Photosynthesis and respiration

• ATP

  • is continuously hydrolysed to release energy and then re-synthesised
  • synthesis or phosphorylation requires energy from respiration or photosynthesis
  • energy released from glucose is used to join a phosphate molecule to ADP to produce ATP
  • cells use ATP as the immediate energy source for biological processes
  • when ATP is hydrolysed ADP and phosphate are produced and energy is released
• ADP + Pi --> ATP

  (energy input from respiration)
• ATP --> ADP + Pi

  (energy output)
• Properties of ATP

  • universal energy carrier as it is used by all biological organisms
  • when hydrolysed energy is released in small amounts
  • energy is released in a single-step reaction
  • it is soluble in water
  • quickly broken down and resynthesised
• Functions of ATP

  • active transport
  • synthesis reactions
  • muscle contraction
  • cell division
  • light independent reactions of photosynthesis
  • first stage of glycolysis
• Turnover and storage of ATP

  • ATP is continuously hydrolysed and then phosphorylated
  • each molecule is recycled
• Respiration can be aerobic or anaerobic
• Aerobic respiration involved the complete breakdown of glucose releases more energy and produces much more ATP
• glucose + oxygen --> carbon dioxide + water + energy
• In anaerobic respiration glucose is not completely broken down and only produces 2 ATP
• glucose --> lactate + energy
• Anaerobic respiration in yeast

  • glucose --> ethanol +2CO2 + energy
• 4 stages of aerobic respiration

  1. Glycolysis (cytoplasm)
  2. Link reaction (matrix)
  3. Kreb's cycle (matrix)
  4. Oxidative phosphorylation (cristae)
• Mitochondria

  • 1-10 micrometers
  • cristae contain stalked particles containing enzymes associated with ATP production by oxidative phosphorylation
  • matrix contains enzymes of the Kreb's cycle
• Glycolysis

  • first stage
  • splitting 1 glucose (6C) into 2 triose phosphate (3C) then into 2 pyruvate (3C)
  • net gain of 2 ATP per glucose molecule
  • coenzyme NAD transports hydrogen to the electron transport chain and more ATP can be produced
  • pyruvate is actively transported into the mitochondrion for the next stage of aerobic respiration
• Glycolysis

  • glucose --> 2 triose phosphate (2 ATP--> 2ADP)
  • 2 triose phosphate --> 2 pyruvate (4ADP + 4Pi --> 4ATP) + (2NAD --> 2NADH)
• Link reaction

  • occurs in the matrix
  • pyruvate (3C) is oxidised and carbon dioxide is removed
  • at the same time coenzyme A is added to acetate (2C) to form acetyl coenzyme A
• Link reaction

  • pyruvate --> acetate (NAD --> NADH) + -CO2
  • acetate --> acetyl CoA
• Kreb's cycle

  • series of oxidation-reduction reactions
  • acetylcoenzyme A (2C) combines with a four carbon molecule to form a six carbon molecule which enters the Kreb's cycle
  • coenzyme A is removed
  • six carbon molecule enters the cycle producing a 4 carbon molecule
  • removal of CO2 and hydrogen atoms
  • hydrogen atoms passed to coenzyme NAD and FAD
  • reduced coenzyme pass the hydrogen atoms to the electron transport chain to make ATP
  • substrate level phosphorylation
• The Link reaction and the Krebs cycle occur twice per glucose molecule as 2 pyruvate molecules are produced in glycolysis
• Oxidation of fatty acids

  • each fatty acid which is released has 2C acetyl fragments removed so that the fatty acid is shortened 2C atoms at a time
  • each 2C acetyl combines with coenzyme A which enters the Kreb's cycle
• Kreb's cycle

  • acetyl CoA --> 6C compound (-coenzyme A)
  • 6C compound --> 5C compound (NAD -->NADH) + -CO2
  • 5C compounds --> 4C compound (ADP + Pi --> ATP) + (FAD --> FADH) + (2NAD --> 2NADH)
  • cycle repeats
• Oxidation of amino acids

  • only used when all carbohydrates and lipid reserves have been used up
  • amino acids first deaminated
  • remaining keto acid can either enter glycolysis or the Kreb's cycle or be converted into a fatty acid to enter the Kreb's cycle
• ATP production in aerobic respiration

  1. substrate level phosphorylation
  2. oxidative phosphorylation
• Substrate level phosphorylation

  • occurs during glycolysis and the Kreb's cycle
  • electron transport chain isn't involved in substrate-level phosphorylation
  • energy from reaction + ADP + Pi --> ATP
• Oxidative phosphorylation (electron transport chain)

  • only occurs under aerobic conditions
  • located on the cristae
  • oxygen is essential as the final electron acceptor so ATP can be produced
  • In oxidative phosphorylation some energy is released as heat
• Oxidative phosphorylation (steps 1-3)

  1. reduced NAD and FAD are oxidised- release the hydrogen atoms to the first electron carrier of the chain. each hydrogen atom is split into and electron and proton
  2. electrons pass down carriers at decreasing energy levels. as electrons are transferred energy is released. energy actively pumps the protons across the inner mitochondrial membrane into the inter-membrane space
  3. a proton gradient is created- higher concentration of protons in the intermembrane space than the matrix
• Oxidative phosphorylation (steps 4-6)

  4. gradient means protons diffuse back across the inner membrane into the matrix via ATP synthase

  5. movement of protons releases energy for ADP + Pi --> ATP

  6. at the end of the electron transport chain the electrons combine with the protons and oxygen to form water. oxygen is the last electron acceptor
• Anaerobic respiration

  • involves glycolysis and the production of pyruvate but the pyruvate doesn't enter the mitochondrion by stays in the cytoplasm
  • pyruvate is reduced using reduced NAD produced in glycolysis
  • enables the regeneration of NAD as the reduced NAD is converted to NAD
  • ensures a continual supply of NAD for glycolysis
• Anaerobic respiration in animals

  • pyruvate + NADH --> lactate + NAD
• Anaerobic respiration in fungi

  • Pyruvate + NAD --> ethanol + carbon dioxide + NAD
  • if no NAD is regenerated glycolysis would stop
• Respiratory quotient

  • ratio of CO2 : O2
  • carbohydrates: 1
  • protein: 0.9
  • fat: 0.7
• RQ = volume of CO2 produced/volume of O2 absorbed
• RQ = moles or molecules of CO2 produced/ moles or molecules of O2 absorbed
• A respirometer is a device used to measure the rate of respiration of a living organism by measuring its uptake of oxygen or release of carbon dioxide
• Respirometer

  • aerobically respiring organisms absorb oxygen; over a set period of time a volume of oxygen is consumed
  • CO2 produced in respiration is released an absorbed by potassium hydroxide reducing the volume of gas in the respirometer
  • the pressure of the respirometer decreases and the coloured liquid moves left
  • the distance moved by the liquid is recorded and the volume of liquid moved is pi r2 d
  • the experiment is repeated replacing KOH
  • the time the movement of coloured liquid represents the difference between oxygen used and CO2 produced
• Respirometer: spring clip

  • when open permits equilibration of contents of chamber with atmosphere
• Respirometer: rubber stop

  • airtightness can be improved by smearing vaseline along the seal between chamber and stopper
• Respirometer: respiratory chamber

  • relatively low volume to ensure that volume changes due to respiratory activity are significant enough to be measured
• Respirometer: filler paper wick

  • ensure maximum surface area of potassium hydroxide solution is available to contents of chamber