Endoplasmic reticulum

Nature and occurrence:

• It is a network of tubular structure which forms a kind of intracellular skeleton.
• These tubes are membrane bound and are found in cytoplasm.
• These extend from nuclear membrane to plasma membrane.
• They are absent in prokaryotic organisms.

Structure:

• Endoplasmic reticulum comprises of many tubular structures which are covered by membrane.
• They may exist as round sac like structure called vesicles.
• This membrane encloses a cavity inside which is known as lumen which is filled with a fluid almost completely.
• The fluid contains water and other important biochemicals like proteins,amino acids, enzymes, carbohydrates, lipids, minerals etc which are essential for maintenance and functioning of ER.

• The membrane of Endoplasmic reticulum can be smooth or rough
• On this basis, ER can be of two types:

1. Smooth Endoplasmic reticulum   

2. Rough endoplasmic reticulum.

Smooth Endoplasmic reticulum:

• The surface of SER is smooth due to absence of ribosome and they originate from the Rough endoplasmic reticulum.
• They have bound molecules which help in synthesis of different types of lipids.

Rough Endoplasmic reticulum:

• They have some structures attached over the surface of its membrane.
• These structures are known as ribosomes.
• Due to the presence of ribosomes the membrane appears rough and thus it is known as rough endoplasmic reticulum.
• Ribosomes are involved in the process of protein synthesis thus the major role of rough endoplasmic reticulum is protein synthesis.

Function:

Cytoskeleton:

• It forms supporting skeletal framework of the cell thus provides mechanical strength to the cell.

Intracellular transport system:

• It forms a system for intracellular transport of different materials.
• It also helps in transport of material from nucleus of one cell to the other as it extends from nuclear membrane to the plasma membrane.

Biosynthesis:

• Rough endoplasmic reticulum is involved in the process of synthesizing proteins.
• Smooth Endoplasmic Reticulum is involved in the process of Lipid biosynthesis.
• Lipid and Proteins can function as enzyme, hormone, regulator etc thus ER plays a crucial role in maintenance living system.
• All Membranes are made up of lipid and protein so ER is directly involved in the process of membrane biogenesis.

Detoxification:

• SER of liver in vertebrates can metabolize the toxic substances so it plays an important role in the process known as detoxification.