Nucleic Acids , Water and Inorganic Ions

• Key molecules required for life

  • Nucleic acids
  • ATP
  • Water
  • Inorganic ions
• Nucleic acids


  Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information carrying molecules

  
• In ALL living cells, DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes

  
• Monomer


  Smaller unit from which a polymer is made
• Polymer


  Molecule made from a large number of monomers joined together in a chain
• Nucleotide


  Monomer of nucleic acids (DNA and RNA)

  
• Polynucleotide


  Polymer of nucleic acids (DNA and RNA)

  
• Polynucleotide formation


  Condensation reaction - removal of water between two nucleotide monomers to form a phosphodiester bond
• Polynucleotide strands are formed when many nucleotides link to form a long chain

  
• A phosphodiester bond is formed between the phosphate group of one nucleotide to the 3rd carbon of the (deoxyribose/ribose) sugar in the next nucleotide

  
• The sugar-phosphate backbone of the nucleic acid is very strong and stable
• DNA molecule


  • Has a double helix structure
  • Consists of 2 polynucleotide chains held together by weak hydrogen bonds between specific complementary base pairings

  
• Complementary base pairs


  • Adenine and Thymine are joined by 2 hydrogen bonds
  • Cytosine and Guanine are joined by 3 hydrogen bonds

  
• If we are given the sequence of bases on one DNA strand, we can work out the sequence on the other strand

  
• If we are given the percentage of one base, we can work out the percentages of the other complementary bases
• The sequence of the bases along the nucleotide chain is variable. This is the basis of the genetic code and how information is stored in DNA

  
• The function of DNA is that it codes for the sequence of amino acids (3 bases = Triplet = 1 amino acid). Long strands of DNA code for the primary structure of polypeptide chains and proteins

  
• mRNA


  • A relatively short polynucleotide chain, which is normally a single stranded helix
  • Used to transfer genetic information from DNA to ribosomes

  
• DNA consists of two antiparallel nucleotide strands

  
• Adenine pairs with Thymine and Cytosine pairs with Guanine to ensure the two strands remain parallel

  
• Each end of the DNA molecule is labelled with a 5'-end and a 3'-end (pronounced 5 prime end and 3 prime end)

  
• The 5' end has a phosphate group and the 3' end has a hydroxyl (OH) group
• This directionality is important for DNA replication and protein synthesis

  
• Structure of DNA


  • Provides strength and stability
  • Protects the information coded in the bases
  • Protects the hydrogen bonding between bases
  • Allows a large amount of information to be stored
  • Allows the molecule to be compact
  • Allows information to be stored and coded for amino acids and proteins

  
• Semi-conservative DNA replication


  Each new DNA molecule contains an original and a new strand, and is identical to the original DNA

  
• Semi-conservative DNA replication


  1. DNA helicase unwinds and unzips the DNA strands by breaking hydrogen bonds

  2. Each strand acts as a template

  3. New DNA nucleotides are attracted to exposed complementary bases on template strands by base pairing

  4. DNA polymerase joins the adjacent nucleotides together through a condensation reaction forming phosphodiester bonds

  
• Semi-conservative replication ensures that each new DNA molecule contains an original and a new strand and is identical to the original DNA

  
• DNA polymerase


  Catalyses the condensation reactions between DNA nucleotides to form the sugar-phosphate backbone of the new strand

  
• DNA helicase


  Breaks the hydrogen bonds between complementary base pairs so each strand can act as a template

  
• You cannot hydrolyse hydrogen bonds, you can only break hydrogen bonds
• The Meselson Stahl experiment proved that DNA replicates semi-conservatively
• ATP (Adenosine triphosphate)


  • Consists of a nitrogenous organic (adenine) base, ribose sugar and three phosphate groups
  • Used as the energy source in cells to carry out essential life processes

  
• Why ATP is useful

  • Releases relatively small amounts of energy with little lost as heat
  • Releases energy instantaneously
  • Can phosphorylate other compounds making them more reactive
  • Can be rapidly re-synthesised
  • Is not lost from/does not leave cells
• Formation of ATP


  ATP is formed from ADP (Adenosine diphosphate) and inorganic Phosphate/Pi through a condensation reaction catalysed by the enzyme ATP synthase

  
• Hydrolysis of ATP


  ATP is easily hydrolysed back to ADP and Phosphate, releasing small manageable amounts of usable energy

  
• ATP is produced in respiration and photosynthesis
• Uses of ATP


  • Provides energy for: Muscle contraction, Active transport, Biosynthesis reactions
  • Phosphorylates other compounds making them more reactive
• ATP


  • Releases relatively small amount of energy/ little energy is lost as heat
  • Releases energy instantaneously
  • Phosphorylates other compounds, making them more reactive
  • Can be rapidly re-synthesised
  • Is not lost from/ does not leave cells
• Formation of ATP


  1. ADP + Pi (phosphorylation)

  2. Requires energy to add a phosphate group to ADP to form ATP creating a high energy bond

  3. Involves a condensation reaction and the enzyme ATP synthase

  
• Hydrolysis of ATP


  1. ATP breaks down to ADP and Pi in a hydrolysis reaction (requiring a molecule of water and the enzyme ATP hydrolase)

  2. Pi can be used to phosphorylate other compounds and make them more reactive