anaerobic respiration in eukaryotes

• ethanol fermentation pathway enzyme

  • pyruvate decarboxylase
  • ethanol dehydrogenase
• lactate fermentation pathway enzymes

  • lactate dehydrogenase
• • lactate made in muscles carried to the liver
  • when oxygen becomes available lactate can be converted to pyruvate or made into glucose and glycogen
  • if lactate is not removed: lactic acidosis - increased acidity, cramping, pain, cellular damage
• lactate fermentation pathway

  1. pyruvate, produced during glycolysis, accepts hydrogen atoms from the reduced NAD, also made during glycolysis. The enzyme lactate dehydrogenase catalyses the reaction. There are two outcomes: pyruvate is reduced to lactate and reduced NAD becomes reoxidised
  2. reoxidised NAD can accept more hydrogen atoms from triose phosphate during glycolysis and glycolysis can continue to produce enough ATP to sustain muscle contraction for a short period
• lactate fermentation pathway

  
• ethanol fermentation pathway

  
• ethanol fermentation pathway

  1. each molecule of pyruvate produced during glycolysis is decarboxylated and converted to ethanal. This stage in the pathway is catalysed by pyruvate decarboxylase, which has a coenzyme, thiamine diphosphate bound to it
  2. ethanal accepts hydrogen atoms from reduced NAD, becoming reduced to ethanol. The enzyme ethanol dehydrogenase catalyses the reaction
  3. reduced NAD is reoxidised and made available to accept more hydrogen atoms from triose phosphate, allowing glycolysis to continue
• eukaryotic cells have two metabolic pathways to reoxidise the reduced NAD

  • fungi, such as yeast, and plants use ethanol fermentation pathway
  • mamals use lactate fermentation pathway

  both take place in the cytoplasm
• ATP yield from anaerobic respiration

  • neither ethanol fermentation nor lactate fermentation produces any ATP.
• energy values of different substrates

  • the greater the number of hydrogen atoms in a molecule the more oxygen needed. Protons need to be able to combine with oxygen to make water
  • the more ATP that can be made as more protons available for chemisomosis

  
• lipids


  • triglycerides hydrolysed by lipase to glycerol and fatty acids
  • glycerol -> triosephosphate -> pyruvate fatty acid + CoA -> fatty acid-CoA
• proteins

  • excess amino acids are deaminated in the liver - amino group removed and converted into urea
  • remaining keto acid enters the pathway as pyruvate, Acetyl CoA or a krebs cycle acid like oxaloacetic acid
  • protein in muscles can be hydrolysed to amino acids - pyruvate or acetate
• respiratory quotient

  • the ratio of the volume of carbon dioxide produced to the volume of oxygen used in the same period of time
  • RQ = $\frac{volume\ of\ CO_2\ given\ out\ }{volume\ of\ O_2\ taken\ in}$
• how amino acids and the products of fat digestion enter the krebs cycle

  
• in glucose - more CO2 being produced than O2 being consumed