Endoplasmic reticulum

The endoplasmic reticulum is a cytoplasmic organelle that acts as a manufacturing and packaging system. Endoplasmic reticulum works closely with the Golgi apparatus, ribosomes, messenger RNA, and transfer RNA. The ER is a network of the membrane. The structure of the ER depends on the type of cell. For example, red blood cells do not possess ER. But on the other hand, the cells that synthesize and release proteins have a large amount of ER.

Types of ER

There are two types of endoplasmic reticulum found in the cells that are rough endoplasmic reticulum and smooth endoplasmic reticulum. Rough ER is rough due to ribosomes attached to it while the smooth ER does not have ribosomes attached to it. About fifty per cent of the membrane surface in cells are provided by the Endoplasmic reticulum.

Rough Endoplasmic reticulum

Rough ER is known as rough because on its outer surface ribosomes are attached to it. These types of ER are found throughout the cell but their density is higher near the Golgi apparatus and nucleus.  Ribosomes that are attached to the rough ER are known as membrane-bound ribosomes.

Membrane-bound ribosomes are involved in the assembly of many proteins. The assembling of proteins is known as translation.  The rough ER along with membrane-bound ribosomes takes polypeptide and amino acids from the cell cytosol and continuous protein assembling.

Proteins that are assembled in the Endoplasmic reticulum are then passed for processing. Some of the proteins are delivered into the lumen for processing while others are processed in the membrane of the ER.

In the lumen, extra groups are added to some proteins to make it functional. for example, to some proteins sugars, or metal groups are added to them.

Smooth endoplasmic reticulum

Smooth ER is a type of ER to which no ribosomes are attached. Smooth ER is evenly distributed throughout the cytoplasm. Smooth ER manufactures lipids and in some cases, it performs the function of lipid metabolism.

Smooth ER detoxify a large number of organic chemicals. Smooth ER converts organic chemicals into water-soluble products. Smooth ERs are abundant in the liver cells where its function is to detoxify the products of natural metabolism.

What is the Structure of endoplasmic reticulum?

The endoplasmic reticulum or ER is a network of membranes that are known as cisternae. cisternae are sac-like structures that are held together by the cytoskeleton. The space present in the ER is enclosed by the phospholipid membrane which separates it from the cytosol but is continuous with the perinuclear space. Ribosomes may or may not attached to the ER. If a ribosome is attached to the ER than it is known as Rough ER and if not then it is known as Smooth ER.

What is sarcoplasmic reticulum?

It is a type of Endoplasmic reticulum found in the myocytes. The difference between both types lies on the basis of proteins and functions.

ER synthesize molecules while the sarcoplasmic reticulum stores calcium ions. The calcium ions that are stored in the sarcoplasmic reticulum are pumped out into the sarcoplasm when the muscle fiber is stimulated. Pumped out calcium ions then interacts with the contractile proteins of muscle that utilize ATP to shorten the muscle fiber.

what are the Functions of the endoplasmic reticulum?

The ER plays a major in many functions that occur within the cell such as protein synthesis, lipid metabolism, detoxification, calcium ion balance, and interaction with mitochondria, etc.

Apoptosis is induced by the ER due to an excess of unfolded proteins in the cell.

Protein synthesis occurs in the rough ER. Some proteins are translated in the cytoplasm and the moves to the endoplasmic reticulum for folding but there are other proteins that are translated in the ER.

Proteins that are folded in the ER are moved into the Golgi apparatus and dispatched toward other organelles.

Smooth ER plays a major role in the synthesis of cholesterol synthesis. Smooth ER also plays a major role in the synthesis of phospholipids that helps in the maintenance of the cell membrane.

Smooth ER is prominent in the cells of the adrenal gland that secrete steroid hormones and influence the metabolism.

Smooth Endoplasmic reticulum is also responsible for the storage and release of calcium ions. The storage of calcium occurs in the modified Smooth ER known as sarcoplasmic reticulum that is present in the muscle fibres.

What would happen to the cell without endoplasmic reticulum?

ER is a very important structure present in the cell. Its absence can cause a huge disturbance in the cells.

There are two types of ER that are Rough ER and smooth ER. Both types of ER perform different functions. So here we will discuss both.

If the Rough ER is absent in the cell then the cell will not be able to synthesize plasma membrane proteins, lysosomal enzymes, and proteins for Golgi bodies because of these kinds of proteins are synthesized in the rough ER.

If the smooth endoplasmic reticulum is absent in the cell then the cell will not be able to store calcium ions and synthesize and metabolize some lipids.  Sarcoplasmic reticulum is a modified form of smooth ER that stores calcium ions. The calcium ions are pumped out when the muscle is excited. The calcium ions interact with the proteins and cause contraction. This means that without smooth ER muscle contraction is not possible.

The absence of smooth ER also diminishes the detoxification that will cause many serious diseases in the body.

Another major effect of the absence of the ER in the cells is the change in apoptosis.

Summary

ER is interconnected membranes sacs that synthesize proteins and lipids. These functions are performed by different types of ER. There are two types of ER that are rough ER and smooth ER. Rough ER is a type if ER to which ribosomes are attached while the Smooth ER is a type of ER to which no ribosomes are attached.

ER is a network if cisternae that are held together by the cytoskeleton. Space is present in the ER that is enclosed by a phospholipid membrane. The endoplasmic reticulum is responsible for the transportation of proteins and plays a major role in the formation of the skeletal framework.

The nuclear membrane is formed by the Endoplasmic reticulum during cell division. Rough Endoplasmic reticulum synthesizes proteins while smooth Endoplasmic reticulum detoxifies many organic chemicals.