The Fundamental Unit of Life

The cells of multicellular organisms require many specialised chemical activities to support their complicated structure and functions. To perform these chemical activities, most eukaryotes have cells with many specialised structures within them. These small structures are called cell organelles. The main cell organelles are the endoplasmic reticulum, Golgi complex, mitochondria, lysosomes, plastids, and vacuoles. These cell organelles make eukaryotes different from prokaryotes.

Endoplasmic Reticulum

The endoplasmic Reticulum is found in eukaryotic cells. The endoplasmic reticulum forms an interconnected large network of flattened membrane enclosed sacs and tubular structures. The endoplasmic reticulum is made up of protein and lipids similar to the plasma membrane. The Endoplasmic Reticulum is the transport system of the eukaryotic cells.

Endo + Plasmic + Reticulum = Endoplasmic Reticulum

In this word,

"endo" means "within"

"Plasma" stands for the plasma membrane.

And, "Reticulum" means "Network".

Thus, the continuous network found in the plasma membrane of a eukaryotic cell is known as Endoplasmic Reticulum. The Endoplasmic Reticulum is abbreviated as "ER".

Types of Endoplasmic Reticulum

There are two types of Endoplasmic Reticulum, Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).

Rough Endoplasmic Reticulum (RER)

Rough Endoplasmic Reticulum has ribosome particles attached to its surface. Because of the attached ribosomes particles, it looks rough and hence named Rough Endoplasmic Reticulum and abbreviated as RER.

Rough Endoplasmic Reticulum lies immediately after the outer nuclear membrane i.e. nuclear envelope.

Ribosomes attached to the Endoplasmic Reticulum are the sites of protein synthesis (manufacturing). After the synthesis, proteins are sent through Endoplasmic Reticulum to various places in the cell depending on the needs. Here, RER (Rough Endoplasmic Reticulum) transports these proteins within the cell. Thus, the Rough Endoplasmic Reticulum is the transport system of the cell.

Smooth Endoplasmic Reticulum (SER)

The Smooth Endoplasmic Reticulum (SER) is found towards the cell membrane. The Smooth Endoplasmic Reticulum does not associate with ribosomes. The Smooth Endoplasmic Reticulum (SER) has a tubular type structure.

The Smooth Endoplasmic Reticulum (SER) synthesises fats or lipids including cholesterol which are important for cell function.

In certain cells, such as the liver cells the Smooth Endoplasmic Reticulum (SER) plays an important role in the detoxification of drugs and harmful chemicals.

Smooth Endoplasmic Reticulum (SER) are in abundance in some cells like testes, and ovaries. In muscles cells, Smooth Endoplasmic Reticulum (SER) regulates calcium ion concentration.

Some of the proteins and fats or lipids synthesised by the Smooth Endoplasmic Reticulum (SER) help in building the cell membrane. This process is known as Membrane Biogenesis.

The Endoplasmic Reticulum (ER) varies greatly in appearance in different cells, it always performs network system.

Golgi Apparatus or Golgi Body or Golgi Complex

Golgi Complex is an organelle found in most of the eukaryotic cells adjacent to the Endoplasmic Reticulum (ER). The Golgi Complex is known as Golgi Body or Golgi Apparatus or simply Golgi also.

It got its name as Golgi in 1898 in the honor of Camillio Golgi who discovered it in 1897.

Golgi Complex has the structure of a series of flattened fused pouches called cisternae. Golgi Complex is also a membrane bound vesicle like other cell organelles.

The main function of the Golgi Complex is modifying and packaging of proteins and lipids into vesicles before transporting them to the targeted destination.

The Endoplasmic Reticulum synthesises proteins and fats and sends them to the Golgi Complex. And Golgi Complex modifies and packs those proteins and lipids or fats into vesicles before transporting them to the target destination as needed. The Golgi Complex makes complex sugars from simple sugars in some cases. The Golgi Complex is also involved in the formation of lysosomes.

Lysosomes

Lysosome is a cell organelle found in most eukaryotic cells. The lysosome is a membrane bound similar to other cell organelles. Lysosome has sac like structure filled with acidic digestive enzymes. The digestive enzyme of the lysosome is synthesised by the Rough Endoplasmic Reticulum (RER) and after the synthesis transported to the lysosome packed in vesicles. The membrane covering keeps the digestive enzyme present in the lysosome separated from mixing with the outer environment of the cell.

Lysosome acts like a scavenger. Lysosomes are a waste disposal system of the cell. Lysosome keeps the cell clean by engulfing and digesting the damaged parts of the cell. Lysosome also acts on unwanted foreign organisms like bacteria and kills them by engulfing and digesting them. In the case of damage or even whole cell, lysosome bursts and the enzyme digests its own cell.

Since lysosome keeps the cell cleaned and even digests the whole cell if damaged, hence lysosomes are called "SUICIDE BAGS" or "SUICIDE SACS" of the cell also.

A Belgian scientist Christian Rene de Duve discovered the lysosomes in the 1950s. For this discovery of the lysosomes, Christian Rene de Duve got the Noble Prize in the year of 1974.