Nucleotides and nucleic acids

• DNA and RNA are nucleic acids
• What is each nucleotide formed from?

  • a pentose sugar
  • nitrogen containing organic base
  • phosphate group
• What are the components of DNA nucleotides?

  • A deoxyribose sugar with hydrogen at 2' position
  • a phosphate group
  • one of the four nitrogenous bases - a,c,g or t
• What are the components of RNA nucleotides?

  • ribose sugar
  • phosphate group
  • one of the four nitrogenous bases - A,C,G or U
• What does the presence of the 2' hydroxyl group do to RNA?

  Makes it more susceptible to hydrolysis.
• Two structural forms of nitrogenous base =

  • purines
  • pyrimidines
• The bases adenine and guanine are purines - they have a double ring structure.
• The bases cytosine, thymine and uracil are pyrimidines they have a single ring structure.
• Separate nucleotides are joined together via condensation reactions.
• condensation occurs between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide.
• the chain of alternating phosphate groups and pentose sugars produced as a result of many phosphodiester bonds is known as the sugar-phosphate backbone.
• synthesis of polynucleotides requires formation of phosphodiester bonds.
• In organisms energy is required for:

  • anabolic reactions
  • moving substances
• In animals energy is also required for:

  • muscle contraction
  • the conduction of nerve impulses
• ATP from respiration is used to transfer all energy-requiring processes in cells.
• ATP is a nucleotide
• ATP is a phosphorylated nucleotide
• DNA is a polynucleotide - meaning its made up of many nucleotides together in a long chain.
• DNA molecules are made up of two polynucleotide strands lying side by side, running in opposite directions - the strands are said to be antiparallel.
• Each DNA polynucleotide strand is made up of alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone.
• The phosphodiester bonds link the 5-carbon of one deoxyribose sugar molecule to the phosphate group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-carbon of the deoxyribose sugar molecule of the next nucleotide in the strand
• • Each DNA polynucleotide strand is said to have a 3’ end and a 5’ end (these numbers relate to which carbon on the pentose sugar could be bonded with another nucleotide)
• As the strands run in opposite directions (they are antiparallel), one is know as the 5' to 3' strand and the other is known as the 3' to 5' strand.
• The nitrogenous bases of each nucleotide project out from the backbone towards the interior of the double-stranded DNA molecule
• The two antiparallel DNA polynucleotide strands that make up the DNA molecule are held together by hydrogen bonds between the nitrogenous bases
• Practical investigations can be conducted to purify (isolate) DNA via the process of precipitation
• A common method used to isolate DNA is known as the 'Marmur preparation'
• • The Marmur preparation involves three basic steps:
  • Breaking (lysing) the cells and disrupting the nuclear membranes to release the DNA
  • Using enzymes to denature and remove the proteins (histones) associated with the DNA
  • Precipitating the DNA using an organic solvent (e.g. ethanol)
• Example practical investigation: extracting DNA from onions

  • Onions are good to use for this investigation as their cells contain a relatively large amount of DNA
  • Fruits that also have relatively large amounts of DNA in their cells, such as strawberries, bananas and kiwis, can also be used