Link reaction



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  • GLYCOLYSIS
  • LINK REACTION
  • KREBS CYCLE
  • ATP Carbon Dioxide Reduced NAD Reduced FAD
  • How many of each one is produced during the following stages of Aerobic Respiration?

Learning Objectives

  • Learning Objectives

Summary so far!

  • Anaerobic respiration makes 2 ATP per glucose.
  • Aerobic respiration makes 32 ATP per glucose
  • Anaerobic respiration only completes glycolysis which makes 2 ATP, hence this is why Anaerobic respiration only makes 2 ATP per glucose molecule.
  • Aerobic respiration makes 32 ATP because 2 ATP come from glycolysis, 2 ATP from Krebs Cycle (as it happens twice per glucose)....

So where does the rest of the energy come from?

  • Where does the remaining 28 ATP come from?
  • The Electron Transport Chain!
  • The ETC makes ATP from the reduced NAD and Reduced FAD made in the earlier stages.
  • Each reduced FAD will generate 1.5ATP
  • Each reduced NAD will generate 2.5ATP

Where they come from and how many?

  • Reduced FAD
  • 2 (from Krebs)
  • 1.5 X 2 = 3 ATP
  • Reduced NAD
  • 2 (from Glycolysis)
  • 2 (from 2x link reaction)
  • 6 (from 2x Krebs)
  • 2.5 X 10 = 25 ATP
  • 3 ATP + 25 ATP = 28 ATP
  • Add this to the 4 ATP made directly in glycolysis and krebs and you have 32 ATP altogether!

What Happens Where?

  • Glycolysis = Cytoplasm of the cell.
  • Link reaction = Matrix of the mitochondria.
  • Krebs cycle = Also in the matrix.
  • Electron transfer chain Utilises proteins found in the membrane of the christae.

The Fate of the hydrogens –The Electron transport chain.

  • Chemiosmosis Theory
  • This method of ATP production is termed
  • Oxidative Phosphorylation

Electron Transport Chain Details

  • tons (H+) and electrons (e-).
  • The oxidised NAD molecules return to the Krebs Cycle to collect more hydrogen.
  • FADH binds to complex II rather than complex I to release its hydrogen.
  • The electrons are passed down the chain of protein complexes from I to IV, each complex binding electrons more tightly than the previous one.
  • In complexes I, II and IV the electrons give up some of their energy, which is then used to pump protons across the inner mitochondrial membrane by active transport through the complexes.
  • Altogether 10 protons are pumped across the membrane for every hydrogen from NADH (or 6 protons for FADH).

Chemiosmosis Details

  • In complex IV the electrons are combined with protons and molecular oxygen to form water. The oxygen diffuses in from the tissue fluid.
  • Oxygen is only involved at the very last stage of respiration as the final electron acceptor.
  • The energy of the electrons is now stored in the form of a proton gradient across the inner mitochondrial membrane.
  • The ATP synthase enzyme has a proton channel through it, and as the protons “fall down” this channel their energy is used to make ATP, It takes 4 protons to synthesise 1 ATP molecule.
  • This method of storing energy by creating a proton gradient across a membrane is called chemiosmosis.

Aerobic Respiration Overview

  • Complete the Application and Summary questions on page 57 of the textbook then self-assess your answers
  • Complete the exam style question on aerobic respiration
  • Statement
  • Glycolysis
  • Krebs cycle
  • NAD is reduced
  • YES
  • YES
  • NO
  • NADP is reduced
  • NO
  • NO
  • YES
  • YES
  • YES
  • YES
  • ATP is required
  • YES
  • NO
  • NO
  • 2. (a)
  • Practice exam question mark scheme
  • (b) (i) pyruvate/succinate/any suitable Krebs cycle substrate; 1
  •  
  • (ii) ADP and phosphate forms ATP; oxygen used to form water / as the terminal acceptor; 2
  •  
  • (iii) Y X W Z; order of carriers linked to sequence of reduction / reduced carriers cannot pass on electrons when inhibited; 2
  • [9]
  •  
  • 4

Learning Objectives

  • Learning Objectives
  • Success Criteria
  • Where the electron transport chain (ETC) takes place
  • How ATP is synthesised during the ETC
  • Describe the role of oxygen in aerobic respiration
  • Label a diagram to accurately show where the ETC occurs
  • Explain how and where chemiosmosis and oxidative phosphorylation occur
  • Describe how oxygen acts as a terminal acceptor of protons and electrons in the ETC


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