Eukaryotic cells are defined as cells containing organized nucleus and organelles which are enveloped by membrane-bound organelles. Examples of eukaryotic cells are plants, animals, protists, fungi. Their genetic material is organized in chromosomes. Golgi apparatus, Mitochondria, Ribosomes, Nucleus are parts of Eukaryotic Cells. Let’s learn about the parts of eukaryotic cells in detail.
Description: It is also called plasma membrane or cell membrane. The plasma membrane is a semi-permeable membrane that separates the inside of a cell from the outside.
Structure and Composition: In eukaryotic cells, the plasma membrane consists of proteins, carbohydrates and two layers of phospholipids (i.e. lipid with a phosphate group). These phospholipids are arranged as follows:
The polar, hydrophilic (water-loving) heads face the outside and inside of the cell. These heads interact with the aqueous environment outside and within a cell.
The non-polar, hydrophobic (water-repelling) tails are sandwiched between the heads and are protected from the aqueous environments.
Scientists Singer and Nicolson described the structure of the phospholipid bilayer as the ‘Fluid Mosaic Model’. The reason is that the bi-layer looks like a mosaic and has a semi-fluid nature that allows lateral movement of proteins within the bilayer.
Fluid mosaic model
Image: Fluid mosaic model. Orange circles – Hydrophilic heads; Lines below – Hydrophobic tails.
The plasma membrane is selectively permeable i.e. it allows only selected substances to pass through.
It protects the cells from shock and injuries.
The fluid nature of the membrane allows the interaction of molecules within the membrane. It is also important for secretion, cell growth, and division etc.
It allows transport of molecules across the membrane. This transport can be of two types:
Active transport – This transport occurs against the concentration gradient and therefore, requires energy. It also needs carrier proteins and is a highly selective process.
Passive transport – This transport occurs along the concentration gradient and therefore, does not require energy. Thus, it does not need carrier proteins and is not selective.