Download Glycolysis and Fermentation

GLYCOLYSIS AND
FERMENTATION
CHAPTER 7 – CELL RESPIRATION
OVERALL EQUATION
C6H12O6 + 6O2  6CO2 + 6H2O + 36ATP
HARVESTING CHEMICAL ENERGY
• Cellular Respiration – The process in which cells make
ATP by breaking down organic compounds
• Cellular Respiration begins with Glycolysis: a biochemical
pathway in which glucose is oxidized into pyruvic acid
Organic
Compounds
ATP
Glycolysis
No Oxygen
Fermentation
Oxygen
Aerobic Respiration
ATP
ANAEROBIC PATHWAYS:
• Chemical reactions that occur without oxygen
GLYCOLYSIS
• Occurs in cytosol in 4 major steps:
• Step 1: 2 phosphate groups are attached to glucose,
forming a new 6-carbon compound
• Phosphates break off ATP  ADP
GLYCOLYSIS
• Step 2: The 6-carbon molecule is split into 2 3-carbon
molecules of PGAL
GLYCOLYSIS
• The 2 PGAL molecules are oxidized (lose electron,
becoming more positive), and each receives another
phosphate group (each now has 2 phosphate groups
attached).
• A new 3-carbon molecule has been formed.
• As PGAL is oxidized, 2 molecules of NAD+ are reduced
to NADH
GLYCOLYSIS
• NAD+ an organic molecule that accepts electrons
(reduced) during redox reactions
GLYCOLYSIS
• Step 4: The phosphate groups added in steps 1 and 3
are removed from the 3-carbon compounds, producing 2
molecules of pyruvic acid. Each phosphate group is
combined with a molecule of ADP to make a molecule
of ATP
GLYCOLYSIS
• Because 2 molecules of ATP were used in step 1, and 4
were produced in step 4, there is a gain of 2 molecules
of ATP for each molecule of glucose that is converted into
pyruvic acid.
FERMENTATION
• A process in which cells make a limited amount of ATP
by converting glucose into another organic compound
such as lactic acid or ethyl alcohol in the absence of
oxygen
• Two common fermentation pathways result in the
production of lactic acid and ethyl alcohol.
LACTIC ACID FERMENTATION
• The process by which pyruvic acid is converted into
lactic acid.
• Involves the transfer of 2 hydrogen atoms from NADH
and H+ to pyruvic acid. NADH is oxidized to NAD+ in
the process.
• The resulting NAD+ is used in glycolysis, where it is again
reduced to NADH
LACTIC ACID FERMENTATION
• Lactic Acid Fermentation by microorganisms helps
produce cheese and yogurt
LACTIC ACID FERMENTATION
• Also occurs in muscles during strenuous exercise. Muscles
switch from aerobic respiration to lactic acid fermentation
when they use more oxygen than they can take in.
• Lactic acid builds up and causes sore muscles.
• Eventually lactic acid diffuses into blood, returning to
the liver.
ALCOHOLIC FERMENTATION
• Alcoholic Fermentation is used by some unicellular
organisms (yeast)
• Process by which pyruvic acid is converted to ethyl
alcohol; anaerobic action of yeast on cells
ALCOHOLIC FERMENTATION
• Requires 2 steps
• 1st – A CO2 molecules is removed from pyruvic acid,
leaving a two-carbon compound.
• 2nd - 2 hydrogen atoms (from NADH and H+) are added
to the two-carbon compound to form ethyl alcohol
ALCOHOLIC FERMENTATION
• Used to make beer, wine, bread
ENERGY YIELD
• Kilocalories: a unit of energy. 1Kcal = 1000 calories
• The complete oxidation of a standard amount of glucose
releases 686 kcal of energy
• The production of a standard amount of ATP from ADP
absorbs 12 kcal of energy
• Efficiency of glucose =
Energy required to make ATP
Energy released by oxidation of glucose
2 x 12 kcal
686kcal
x 100% = 3.5%
• 2 ATP molecules produced during glycolysis receive only
a small percentage of the energy that could be released
by the complete oxidation of each molecule of glucose
• Most energy originally contained in glucose is still held
in the pyruvic acid
• Anaerobic pathways are not very efficient
• The anaerobic pathway probably evolved early in the
history of life on earth.
• The first organisms were bacteria. They produced all
their ATP through glycolysis.
• It took over a billion years for the first photosynthetic
organism to appear. The oxygen they released as a
byproduct stimulated the evolution of organisms that
make their ATP through aerobic respiration
• Anaerobic pathways provide enough energy for many
present day organisms like unicellular and very small
multicellular organisms.
• Larger organisms have much greater energy
requirements that cannot be met with anerobic
respiration  must use aerobic respiration