Cell biology Important for SSC,RRB(ntpc),RRC

Cell biology 

 study of form structure and composition of cells is called cytology. branch of biology that deals with various aspects of structure, chemistry, development ,Genetics and functioning of cells is called cell biology.

Cell is a basic unit of of life as no living organism can have life without being  Cellular because cell is a unit of both its structure and function. All life begins as a single cell. A number of organisms are made of single cells. They are called unicellular or  acellular, e.g, amoeba, bacteria,  yeast. 

A multicellular organism is made of  many cells. Animal or a plant contains billions of cells. For example as a newly born human infant has 2x10^12  cells. The number increases  hundred trillions cells in the body of 60 kg human being. About 25% of them are found in  the blood.

*In the year 1665 Robert hooke first discovered cells in the piece of cork and also coined the word cell. 

*Anton van leeuwenhoek  who was the first person who observed living cells under microscope and named them animalcules,  meaning little animal

* living matter in plant cell was named Protoplasm by purkinje and von-mohl.

*C,H,O,N 99% off living system(0>c>H>N)on the basis of internal architecture all cells can be subdivided into two major classes prokaryotic cells and Eukaryotic cells.

NOTE:

1.A typical Eukaryotic cell size 10 to 20 micrometre.

2. Typical bacteria size 1- 2 micrometre.

3.PPLO size 0.1 micrometre.

4. Virus 0.02- 0.2 micrometre.

5. In prokaryotes cell wall is present except PPLO.

6. Study of cell is called cytology.

7. Study of tissue is called Histology.

 8.Cell wall, plastids, and vacuoles are present only in plant cell.

9. Cell wall is made up of cellulose. Cellulose is most abundant homopolysaccharides on earth.

10.Biological hierarchy Cell- tissue- tissue system- organ- organ system- organism.

 on the basis of number cell divided into two types- unicellular:-amoeba, Paramecium, multicellular:- birds, reptiles, mammals. non Cellular:-- virus

Cell theory 

In 1939 SCHEIDEN,German botanist and schwann,A British zoologist ,led to development of the cell theory or  aur cell doctrine.

According to this theory all living things are made of cells and cell is the basic structure and functional unit of life. In 1855 Rudoff virchow Proposed and important extensions of Cell Theory that all living cells arise from preexisting cells( Omnis Cellula e cellula) 

virus is exception of Cell Theory.

1. viruses are acellular and do not have cellular machinery. Even then they are considered to be organism .

2.RBC’s and sieve tube cells continue to live without nucleus.

3. Protoplasm is replaced by non living materials in the  surface cells of skin and cork .

Difference between Plant cell and Animal cell 

PLANT CELL	ANIMAL CELL
a plant cell has a rigid wall on outside	cell wall is absent
It cannot change its  shape	an animal cell can often change its shape
plastids are found in plant cell	plastids are usually absent
mature cell has large central vacuoles	an animal cell may have many small  vacuoles
centrioles are usually absent	centrioles are found in animal cell
lysosomes are  rare	typically lysosomes occur in animal cell
reserve food is generally starch and fat	reserve food is usually glycogen and  fat

Structures present in animal cell and plant cell

NAME	COMPOSITION	FUNCTION
Plasma membrane	Phospholipid bilayer with embroidered protein	Selective passage of molecules into and out
cytoplasm	Consist of  aqueous ground substance, having starch,  glycogen etc.	provide medium for suspension
Mitochondria	inner membrane and outer membrane	powerhouse of cell
ribosomes	large ribonucleoproteins consisting of   RNAs and proteins with ribosome	role in protein synthesis
rough endoplasmic reticulum	with ribosomes	protein synthesis
Smooth endoplasmic reticulum	without ribosomes	Leopard synthesis
Golgi complex	consist of tubules	Cell wall formation

Structures present only in plant cell: 

(A) CELL WALL:--

It is the outer rigid protective  supportive and semi transparent covering of plant cells, fungi and some Protista

 cell wall perform a number of functions:-

1.Protects the Protoplasm against the mechanical injury.

 2.Protects the cell from attack of pathogens

 3.Provides rigidity and shape to the cell

 4.Cuin and suberin of cell Wall reduce the loss of water through the transpiration 

Structure of cell wall: A cell wall can have up to three parts- Middle lamella, primary wall and second

1. Middle lamella:- It is a Thin, amorphous and cementing layer between two adjacent cells. It is made up of calcium and magnesium. The softing  of ripe fruits is caused by partial solubilisation of pectin compound to produce Jelly like consistency.

2.Primary wall :-It is the first formed wall of cell which is produced Inner to the middle lamina .The matrix of wall consists of water, practin is the filler substance of matrix. 

3.Secondary wall: Secondary wall is laid inner to primary wall.It is formed when the cell has stopped growing. Cellulose content is comparatively high. 

(B)Plant cell vacuole:- more than 90% of the space of plant cell is occupied by single membrane bound fluid-filled vacuole.It maintain turgidity in the plant cell .It stores water, mineral, salt, food pigment, waste etc.

(C)Plastids: Largest cytoplasm organelles in the cell .Plastid was introduced by E.Haeckel in 1866. Plastids are semi autonomous organelles having DNA and double membrane and double membrane envelope which Store or synthesis Various types of organic compounds. With exceptions of some  protistants, Plastids, are  restricted to plants  only. Plastids develop from colourless precursors called  proplastids. Proplastid have the ability to divide and differentiate into various type of plastids. Depending upon their colours, plastids are of three main types- leucoplasts, chromoplasts, chloroplasts.

