What is cell membrane
All organisms have a semipermeable or differentially permeable membrane surrounding the protoplasm. This permeable membrane is called the cell membrane. It is also known by the names of cell art, protoplasm art etc.
Generally, the membrane present outside the cell is called the cytoplasm. In animal cells it forms the outermost covering but in plant cells it is found just below the cell wall.
Structure
Many scientists have presented their views to know the structure of the cell wall clearly. These things are presented below.
Görter and Grendel : They studied the membrane of RBC for the first time in 1925 and concluded that two layers of lipids are found in the cell membrane. In these layers the lipid poles are on the outside from the tip and the tail is on the inner side. That is to say, it is found on the opposite side of each other.
Overton : Overton pointed out that fat-soluble substances easily cross the cell membrane. That is to say, the wall is made up of levels of lipids.
Unit Art Model : This model was introduced in 1949 by GD Robertson. He told that the cell membrane is made of 3 layers only. Its thickness in this model is about 75 angstroms.
Danielli and Davson : These scientists told about the presence of lipids and proteins in the cell membrane. He did this work in 1935. He explained that the cell membrane is made up of two layers of lipids, on either side of which a layer of globular protein is found.
Liquid Mosaic Model: This theory was presented by scientists named Jonathan Singer and Garth Nicholson in 1972. According to this theory, the distance between the cell membrane is the molecular layer of lipids.
Functions
There are several main functions of the cell membrane which are shown below. ,
1. Passive Access
In this type of transport, some ions, water molecules, etc., can come directly in or out through the cell membrane without expending energy. This process is accomplished by simple diffusion or facilitative diffusion.
2. Permeability
The cell membrane is differentially permeable or semipermeable in nature. It allows only molecules of certain sizes to pass through it.
3. Active Access
In active learning, energy is used by different types of carrier molecules present in the cell membrane to move different types of molecules in the opposite direction of their concentration potential. For example, sodium is taken out by this method in sodium and potassium pump and potassium is taken inside the cell.
Chemical composition
The cell membrane is made of lipids, arranged in two surfaces. The lipid is inside the wall with the polar end facing out and the water tail end facing in. The lipid components found in cell membranes are made up of phosphoglycerides.
Carbohydrates and proteins are also present in the cell membrane. The ratio of proteins and lipids is different in different cells. The membrane of human blood contains 52% protein and 40% lipid.