Nucleic Acids

• DNA structure

  Double helix/ double stranded Deoxyribose sugar Phosphate ion Adenine, Thymine, Guanine and Uracil bases Hydrogen bonds between bases, phosphodiester between nucleotides
• Purine bases

  Double ring Adenine and Guanine
• Pyramidine bases

  single rings Cytosine and Thymine/Uracil
• DNA vs RNA

  DNA double strand, RNA single stranded DNA deoxyribose, RNA ribose RNA shorter RNA has Uracil instead of Thymine
• DNA structure to function

  Helical- compact for storage of genetic info

  H bonds between bases- so strands can be easily unzipped for replication/ to be transcribed

  Long so stores all genetic info in genome of organism

  Sugar-phosphate backbone so stable and strong and bases are protected

  Double stranded so both strands can be used during replication as templates

  Sequence of bases- amino acids sequence of proteins can be coded

  Comp base pairing- for accurate replication/transcription
• Semi-Conservative replication

  DNA helicase unwinds DNA by breaking h bonds between comp bases and both strands act as templates

  Free nucleotides attach themselves to complimentary bases of the templates by comp base pairing

  DNA polymerase joins free nucleotides together by phosphodiester bonds forming sugar-phosphate backbone, requiring atp to form bonds

  Two new molecules are made of one old and one new strand
• Who showed the process of semi-conservative replication

  Mehselson+Stahl grew e-coli on agar plates with either 14N or 15N In bacteria grown on 15N then the less dense 14N, DNA extracted was less dense than purely 15N Because N was incorperated into DNA by nitrogenous bases and the density change shows replication is semi-conservative because in 1st gen there was 1 density line roughly between 14N and 15N expected values