Download Cellular Respiration - Seattle Central College

Cellular Respiration
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Glycolysis – each glucose molecule is split and converted to pyruvate (2-three
carbon units.
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Stages of glycolysis
Stage 1: glucose is phosphorylated and cleaved to form to 2 molecules of
glyceraldyde-3-phosphate (G-3-P). The two ATP molecules consumed during
this stage are later used in ATP synthesis.
Stage 2: G-3-P is converted to pyruvate. Four ATP molecules and two NADH
are produced. ATP are consumed in the formation of Glucose-6-phosphate from
glucose and the conversion of Fructose-6-phosphate to Fructose-1,6-diphosphate.
The net production of ATP per glucose is 2.
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The energy captured during the process is stored temporarily in 2 molecules each
of ATP and NADH.
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The pyruvate can be oxidized to CO2 and H2O in aerobic respiration .
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In anaerobic respiration the pyruvate is converted to either lactic acid or ethanol.
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In the presence of oxygen, the energy rich pyruvate produce substantial amount of
ATP through the TCA cycle.
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In the absence of oxygen, additional ATP cannot be generated from pyruvate.
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Under anaerobic conditions, alcoholic fermentation occurs in yeast. Pyruvate is
decarboxyated to form acetaldehyde, which then reduced by NADH to form
ethanol,
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Yeast also contain the enzyme lactic acid dehydrogenase which catalyzes the
reduction of pyruvic acid to lactic acid. NADH is oxidized to NAD+ in the
process.
Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman
NADH
• The transfer of electrons from biomolecules is initiated by a compound that is
abbreviated as NAD+, Nicotinamide Adenine Dinucleotide.
• This is an oxidation reaction where 2 hydrogen atoms (or 2 hydrogen ions and
2 electrons) are removed from the organic metabolite. When electrons are
transferred from a metabolite by NAD+, NAD+ additionally removes two
protons, hydrogen ions, H+
MH2 + NAD+ → NADH + H+ + M + energy
This converts NAD+ into NADH + H+
In such reactions NAD+ serves as the electron acceptor and the metabolite
from which the electrons are stripped serves as the electron donor.
• NAD+ is reduced to form NADH + H+ and the electron-donating metabolite is
similarly oxidized
Procedure:
Part 1
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Fermentation: Measure the volume of CO2 produced during fermentation.
#4. Heat water on a hotplate and use the hotwater to keep the waterbath constant.
After setting up the experiment proceed to Part 2.
Part 2
Glycolysis: Methylene blue (MB) is used in place of NAD+ and is blue in the
oxidized state and is colorless when in the reduced state (MBH2) mimicking NADH.
#3. Place the test tubes marked with you initial in the 37o C incubator. Keep the
glass door closed to examine the color.
Heading for Table 2:
Write the Initial Color on the 0 minute column
Column 4 Final Color