Virus

• Virus was discovered by => Dimitri Ivanovsky (In 1892).
• Dimitri Ivanovsky discover virus during investigation of plant disease called Tobacco mosaic.
• Study of Virus is called as Virology.
• First discovered virus => Tobacco mosaic virus.

Characteristics of Virus:

1. Complete lack of cellular level composition like Cytoplasm, Cell membrane, Cell organelles etc.
2. Inside plant viruses transmit through phloem and Inside animal viruses transmit through blood.
3. Viruses have either DNA or RNA but both never.
4. viruses is composed of neucleoproteins.
5. Viruses is assumed as accessories of living and non-living organisms. Thus viruses exhibit the properties of both living & non-living.

Sr. No.	Living properties of Virus	Non-Living properties of Virus
1	The presence of DNA or RNA.	Absence of cell.
2	Structural diversity.	Lack of protoplasm.
3	Geneticity & Parasitic properties.	Non re-productivity & growth outside
4	Sensitivity and Evolution.	Stored in the form of crystal outside
5	To spread diseases.	Lack of metabolic activities like

Structure of Virus:

 

      There are three main constituents(Components) in the structure of virus.

1. Protein caspid.
2. Nucleic acid (DNA or RNA).
3. Thick outer layer.

• In plant virus nucleic acid RNA is present.
• In animal virus nucleic acid DNA is present.

Types of Virus:

1) Plant Virus:

• This is a nucleic acid of RNA.
• The virus yellow mosaic virus (YMV) is a plant virus.

2) Animal Virus:

• This is a nucleic acid of DNA or RNA & usually spherical in shape.
• The virus like influenza, mups etc. are animal virus.

3) Bacteriophase:

• Such virus only depend on bacteria.
• In this virus DNA are present only & can destroy other viruses.
• It is also called as T2 Phase virus.

Advantages of Viruses:

• Used in study of Biotechnology.
• Bacteriophase virus used as a water preservative & due to its presence water doesn't rotten & remains fresh. 
• Viruses are useful in cleaning the blue green algae. 

   <Biology Index> 

Monera Kingdom, Bacteria

Monera Kingdom:

• Unicellular.
• Prokaryotic.
• Contain 70S Ribosome.
• DNA is not bounded by nuclear membrane.
• Lack of organelles mitochondria, lysosomes, plastids, Golgi bodies, endoplasmic reticulum, centrosome, etc.
• Eg:- Bacteria, Blue green algae (Cynobacteria).

    Bacteria: 

• Invented by => Antony van Leeuwenhock (In1683).
• Father of bacteriology => Antony van Leeuwenhock.
• Name bacteria was given by => Aranberge (In 1829).
• This is a prokaryotic cell & kept under Monera kingdom.
• In 1881 Robert Coach detected & separated bacteria of anthrax & tuberculosis.
• Chlorophyll & Mitochondria are absent & respiratory activities done by misosomes.
• Cell wall is made up of Phospholipid.

Cell Division

• Firstly observed by Flemming (in 1882).
• Hence Flemming is known as Father of Cell division.
• According to theory of cell division old cells splits into new cells & formation of new cell is called Cell division.
• This process is also called as Cell production.

• Types of cell division:
• Amitosis
• Mitosis
• Meiosis

Cell Cycle

• In cell division old cells are split and new cells are form and the repetition of this process is called as cell cycle.
• Cell cycle has four stages:
• Gap1 Phase (G1)
• Synthesis Phase (S)
• Gap2 Phase (G2)
• Mitosis Phase (M)
• G1, S and G2 phase are collectively known as Inter phase.

1. Gap1 Phase (G1):
• Cell is prepare for cell division.
• At restriction point cell is committed to division and moves into S phase.

Genetics

• Genetics word first used by => W. Watson (in 1905).
• Transmission of character from one generation to next generation is called Heredity.
• The process of transfer of hereditary character from generation to generation called as Genetics.
• The characteristics which transmit from generation to generation is transported by Gene.

Gene: Gene word first coined by => W. Johannsen (in 1909). It is a unit of hereditary material located on chromosome. Gene itself or with other gene determine character of organism. Gene exist in number of alternative forms termed as alleles. Gene occasionally undergo for radial changes called as Mutation. The modern concept of perception about the gene was given by => Benjer (in 1956). Functional unit of gene => Cistron Unit of gene responsible for mutation => Muton Unit of gene take a part in recombination => Recon In Human 35000 gene are present.

• Gregor Johann Mendel said that hereditary character is transfer by gene.
• Hence Gregor Johann Mendel is known as Father of Genetics.

Mendel's Experiment:

• Mendel chooses 7 pair of pea plant species for his experiment.

