Category: Biology Second Paper

All protocellular organisms contain DNA. DNA is always located in chromosomes. Hence it is called chromosomal DNA. Chromosomes are also called nuclear DNA as they are located in the nucleus. Circular DNA is present in the mother body of mitochondria and in the stroma of chloroplasts.
Protocellular organisms Bacteria and cyanobacteria (blue green algae) contain circular nucleoid DNA and plasmid DNA in their cytoplasm. Such DNA molecules do not contain histone proteins.
Viruses such as vaccinia, variola, adeno herpes simplex, T2, TIV, ϕX174, M13, CMV etc. contain DNA. Smallpox, chickenpox and herpes viruses contain DNA.

The amount of DNA in the cells of each species of organism is specific. If the DNA molecules of the human body are joined together, the chain that will be created is 5-6 times the distance between the Earth and the Sun. The amount of DNA is expressed in picograms. 1 picogram = 10-12 grams. Chicken diploid cells contain 2.5 picograms and sperm contain 1.25 picograms of DNA. Human cells contain 5-6 picograms of DNA. An adult human body contains 100 picograms of DNA.

In 1869, Swiss physician and chemist Friedrich Miescher isolated DNA from the nuclei of sperm, sperm cells, and red blood cells of birds. He named it Nuclein. In 1874 he isolated nucleic from salmon sperm and named it protamine. In 1880 scientist Fisher discovered purine and pyrimidine. In 1889, Altmann named nucleic acid as nucleic acid. Albrecht Kossel discovered adenine, guanine, cytosine and thymine in 1910. In 1910 scientist Leven discovered deoxyribose sugar. In 1914, German chemist Robert Feulgen invented the Feulgen staining method for DNA. In 1928, British scientist Frederick Griffith realized that DNA contains all genetic information. In 1950 Erwin Chargaff mentioned Chargaff’s rule of DNA. At the same time, Maurice Wilkins and Rosalind Franklin presented the physical structure of the DNA molecule using X-ray crystallography. In 1952, Hershey and Chase proved that DNA is the genetic material of organisms. In 1953, J. D. Watson and F. H. Crick proposed the generally accepted model of DNA.

Deoxyribonucleic acid is abbreviated as DNA. The smallest part of the chromosome that is self-reproducing, regulates biological functions and transmits heritable characteristics and is capable of causing variation, mutation and evolution of organisms is called DNA. This is called the molecular basis of life. About 90% of the chromosomes of organisms contain DNA. There are two types of nucleotides in the DNA molecule. Exon and Intron Nucleotides. Meaningful parts are called exons and nonsense parts are called introns. The molecular weight of DNA is 106-109 daltons.

A molecule of pentose sugar and a molecule of nitrogenous base is called a nucleoside. It is of two types. Purine nucleosides and pyrimidine nucleosides.
(i) Purine Nucleosides: If the nitrogenous base forming the nucleoside is purine, it is called purine nucleoside. Carbon 1 of pentose sugar is linked to nitrogen 9 of base by glycosidic bond to form purine nucleoside. It is of two types. Adenosine nucleoside and guanosine nucleoside. Pentose sugars combine with adenine to form adenosine nucleosides and pentose sugars combine with guanine to form guanosine nucleosides.
(ii) Pyrimidine Nucleosides: When the nitrogenous base forming the nucleoside is pyrimidine, it is called a pyrimidine nucleoside. The 1st carbon of the pentose sugar is joined to the 1st nitrogen of the base by a glycosidic bond to form a pyrimidine nucleoside. It is of three types. Thymidine nucleoside, cytidine nucleoside and uridine nucleoside. Pentose sugar and thymine combine to form thymidine nucleoside, pentose sugar and cytosine combine to form cytidine nucleoside and pentose sugar and uracil combine to form uridine nucleoside.

Nucleotides
A molecule of phosphate and a molecule of nucleoside combine to form a nucleotide. That is, one molecule of pentose sugar, one molecule of phosphate and one molecule of nitrogenous base is called nucleotide. Nucleotide is the structural unit of nucleic acid. A nitrogenous base is attached to the 1st carbon of a pentose sugar and a phosphate is attached to the 3rd or 5th carbon to form a nucleotide. It is of two types. Purine nucleotides and pyrimidine nucleotides.
(i) Purine Nucleotide: If the nitrogenous base forming the nucleotide is purine, it is called purine nucleotide. It is of two types. Adenosine nucleotide and guanosine nucleotide. Pentose sugars combine with adenine to form adenosine nucleotides and pentose sugars combine with guanine to form guanosine nucleotides.
(ii) Pyrimidine Nucleotide: If the nitrogenous base forming the nucleotide is pyrimidine, it is called pyrimidine nucleotide. It is of three types. Thymidine nucleotide, cytidine nucleotide and uridine nucleotide. Pentose sugars and thymine combine to form thymidine nucleotides, pentose sugars and cytosine combine to form cytidine nucleotides, and pentose sugars and uracil combine to form uridine nucleotides.
Different types of nucleotides are AMP, GMP, CMP, UMP, TMP, dAMP, dGMP, dCMP, dUMP, dTMP etc.

