DNA Structure1) 2 polynucleotide chains, which are anti-parallel, interlock about the same axis2) Each form a right hand helix and both are bonded by hydrogen bonds to form a double helix3) 3’ to 5’ sugar phosphate backbone4) Width = width of a base pair = width of pu + py5) Nitrogenous bases project inside helical structure at 90 deg6) A=T and C G (3 H)7) Complete turn = 3.4 nm8) 1 base pair = 0.34nm9) Base sequence is not fixed but one strand’s base sequence determines the other by

complementary base pairing

DNA packing Negatively charged phosphate backbone form strong ionic bonds with positively charged

lysine residues on histones DNA double helix coil around 8 histones, forming a nucleosome 6 adjacent nucleosome linked by linker DNA further coils into a solenoid = 30nm Solenoid further coil by forming looped domains on non-histone protein scaffold

euchromatin heterochromatin (During metaphase) Heterochromatin further condense to form rod-like structure =

chromosome

mRNA structure1) temporal, single stranded polynucleotide2) Synthesised in nucleus, mitochondria, chloroplast by transcription3) Transported from nucleus to cytoplasm via nuclear pores4) Complementary to parental template strand5) Carries DNA message from nucleus to cytoplasm in the form of codons 6) Act as template for translation7) Specific binding sites for amino-acyl tRNA complexes to form specific amino acid

translation

tRNA structure1) 20 kinds = 20 amino acids2) H bonds b/w complementary base pairing along chain fold up to form a cloved shape

structure3) Sequence ends with A at 5’ end, CCA at 3’ end4) Anticodon = 3 nucleotides complementary to one or more codons on mRNA5) Carry specific amino acid to specific codon mRNA for translation

rRNA structure1) Complex molecules = double or single helices2) Synthesised in nucleolus3) rRNA + specific proteins in cytoplasm = ribosomes4) Provides structural support for temporarily stabilizing union of mRNA and tRNA5) Keeps ribosome functional orientating large variety of amino-acyl tRNA complexes in

correct position6) Align mRNA such that incoming amino-acyl tRNA complexes can base pair conveniently7) Enzyme peptidyl transferase in large subunit Ribosome

o A site: incoming tRNA with next amino acido P site: tRNA with growing polypeptide chaino E site: site of discharge of tRNAo mRNA binding site

Nucleotide

Nitrogenous base + C1 of pentose sugar = nucleoside condensation reaction with elimination of water

Nucleoside + phosphate group = nucleotide, held by phosphoester linkage condensation reaction with elimination of water

Dinucleotide Condensation reaction between 5’ phosphate group on carbon 5 of pentose sugar and the

adjacent 3’ hydroxyl group on carbon 3 of adjacent pentose sugar, held by strong phosphodiester bonds

Further condensation reactions forms a polynucleotide chain with 3’ to 5’ sugar phosphate backbone made up of identical pentose sugar and phosphate group along polynucleotide chain

Nitrogenous bases project 90 deg sideways

Semi-conservative DNA replication = both parental templates act as template and form a newly-synthesised DNA double helix made up of one parental strand and one daughter strand (hybrid)