CELL MEMBRANE
The cell membrane or ’’plasma membrane” was given by Nageli and Cramer. It is the outermost boundary of an animal cell. The cell membrane envelops the cell body like a protective sheath.
The membrane separates the intracellular fluid (ICF), which is the fluid inside the cell, from the extracellular fluid (ECF), which is the fluid outside the cell.The cell membrane is a semipermeable membrane; thus, certain compounds can be freely exchanged between the ICF and ECF. The thickness of the cell membrane ranges from 75 to 111A.
The Cell membrane is mainly composed of three types of substances:
1. Proteins (55%)
2. Lipids (40%)
3. Carbohydrates (5%)
The cell membrane is called a unit membrane or a threelayered membrane. Three layers of the cell membrane are visible under the electron microscope: two electron-dense layers and a middle layer that is electron-lucent. One electron-dense layer is on each side of the central layer (electron-lucent). The core layer is a lipid layer, and two protein layers are on either side of the lipid layer. The cell membrane contains some carbohydrate moieties also.
The phospholipids, which are the primary lipids, are organized in a bilayer structure. Within the membrane, these lipids are positioned with their polar heads facing the outer sides and their hydrophobic tails facing the inner region. The predominant lipid constituents of the membrane are primarily phosphoglycerides. Protein layers provide protection to the central lipid layer. The glycoprotein compounds are mainly present in protein layers. Proteins and the glucose (carbohydrate) molecules found in cell membranes combine to form glycoproteins, also known as proteoglycans. Glycolipids are created when certain carbohydrates are joined to lipid molecules. The glycocalyx is a thin, loose layer of carbohydrates that covers the whole surface of the cell membrane.
1. Cell membrane serves to safeguard the cytoplasm and cell organelles.
2. Cell membrane acts as a semipermeable membrane (selective permeable), permitting certain substances to cross while blocking others.
3. Nutrients are absorbed by the cell through the cell membrane, serving the absorptive function.
4. Waste products and metabolites are eliminated from the cell by passing through the cell membrane.
5. The cell membrane facilitates the exchange of gases, allowing oxygen to enter the cell from the blood while carbon dioxide exits the cell and enters the blood.
6. The cell membrane is accountable for preserving the shape and size of the cell.
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