1 The fundamental unit of life: Cell

Our earth is inhabited by different kinds of living organisms, which look very different from each other.These living organisms are archaebacteria,eubactaria,protista,fungi,plants and animals.The bodies of living organism are made up of microscopic units called cells. The cell has same Central position in biology as the atom in the physical sciences. The cell is the basic structural and functional unit of living organisms.

On the one hand presenting cells share common fundamental properties. For example, all cells employ DNA as genetic material commerce surrounded by a plasma membrane and the use of basic mechanisms for energy metabolism. On the other hand on my present is cell is awarded the variety of different lifestyle. Many organism commerce such as bacteria protozoa and is consist of single cells that are capable of independent self-replication.More complex organisms or multicellular organism, are composed of collection of cells that function in a coordinated manner with different cell specialised to perform the particular. The human body coma for example, is composed of more than 200 different kinds of cell is specialised for this function as memory commerce side movement and digestion. The diversity exhibited by many different kinds of animal is striking for example considered the difference between bacteria and the cell of human brain.

All cells, whether they exist as one celled organism or a part of multicellular organism are capable of carrying out certain basic functions such as nutrition, respiration a growth and reproduction. These functions are essential for the survival of the cells.

Thus, the most important and fundamental label in organisation of living world is a cellular level. Cell is the fundamental structural and functional unit of living organism and basic unit of life. Cell biology is the study of cell in all expects of structure and function.

Discovery of Cell

While studying the thin slice of cork robot so that the cockroaches Amber the structure of honeycomb consisting of many little compartment. cock is a substance which is obtained from the bark of a tree. in this it was in the year 16651 who made this chance Discovery through a shelf design microscope. Robert hooke all this box is cell cell is a Latin word for a little room. Robert hooke Discovery was important because it indicated for the first time that living organism consisted of a number of smaller structures or units.

Prokaryotic and Eukaryotic Cells

All living organisms present on earth can be classified into following two types:

1.Non-cellular organisms:which do not contain any cell in their body organism com example why does. Viruses leg and knee membrane and hence don't show characteristic of life until they enter the living body to use it cell missionary to reproduce.

2.Cellular organisms:which contain either one or many cells in their bodies example common bacteria, plants and animals.

Cellular organisms are again divided into following two main types:

(a) Prokaryotes:These organism have primitive and incomplete cell does they contain prokaryotic cell in the body structure. Prokaryotic cell have all three basic structure of a typical cell but lake nuclear membrane around the genetics substances(DNA).

Nuclear material of a prokaryotic cell consists of cell chromosome which is indifferent contact with cytoplasm. Here the undefined nuclear region in the cytoplasm is called nuclear that is there is no nuclear membrane. In a prokaryotic and other membrane bound organelles such as micro country are also absent. Ribosome however present in prokaryotic cells. The prokaryotes include archabacteria bacteria and cyanobacteria (which are earlier called blue-green algae).

(b) Eukaryotic.These have advanced and complete cells. these cells contain membrane-bound nuclei and other cellular organism organelles anda called eukaryotic cells. such cells are found in unicellular and multicellular plants and animals and contain plasma membrane,nucleus,DNA and cytoplasm with ribosomes and cellular organelles searches mitochondria.

CELL SHAPE

The basic shape of eukaryotic cell is but the shape of the cell is ultimately determined by the specific function of the cell. The common the shape of the cell may be variable or fixed. variable or irregular shaped occures in amoeba and white blood cell or leucocytes.In fact, leucocytes aspera kal in the circulating blood, but in the other condition they may produce pseudopodia and become irregular in shape. fixed shape of cell orchids in most plant and animal. In unicellular organism, the cell shape is maintained by the plasma membrane and exhaust skeleton. In multicellular organism are the shape of the cell depends mainly on the functional appreciation and partly on the surface tension, viscosity of protoplasm in the mechanical action exerted by adjoining cell and rigidity of the cell membrane. Thus, cell may have diverse shape such as polyhedral,spindle-shaped, elongated, branched ,discoidal and so on.

CELL SIZE

The size of differential ranges between broad limits. Some plant and animal cells are visible to the naked eye. Most cells visible only with a microscope, since they are only a few micrometre in diameter. A micrometre is one thousand of millimeter. The size of cell where is from the very small cells of bacteria to the very large eggs of the ostrich.Some nurse cell of human beings 7 metre long tail or axon. The single marien alga,Acetabularia, measures nearly 10 cm in height.The fibre cells of Manila hemp similarly are over 100cm in length.

