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.
2. Ribosomal RNA (rRNA):
• It is attached on Ribosome and helps in protein synthesis.
• It forms from DNA in the nucleus of the cell.
• It is nearly 80% of total RNA.
3. Transfer RNA (tRNA):
• It is a carrier of amino acid and transfer it to Ribosome where protein in formed.
• It is 10-15% of total RNA.
• It is smallest among all.
• It has two dimensional structure like clove leaf.

Some Important Points:

• Transcription: Formation process of RNA from DNA is called Transcription.
• Reverse Transcription: Formation process of DNA from RNA is called Reverse Transcription.
• Translation: Last process of protein synthesis is called Translation.
• Duplication/Replication: Formation process of DNA from DNA is called Duplication/Replication.

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