CELL- THE UNIT OF LIFE(cell biology blueprint)

 Cell

Cell is the structural, functional and fundamental unit of life. Dutch scientist "Leeuwenhoek" was first discover a living cell. A new cell generally take 24hrs. to form in case of human beings through cell cycle which includes mainly 4 phases which are G1, S, G2 and M phase respectively. A cell is made up of three layers which are glycocalyx, cell wall and cell membrane from outside to inside. All the three layers present in bacteria but in plant case of plants glycocalyx is absent and in  animals only cell membrane is present.

Glycocalyx provide protective layer   and sticky nature to the bacterial cell and  hide the bacteria from host immune system.

 

The cell wall provide  the shape to the cell , cell to cell interaction , mechanical support to the cell and provide barrier for undesirable macromolecules.

  

Cell wall is a rigid and non living structure. Plant cell wall is mainly made up of cellulose along with hemicellulose, protein and pectin while algal cell wall is made up of cellulose, galactans, mannans and calcium carbonates.

Calcium and magnesium are the important components of cell wall (Ca mainly). 

Cell membrane is mainly made up of lipids (phospholipids) and proteins. In plasma membrane proteins are embeded in lipid bilayers forming peripheral and integral protein. Structure of cell membrane was better explained by Singer and Nicolson in their fluid mosaic model. According to fluid mosaic model quasi fluid nature of lipid enable the lateral movement of the protein that measure it's fluidity. Cell membrane of human RBC contain 52% protein and 40% lipids.

Including cell membrane all the biological membrane are selectively permeable. One of the most important function of the plasma membrane is the transport of the molecule across it.  Plasma membrane have lipid with hydrophilic(water repellant) head towards outer side and hydrophobic( water attracting) tail towards inner side made up of hydrocarbons. That's why hydrophilic molecules don't pass the cell membrane.

Fluid nature of the cell membrane is important for the cell growth formation of intercellular junction, secretion and cell division. Inside the cell, cell organelles are present in cytoplasm. Cytoplasm is the main arena for all the cellular activity to keep the cell in living state.

 The cell organelles present in cytoplasm are endoplasmic reticulum, golgi body, mitochondria, lysosomes, chloroplast, nucleus, ribosomes and vacuoles etc. 

Endoplasmic reticulum, Golgi body, Ribosomes, Vacuoles and  Lysosomes are form endo membrane system because their functions are co-ordinated. Mitochondria, Plastid and nucleus are the double membrane bound structure. 

Mitochondria -

Mitochondria is known as power house of cell because it produce energy in form of ATP( energy currency) by respiration. Mitochondria is the site of cellular respiration and are divide through fission. 

Plastid -

 Plastid are of three types Chloroplast, Chromoplast and Leucoplast . Chromoplast and Leucoplast perform the storage function and store many substances like oils, proteins and fats etc. Chloroplast are present in case on plant cell and are double membrane bound structure  which are responsible for photosynthesis, process through which plant produce their food and release oxygen as by product.

Ribosome -

 Ribosomes is only the cell organelle that present in both prokaryotes and eukaryotes. Ribosomes of prokaryotes are of 70s type and for eukaryotes are of 80s type. Magnesium ion is the essential component of ribosomes. Ribosomes are also known as palade particles because discovered by George palade. Ribosomes are present in cytoplasm, mitochondria, chloroplast, nucleus, and on the surface of the endoplasmic reticulum.

Endoplasmic reticulum -

 Endoplasmic reticulum are the network of tiny tubular structure scattered in cytoplasm. there are two types of ER(endoplasmic reticulum) - rough ER and smooth ER. Rough endoplasmic reticulum is rough because of presence of ribosomes on it and in case of smooth endoplasmic reticulum ribosomes are absent on their surface. smooth ER are primarily responsible for lipid synthesis and detoxification of drugs. While rough ER is responsible for protein synthesis and are  present in large amount in the cells which more actively take part in protein synthesis. 

Golgi body -

Golgi body are the disc shape structures and are primarily responsible for packaging of materials and also for glycosylation. Golgi body has two faces one is cis face and another is trans face. cis face is also known as forming face and trans face is also known as maturing face.

Lysosome -

Lysosomes are the single membrane bound structure and contain many hydrolytic enzymes that include lipases, protease and nucleases etc. which are responsible for digestion of  lipid, protein and nucleic acids etc.

Vacuole -

vacuoles are also single membrane bound structures, the membrane of vacuole is known as tonoplast.

concentration of the sap within the vacuole is more then that of cytoplasm. there are many types of vacuole are present that performs different functions such as  gas vacuole in cyanobacteria and food vacuole in protists.

Nucleus -

nucleus is a double membrane bound structure that regulate many function of the cell and  was first described by the Robert brown in 1831. Space between two membranes of the nucleus is known as perinuclear space and at some places of the membrane pores are formed due to the fusion of two membranes which allow the movement  of molecules such as RNA and proteins in both directions of the membrane. The nuclear matrix or nucleoplasm contain nucleolus and chromatin. nucleolus are the spherical structures present in nucleus. nucleolus are the site of active r-RNA synthesis. chromatins are the network of nucleoprotein fibres that form chromosomes in dividing cell. chromatin fibres contain DNA, RNA, histone and non histone protein.