The prokaryotic cells usually range between 1 to 10 mm.The eukaryotic cells are typically larger .Size of unicellular organisms is larger than a typical cell of multicellular organisms. For example protests is biggest among the unicellular organisms its length 0.6 m m. The size of the typical cells of multicellular organisms ranges between 20 to 30 mm the smallest cell of those of Mycoplasma galleisepticum,an organism intermediate between virus and bacteria.There size is about 10 mm.

CELL VOLUME

Thevolume of a cell is firmly constant for a particular cell type and is independent of the size of the organism. For example, kidney or liver cell are about the same size in the bull horse and mouse. The difference in the total mass of the organ or organism depends on the number not on the value of the cells.Thus, the cells of an elephant are not necessarily larger than those of other animals or plants. The large size of the elephant is due to the larger number of cells present in its body.

1.PLASMA MEMBRANE

Nature and Occurrence

Most cellular organelles such as mitochondria and chloroplast, peroxisomes, Golgi apparatus, nucleus and endoplasmic reticulum are all enclosed by the unit membrane.The cell surface membrane aur plasma membrane is the outer covering of itself. It is present in cells of plants,animals and microorganisms.

Structure

Plasma membrane is a living,thin, delicate, elastic, selectively permeable membrane.It is about 7 nm thick.Underthe light microscope is nearly appears as a single line. However, the development of electron microscope has made it possible to investigate the detailed structure of biological membrane.

Chemical analysis has shown the membrane to be 75% phospholipids.In addition, the membrane contains protein, cholesterol and polysaccharides.However,it is the phospholipids that form key elements in the structure of plasma membrane.

In 1972 Singer and Nicoloson suggested a model,called fluid mosaic model,for explaining the the ultrastructure of the plasma membrane or any other membrane of the cell. According to the plasma membrane is made up of two molecule thick layer of phospholipids.Two types of protein molecule floated about in the fluid phospholipids layer: Intrinsic proteins, which completely span the liquid and bilayer and extrinsic proteins, which occur either on the outer surface on the inner surface of the liquid membrane. The fluid mosaic model of the membrane has been described as a number of protein icebergs floating in the sea of lipids. This model is most expected one since it describes both property and organisation of the membrane.

The proteins are present known to give rent the membrane but to serve as

(1) enzymes, (2) transport proteins or permeases,(3)pumps,(4)receptor proteins.

Presence of lipids and protein provide flexibility to the plasma membrane.This property of flexibility of the plasma membrane help endocytosis.

Functions

Plasma membrane permits the entry and exit of some materials in the cells.It also prevents movement of some other materials. Therefore ,the plasma membrane is called a selectively permeable membrane.

(1) Diffusion:Some substances such as carbon dioxide and oxygen water can move across the plasma membrane by the process called diffusion. This substances are very small size diffuse readily through the phospholipids layer of the plasma membrane.

(2) Osmosis:Wateralso follows the law of diffusion. The spontaneous movement of water molecules through a selectively permeable membrane is called osmosis. At the moment of water across the plasma membrane of the cell is affected by the amount of substance dissolved in water. This process is the passage of water from a reason of high water concentration to a semipermeable membrane to a reason of low conserve water concentration. Osmosis is a pure mechanical diffusion process by which cells absorb water without spending any amount of energy.

(3)Mediated transport

We hap seen that cell is an effective barrier to the free diffusion of most molecule of biological significance. At it is essential that some materials enter and leave the full stop nutrients such as sugar and material of growth such as an amino acid must enter the self and the west of the metabolism must leave. Such models are moved across the membrane by special proteins called transport protein or permeases. Permeases from small passage with through the membrane enabling the solute molecules cross the phospholipids layer.

TYPES OF MEDIATED TRANSPORT

It is of two types:

(1)Facilited transport/diffusion

(2)Active transport

(4) ENDOCYTOSIS

Endocytosis is the the danger station of material by the cell through the plasma membrane. it is collective term that describes three similar process that is phagocytosis, potocytosis and receptor meditated endocytosis.

(5) EXOCYTOSIS

Just as materials can brought into the cell by investigation and formation of vesicles the membrane of a vesicle can fuse with the plasma membrane and extrude its content to the surrounding medium.

(2)CELL WALL

In plant cells come there occurs a rigid cell wall which lies outside the plasma membrane. Cell wall is non living and freely permeable and is secreted by the cell itself for the protection of the plasma membrane and cytoplasm.It determines the shape of the plant cell and prevent desiccation of cells.It is made up of fibrous carbohydrate content cellulose. The plant cell wall that consists of tiny cellulose fibre called microfiber glued together by a mixture of polysaccharide.

FUNCTION OF CELL WALL.

1.It permits the plant cell to become turgid. As water enters the vehicle by osmosis combat the plant cell expands. The cell wall has to be strong enough to resist this extension and so enable the cell to become turgid.