 

Characters	Dominant characters	Recessive characters
Shape of the seed.	Spherical smooth seed.	Wrinkled seed.
Color of the cotyledon.	Yellow	Green
Color of flower.	Red	White
Shape of the fruit.	Smooth	Shrinked
Color of the fruit.	Green	Yellow
Position of the flower.	Tall	Farthest
Length or Height of the plant.	Tall	Dwarf

Mono-hybrid Cross:

Mendel made cross between 2 pure plant having contracting character for single trait called Mono-hybrid cross (i.e. Tall & Dwarf plant for height)

 

Phenotype ratio => 3 : 1

Genotype ratio => 1 : 2 : 1

Di-hybrid Cross:

Mendel made cross between 2 pure plant having in 2 pair of contracting character i.e. color & shape of seed called Di-hybrid cross. (i.e. Plant having round seed with yellow color & wrinkle seed with green color.)

 

Phenotype ratio => 9 : 3 : 3 : 1

Genotype ratio => 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1

 

Mendel's Law of Heredity:

• On the basis of mono-hybrid and Di-hybrid cross Mendel proposed law of heredity.

1. Mendel's First Law: (Law of dominance)

• According to it when two dissimilar unit factors are present in an individual only one is able to express.
• One that express itself is dominant character while which fail to express is recessive character.
• In the first generation only the dominant character is visible, while the recessive character is hidden and it appears in the next generation.

 

2. Mendel's Second Law: (Law of segregation)

•  According to this law during the gametes formation both the character which governed by gene is segregated and out of these factors only one factor is reached in the gamete.
• Both factors never come at a time in the gamete.
• This law is also called the Law of purity of Gametes.

3. Mendel's Third Law: (Law of Independent Assortment)

•  According to this law various pairs of the factors which exist in organism are independent to each other.
• Thus organism of new appearance may born.

 

Terms Related to Genetics:

1. Phenotype:
• The characteristics of the organism which are directly & visibly appreciable is called Phenotype.

Chromosome, DNA, RNA

Chromosome:

• Chromosome name was given by => Waldeyer (in 1888)
• Chromosome is thread like structure found in nucleus.
• Chromosomes are basic constituents of genetic substance Chromatin.
• During Cell division Chromatin breaks into pieces and form Chromosome.
• Each Chromosome is made up of two Chromatids, which joint together at a point called centromere.
• On Chromosome various genes are located.
• Gene is the functional unit of DNA, made by segment of DNA.
• Characteristics which transmit from generation to generation is transported by Genes and these genes are carried out by Chromosome.
• Thus Chromosome are called as Vehicle of Heredity.

Number of Chromosome in different organism:

Organism	Number	Pair
Pigeon	40	80
Chimpanzee	24	48
Cat	19	38
Onion	8	16
Dog	39	78
Human	23	46
Frog	13	26
Pea	7	14
Horse	32	64
Wheat	21	42
Tomato	12	24
Ascaris	1	2
Housefly	6	12
Mosquito	3	6
Monkey	21	42
Tobacco	24	48

• One set of Chromosome (Haploid) is called Genome.
• Two sets of Chromosome (Diploid) found in somatic cells.

DNA: (Deoxyribo Nucleic Acid)

• First who isolated DNA from nucleus of pus cells => Friedrich Miescher (in 1869).
• DNA is Polynucleotids.
• Almost all amount of DNA is present in nucleus of cell but very small amount also present in Mitochondria and Green Plastids.
• In 1953 Watson and Crick gives double helix model of DNA, each helix has a diameter of nearly 20Å.
• DNA is macro molecule in which large number of nucleotides are present.
• These nucleotides has three components.
• Nitrogen base
• Sugar
• Phosphate group.

• Nitrogen  base of double helix form a pair with the help of hydrogen bonds.
• Adenine pairs with Thymine (A = T).
• Guanine pairs with Cytosine (G = C).
• Adenine and Thymine are complementary to each other. 
• Guanine and Cytosine are complementary to each other.
• Hydrogen bond between nitrogen base holds two strands together.

Function of DNA:

• It contain genetic information in coded form.
• DNA synthesis RNA.

RNA: (Ribo Nucleic Acid)

• It is a single standard nucleic acid but in some virus it has double standard structure like in Retrovirus.
• Main function of RNA is to assist Protein synthesis but in some plant and virus it acts like carrier of genetic substance.
• Thus in viruses genetic substances are either DNA or RNA but not both.
• RNA is made up of Phosphate, Ribose sugar and Nitrogen base.
• RNA is found in nucleus as well as cytoplasm.

RNA is of three types:

1. Messenger RNA (mRNA):
• It carries the information of protein synthesis from DNA of the nucleus to Ribosome in coded form.
• It is 3-5% of all RNA.
• It also help in selecting amino acids.

Difference between Plant cell and Animal cell

Sr. No.	Plant Cell	Animal Cell
1	Plant cells are larger in size.	Animal cells are generally smaller in size.
2	Cell wall is present and made up of cellulose and chitin.	Cell wall is absent.
3	Plastid is present.	Plastid is absent.
4	Centrosome is absent.	Centrosome is absent.
5	Vacuoles are larger in size.	Vacuoles are smaller in size.
6	Chlorophyll is present except fungi & bacteria.	Chlorophyll is absent.

<Biology Index>