Lab 5 summary CC-BY-NC

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Summary of Lab 5 for BIOL 112 (Winter 2011). Week of Feb 7, 2011.


1Aerobic respiration

  • Respiration: process whereby the chemical energy of organic molecules such as carbohydrates is converted into another kind
    • Specifically, the high-energy phosphate bond in ATP
  • In aerobic respiration: consume oxygen, release carbon dioxide
    • For sugar (and other carbohydrates), equal quantities are consumed/produced
    • But the molar ratios vary depending on the thing being respired
  • Experiment: determine respiration rate by measuring volume changes
    • If we used an alkaline solution, any carbon dioxide present would react with it, be converted to a salt
    • Thus resulting in a decrease in volume of the chamber due solely to the consumption of oxygen
    • Thermobarometer: empty tube, control (no peas)
      • Measures changes in the enclosed air volume due to external factors (changes in room temp and pressure etc)
    • Also sulfuric acid - does not react with carbon dioxide, so air volume should not change volume
    • Equal weight of peas in acidic/alkaline tubes; placed in 37 C water
    • Let the peas do their thing, after half an hour, measure the volume (get the change in volume)
  • Respiratory quotient: $\displaystyle \frac{\text{carbon dioxide produced}}{\text{oxygen consumed}}$
    • Varies according to the substrate
    • For example, carbohydrates have an RQ of 1; fats, 0.7; proteins, 0.8
    • A respiratory quotient can thus give us an indication of the composition of a substance
  • Results of experiment:
    • Oxygen consumed = volume change in NaOH tube minus volume change in thermobarometer
    • Carbon dioxide released = volume change in sulfuric acid tube minus volume change in thermobarometer
    • Should get an RQ of about 0.8 or so

2Anaerobic respiration

  • Anaerobic: convert crap to energy without oxygen; ex: fermentation
    • Fermentation: sugar + enzymes --> carbon dioxide, ethanol and a bit of ATP
  • Yeast: can respire by both aerobic and anaerobic pathways
  • Experiments: measure the fermentation of various substrates to carbon dioxide by yeast
    • Also the inhibiting effect of sodium fluoride on the reactions
      • High concentrations of fluoride should have an inhibiting effect on respiration
      • Because Mg2+, an essential cofactor (ion) for the activity of certain enzymes in the pathway, combines with F-
      • Forms an insoluble salt, so there is less Mg2+ available for the enyzme (dehydrogenase)
      • So respiratory reactions beyond the one requiring Mg2+ cease
    • Sugars tested: two hexoses (glucose and galactose)
      • Note: same chemical formula, but they are structural isomers
      • The positions of a hydroxide and hydrogen are switched
  • Procedure: five test tubes, each contained within a larger test tube
    • Record initial volumes of gas, after 1.5 hours, record gas volume
    • Test tube 1: only yeast and water; control for residual glucose or something
    • Test tube 2: yeast, water, glucose; measures the rate of respiration of glucose
    • Test tube 3: yeast, water, galactose; measures the rate of respiration of galactose
    • Test tube 4: yeast, glucose, sodium fluoride; measures the inhibiting effects of sodium fluoride
    • Test tube 5: just water; control for external changes etc
  • Results:
    • Test tube 1: Little to no change due to residual glucose or whatever
    • Test tube 2: Largest change
    • Test tube 3: Should be little to no change; can't really respire galactose
    • Test tube 4: Little to no change due to the inhibitor
    • Test tube 5: Control, little to no change
    • Only glucose should have given a positive reaction
    • Yeast cannot respire galactose - it lacks isomerase (the enzyme to convert galactose to glucose)
    • This experiment should measure only anaerobic and not aerobic respiration - the air space is too small to be considered aerobic
    • Note that the yeast was aerated for several days to deplete the stored glucose, but there might be some left, which explains the "little" reaction