Respiration

• Why is respiration important?

  • It produces ATP (to release energy)
  • For active transport, transcription and translation
• Summarise the stages of aerobic respiration:

  1. Glycolysis - cytoplasm
  2. Link reaction - Mitochondrial matrix
  3. Krebs cycle - Mitochondrial matrix
  4. Oxidative phosphorylation - Inner mitochondrial membrane
• Summarise the stages of anaerobic respiration:

  1. Glycolysis - Cytoplasm
  2. NAD regeneration - Cytoplasm
• Describe the process of glycolysis:

  1)Glucose enters the cell via facilitated diffusion

  2)Glucose is phosphorylated to glucose phosphate

  • Using inorganic phosphates from 2 ATP (ATP is oxidised)

  3)Glucose Phosphate is then hydrolysed to 2x triose phosphate

  4)Triose phosphate is then oxidised to 2 pyruvate

  • ADP is reduced to ATP
  • 2 NAD are reduced to NADH
  • 4 ATP regenerated (net gain of 2)
• Explain what happens after glycolysis if respiration is anaerobic:

  1. Pyruvate is converted into lactic acid (animals & some bacteria) or ethanol (plants & yeast )
  2. NADH is then oxidised = NAD regenerated
  3. So glycolysis can continue (which needs NAD) allowing continued production of ATP
• Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration:

  • Only glycolysis involved so produces little ATP (2 molecules)
  • No oxidative phosphorylation which forms majority of ATP (around 34 molecules)
• What happens after glycolysis if respiration is aerobic?

  Pyruvate is actively transported into the mitochondrial matrix
• Describe the link reaction:

  1)Pyruvate oxidised to acetyl

  • Co2 produced
  • NAD is reduced to NADH

  2)Acetyl combines with coenzyme A, forming Acetyl coenzyme A
• Describe the Krebs cycle:

  1)Acetyl coenzyme A (2C) reacts with a 4C molecule

  • Releasing coenzyme A
  • Producing a 6C molecule that enters the kreb cycle through a reduction reaction

  2)In a series of oxidation-reduction reactions, the 4C molecule is regenerated and:

  • 2x CO2 lost
  • Coenzymes NAD and FAD are reduced to NADH and FADH
  • Substrate level phosphorylation (direct transfer of Pi from intermediate compound to ADP)

  =ATP produced
• What are the products per glucose molecule during the link reaction?

  • 2x Acetyl coenzyme A
  • 2x CO2
  • 2x NADH
• What are the products per glucose molecule during the Kreb cycle?

  • 6x NADH
  • 2x FADH
  • 2x ATP
  • 4x CO2
• Describe the first step of oxidative phosphorylation:

  1)NADH and FADH are oxidised to release H atoms - split into protons (H+) and electrons (e-)
• Describe the second step of oxidative phosphorylation:

  2)Electrons are transferred down electron transfer chain (chain of carriers at decreasing energy levels)

  • By redox reactions
• Describe the third step of oxidative phosphorylation:

  3)Energy released by electrons used in the production of ATP from ADP + Pi (Chemiosmotic theory):

  • Energy used by electron carriers to actively pump protons from the matrix into the intermembrane space
  • Protons diffuse into matrix down an electrochemical gradient, via ATP synthase (embedded)
  • Releasing energy to synthesise ATP from ADP + Pi
• Describe the fourth stage of oxidative phosphorylation:

  4)In matrix at end of ETC, oxygen is final electron acceptor (electrons can't pass on otherwise)

  • So protons, electrons and oxygen combine to form water
• Give examples of other respiratory substrates:

  Breakdown products of lipids and amino acids, which enter the krebs cycle e.g.

  • Fatty acids from hydrolysis of lipids - converted into Acetyl coenzyme A
  • Amino acids from hydrolysis of proteins - converted to intermediates in krebs cycle