DNA and RNA

• a nucleotide consists of a nitrogen containing base, a phosphate group and a pentose sugar
• the nucleotides join in a condensation reaction from the phosphate group to the pentose sugar of the other, forming a phosphodiester bond
• DNA is a double helix and is highly coiled and compact
• the pentose sugar in DNA is deoxyribose
• DNA has complemetary base pairing, adenine pairs with thymine, cytosine pairs with guanine
• there is two hydrogen bonds between adenine and thymine
• there is three hydrogen bonds between cytosine and guanine
• the two strands in DNA are antiparallel
• the pentose sugar in RNA is ribose
• uracil replaces thymine in RNA
• RNA is single stranded and is much shorter than DNA
• semi conservative replication is when half of the strands in each new DNA molecule is from the original strands
• 1. DNA helicase unwinds the double helix and breaks the hydrogen bonds
  2. each strand acts as a template for the complementary free floating DNA nucleotides
  3. DNA polymerase joins the nucleotodes in a condensation reaction and reforms the hydrogen bonds
• DNA polymerase works in opposite directions since its only complementary to the 3’ end of the DNA strand
• 1. two samples of bacteria were grown for many generations , one with light nitrogen (14) and one with heavy nitrogen (15)
  2. a sample of DNA was taken from both batches and was spun in a centrifuge the heavy nitrogen settled lower than the light nitrogen
  3. there was a band in the middle proving semi consecutive replication