2 - Nucleic acids

• Nucleic acids


  Macromolecules that carry genetic information
• RNA (Ribonucleic acid)


  • Polymer made up of nucleotides
  • Single, relatively short chain
  • Pentose sugar is ribose
  • Organic bases are Adenine, Cytosine, Guanine, Uracil
  • Transfers genetic information from DNA to ribosomes
  • Ribosomes are made up of proteins and another type of RNA
  • Involved in protein synthesis
• DNA (Deoxyribonucleic acid)


  • Made up of two strands of nucleotides
  • Each strand is extremely long
  • Strands joined by hydrogen bonds between bases
  • Pentose sugar is deoxyribose
  • Organic bases are Adenine, Cytosine, Guanine, Thymine
• Nucleotide

  Made up of 3 components: Pentose sugar, Phosphate group, Nitrogen-containing organic base
• Formation of nucleotides

  Pentose sugar, phosphate group and organic bases joined by condensation reaction
• Phosphodiester bond

  Bond formed between deoxyribose sugar of one mononucleotide and phosphate group of another
• Base pairing


  • Adenine pairs with Thymine (complementary pair)
  • Guanine pairs with Cytosine (complementary pair)
• Stability of DNA

  • Phosphodiester backbone protects organic bases
  • Hydrogen bonds link organic base pairs, more C-G pairings = more stable
• DNA adaptations

  • Very stable structure that rarely mutates
  • Two separate strands joined by hydrogen bonds allow separation during replication and protein synthesis
  • Extremely large molecule carrying immense genetic information
  • Genetic information protected from outside forces by being within helical cylinder
  • Base pairing allows replication and transfer of information as mRNA
• DNA replication

  1. Nuclear division - mitosis and meiosis

  2. Cytokinesis - whole cell divides
• Before a nucleus divides, its DNA must be replicated to ensure all daughter cells have the genetic information to produce the enzymes and other proteins they need
• Requirements for DNA replication

  • Four types of nucleotide, each with bases of adenine, cytosine, guanine, thymine
  • Both strands of DNA molecule act as template
  • Enzyme DNA polymerase
  • Source of chemical energy
• DNA replication process

  1. DNA helicase breaks hydrogen bonds linking base pairs

  2. Double helix separates into two strands and unwinds

  3. Exposed polynucleotide strands act as template for complementary free nucleotides to bind

  4. Nucleotides joined by DNA polymerase to form 'missing' polynucleotide strand

  5. Each new DNA molecule contains one original DNA strand
• Nucleic acids

  Macromolecules that store and transmit genetic information
• Energy

  Required by all living organisms to remain alive
• ATP (Adenosine Triphosphate)


  The main energy source used to carry out processes within cells
• Photosynthesis

  Plants use solar energy to combine water and carbon dioxide into complex organic molecules
• Oxidation of organic molecules

  Both plants and animals use to make ATP
• Structure of ATP

  • Adenine (nitrogen containing organic base)
  • Ribose (5-carbon sugar)
  • Phosphates (chain of 3)
• How ATP stores energy

  Bonds between phosphate groups are unstable and easily broken, releasing energy
• ATP hydrolysis

  ATP + Water -> ADP + Inorganic Phosphate + Energy
• ATP synthase

  Enzyme that catalyses the conversion of ADP to ATP
• ATP synthesis

  Phosphate added to ADP to reform ATP (condensation reaction)
• Ways ATP is synthesised

  • Photophosphorylation (in photosynthesis)
  • Oxidative phosphorylation (in respiration)
  • Substrate-level phosphorylation (phosphate transfer)
• ATP

  • Not a good long-term energy store, but an immediate energy source for cells
  • Rapidly reformed from ADP and inorganic phosphate
• Mitochondria

  Where ATP is continuously made in cells that require energy
• Processes ATP is used for in cells

  • Metabolic processes
  • Movement
  • Active transport
  • Secretion
  • Activation of molecules
• Water molecule

  • Made up of two atoms of hydrogen and one of oxygen
  • Has no overall charge, but oxygen atom has a slight negative charge and hydrogen atoms have a slight positive charge
  • Has both positive and negative poles - dipolar
• Water and hydrogen bonding

  1. Positive pole of one water molecule attracted to negative pole of another molecule

  2. Attractive force between opposite charges is called a hydrogen bond

  3. Hydrogen bonds cause water molecules to stick together, giving water its unusual properties
• Specific heat capacity of water

  • It takes more energy (heat) to separate water molecules than if they did not bond to one another
  • Boiling point of water is higher than expected
  • Without hydrogen bonding, water would be a gas at temperatures commonly found on Earth and life as we know it would not exist
  • Water has a high specific heat capacity
• Water's high specific heat capacity

  • Allows it to act as a buffer against sudden temperature variations, making the aquatic environment a temperature-stable one
  • Also buffers organisms, mostly made of water, against sudden temperature changes especially in terrestrial environments
• Latent heat of vaporisation of water

  Hydrogen bonding between water molecules means it requires a lot of energy to evaporate 1 gram of water
• Cohesion and surface tension in water

  • Tendency of molecules to stick together is known as cohesion
  • Water has large cohesive forces due to hydrogen bonding, allowing it to be pulled up through a tube - this force is called surface tension
• Importance of water to living organisms


  • Used to break down complex molecules by hydrolysis
  • Produced in condensation reactions
  • Chemical reactions take place in an aqueous medium
  • Major raw material in photosynthesis
  • Readily dissolves gases, wastes, inorganic ions, small hydrophilic molecules, enzymes
  • Evaporation cools organisms and allows temperature control
  • Not easily compressed, providing support
  • Transparent, allowing photosynthesis and light penetration in the eye
• Inorganic ions


  • Found in organisms in solution in cytoplasm, body fluids, and as part of larger molecules
  • Occur in concentrations ranging from very high to very low
  • Perform a range of functions related to their properties