The Basic to know Biotechnology

THE CELL

Basic Information on Living Systems

The cell is the structural and functional unit of life. It is the basic unit of biological activity. The concept of cell originated from the contributions of Schleiden and Schwann (1838). However, it was only after 1940, the complexities of cell structure were exposed.

 Prokaryotic and Eukaryotic cells

The cells of the living Kingdom may be defined into two categories

1. Prokaryotes : ( Greek : pro-before ; Karyon- nucleus) They lack a well defined nucleus and possess relatively simple structure. These include various Bacteria. 
2. Eukaryotes : (Greek : eu- true ; Karyon- nucleus) They possess a well defined nucleus and are more complex in their structure and functions. The higher organisms animals and plants are composed of eukaryotic cells.

 Eukaryotic cells

The human body is composed of about 10¹⁴ cells. An eukaryotic cell is generally 10 to 100 micro meter in diameter. 

The cell consists of a well defined subcellular organelles, enveloped by a plasma membrane.The sub cellular organelles are described as follows:

Nucleus

1.  It is the largest cellular organelle, surrounded by a double membrane nuclear envelope.
2.  It contains DNA, the repositary of genetic information.
3.  The nucleus of the eukaryotic cell contains a dense body known as nucleolus. It is rich in RNA, particularly the ribosomal RNA.
4.  The ground material of the nucleus is often reffered to as nucleoplasm. It is rich in enzymes such as DNA polymerases and RNA polymerases.

To the surprise of biochemists, the enzymes of glycolysis, citric acid cycle, and hexose monophosphate shunt have also been detected in the nucleoplasm.

 

Mitochondria 

1. They are the centres for the cellular respiration and metabolism.
2. They are regarded as the power house of the cells with variable size and shape.
3. The structure and functions of mitochondria closely resemble prokaryotic cells.
4. It is hypothesized that mitochondria have evolved from aerobic bacteria. Further, it is believed that during evolution, the aerobic bacteria developed a symbiotic relationship with primordial anaerobic eukaryotic cells that ultimately led to the arrival of aerobic eukaryotes.

 

Endoplasmic reticulum

1. The network of membrane enclosed spaces that extends throughout the cytoplasm constitutes endoplasmic reticulum.
2.  A large portion of ER is studded with ribosomes to give a granular appearance which is reffered to as rough endoplasmic reticulum.
3. The smooth endoplasmic reticulum does not contain ribosomes. It is involved in the synthesis of lipids and metabolism of drugs, besides supplying calcium ion for the cellular functions.  

    

 Golgi apparatus

1. They are clusters of membrane vesicles
2. The newly synthesized proteins are handed over to the Golgi apparatus which catalyse the addition of  carbohydrates, lipids or sulfate moieties to the proteins.
3.  They are also involved in the membrane synthesis, particularly for the formation of intracellular organelles (e.g. peroxisomes, lysosomes)

 

 

 

 

Lysosomes

1. They are spherical vesicles enveloped by a single membrane.
2. They are digestive tracts of the cell.
3.  The digestive enzymes of cellular compounds are confined to the lysosomes in the best of interest of the cell.
4. Escape of these enzymes into cytosol will destroy the functional macromolecules of the cell and result in many complications.
5.  The occurance of several diseases (e.g. arthritis, muscle diseases, allergic disorders) has been partly attributed to the release of lysosomal enzymes.