Membrane?

Agent. However, at high temperatures, cholesterol reduces the movement of fatty acid chains, and therefore reduces the fluidity and permeability of the cell membrane. In plants, the same role is played by sterols.

Membrane carbohydrates are mostly present in the form of glycolipids, glycoproteins and proteoglycans. The carbohydrate part is mostly present outside the cell surface. This forms a loose carbohydrate coat that is present outside the cell membrane, known as the glycocalyx.

Proteins make an important contribution to the cell membrane, accounting for about 50% of the total membrane volume. There are mainly 3 types of membrane proteins.

Figure 8: Membrane proteins variety in the plasma membrane. Image credit: Lehninger’s Principles of Biochemistry – The Supramolecular Architecture of Membranes.

Phospholipid — Structure & Function

Moving on to the vital roles and functions that the cell membrane serves in the biological functioning of a cell, we can decipher the following points.

1) Shape & structure of the cell – The cell membrane acts as an anchor to the cytoskeleton.

2) Barrier and gatekeeper of the cell – The cell membrane protects the cytosol from the external environment.

So, when asked what the cell membrane does and why the cell membrane is important, we can repeat these points.

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Is one of the ways cells communicate with each other. It is possible through specific cell adhesion molecules on the surface of the cell. An example of cell recognition is integrin (LFA-1) of T cell binding to ICAM of endothelial cell. Another is

. The cell membrane is involved in both passive and active transport types. In passive transport, substances move along the concentration gradient. This is in contrast to active transport, which is a type of transport characterized by an uphill movement of substances (i.e. from lower to higher) and therefore requires chemical energy, e.g. ATP. When moving substances across a biological membrane, passive transport may or may not require the help of a membrane protein.

There are four main types of passive transport are (1) simple diffusion, (2) facilitated diffusion, (3) filtration, and (4) osmosis.

Refers to the diffusion of a solute (usually water molecules) through a semipermeable membrane from lower to higher solute concentrations.

Chapter 7.2 And 7.4, The Cell’s Plasma Membrane And Cellular Transport

Is the movement of water and solute molecules across the cell membrane driven by hydrostatic pressure generated by the cardiovascular system.

Is the process in which a cell takes in materials (e.g., proteins and hormones) from the outside by fusing and fusing them with its plasma membrane. There are two main types of endocytosis: phagocytosis, which literally means cell eating, and pinocytosis, which literally means cell drinking.

By creating a small inward deformation (invagination) that contains the substance transported in the cell. The invagination is then cut off from the cell membrane, resulting in a vesicle containing the substance. Since endocytosis requires ATP, it is considered a form of active transport.

Material from the cell. Thus, exocytosis appears to be the opposite process of endocytosis. The vesicle containing the material fuses with the cell membrane and then the contents are extruded outside the cell into the surrounding medium.

The Cell Membrane And Its Function

The structure and composition of the cell membrane make it selectively permeable (or semipermeable), meaning that not all substances are allowed to enter or leave the cell. The cell membrane controls which substances can enter the cell. It can allow a certain substance to pass through at a certain time and then reject the same substance at a later time. The presence of surface molecules (eg glycoproteins, glycolipids, etc.) serves as a ‘signature’ of a cell. Each cell has a different ‘signature’ or ‘marker’ that is believed to function in cell recognition, or some sort of cellular identification system. Its other main functions include cell adhesion, ion channel conductance, cell signaling, and attachment point for cytoskeleton (which is important for maintaining the shape of the cell).

Both prokaryotes and eukaryotes possess cell membranes. Prokaryotes are mainly studied under 2 categories namely Archaea and Bacteria. Unlike eukaryotes that have a cell membrane and membrane-bound organelles, prokaryotes only have a cell membrane but no membrane surrounding their organelles. In addition, among bacterial prokaryotes, two types arose; they are gram-positive bacteria and gram-negative bacteria. Gram-negative bacteria have an additional outer membrane outside the cell

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