2 - Nucleic Acids

• DNA nucleotides contain:

  Phosphate group

  Pentose Sugar (deoxyribose)

  Nitrogenous bases (A, C, T, G)

  
• What are 2 differences between DNA/RNA nucleotides?

  1. DNA has deoxyribose, RNA has ribose
  2. DNA has the base thymine whereas RNA has uracil
• What reaction & bond joins DNA/RNA nucleotides?

  Condensation reaction forming phosphodiester bonds
• Between which molecules in the nucleotide does the bond form?

  The phosphate group and the pentose sugar
• A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs. The two chains align antiparallel to each other.

  
• What are the three RNA polymers?

  mRNA, tRNA, rRNA
• mRNA - RNA transfers genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm.

  
• tRNA - Carries specific amino acids to the mRNA on the ribosome.

  
• rRNA - Combines with proteins to form a ribosome

  
• Is RNA or DNA shorter?

  RNA
• Why did scientists doubt DNA carried genetic code?

  Due to the relative simplicity of the DNA molecule
• Before cells divide (by mitosis or meiosis), all the DNA must replicate to provide a copy for the new cell. DNA replication is described as being semi-conservative. What does this mean (2 marks)?

  When DNA replicates, one strand of the original DNA is conserved and one strand is newly synthesised.

  
• What is the process of DNA replication (5 marks)?


  1. The double helix unwinds

  2. Hydrogen bonds between the complementary bases of the two strands break so the strands separate and act as templates

  3. DNA helicase is responsible for the unwinding of the double helix and breaking of hydrogen bonds

  4. DNA nucleotides within the nucleus are attracted to the complementary exposed bases on the template strands.

  5. DNA polymerase catalyses the condensation reactions to join adjacent nucleotides together and form phosphodiester bonds.
• What is the structure of ATP?

  • 1 Adenine
  • 1 Ribose
  • 3 Phosphate groups

  
• What's the word equation for the hydrolysis of ATP?

  ATP + water --> ADP + Pi (energy)
• What's the word equation for the synthesis (condensation reaction) of ATP?


  ADP + Pi (energy) --> ATP + water
• Name the enzyme that catalyses the hydrolysis of ATP: ATP hydrolase
• What enzyme catalyses the synthesis of ATP?
• ATP can also transfer energy to different compounds. The inorganic phosphate released during the hydrolysis of ATP can be bonded onto different compounds to make them more reactive.

  
  

  This is known as phosphorylation and this happens to glucose at the start of respiration to make it more reactive.
• What's the role of hydrogen ions?


  Lower the pH of solutions and impact enzyme function and haemoglobin function. OR role in chemiosmosis.
• What's the role of iron ions?


  A component of haemoglobin in the transport of oxygen
• What's the role of sodium ions?

  Involved in the co-transport of glucose and amino acids in absorption. Or, role in generating action potentials.
• What's the role of phosphate ions?

  A component of DNA (forms phosphodiester bonds with deoxyribose) and ATP (makes ADP more reactive)
• Water Properties: Metabolite

  • Water is involved in many metabolic reactions, including condensation and hydrolysis reactions and photosynthesis. This is due to its dipolar nature.
• Water Properties: Good solvent

  • Due to the dipolar nature of water, it is an important solvent in which metabolic reactions occur. Polar substances will dissolve in water. This means molecules can be easily transported in the blood, or xylem and phloem of plants. Chemical reactions also happen faster in solution.
• Water Properties: Strong cohesion

  • Due to the hydrogen bonds between water molecules, it has strong cohesion between water molecules. This supports columns of water in the tube-like transport cells of plants, such as the xylem. It also produces surface tension where water meets air, so animals and plants can live on the surface of the water.
• Water Properties: Large latent heat of vaporisation

  • Due to the hydrogen bonds between water molecules, it has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation.
• Water Properties: High specific heat capacity

  • Due to the hydrogen bonds between water molecules, water has a relatively high heat capacity; buffering changes in temperature.