cell/plasma membrane-The Knowledge

Cell membrane/Plasma membrane

Difference between cell membrane and plasma membrane:

Plasma membrane and cell membrane are quite different terms used in biology. These are the differences between plasma membrane and cell membrane.

Cell membrane	Plasma membrane
It sorrounds the cell.	It sorrounds the cell organelles.
Cell membrane has initial receptors for signalling and is the first step in signalling.	Plasma membrane is not first step but is involved in signalling.
It can be transformed and is involved in movement in organisms such as amoeba.	It cannot be transformed..
During the cell division, It plays an important role in cytoktnesis (division of cytoplasm).	Plasma membrane does not play an important role in cytokinesis.
It contains cilia for feeding and locomotion.	It does not contain cilia.

 

Cell membrane

Cell membrane sorrounds the cell and is the outermost layer of the cell, found in both animal and plant cell. Both prokaryotes (Bacteria) and eukaryotes (animals, plants, fungi, protists [Algae and protozoa]) have cell membrane. Cell membrane is a type of plasma membrane that sorrounds the entire cell. It functions as a barrier between internal parts of the cell and outside environment of the cell. The structure of cell membrane is similar to the plasma membranes that enclose the organelles of cell

Function of cell membrane

Cell membrane has following functions:

•It acts as semi-permeable membrane which allows specific particles to pass in or out of the cell.

•It protects the cell from bacteria, viruses and other harmful substances.

•It is involved in cell signalling system.

Regulate material moving in and out of the cell. And from one part of cell to another.

•It separates inside of the cell from outside.

•Provide a large surface area on which specific reactions can take place.

•Cell membrane separates cells from another.

•Contains receptors containing specific cell identification markers that differentiate one cell type from another.

•Selective permeability of cell membrane maintain cellular homeostasis.

 Plasma membrane

Plasma membrane encloses the organelles of cell. It acts as barrier between organelles and outer environment within the cell.

Function of Plasma membrane

Plasma membrane acts as barrier between cell organelles and their environment. Its semi-permeability allows selected molecules to pass through the membrane (exit of molecules from inside to the cytoplasm or entrance on molecules from cytoplasm to inside).

Structure of cell/plasma membrane

In 1972, S Jonathan Singer and Garth Nicolson developed the fluid mosaic model of membrane structure.

Fluid-mosaic model

Fluid mosaic model describe that, a membrane is a double layer (bilayer) of proteins and phospholipids, and is fluid rather than solid. This phospholipid bilayer forms a fluid “sea” in which specific proteins float like ice bergs. Being fluid, the membrane is in a constant state of flux— shifting and changing, while retaining its uniform structure. The word mosaic refers to the many kind of proteins dispersed in the phospholipid bilayer.

The following are the important points of fluid mosaic model:

1.                                                                                                                                                  The phospholipids have one polar end and one non polar end. The polar ends are oriented on one side towards the outside of the cell and into the  fluid cytoplasm on the other side, and non polar end face each in the middle of bilayer. Here is a double action, the tail of both phospholipid molecules attract each other, on the same time, are repelled by water. Hence, these molecules are hydrophobic,(water dreading). As a result, the polar spherical ‘heads” (phosphate portion) are located over the cell surfaces (outer and inner) and are hydrophilic  (water attracting).

2. 

The another component of plasma membrane is cholesterol. Cholesterol is present in plasma membrane and other organelles of eukaryotic cells. These molecules are embedded in the interior of the membrane. Cholesterol molecules help to make the membrane less permeable to water soluble substances. More, the relatively rigid structure of cholesterol molecules help to stabilize the membrane.

3.  

Peripheral proteins are attached to the inner or outer membrane surface. These proteins   that are embedded in membrane, are “intrinsic proteins. Some intrinsic proteins help to move ions or molecules across the membrane. Other intrinsic proteins are “links’ to sugar-protein markers on the cell surface. And other proteins attach the membrane to the cell’s inner scaffoldindgs (cytoskeleton) or to various molecules outside the cell.

4.                                                                                                                                                          Carbohydrates and proteins combine and form glycoproteins, but if carbohydrate unite with lipids they form glycolipids on the surface of membrane. Surface carbohydrates and portions of proteins and lipids make glycocalyx (cell coat).Sugar molecules of glycocalyx act as a molecular “fingerprint” for each cell type. This characteristic is due to complex arrangement distinct shape of sugar molecules of glycocalyx. It is important for cell-to-cell recognition and the behavior of certain cells. It is also an important component in coordinating cell behavior in animals.