: 200
DNA: Deoxyribose sugar (no 2'-OH), bases A/T/G/C, double-stranded helix, stores genetic information, more stable (no 2'-OH to catalyze hydrolysis), found mainly in nucleus, Chargaff's rules apply (A=T, G=C). RNA: Ribose sugar (2'-OH present), bases A/U/G/C (uracil replaces thymine), usually single-stranded, involved in protein synthesis, less stable, found in nucleus and cytoplasm, Chargaff's rules do NOT apply (no complementary strand). Three RNA types: mRNA carries code (5% of RNA), tRNA carries amino acids (15%, cloverleaf shape, has anticodon), rRNA forms ribosomes (80%, most abundant, has catalytic activity). Base pairing: A= (2 H-bonds), G≡C (3 H-bonds). Central dogma: DNA → mRNA → Protein. Key calculations: In dsDNA, if %A = x, then %T = x, %G = %C = (50-x). Total purines = total pyrimidines = 50%. Number of H-bonds in n bp with a AT pairs: 2a + 3(n-a). Higher GC content → higher Tm (melting temperature). These comparisons appear every year in JEE.