Lecture 2

• Where does biological energy on Earth come from?


  Sun (heat & light energy)
• Where do humans get energy from?


  Food: fats, proteins, carbohydrates (sugars & polysaccharides)
• Reduction:


  Gain of electrons
• Oxidation:


  Loss of electrons
• What is metabolism?


  All chemical reactions being performed in cells
• What are the 2 main classes of metabolic pathways?

  • Catabolic (breaking down food molecules to generate energy-some can be lost as heat)
  • Anabolic (Using energy to build complex biomolecules required for life)
• What is a metabolic pathway?


  Series of enzyme-catalysed reactions in which:

  • Each reaction is specific (e.g, enzyme 1 always makes product B)
  • Overall the set of reactions is energetically favourable (Delta G negative)
• Adenosine triphosphate (ATP):

  Nucleotide- form of energy made by cells

  Made of ribose sugar, adenine base (attached to carbon 1) & 3 phosphate groups (5th carbon)

  Phosphoanhydride bonds between phosphate groups
• How do you make adenosine diphosphate (ADP)?


  Hydrolysis of ATP into ADP & inorganic phosphate

  (energetically favourable)
• Why do plants, some bacteria & algae photosynthesize?


  Use sunlight to generate energy & reduce CO2 in atmosphere to turn it into useful molecules (e.g, sugars) which store the energy.
• What can ATP hydrolysis be used to drive?


  Energetically unfavourable reactions

  
• How is creatine made?


  Creatine phosphate + ADP = ATP + Creatine
• What is ATP -> ADP reaction used for?


  Motion (e.g, muscle contraction), active transport, biosynthesis, signal amplification
• What is ADP -> ATP reaction used for?


  Oxidation of fuel molecules or photosynthesis
• How do food molecules release energy?


  Oxidation
• What are activated carriers?


  Biomolecules that store energy in form of transferable chemical groups

  (e.g, energy from catabolic reaction passed onto activated carrier (in inactive state)- transferred onto anabolic pathway to drive them forward as anabolic is energetically unfavourable)
• What is an example of an activated carrier?


  • ATP (can transfer phosphate group)
  • NADH (stores energy as transferable electrons)
  • Coenzyme A (carries acyl groups)
• Nicotinamide adenine dinucleotide (NAD+) structure:


  2 nucleotides

  Ribose + adenine + 2 phosphate + ribose + nicotinamide

  Nicotinamide group is the reactive site which accepts electrons to store energy & release electrons to release energy

  ( + charge on N in ring)
• How is NADH formed?


  NAD+ accepts 2 electrons & a proton

  
• Why is NADH a good store of potential energy?


  Reducing power (reduces molecules by passing on electrons & releasing energy in energetically favourable way)
• How is acyl-CoA formed?


  Acyl groups form thioester bonds to CoA
• Structure of Acetyl-CoA :


  (Common derivative of CoA)

  
• Structure of Coenzyme A: 


  (Thiol group reactive & forms thioester bond with acyl group)

  
• Where do electrons end up in aerobic respiration?

  Passed onto oxygen, making water

  (electrons come from oxidation of food molecules)
• More reduced carbon fuels have more...


  Stored energy (more oxidation potential- more electrons so can release more energy)
• Oxidation of carbon fuels:


  Carbon loses electrons (energetically favourable)
• Reduction of carbon fuels:


  Carbon gains electrons (energetically unfavourable)