Chap 12: Respiration

• Energy in living organisms is needed for active transport, exocytosis/endocytosis, DNA synthesis, protein synthesis, muscle contraction, movement of chromosomes via spindle fibres, maintaining body temperature.
• Active transport using transport proteins (carrier proteins) across the cell membrane. Bulk transport such as exocytosis of substances out of the cell.
• Anabolic reactions is the synthesis of DNA from nucleotide and synthesis of protein from amino acids.
• Movement involves movement of chromosome via spindle fibres and contraction of muscles.
• Maintaining body temperature is only in mammals or birds.
• ATP structure has a ribose sugar, a nitrogenous base, specifically adenine, and 3 phosphate groups.
• ATP is a universal energy currency because it is:

  • Water soluble
  • Easily transported around the cell
  • ATP loses a phosphate group
  • Hydrolysed by ATPase 
  • To release energy immediately / in small packets - ref. 30.5kJ
  • Can be recycled/regenerated 
• Suggest reasons why the actual number of net ATP synthesised is less than the theoretical number

  • ATP used to transport pyruvate into mitochondria
  • Some protons leak from intermembrane space
  • Some energy lost as heat
  • Glucose may not be completely broken down
  • Reduced NAD may be used for other metabolic reactions
• How is ATP synthesised?

  1. Substrate-linked reaction: transfer of phosphate in glycolysis and Krebs cycle
  2. Chemiosmosis: movement of protons/H+ ions across a membrane, synthesising ATP in mitochondria or chloroplast
• Inner membrane:

  • Folded/cristae to increase surface area
  • Contains ATP synthase and ETC
  • Site of oxidative phosphorylation/chemiosmosis
  • Impermeable to protons
• Intermembrane space:

  • Has low pH/high concentration of protons
  • Protons are pumped into the intermembrane space
  • Creates a proton gradient between the intermembrane space and matrix
• Matrix:

  • Contains coenzymes for the link reaction/Krebs cycle
• Outer membrane:

  • Permeable to pyruvate, reduced NAD, and oxygen
  • Contains ribosomes/DNA involved in protein synthesis
• Mitochondria:

  • Process: Oxidative phosphorylation
  • Location: Inner mitochondrial membrane/cristae
  • Electron source: Reduced NAD gives electron
  • H+ pump destination: Intermembrane space
  • Final electron acceptor: Oxygen
  • Product: Makes water/H2O
• Chloroplast:

  • Process: Photophosphorylation
  • Location: Thylakoid membrane
  • Electron source: Water gives electron (photolysis)
  • H+ pump destination: Thylakoid space/lumen
  • Final electron acceptor: NADP
  • Product: Makes reduced NADP
• Describe oxidative phosphorylation.

  1. Reduced NAD/FAD
  2. Releases hydrogen - hydrogen splits into proton and electron
  3. At inner mitochondrial membrane or cristae
  4. Electron pass through electron transport chain (ETC)
  5. Energy released
  6. Protons transferred through inner membrane/into intermembrane space
  7. Proton gradient established // high proton concentration in intermembrane space
  8. Protons diffuse through ATP synthase
  9. ATP produced from ADP and Pi
  10. Chemiosmosis
  11. Oxygen acts as final electron acceptor to form water
• Explain the consequences when there is not enough oxygen available for respiration.

  1. No final electron acceptor
  2. E- cannot pass down the electron transport chain (ETC)
  3. Oxidative phosphorylation cannot occur
  4. Reduced NAD and reduced FAD are not oxidised (does not release H)
  5. No NAD and FAD available for Krebs cycle
• Describe the role of coenzyme A in respiration

  • Combines with acetyl group
  • For link reaction
  • Delivers acetyl group to the Krebs cycle
  • Acetyl group combines with oxaloacetate
• Describe the role of NAD and FAD

  • Coenzymes
  • For dehydrogenation 
  • In glycolysis/link reaction/Krebs cycle
  • carry /transfer H+
  • To ETC/inner mitochondrial membrane/cristae
• Define the term respiratory quotient (RQ).

