DNA and RNA

The Structure of DNA - Deoxyribonucleic acid

• DNA = a polynucleotide - made up of lots of nucleotides joined together
• Nucleotide = made  up of a deoxyribose sugar, a phosphate group and a nitrogenous base
• Each nucleotide has the same sugar and phosphate, but base can vary
• Four bases: Adanine (A), Thymine (T), Cytosine (C), Guanine (G)
• A+T= purines
• C+G=pyramidines

The Structure of RNA - Ribonucleic acid

• Similar to DNA - both made of nucleotides - sugar, nitrogenous base and phosphate
• Make proteins from instructions in DNA
• Nucleotides form polynucleotide strand, joined between sugar and phosphate

Differences between DNA and RNA

• Sugar in RNA nucleotides - ribose sugar, not deoxyribose sugar
• Nulceotides form a single polynucleotide strand (not double)
• Uracil (a pyramidine) replaces thymine as a base. Uracil always pairs with adanine in RNA

The formation of a DNA molecule

• DNA nucleotides join together = polynucleotide strands
• Nucleotides join together between phosphate of one nucleotide and the sugar of another
• Two DNA polynucleotide strands join by hydrogen bonding between bases
• Adanine always pairs with thymine and cytosine always pairs with guanine - this is complementary base pairing
• Two hydrogen bonds form between A and T. Three hydrogen bonds form between C and G
• Two anti-parallel polynucelotide strands twist forms DNA double helix

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