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WRITE THE STRUCTURE OF ENDOPLASMIC RETICULUM WHAT IS DIFFERENCE BETWEEM SER AND RER
Endoplasmic reticulum is a continuous membrane, which is present in both plant cells, animal cells and absent in prokaryotic cells. It is the membrane of network tubules and flattened sacs, which serves a variety of functions within the cell. The space, which is present in the endoplasmic reticulum, is called as the lumen. It consists of membrane lined channels or spaces.  The channels or spaces contain a fluid called endoplasmic matrix.  It is quite different from cytoplasmic matrix present out side the reticulum. The membranes of endoplasmic reticulum or 50-60 A° thick.Cisternae are flattened, unbranched, saclike elements with a diameter of 40-50 nm.  The lie in stacks parallel to one another and the sacs in the stack are interconnected with one another.Tubules tube light extensions which may be connected with cisternae or to form a reticular system.The ER facilitates transport of materials from one part of the cell to another, thus forming the cells circulatory systems.
Tubular ER extensions called desmotubules extend to the plasma desmata to make ER continue in the two adjacent plant cells.

Endoplasmic reticulum is an extensive membrane network of cisternae (sac-like structures), which are held together by the cytoskeleton. The phospholipid membrane encloses a space, the lumen from the cytosol, which is continuous with the perinuclear space.
Difference:

The surface of the rough endoplasmic reticulum (RER) is studded with the protein manufacturing ribosome, which gives it a rough appearance. Hence it is referred as a rough endoplasmic reticulum.Rough endoplasmic reticulum synthesizes proteins, while smooth endoplasmic reticulum synthesizes lipids and steroids. It also metabolizes carbohydrates and regulates calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins.Ribosomes present postioned near the nucleus.Mainly found in protein forming cells.

The smooth endoplasmic reticulum(SER) consists of tubules, which are located near the cell periphery. This network increases the surface area for the storage of key enzymes and the products of these enzymes.Ribosomes are absent,present nearly to the cell membrane,mainly found in lipid forming cells.The component is mainly formed of tubules.

Endoplasmic reticulum varies extensive extending from the cell membrane through the cytoplasm and forming a continuous connection with the nuclear envelope.
Functions:
    It is mainly responsible for the transportation of proteins and other carbohydrates to another organelle, which includes lysosomes, Golgi apparatus, plasma membrane, etc.
    They play a vital role in the formation of the skeletal framework.
    They provide the increased surface area for cellular reactions.
    They help in the formation of nuclear membrane during cell division.
    They play a vital role in the synthesis of proteins, lipids, glycogen and other steroids like cholesterol, progesterone, testosterone, etc.


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