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Cell Respiration Part 5
Anaerobic Respiration, Respiratory Quotient, and Rice Adaptations
Anaerobic Respiration
• No free oxygen = nothing pulling electrons and
hydrogen ions into the mitochondria
• Remember, reduced NAD from glycolysis are supposed
to head into mitochondria for ETC
• No oxygen = no mitochondria for those electron carriers
• ETC stops working
• No large supply of ATP from oxidative
phosphorylation
• 1 glucose  4 ATP (2 net ATP) and 2 reduced NAD
• 2 anaerobic pathways solve problem of “dumping”
hydrogen from reduced NAD
• Lactic Fermentation
• Alcohol Fermentation
Anaerobic Respiration
• “Fermentation”
• Lactic Fermentation and
Alcohol Fermentation
• Both:
•
•
•
•
•
Occurs in absence of oxygen
Take place in Cytoplasm
Begin with glycolysis
Regenerate NAD
Enable glycolysis to occur
again to produce more ATP
• “Buy time” by making small
amounts of ATP
• Both products (lactate and
ethanol) are toxic to
organism
• Reactions cannot continue
indefinitely
Alcohol Fermentation
• Def: Conversion of glucose to ethanol
• Microorganism (yeast) and some plant tissue
• Hydrogen from reduced NAD is passed to
ethanal (CH3CHO)
• NAD is then made available for glycolysis to
occur again
• Steps:
• Pyruvate (3C) is decarboxylated to ethanal (CO2
removed)
• Ethanal (2C) is reduced to ethanol (C2H5OH)
• By enzyme alcohol dehydrogenase
• Pathway is IRREVERSIBLE
• Carbon dioxide is lost
• Remaining potential energy in ethanol is
wasted
Lactic Fermentation
• Def: Conversion of glucose to lactic
acid
• Microorganisms and mammalian tissue
• Pyruvate (3C) acts as a hydrogen
acceptor
• Reduced NAD drops of hydrogen to
pyruvate, yielding a lactate molecule (3C)
• By enzyme Lactate dehydrogenase
• Named after reverse reaction (which it also
catalyzes)
• NAD is then made available for
glycolysis to occur again in anaerobic
conditions
• Pathway REVERSIBLE
Lactic Fermentation
• Pathway REVERSIBLE
• Lactate carried by blood plasma to
liver
• Lactate converted back to pyruvate
in liver
• Liver oxidizes 20% of incoming lactate
to carbon dioxide and water via aerobic
respiration (when oxygen is available
again)
• 80% remaining lactate is converted by
liver into glycogen
Lactic Fermentation
• Figure to the left shows what happens to oxygen
uptake of a person before, during, and after strenuous
exercise
• At Rest = absorbing oxygen at less than 1000 mL min-1
• Beginning exercise = more oxygen needed to support
aerobic respiration in muscles
A.
B.
C.
D.
E.
Demand for oxygen begins increasing
Takes heart & lungs 2 minutes to meet demand
Lactic acid fermentation occurs in the mean time
Person builds up oxygen deficit
Next few minutes, enough oxygen is supplied
• Exercise ends = person breathing deeply, absorbing
oxygen at higher rate than at rest
• Extra oxygen uptake after work out is to pay that
oxygen deficit established at the beginning of working
out
• Oxygen debt  post-exercise uptake of extra oxygen
• Oxygen needed for:
• Conversion of lactate to glycogen in liver
• Reoxygenation of hemoglobin in blood
• A high metabolic rate
E
Respiratory Substrates
• Cells require substrates to breakdown
for energy
• Glucose not the only substrate used
for energy
• Neurons, RBCs, and lymphocytes  can oxidize
glucose
• Brain neurons can ONLY respire Glucose
• Other cells can oxidize lipids and amino acids
• Lipids as a substrate
• Carbon atoms removed in pairs (acetyl
coenzyme A) from fatty acid chains of
triglycerides
• These pairs enter Krebs cycle
• Amino Acids as a substrate
• Carbon-hydrogen skeleton converted into
pyruvate or acetyl coenzyme A
Energy Values of Respiratory Substrates
• Where does most energy come from in
aerobic respiration?
• Oxidation of hydrogen to water when
reduced NAD and reduced FAD get to the
ETC
• Main Idea:
• The greater the number of the hydrogens
in the substrate molecule = the greater
the energy value
• “Energy Density”  energy value per unit
mass (aka amount of energy packed into
a substrate molecule)
• Fatty acids have more hydrogens than
carbohydrates
• Therefore, fatty acids have greater energy
density
Measuring Energy of Substrates
• How to determine energy in s substance
• Burn know mass of substance in a
calorimeter
• Calorimeter measures the energy value of a
respiratory substrate
• Energy released by burning (oxidizing)
substrate will cause the a known mass of
water’s temperature to rise
• Measuring the change in water temperature
will determine energy value of substrate
oxidized
Respiratory Substrates
Respiratory Substrate
Energy Released/kJ
Carbohydrate
16
Lipid
39
protein
17
Respiratory Substrate
RQ
Carbohydrate
1.0
Lipid
0.7
protein
0.9
g-1
• Lipids provide TWICE as much
energy per gram as carbs or proteins
• Lipids contain more carbonhydrogen bonds (more H atoms)
• H atoms used to generate the
most ATP is oxidative
phosphorylation
• Brain cells only use glucose
• Heart muscle prefers fatty acids
• Other cells carbs, lipids, or fats
Determining Respiratory Quotient
• Two ways:
• Look at Carbon Dioxide produced
• Look at Oxygen used
• Use:
• Volume (if given volume/data
table/graph)
• Moles (if given equation)
Determining Respiratory Quotient Anaerobic
• Alcohol Fermentation:
•
•
•
•
No oxygen is used…
Dividing carbon dioxide produce by 0
RQ = infinity
Yeast use some aerobic respiration so small amounts of oxygen are used….
• High values of RQ indicate alcohol fermentation is occurring
• Lactic Fermentation
• No oxygen is used…
• No carbon dioxide produced….
• No respiratory quotient can be determined
Practice problems
1. During 30 minutes of steady-state exercise a subject averages an
oxygen consumption of 3.22 L/min with a CO2 production of 2.78
L/min. Determine RQ
2. Determine respiratory quotient of complete oxidation of oleic acid
(C18H34O2) from olive oil. Hint: balance equation first….oxygen can
be half a molecule.
Answers
1. RQ or RER = 2.78 / 3.22 = 0.86
2. RQ= 18/25.5= 0.7
(C18H34O2) + 25.5O2  18 CO2 + 17H2O + energy