OVERVIEW FOR THE OXIDATION OF GLUCOSE (GLYCOLYSIS + RESPIRATION)
C6 H12O6 + O2 CO2 + H2O + 686 kilocalories
I. AEROBIC GLYCOLYSIS
A. Occurs in the cytoplasm, in the presence of oxygen
B. Involves the splitting of ONE glucose molecule into
TWO pyruvate molecules
1. reaction is first ENDERGENIC, then EXERGENIC
2. energy is generated by a series of oxidation/reduction
reactions ultimately used to form ATP from ADP
3. Net gain of ATP for aerobic glycolysis = 6-8 ATP
a) 2 ATP molecules are USED to "kick-off" the reaction, 4 additional
molecules are generated during the exergonic steps: net yield
= 2 ATP (direct)
b) 2 molecules of NAD+ are reduced to NADH
1) NADH = a coenzyme electron-carrier
2) the energy that 1 NADH can carry is enough
to phosphorylate 3 ADP to 3 ATP
II. Anaerobic Glycolysis
A. occurs in the cytoplasm, in the absence of oxygen
B. can follow several pathways, fermentation and the reactions
in muscle tissue being the most common
C. follows the same steps as aerobic glycolysis, but then
switches to a different track at the stage where PYRUVATE would
then change to Acetyl Coenzyme A and enter the Krebs cycle
1. Fermentation (the formation of alcohol from glucose)
a) needs yeast mixed with the juices of sugar-containing
plants, stored under anaerobic conditions
b. is a basically ENDERGENIC reaction, yielding
only a net gain of 2 ATP per molecule of Glucose
(36-38 ATP from the full cycle of aerobic glycolysis + respiration)
c) Once the sugar content is used up, fermentation
stops, alcohol level is fixed
PYRUVIC ACID ALDEHYDE ETHANOL
2. Lactic Acid (formed from animal muscle cells when oxygen
is scarce or absent)
a) commonly produced during strenuous exercise exceeds the immediate
demands of the muscle tissue
b. excess lactic acid in the muscles produces pain,
fatigue - is diffuses into the blood, carried to the
liver, later resynthsiezed to pyruvate + later glucose
c) also yields only 2 ATP - BUT!! enough to keep
the body going in time of need.
PYRUVIC ACID LACTIC ACID
D. Anaerobic pathways probably evolved early in the evolution of life - needs no oxygen to support it (prokaryotes + protists were small, needed little energy)
III. Respiration (2 steps)
A. Occurs in the cristae of the mitochondria
1. Mitochondria are double-membraned
a) Outer membrane = semi-permeable, smooth
b) Inner membrane = folded into cristae, HIGHLY SELECTIVE mainly
lets ATP, pyruvate have passage only
c) inner compartment filled with a dense solution
called the MATRIX
B. involves the generation of 3 more ATP from the oxidation of
pyruvic acid, the Kreb's cycle, and the electron transport shuttle for
a total of 36-38 ATP, 95% of the ATP generated by heterotrophic cells)
C. Oxidation of Pyruvic Acid
A. Pyruvic Acid passes through the outer + inner membranes
of the mitochondria
1. In very energetic cells, this effort may take some
energy, reducing the total amount ATP generated
B. Molecules of pyruvic acid are broken down into
CARBON DIOXIDE, NADH (stored energy) and molecules of
Acetyl Coenzyme A
D. Kreb's Cycle
A. A select number of products are oxidized and reduced,
generating molecules of CARBON DIOXIDE, NADH, a molecule of
FADH2, and a molecule of ATP for a total of 24 ATP
1. FADH2 is also a coenzyme electron carrier that holds
its electrons at a slightly lower level than NADH
allowing it to only give of the energy to phosphorylate
2 ATP per molecule of FADH²
FLAVIN ADENINE DINUCLEOTIDE (NADH2)
3. beginning product (citric acid) is regenerated at the end of the cycle, making it a true circle
E. Electron Transport Shuttle
1. Involves the acceptance of electrons from NADH and FADH2 (generated
from the previous steps. to a series of electron carriers whose energy
ultimately converts ADP to ATP and forms molecules of WATER along the way
2. Electron carriers = coenzymes and CYTOCHROMES
3. Involves a drop in energy levels from one product to
the next
4. depends upon a proton gradient in the cristae to work
(CHEMOSMOSIS)