STRUKTUR DAN FUNGSI ASID NUKLEIK (DNA/RNA) A. Chemistry and Composition of Acid Nucleic -
Composition Nitrogenous Bases (purine vs pyrimidine) Nucleoside vs nucleotide Nucleoside mono-, di- and triphosphate Polynucleotide
B. Structure of DNA/RNA DNA/RNA Composition Studies (bases): 1. Erwin Chargaff (1950) - A=T - CΞG - A + G = C + T ↔ (A + G)/(C + T) = 1.0 - but, (A + T)/(C + G) ≠ 1.0
1.
X-ray Diffraction – William Ashbury (1947) – periodicity of 3.4 Å and the the bases are stacked on top of each other – Rosalind Franklin and Maurice Wilkins (1950 - 1953) – confirmed periodicity and proposed the helical structure of DNA – Linus Pauling visualized DNA as a triple helix
DNA – Watson-Crick (1953) - Two polynucleotide strands are coiled around one axis forming a double helic - Both strands are in anti-parallel orientation - Sugar-phosphate backbone located on the outside - The bonded bases of both strands are located within the helix and are stacked 3.4Å (0.34 nm) apart, and are perpendicular to the axis - Nitrogenous bases of each strands are bonded pair-wise to bases of the other strands via hydrogen bonding (A=T dan CΞG) - Each complete helical turn is 34Å (3.4 nm) long, so there are 10 base pairs per helical turn - Presence of major and minor grooves - The helix diameter is 20Å (2.0 nm) - Right-handed helical turn - Type B DNA
Other Forms of DNA: DNA-A ─ 11 base pairs/helical turns, dameter 23Å DNA-B ─ 10 base pairs/helical turns, diameter 20Å DNA-C ─ 9.3 base pairs/helical turns, diameter 19Å DNA-D ─ base pairs/helical turns, no CΞG pairs DNA-E ─ 7.5 base pairs/helical turns, no CΞG pairs DNA-Z ─ base pairs/helical turns, diameter 18Å, only CΞG pairs, left handed turn
Struktur of RNA - Mostly single stranded - Berstruktur sekunder - Three major Classes: - ribosomal RNA (rRNA) - messenger RNA (mRNA) - transfer RNA (tRNA)