Plasma Membrane Function and Structure

All living cells, both eukaryotic and prokaryotic, have a plasma membrane that surrounds the cells contents while serving as a semi-porous barrier to the outside environment. Such a membrane acts as a boundary and holds the cell constituents together in order to keep other substances from entering. The plasma membrane is known to be a permeable membrane only to certain molecules but it still allows essential elements and nutrients to enter the cell and the waste materials to leave the cell. Carbon dioxide, oxygen, water and other small molecules are able to pass freely across the membrane but the passage of sugars, amino acids and other larger molecules are carefully regulated.

The primary plasma membrane function is to protect, contain and provide unit structure to cells. It is composed of thinly structured phospholipid bilayer and protein molecules and it found as a major component of every biological cell, while serving to divide the inner environment of the cell from the outer environment such as the animal skin. The plasma membrane is usually around ten nanometers thick. It is studded with proteins that conduct several functions such as the anchoring of the flagellum and the reception of nutrients.

The fluid mosaic model is the common term for the structure of the plasma membrane due to its two dimensional fluid of freely diffusing lipids, which is dotted with proteins. Such proteins either stick to the sheath, or span it to provide a bond from the inside to the outside. The cytoskeleton is found beneath the plasma membrane. It provides anchoring points for the integral membrane proteins in order for them not to move around too much.

With respect to the lipid distribution, the plasma membrane is assymetric and the components of the lipids that make up the bilayer mostly consist of phospholipids and to smaller extend of glycolipids. Glycoproteins as well as glycolipids are embedded in the plasma membrane that acts as the cell identity markers. Another vital component of the plasma membrane function in animals concerns cholesterol. There are times wherein the cholesterol content is as high as one molecule cholesterol in every one phospholipid molecule. Cholesterol partially immobilizes the tails of fatty acid, making the membrane less flexible thus, less permeable to smaller molecules.

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