Lab 5 summary

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

Respiration.

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