Nucleic acids (Biology)
- DNA is made up deoxy ribo necleotides arranged in a double stranded chain.
- Three components of a nucleotide are (i) Sugar (ii) Phosphate (iii) N2 bases
- Nucleotide – Phosphate = Nucleoside.
- Nitrogenous bases of DNA are Adenine (A), Thymidine (T), Guanine (G), and cytosine (C) Where A and G are purines; T and C are Pyrimidinines. RNA has uracil instead of Thymine
- The length of E.coli DNA is 4.6 × 106 BP and Human haploid DNA is 3.3 × 109 BP.
- The nucleotides in a DNA strand are connected to each other nucleotide by a phosphodiester bond (3 → 5 likage).
- Glycosidic linkage is created between N2 base and pentose sugar.
- The linkage between sugar and phosphate is made by covalent bond.
- The width of a DNA molecule is 20 A′ (P – P), 11.1A′ (Sugar – Sugar); 2.8 – 3.0A′ (4 bond)
- Length of a helix in a DNA is 34 A′ Hence distance between 2 nucleotide in a DNA is 3.4A′ As only 10 nucleotides are present in a helix 9 DNA.
- Watson and crick proposed the model of Double helical structure 9 DNA with the help of chargaff and franklin t wilkins.
- A pairs with T ; G pains with C; amount of 1 = amount & A; amount & 4 = amount & C with 2H bonds with 3H bonds
A+T/ G+C ratio is constant for the species, are the rule of chargaff.
- Franklin and wilkins performed X-ray crystallography to prove the crystalline nature g DNA, diameter, length and its helical nature.
- One end of DNA is represented by ′5″ as its 5th carbon atom possess free hydroxyl group. Other end of DNA is marked by ‘3’ as its 3rd carbon atom possess free hydroxyl group.
- DNA runs antiparallel in nature. A, B, C, D [right handed] and Z [left handed] are the different types g DNA , in which type B is found in human beings.
- DNA is packed as chromosomes with the half of histone proteins (H1, H2A, H2B, H3, H4) in which H1 is linked DNA and rest proteins act as dimer finally to get atamer structure.
- DNA is negatively charged which binds with positively charged histones which is made up of positively charged amino acids like lysine and Arginine.
DNA in Prokaryotes in Circular and prokaryotes are linear.
View this video for the topic Nucleic acids from 26:56 to 53:37
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