Nucleic acids

• Nucleic acids


  Polymers made of monomers called nucleotides
• Nucleotide


  • Contains a phosphate group, a pentose sugar, and an organic/nitrogenous base
• Pyrimidine bases

  • Thymine
  • Cytosine
  • Uracil
• Purine bases

  • Adenine
  • Guanine
• Adenosine triphosphate (ATP)

  Contains three phosphate groups, a ribose sugar, and the organic base adenine
• ATP formation


  1. Endergonic reaction (respiration)

  2. ATPase hydrolyses bond between second and third phosphate group

  3. ADP + inorganic phosphate ion formed

  4. ADP + inorganic phosphate ion can combine in condensation reaction to make ATP
• Chemical energy in biological systems

  Causes bonds to be made or broken, allowing reactions to happen
• Heterotrophic organisms

  Get their chemical energy from food
• Autotrophic organisms


  Get their chemical energy from light energy
• ATP


  Adenosine triphosphate
• ADP


  Adenosine diphosphate
• ATP releases energy in small, usable amounts
• ATP


  • Used for muscle contraction, nerve transmission or active transport
• DNA


  Deoxyribonucleic acid
• DNA structure


  • Two nucleotide strands linked by hydrogen bonds between the bases, forming a double helix
  • Phosphate, deoxyribose, nitrogenous base
• Adenine


  Pairs with Thymine (complementary bases)
• Guanine


  Pairs with Cytosine
• DNA strands run antiparallel
• Genetic information remains unchanged for generations
• DNA is a large molecule and carries large amounts of genetic information
• Advantages of ATP as an energy provider in comparison to glucose


  * Involves a single reaction to hydrolyse, whereas the breakdown of glucose takes a long time

  * only one enzyme needed to release energy from ATP
• RNA


  • Single stranded polynucleotide
  • Contains ribose sugar
  • Contains the bases adenine, guanine, cytosine and uracil
  • Guanine pairs with cytosine
  • Adenine pairs with uracil
• Types of RNA involved in protein synthesis

  • Messenger RNA (mRNA)
  • Ribosomal RNA (rRNA)
  • Transfer RNA (tRNA)
• Messenger RNA (mRNA)


  • Synthesised in the nucleus and carries genetic information from the DNA to ribosomes
  • Made as a complementary code in the nucleus during transcription
  • The molecule length is related to the length of the gene transcribed
• Ribosomal RNA (rRNA)


  • Forms ribosomes along with proteins
  • Site of translation of genetic code into protein
• Transfer RNA (tRNA)


  • Carries an amino acid at the 3' end and an anticodon arm to attach to the mRNA
  • Single stranded molecule which folds, so that there are base sequences forming complementary pairs
  • Carries a sequence of 3 bases (anticodon)
  • Transports specific amino acids to the ribosomes in protein synthesis
• Hydrogen bonds between complementary base pairs in tRNA
• 3 bases of anticodon in tRNA
• DNA


  • Deoxyribose
  • Purines- G.A
  • Pyrimidines- CT
  • Two strands in double helix
  • Length long
• DNA replication


  1. Parental DNA separates into two strands

  2. Each strand acts as a template for a new strand

  3. Parental DNA remains intact and a whole new double helix is made
• Semi-conservative Replication


  Parental DNA separates into two strands, each of which acts as a template for a new strand
• Conservative Replication


  Parental double helix remains intact and a whole new double helix is made
• Functions of DNA


  • DNA replication
  • Chromosomes make copies of themselves so that when cells divide, each daughter cell receives on exact copy of the genetic information
• MRNA


  Varies in length
• DNA replication


  1. DNA helicase breaks hydrogen bonds between bases in double helix

  2. DNA unwinds and exposes unpaired bases

  3. Free nucleotides in the nucleoplasm are bound to their complementary bases on the unzipped strand

  4. DNA polymerase joins the nucleotides together by a condensation reaction between sugar and phosphate groups of adjacent nucleotides

  5. 2 new DNA molecules are formed from 1 new and 1 old strand of the DNA
• Meselson-Stahl experiment gives evidence to the theory of semi-conservative replication
• Meselson-Stahl experiment


  1. Grow a bacteria with a heavy isotope of nitrogen

  2. Centrifuge a sample - a heavy band is seen

  3. Remove bacteria and place into a medium with light nitrogen N14 and allow bacteria to divide

  4. They will synthesise DNA with the nitrogen isotope and the DNA will contain 1 old and 1 new strand, making it intermediate in density

  5. Allow 1 more generation to grow and the hybrid strands will now be copied in a semi conservative way, creating 50% light and 50% hybrid DNA
• Hybrid DNA


  DNA containing 1 old and 1 new strand
• Servi-conservative reputation


  DNA helicase breaks hydrogen bonds between bases in double helix
• DNA replication


  1. DNA unwinds and exposes unpaired bases

  2. Free nucleotides in the nucleoplasm are bound to their complementary bases on the unzipped strand

  3. DNA polymerase joins the nucleotides together by a condensation reaction between sugar and phosphate groups of adjacent nucleotides

  4. 2 new DNA molecules are formed from 1 new and 1 old strand of the DNA