nucleic acids

• best known nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)
• DNA has a double helix structure
• the monomer of DNA is nucleotides
• nucleotides consist of a pentose sugar, a phosphate group, and a nitrogen-containing organic base.
• bases can be:

  cytosine

  guanine

  thymine

  adenosine

  uracil
• the bond between two nucleotides is a phosphodiester bond, forming a dinucleotide
• RNA is a single relatively short polynucleotide chain where the pentose sugar of its nucleotides is always ribose
• the organic bases in RNA is uracil, adenine, cytosine and guanine
• two strands of very long DNA are held together by hydrogen bonds between complementary bases
• adenine pairs with thymine

  cytosine pairs wits guanine
• DNA is a stable molecule because:

  • phosphodiester backbone protects more chemically reactive bases inside the double helix
  • there are three hydrogen bonds between cytosine and guanine and two hydrogen bonds between adenine and thymine. the more C-G pairings, the more stable the DNA molecule
• test for non-reducing sugars

  heat solution with acid and neutralise

  Add Benedict's reagent

  Red precipitate
• DNA is adapted to its function:

  • as it has a very stable structure, can pass on from generation to generation without change, only rarely mutates
  • two separate strands joined only by hydrogen bonds, which allows them to separate during DNA replication and protein synthesis
  • extremely large molecule, allows it to carry a massive amount of information
  • base pairs protected from corruption by phosphodiester backbone
  • base pairing leads to DNA being able to replicate
• gene is a sequence of DNA that codes for a specific protein or RNA
• 5‘carbon is attached to a phosphate group

  3’carbon is attached to a hydroxy group
• the two strands of DNA are antiparallel, meaning they are in opposite directions.

  one strand runs 5’ to 3‘ the other strand runs 3’ to 5’
• DNA polymerase acts in the 5' to 3' direction and adds nucleotides to the growing strand
• semi conservative replication requirements

  • four types of nucleotide bases
  • both strands of DNA act as a template
  • enzyme is DNA polymerase
  • chemical energy is required to drive the process
• process of semi-conservative replication

  DNA helicase breaks the hydrogen bonds between base pairs

  double helix separates into two strands

  the DNA strand acts as a template to which complementary free nucleotides bind by specific base pairing

  DNA polymerase form phosphodiester bonds between nucleotides of each new strand on each original DNA strand in a condensation reaction .
• each DNA molecule has one strand of original DNA and a new strand of new nucleotides
• meselsohn and stahl

  • N-14 bacteria is grown in N-14 medium, is then centrifuged, DNA settles at the top
  • N-15 bacteria grown in N-15 medium, then centrifused, DNA settles at the bottom
  • N-14 bacteria is grown in N-15 medium for one generation, then centrifuged, DNA settles in the middle
  • indicated that the new strand of DNA was made of N-15
• structure of ATP (adenosine triphosphate)

  • adenine
  • ribose
  • phosphates
• bonds between phosphate groups are unstable and so have low activation energy
• when the bonds between phosphates break, they release a considerable amount of energy
• atp -> adp + inorganic phosphate + energy
• atp to adp is a hydrolysis reaction, catalysed by ATP hydrolase
• atp is synthesised in three different ways

  • photophosphorylation - in chlorophyll containing plant cells during photosynthesis
  • oxidative phosphorylation - in plant and animal cells during respiration
  • substrate-level phosphorylation - in plant and animal cells when phosphate groups are transferred to donor molecules to ADP
• ATP is :

  • an immediate source of energy - unstable bonds between P ions
  • can be rapidly re-formed
• ATP releases less energy than each glucose molecule, so it is released in smaller more manageable quantities
• hydrolysis of ATP is a single reaction that releases immediate energy

  breakdown of glucose is a long series of reactions
• ATP is used in :

  • metabolic processes - provides energy to build up macromolecules
  • movement - for muscle contraction
  • active transport - provides energy to change shape of carrier proteins in plasma membranes
  • secretion - to form lysosomes for the secretion of cell products
  • activation of molecules - to phosphorylate other compound to make them more reactive by lowering their activation energy
• purines - adenine and guanine

  pyrimidines - cytosine and thymine