5.2.2 Respiration

• Respiration


  The need for cellular respiration
• Mitochondrion


  • Inner and outer mitochondrial membranes, cristae, matrix and mitochondrial DNA
• Photosynthesis produces organic glucose from inorganic carbon dioxide and water
• Plants and organisms that eat them need to respire to use the chemical energy in glucose
• Flow of energy through a system

  1. Plants produce organic molecules

  2. Molecules are used in respiration to make ATP

  3. ATP is used to do work in the cell
• ATP is broken down

  ATP is reformed
• ATP is used for movement, synthesis of urea, anabolic reactions, active transport, Calvin cycle, cell division
• ATP


  Small, water soluble, releases small quantities of energy, hydrolysed and reformed in one step
• Synthesis of ATP


  1. Substrate level phosphorylation

  2. Chemiosmosis
• Substrate level phosphorylation occurs in glycolysis and Krebs cycle
• Chemiosmosis


  A special membrane protein associated with ATP synthase allows H+ ions across the membrane, the energy released is used to attach a Pi group to ADP to produce ATP
• Mitochondria contain the link reaction, Krebs cycle and oxidative phosphorylation
• Mitochondria


  • Presence of 70s ribosomes and naked DNA suggests they were once free-living prokaryotic cells
  • Ribosomes can synthesise their own proteins
  • Inner membrane is permeable to H+
  • Cristae provide large surface area for electron transport chain and ATP synthase
• Cofactor


  Non-protein component needed for an enzyme to function
• Coenzyme


  Organic cofactor
• Prosthetic group


  Permanent non-protein component of an enzyme/protein needed for function
• Glycolysis


  Phosphorylation of glucose to hexose bisphosphate, splitting into two triose phosphate molecules, further oxidation to pyruvate, production of ATP and reduced NAD
• Coenzymes


  Vital in transferring protons, electrons and functional groups between different respiratory reactions
• NAD


  Takes part in all stages of respiration, NADH is reoxidised in oxidative phosphorylation to produce 3 ATP
• FAD


  Only involved in Krebs cycle and oxidative phosphorylation, FADH is reoxidised to produce 2 ATP
• Coenzyme A


  Transfers a 2 carbon acetyl fragment to the Krebs cycle
• Redox reactions involve one substance being oxidised and another being reduced
• NAD and FAD allow the oxidation of other substances by accepting hydrogen and becoming reduced
• Glycolysis


  Occurs in the cytoplasm, glucose is split into two pyruvate molecules, produces net 2 ATP, 2 NADH
• Link reaction


  Occurs in the mitochondrial matrix, decarboxylation of pyruvate to acetate, reduction of NAD, combination of acetate with coenzyme A
• Krebs cycle


  Occurs in the mitochondrial matrix, formation of citrate from acetate and oxaloacetate, reconversion of citrate to oxaloacetate, decarboxylation, dehydrogenation, reduction of NAD and FAD, substrate level phosphorylation
• Link reaction


  Kreb's cycle
• the link reaction and its site in the cell

  To include the decarboxylation of pyruvate to acetate, the reduction of NAD, and the combination of acetate with coenzyme A.
• the process and site of the Krebs cycle

  To include the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate (names of intermediate compounds are not required) AND the importance of decarboxylation, dehydrogenation, the reduction of NAD and FAD, and substrate level phosphorylation.
• Link reaction


  Occurs in the matrix of the mitochondrion
• During aerobic respiration pyruvate is actively transported from the cytoplasm into the mitochondrion for the link reaction.
• Link reaction


  1. Decarboxylation by pyruvate decarboxylase (CO2 is removed)

  2. Dehydrogenation by pyruvate dehydrogenase (two H are removed and used to reduce NAD - this is later used to produce ATP)

  3. Forming is a 2C molecule called an acetyl group which combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA)
• The link reaction occurs twice for each molecule of glucose (two molecules of pyruvate are produced from glycolysis).
• Overall final products of the Link Reaction, from one molecule of glucose

  • 2 x acetyl co-enzyme A - to Kreb's cycle
  • 2 x CO2 - waste product, diffuses away
  • 2 x reduced NAD (NADH) - to oxidative phosphorylation
• Pyruvate


  Has 3 carbon atoms
• Acetyl


  Has 2 carbon atoms
• For each molecule of glucose that enters glycolysis two molecules of acetyl CoA will be produced as one molecule of glucose yields two pyruvate molecules (which are converted to acetyl CoA).
• Summary


  1. Glycolysis produces 2 molecules of pyruvate.

  2. If oxygen is present each molecule of pyruvate will pass into the matrix of the mitochondria.

  3. Here it will undergo a link reaction in which hydrogen and Carbon dioxide are removed in a process known as oxidative decarboxylation.

  4. Coenzyme A acts as an acceptor for the 2C acetyl group that is produced, the CoA carries the acetyl group into the next stage of aerobic respiration known as the Krebs cycle.
• Fats are converted to glycerol and fatty acids... the glycerol is metabolized to TP and broken down in glycolysis, the fatty acids are broken down in the matrix of the mitochondria and converted to acetyl CoA.
• The Krebs Cycle


  • ONE step directly synthesises ATP
  • TWO of the steps involve decarboxylation (CO2)
  • FOUR of the steps involve the removal of pairs of H+ atoms (dehydrogenation) (3 times NAD+->NADH+H+, once FAD+->FADH+H+)