Structure of the Cell Membrane

A rigid cell wall surrounds bacteria, algae, fungus, and higher plants in addition to the plasma membrane. Animal cells do not have a membrane. Bacteria and eukaryotes have structural differences. The wall is mainly made up of polysaccharides in bacteria, which are cross-linked by tiny peptides to give stiffness, form, and protection from osmotic pressure, and polysaccharides in eukaryotes (plants and fungi). The cell wall regulates the state of the cell and inhibits osmotic pressure-induced cell bursting. It also aids cell-cell communication and offers mechanical strength and infection resistance. The cell wall and cell membrane are crucial organelles in living organisms. The former is only present in plants, fungi, and a few bacteria. Unlike the cell wall, the cell membrane structure is flexible and may change form as needed. It also exhibits selective permeability and is metabolically active.

What are Cells? 

Cells make up every living thing. Unicellular species are made up of just one cell, whereas multicellular organisms, like ourselves, are made up of numerous cells. Unicellular organisms are capable of independent existence and (ii) carrying out life’s primary duties. A cell’s structure must be complete for it to live independently. As a result, the cell is the most basic structural and functional unit of all living things. Anton Von Leeuwenhoek was the first to see and describe a living cell. Robert Brown subsequently identified the nucleus. 

Cell Theory 

German botanist Matthias Schleiden analysed many plants in 1838 and discovered that all plants are made up of distinct cells that create the plant’s tissues. Around the same time, British biologist Theodore Schwann (1839) researched many kinds of animal cells and discovered that they possessed a thin outer covering now known as the ‘plasma membrane.’ His research on plant tissues also concluded that a cell wall is a distinct feature of plant cells. Schwann hypothesised that animals’ and plants’ bodies are composed of cells and cell products based on this.

Schleiden and Schwann developed the cell theory. This idea could not explain how other cells were produced, according to Rudolf Virchow (1855). To firmly shape the cell theory, he modified Schleiden and Schwann’s  theory. All cells develop from pre-existing ones.

Cell Membrane 

Only after the invention of the computer was the exact structure of the membrane investigated. In the 1950s, the electron microscope was invented. Meanwhile, chemical research is being conducted on the cell membrane, particularly in human red blood cells (RBCs). Scientists are trying to determine the structure of the plasma membrane.

The cell membrane structure is made up of lipids organised in a bilayer. Lipids are also contained with polar heads on the outside and hydrophobic tails on the inside. The nonpolar backside of saturated hydrocarbons is shielded from the aqueous environment. Phosphoglycerides make up the majority of the membrane’s lipid component.

Biochemical analysis later revealed that the structure of cell membranes contains protein and glucose. In different cell types, the protein-to-lipid ratio varies greatly. The erythrocyte membrane contains around 52% protein and 40% lipids in humans. Membrane proteins are classed as integral or peripheral depending on how easy they are to remove. Essential proteins are partially or entirely buried in the membrane, whereas peripheral proteins are on the surface.

Singer and Nicolson (1972) provided an improved model of the structure of cell membrane construction that is now widely recognised as the fluid mosaic model. The quasi-fluid property of lipids, according to this, allows for lateral mobility of proteins within the total bilayer. The fluidity of a membrane is a measure of its capacity to move inside it. 

The fluid nature of the membrane is also critical for tasks such as cell proliferation, intercellular connection creation, secretion, endocytosis, and cell division. The transport of molecules through the plasma membrane is one of the plasma membrane’s most significant tasks. Some molecules on each side of the membrane are selectively permeable across the membrane. The term “passive transport” refers to the ability of several molecules to travel across a membrane without requiring any energy.

Simple diffusion along a concentration gradient can transport neutral solutes across the membrane from a higher to a lower concentration. Water can also travel from a greater to a lower concentration over this barrier. Osmosis is the movement of water by diffusion. Because polar molecules cannot pass through the nonpolar lipid bilayer, they must be transported across the membrane by a membrane carrier protein. 

Some molecules or ions get transported across the membrane in the opposite direction of their concentration gradient, from lower to greater concentration. Active transport, for example, is an energy-dependent activity that uses ATP and is referred to as Na+/K+ Pump.

Conclusion 

The cell membrane structure is made up of lipids organised in a bilayer. The lipids are also contained within the membrane with the polar heads on the outside. The cell wall and cell membrane are crucial organelles in living organisms. The former is only present in plants, fungi, and a few bacteria. A cell wall is often thought to be the layer of polysaccharides that lies outside the plasma membrane. It has a complex structure and provides structural and supporting purposes. All living things, including plants, have a cell membrane. In mammals, it is the cell’s outermost layer, which encloses other cellular organelles. Unlike the cell wall, the cell membrane structure is flexible and may change form as needed. It also exhibits selective permeability and is metabolically active.