1) leucoplasts:- they are colourless plastids.  leucoplast have variable size and form e.g. rounded, oval, cylindrical, filamentous etc. There are three type of spherical leucoplast 

(A) amyloplast- they are containing leucoplast, here  food is stored. 

B)Elaioplasts-The colourless plastids store fat.

C)Aleuroplasts-the plastids contain protein in the amorphous crystalloid state.

2).Chromoplasts:- the plastid Yellow or reddish in colour because of the presence of carotenoid pigments,Chlorophylls are absent.Change of colour from Green to red during the ripening of tomato and chilli is due to transformation of chloroplast to chromoplast.The orange colour of carrot roots is due to chromoplast. chromoplast provide colour to many flowers for attracting pollinating insects they provide bright red or Orange colour to fruits for attracting animal for dispersal. 

3).Chloroplast:- they are green is plastids which  posses photosynthetic pigments, chlorophylls and carotenoids, and take part in synthesis of food from in organic raw materials in the presence of radiation energy .Chloroplast of algae other than green ones are called chromatophores

Mitochondria: -

Mitochondria are cell organelles aerobic eukaryotes which take part in oxidative phosphorylation and krebs cycle of aerobic respiration.They are called powerhouse of cell because they are the major centres of release of energy in the aerobic respiration.They were first observed by kolliker  in 1850.In muscles cells of insects and called  them sarcosomes.Later on altmann discovered mitochondria in plants and called them as a bioplastic.Benda(1897)gave the present name of Mitochondria to the organelles. 

Mitochondrial  ribosomes are 55 s to 70s in nature. They do resemble the chromosome of prokaryotes. DNA is naked. It is commonly circular but can be  linear. DNA makes the  mitochondrion semi autonomous. An organism generally receives mitochondria from its mother. 

Nucleus :-

Nucleus is a specialised double membrane bound protoplasmic body which contains all the genetic information for controlling cellular metabolism and transmission to the posterity.

A nucleus is the largest cell organelle. Nucleus was first  studied  in  orchid root cells by Robert Brown in 1831. A nucleus is present in all living Eukaryotic cell with the  exceptions of mature sieve  tube of vascular plant and red blood corpuscles of mammals. Even here A nucleus is present during the early stages of their development. In nucleus thread-like structure is present which is called chromatin .

Chromatin:-It is hereditary DNA protein Complex which is named so because of its ability to get stained with certain basic dyes.

Functions:-

 Nucleus is an essential and integral part of Eukaryotic cells. Stores genetic information in its DNA molecules which can be passed on to daughter cells. It also controls cellular activities.

1.Nucleus contains Hereditary material called chromatin.Chromatin is a DNA protein complex. Ribosomes are formed in nucleolus part of the nucleus. 

2.Nucleic acid was first isolated by Frederich meischer From the nuclei of  pus cells.

nucleoside = pentose sugar+ nitrogenous base

nucleotide= pentose sugar+ nitrogenous base+ phosphate

3. In 1953 Watson and Francis crick proposed the three dimensional structure of DNA 

NOTE:-    DNA contain- Adenine(A),Guanine(G),Cytosine(C),Thymine(T).

        RNA contains-Adenine(A),Guanine(G),Cytosine(C),Uracil(U).

Chromosomes:-

They are Rod  or thread like deeply  stainable condensed chromatin fibre which are hereditary vehicles as they store and transmit coded hereditary information.They are meant for equitable distribution of genetic material. The number is fixed and is the same in all the individuals of a species. There is a single set in in Gametophytic or haploid form and two sets of  sporophytic or  diploid form.

Every chromosome is made from two chromatid, two chromatids mutually join at a place which is called  centromeres.

On the basis of position of centromere chromosome are  following type:-

 1. Acentric:- if centromere  is absent the chromosome is called acentric chromosome.

2.Telocentric:- when the centromere is suitable at one end of the chromosome, chromosome is called telocentric.

 3. Acrocentric:- when the chromosome is divided into a very small segment at one end and a very large segment on the other end ,It is called acrocentric.

4. Submetacentric:- when the chromosome is divided into two unequal segments, one of which is slightly larger than the other forming L or J shaped chromosomes, it is called submetacentric.

5. metacentric:- when two segments are equal or at most forming v- shaped  structures because the centromere is treatable in the centre, it is called metacentric.

 Chromosome functions:

Chromosomes contain genes. All the hereditary information is located in the  genes.

Chromosomes form a link between the offspring and the parents.

Some chromosomes called sex chromosomes( x  and y) determine sex  of individuals.

Through the process of crossing over, chromosomes introduce variation 

GENE:- A gene is a locus of DNA a that encodes a functional RNA or protein product,and is the molecular unit of heredity,Gene was coined in 1909 by Dennish botanist wilhelm Johannsen, while the related word  Genetics was first used by William beteson in 1905.

Chromosomes are the r Carriers of genes.

 In humans 30 thousand genes Are present .When  one gene controls more than one character then it is called pleiotropic gene.

 Ribosomes:-

Palade( 1955) Also coined the term of ribosome. Ribosomes are neked  ribonucleoprotein  protoplasmic particles( rnp) with a length of 200- 300  angstrom And diameter of 170 -240angstrom  which function as the sides for protein or polypeptice Synthesis. Ribosomes are popularly known as protein factories. Each ribosome consists of two unequal subunits, larger dome-shaped and smaller oblate ellipsoid.

 some important points:-

Ostrich’s egg is largest cell

 cell organelles is the living structures present in cell 

 centrosome is present only in an animal cell that helps to initiate cell division in an animal cell by providing spindle fibre.

 all cells perform some life activities like growth ,reproduction, respiration, excretion, movement etc. on the basis of life activities we can differentiate living and nonliving.

 life activities( life process) occurs in cell