  • Volume of carbon dioxide produced divided by the volume of oxygen consumed
  • Per unit time
• Respiratory quotient (RQ) for:

  Carbohydrates - 1.0 

  Lipids - 0.8

  Proteins - 0.9
• Explain why the respiration of glucose in anaerobic conditions produces less ATP than in aerobic conditions.

  • Only involves glycolysis
  • Net total of 2 ATP
  • Only substrate-linked phosphorylation occurs
  • Pyruvate converted to lactate through anaerobic respiration
  • O2 not available as final electron acceptor → oxidative phosphorylation does not occur
• How rice is adapted to grow with its roots submerged in water

  1. Aerenchyma 
  2. In stem and roots
  3. Help oxygen to move/diffuse to roots
  4. Shallow roots
  5. Air trapped on underwater leaves
  6. Greater internode growth // leaves or flowers grow above water level
  7. Growth regulated by gibberellin
  8. Anaerobic respiration in roots
  9. Tolerant to high ethanol
  10. Ethanol dehydrogenase
• Draw a diagram of glycolysis in the cytoplasm
• Draw a diagram of link reaction in the matrix of mitochondria
• Draw a diagram of Krebs cycle in the matrix of mitochondria
• Describe glycolysis

  • Trapping glucose in the cell by phosphorylating molecule (glucose to fructose-1,6-bisphosphate)
  • Splitting of glucose into 2 
  • Formation of triose phosphate (3C) using 2ATP
  • Triose phosphate converted to pyruvate (3C), releasing 2ATP and reduced NAD
• What is the net production from glycolysis?

  • 2 pyruvate molecules
  • 2 ATP
  • 2 reduced NAD
• Describe link reaction

  • Decarboxylation and dehydrogenation of pyruvate by enzymes to produce an acetyl group
  • Combination with coenzyme A to form acetyl coA
• What is the net production from link reaction?

  • Acetyl coA
  • CO2
  • Reduced NAD
• Describe Krebs cycle

  • Oxaloacetate is regenerated: citrate is converted back to oxaloacetate through a series of small reactions
  • Decarboxylation of citrate: releasing CO2 as waste gas
  • Dehydrogenation of citrate: releasing H atoms that reduce coenzymes NAD and FAD
  • Substrate level phosphorylation
  • Citrate is regenerated: oxaloacetate (4C) combines with acetyl coenzyme A (2C) from link reaction to form citrate (6C)
• Metabolism of lactate

  • Lactate oxidised back to pyruvate, requires O2 - channelled into Krebs cycle for ATP production
  • Converted into glycogen for storage in liver
  • Recovery of oxygen debt: oxidation of lactate back to pyruvate requires O2
• Describe ethanol fermentation

  • Glucose converted into pyruvate, releasing ATP
  • Pyruvate is decarboxylated to ethanal, producing CO2
  • Ethanal is reduced to ethanol by enzyme alcohol dehydrogenase
  • Reduced NAD transfer hydrogen to ethanal to form ethanol
  • Ethanol is a waste product
• Describe lactate fermentation

  • Glucose converted to pyruvate, releasing ATP
  • Pyruvate is reduced to lactate by enzyme lactate dehydrogenase
  • Reduced NAD transfers hydrogen to pyruvate to form lactate
• Similarities and differences between anaerobic respiration in mammals and in yeast.

  Similarities

  • Occur in cytoplasm
  • Only involves glycolysis
  • Make 2 net/small amounts of ATP
  • Regeneration of NAD

  Differences

  Mammalian tissue: H acceptor is pyruvate, lactate as end product, no decarboxylation, only 1 step, enzyme lactate dehydrogenase, process is reversible

  Yeast cell: H acceptor is ethanal, ethanol as end product, decarboxylation occurs, 2 step process, enzyme ethanol dehydrogenase, process is irreversible