Dinucleotide

Two molecules of nucleotide together are called dinucleotide. The 5th carbon of the pentose sugar of one nucleotide and the 3rd carbon of the pentose sugar of the other nucleotide are joined by a phospho-diester bond to form a dinucleotide.

Polynucleotide
Several nucleotides are linked together by phospho-diester bonds to form a long chain. It is called polynucleotide. In polynucleotides, the phosphate molecule is attached to the 5th carbon of the pentose sugar on one side and to the 3rd carbon of the pentose sugar on the other side. Nucleotides in polynucleotides are oriented towards each other R5 → R3 carbons. Each single helix of a DNA molecule is a polynucleotide chain.

Several nucleotides are linked together by phospho-diester bonds to form a long chain. It is called polynucleotide. In polynucleotides, the phosphate molecule is attached to the 5th carbon of the pentose sugar on one side and to the 3rd carbon of the pentose sugar on the other side. Nucleotides in polynucleotides are oriented towards each other R5 → R3 carbons. Each single helix of a DNA molecule is a polynucleotide chain.

Two molecules of nucleotide together are called dinucleotide. The 5th carbon of the pentose sugar of one nucleotide and the 3rd carbon of the pentose sugar of the other nucleotide are joined by a phospho-diester bond to form a dinucleotide.

A molecule of phosphate and a molecule of nucleoside combine to form a nucleotide. That is, one molecule of pentose sugar, one molecule of phosphate and one molecule of nitrogenous base is called nucleotide. Nucleotide is the structural unit of nucleic acid. A nitrogenous base is attached to the 1st carbon of a pentose sugar and a phosphate is attached to the 3rd or 5th carbon to form a nucleotide. It is of two types. Purine nucleotides and pyrimidine nucleotides.
(i) Purine Nucleotide: If the nitrogenous base forming the nucleotide is purine, it is called purine nucleotide. It is of two types. Adenosine nucleotide and guanosine nucleotide. Pentose sugars combine with adenine to form adenosine nucleotides and pentose sugars combine with guanine to form guanosine nucleotides.
(ii) Pyrimidine Nucleotide: If the nitrogenous base forming the nucleotide is pyrimidine, it is called pyrimidine nucleotide. It is of three types. Thymidine nucleotide, cytidine nucleotide and uridine nucleotide. Pentose sugars and thymine combine to form thymidine nucleotides, pentose sugars and cytosine combine to form cytidine nucleotides, and pentose sugars and uracil combine to form uridine nucleotides.
Different types of nucleotides are AMP, GMP, CMP, UMP, TMP, dAMP, dGMP, dCMP, dUMP, dTMP etc.

A molecule of pentose sugar and a molecule of nitrogenous base is called a nucleoside. It is of two types. Purine nucleosides and pyrimidine nucleosides.
(i) Purine Nucleosides: If the nitrogenous base forming the nucleoside is purine, it is called purine nucleoside. Carbon 1 of pentose sugar is linked to nitrogen 9 of base by glycosidic bond to form purine nucleoside. It is of two types. Adenosine nucleoside and guanosine nucleoside. Pentose sugars combine with adenine to form adenosine nucleosides and pentose sugars combine with guanine to form guanosine nucleosides.
(ii) Pyrimidine Nucleosides: When the nitrogenous base forming the nucleoside is pyrimidine, it is called a pyrimidine nucleoside. The 1st carbon of the pentose sugar is joined to the 1st nitrogen of the base by a glycosidic bond to form a pyrimidine nucleoside. It is of three types. Thymidine nucleoside, cytidine nucleoside and uridine nucleoside. Pentose sugar and thymine combine to form thymidine nucleoside, pentose sugar and cytosine combine to form cytidine nucleoside and pentose sugar and uracil combine to form uridine nucleoside.
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One of the chemical components of chromosomes is phosphoric acid. It contains 10% phosphorus element. Its molecular symbol is H3PO4. It contains one divalent oxygen atom and three monovalent hydroxyl groups. Oxygen and hydroxyl groups combine with a pentavalent phosphorus atom to form phosphoric acid.