2.It provides mechanical strength to support the cell is microwave are very strong. The strength be increased by the addition of in tissues such as xylem. In cells such as college extracellular is added to the cell wall to increase mechanical support.

3.It is freely permeable to water and substances in solution.

4.Itis narrow ports called speeds through which fine strands of cytoplasm, plasmaodesta are able to pass.

5.The cell walls of adjacent glued together by the middle lamella. Middle lamella is a jelly like substance made up of calcium and magnesium pectate.

Plasmolysis.When living plant cell loses water through osmosis there is a shrinkage contraction of the protoplasm or away from the cell wall.This phenomenon is called plasmolysis.Thus,if are living plant cell is immersed in a concentrated sugar solution concentration of water molecule inside the seller will be higher than outside. As a result of water will move by osmosis is from the higher water potential inside the cell to the lower water potential outside. The cell contained will shrink away from the cell wall and it will be plasmolysed.

NUCLEUS

Nature and occurrence. The nucleus is a major, centrally located spherical cellular component.It is bounded by two nuclear membranes,both forming a nuclear envelope. Nuclear envelope and closes the space between two nuclear membrane and is connected to a system of membrane called the ER or endoplasmic reticulum.

The nuclear envelope separates the nucleus from the cytoplasm. The nuclear envelope contains many pores and encloses the liquid ground substance ,the nucleoplasm. Nucleoplasm transfer of materials between the new ko plaza man the cytoplasm. Within the nucleoplasm are embedded to types of nuclear structure the nucleus and chromatin material. The nucleolus may be one or more in number and is not bounded by any membrane it is rich in protein and RNA molecules and is the site of the ribosome formation. Nucleus is known as the factory of ribosomes.Ribosomes are helpful in protein synthesis in the cytoplasm.

The chromatin material is a thin, thread-like intertwined mass of chromosome material and composed of the genetic substance DNA( Dexoyribonucleic acid) and proteins (i.e.,histones). Basically chromatin is formed of repeating subunits, the nucleosomes each of which has a DNA molecule called around a disc of histones. DNA stories on information necessary for the cell to function to grow and to reproduce for the cell of the next-generation. Distinct segments of DNA are called gens. The chromatin is condensed into two or more thick ribbon like chromosomes during the division of cell.

STRUCTURE OF CHROMOSOME

Chromosome are thread like structure as usually present in the nucleus and became visible only during cell division. Chromosomes contain hereditary information of the cell in the forms of genes each chromosome is made up of two components:

1.DNA( Deoxyribonucleic acid)

2.Proteins(e.g., histones and acidic proteins)

DNA is the most important component of chromosome. It is the material of genes. most chromosomes consists of two arms that extend out from a specialised reason of DNA called centromere. Primary constriction gives a particular shape to the chromosome due to its position. The chromosome terminal reasons on either side are called telomeres.

Chromatids before a cell divides it duplicate its chromosome . The two copies of chromosome remain at rest and their centromeres. As long as two copies of chromosomes are attached to the common they are called sister chromatids. Both croma types of a chromosome are identical having identical genes. During cell division, the two sister chromatids separate and each chromatid become and independent daughter chromosome.

DIPLOID AND HAPLOID NUMBER OF CHROMOSOMES

Every eukaryotic spaces as a fixed number of chromosome in itself. The number of chromosomes vary from minimum two to a few hundred in different species. In human beings chromosomes in each body. There is always a pair of chromosome of each kind. The paired condition of chromosomes is known as diploid and the cell which is a full number of chromosomes is called diploid cell. Body cell in human beings are diploid.

FUNCTIONS:

1.The nucleus controls all metabolic activities of the cell. If the nucleus is removed from muscle the protoplasm ultimately tries up and dies.

2.It regulate the cell cycle.

3.It is concerned with the transmission of hereditary traits from the parent to offspring.

CYTOPLASM

Nature and occurrence.The part of the cell which occurs between the plasma membrane and nuclear envelope is called the cytoplasm. the integrand molar mass of the cytoplasm is often called the cytoplasm.The inner granular mass of the cytoplasm is often called endoplasm. while the outer clear layer is called cell cortex or ectoplasm.

Cytoplasm consists of an Aquarius ground substance the cytosol, containing a variety of cell organelles and their inclusion is called as insoluble waste and storage product.

(a)CYTOSOL

It is the soluble part of cytoplasm. it forms the ground substance or background material of the cytoplasm and is located between the cell organelle.Cytosol contains a system of protein fibres called cytoskeleton but otherwise appears transparent and structureless in the electron microscope. Cytosol is about 90% water and forms a solution which contains all biochemicals of life. Some of these are ions and small molecules forming a true solution such a salt, sugars,amino acid,nucleotide, vitamin and dissolved gases.Others a large molecules such as proteins which form colloidal solution. A colloidal solution may be solved or a gel often ecoplasm is more gel like.

