Download Anaerobic Pathways Lesson Plan

Lesson Plan – Anaerobic Pathways (SBI4U)
Curriculum : Metabolic Processes
Overall Expectation:
-
C3: demonstrate an understanding of the chemical changes and energy conversions that occur
in metabolic processes
Specific Expectation:
-
C3.1: explain the chemical changes and energy conversions associated with the processes of
aerobic and anaerobic cellular respiration (e.g., in aerobic cellular respiration, glucose and
oxygen react to produce carbon dioxide, water, and energy in the form of heat and ATP; in
anaerobic cellular respiration, yeast reacts with glucose in the absence of oxygen to produce
carbon dioxide and ethanol)
Lesson
Alcohol/Ethanol Fermentation
-
-
-
Reaction
o Draw reaction (glucose  2 pyruvate  2 acetaldehyde  2 ethanol)
o Formula: pyruvate + NADH + H+  NAD+ + CO2 + ethanol
Description
o Occurs in bacteria and yeast (e.g. baker’s yeast, Saccharomyces cerevisiae)
o Involves decarboxylation and redox reactions
o Commercial use: bread dough, beer, wine (fermentation of grapes/grain starches in an
environment with low oxygen and permeable to carbon dioxide; starches converted to
sugars by amylase for fermentation)
Net Equation
o Glucose + 2 ADP + 2 Pi  2 ATP + 2 CO2 + 2 ethanol
Lactate Fermentation
-
-
Reaction
o Draw reaction (glucose  2 pyruvate  2 lactate)
o Formula: pyruvate + NADH + H+  NAD+ + lactate
Description
o Clarify lactate (carboxylate, deprotonated, pKa 3.9) vs lactic acid
o Occurs in bacteria and many eukaryotes
o Occurs in humans when ATP demand is greater than the supply from oxidative
phosphorylation e.g. during strenuous exercise
o There is a limit to how much oxygen is delivered per minute
o
-
-
Compensation: glycolysis speeds up for ATP production & excess pyruvate is converted
to lactate to regenerate NAD+ and maintain the rate of glycolysis (results in an oxygen
debt)
o After strenuous exercise, reaction is reversed (lactate  pyruvate  citric acid cycle)
Lactate Threshold
o Misconceptions about lactic acid: muscle stiffness/soreness, acidosis; lactate production
enables intense exercises and does not cause acidosis because it is deprotonated
o lactate thought to be the cause of muscle stiffness and soreness, but lactate levels in
muscles return to normal within an hour after exercise
o Reducing pyruvate to lactate consumes a proton (counters acidosis)
o Acidosis caused by many factors, one of which is the rapid rate of ATP hydrolysis during
intense exercise
o Lactate from muscle is oxidized to pyruvate in liver to prevent build up in muscle
o When lactate production surpasses the rate of lactate transport to liver, you have
reached your “lactate threshold” and lactate will begin to accumulate in muscles
o Draw Lactate Threshold diagram
o Lactate Threshold value used by athletes to set exercise intensity limits in endurance
sports; value can be increased through training
Net Equation
o Glucose + 2 ADP + 2 Pi  2 ATP + 2 lactate
Fermentation Overview
-
Draw diagram (glucose  pyruvate; with oxygen, pyruvate  citric acid cycle  electron
transport chain; without oxygen, pyruvate  fermentation)
Identical reactants in both fermentation reactions
Regeneration of NAD+ by means other than electron transport chain
Inefficient compared to aerobic respiration (2 ATP vs 38 ATP) because of the production of other
compounds e.g. ethanol produced from fermentation is high in energy, used as fuel
Anaerobic Respiration
-
Lack mitochondria but still have electron transport chains for cellular respiration
Found on internal membranes made from plasma membrane
Some prokaryotes can use O2 as their terminal electron acceptor
Others use a different terminal electron acceptor and undergo anaerobic respiration: SO42(sulfate), NO3- (nitrate), Fe3+ (iron)
http://www.youtube.com/watch?v=O__oZjw8Ljc
http://www.youtube.com/watch?v=1QcIHRUELuY