FUNCTIONS:

1.Cytosol accessories store of vitral chemical such as amino acids, vitamins, glucose, vitamins,ions etc .

2.It is the site of certain metabolic pathways such as glycogen. Synthesise of fatty acid, nucleotides and some amino acid also take place in the cytosol.

3.Living cytoplasm is always in the state of movement.

CELL ORGANELLES

A cell hase to perform different function with the help of various membrane bound organelles.

1. it is to synthesise substances on the surface of smooth endoplasmic reticulum photosynthesis of food by chloroplast.

2.It has to secret cell products.,e.g., enzymes, hormones,mucus,etc.

3.It has to digest the substance which are taken off by the cell during endocytosis. Such intra-cellular digestion is done by enzymes of ribosomes.

4.It has to generate energy example synthesis of energy rich ATP.

Membrane is A remarkable cellular structure. every cell is bounded by a membrane and thus keeps its own content separate from the external environment. larger or more cells or cells from multicellular organisms have a great deal of metabolic activities to support their complicated structure or functions. To keep metabolic activities of different kind separate from each other cells have developed membrane bound organelles within themselves.Cell organelles are small organs of the cell and found embedded in the cytosol. the form living part of the cell and each of them has a definite shape structure and functions. examples of such organelles are nucleus,mitochondria, chloroplast, endoplasmic recticulum ,Golgi apparatus, lysomes , ribosomes,etc.

ENDOPLASMIC RECTICULUM

Nature undercurrents. inside the cell there exist membranous Network and closing of fluid filled lumen which almost feel of the intracellular cavity.It is called endoplasmic reticulum. On the other end of the plasma membrane.ER occurs in three forms: cisternae,vesicles and tubules.It is of two types: rough endoplasmic reticulum and smooth endoplasmic reticulum.

The ER is absent in the red blood cells of the mammals.

FUNCTION:

1.It form supporting skeletal framework of the cell.

2.ER properties of pathway for the distribution of nuclear material from one cell to the other.

3.Certain enzymes present in smooth ER synthesise fats,steroids and cholesterol.

4.Rough ER is concerned with the transport of proteins which are synthesized by ribosomes on their surface.

Some special functions of endoplasmic reticulum. Endoplasmic reticulum performs the following important functions:

1.Smooth ER of liver of vertebrates is involved in the process of detoxification. It metabolize various toxic or poisonous substances such as drug, aspirin, insecticide, petroleum products and pollutants.These toxic substances make their entry in animals body through food, water or air.

2.Smooth ER plays an important role in biosynthesis of glycolipids, phospholipids and cholesterol. This lipids are used in the formation of Plasma cell membrane and various steroid hormones.

3.Hormones are proteins are steroids. Smooth endoplasmic reticulum synthesise steroid hormone such as estrogen, testosterone and cortisol.

4.Enzymes are proteins. digestive enzymes of lysosomes are produced by of ER. Any enzyme which is mean for lysosomes is synthesized on the ribosome attached to the surface of rough ER. Then it is in the lumen of rough ER. From the role of ER this enzyme protein is transported to Golgi apparatus where it is marked to be included into lysosomes.

5.Plasma membrane and other cellular membranes are also formed by endoplasmic reticulum. the lipid molecules of cell membrane are formed an inserted into membrane of smooth ER by smooth ER itself. The protein molecules of cell membrane and mostly synthesized and inserted into memory in at the level of endoplasmic reticulum. In the process of glycolysis, short chain of sugar called oligasaccharides added to molecules of protein and lipid at the level of Golgi apparatus. For example the formation of the plasma membrane called brain by Genesis involves the following organelles all forming the so-called and endomembrane system:

Rough ER-Smooth ER -Golgi apparatus- Secretory vesicle-Plasma membrane.

6.Proteins which are synthesized by the cell and then released into outer membrane of the cell are called secretory proteins.Examples of secretory proteins include mucus digestive enzymes and hormones. These proteins are synthesized by of ER. Here we can consider the case of secretion of inactive enzymes, called proenzymes by the cells of mammalian pancreas.

RIBOSOMES

Nature and occurrence.Ribosomes a dense, spherical and granular particles which of freely in the matrix or remain attached to the endoplasmic reticulum. Chemically the major constituents of ribosomes are the ribonucleic acid and proteins. Lipids are not present in ribosomes. Ribosomes are not bounded by a membrane. They are present both and prokaryotic and eukaryotic cells.