Modern Biology Holt, Rinehart, & Winston © 2009
Chapter 7: Cellular Respiration, pp 131-145.
Main Ideas
I. Glycolysis & Fermentation (anaerobic)
A. Glycolysis (1st step in cellular respiration)
1. In autotrophs’ & heterotrophs’ cytoplasm; eukaryotes or prokaryotes
2. Anaerobic 6-step process (does NOT require oxygen) **
3. Specific enzymes required
4. 2 ATPs required to begin glycolysis, but 4 ATPs are produced (net gain = 2 ATP)
a. ~ 2% energy efficiency
b. Bacteria evolved glycolysis early in Earth’s history (109 yrs before photosynthesis/ O2)
c. Can sustain unicellular and very small multicellular organisms
+
5. NAD reduced to NADH (carries electrons to eukaryotic cristae or prokaryotic cell membrane.)
a. In transport chain, each NADH contributes to production of 3 ATPs
6. Breaks down glucose’s chemical bonds, releasing energy for ultimate production of ATP
a. glucose  2 pyruvic acid + 2 NADH + 2 ATP
B. Fermentation
1. In cytoplasm (as above)
2. Anaerobic conditions further process pyruvic acid
3. Regenerates NAD+ to replenish those used in glycolysis (allowing further ATP production)
4. Different types of fermentation, each with own set of enzymes and final products
a. Alcoholic fermentation (yeast etc…)
i. Pyruvic acid + NADH + H+  2-C ethyl alcohol + CO2 + NAD+
ii. CO2 makes bread dough rise & bubbles in wines & beers
b. Lactic acid fermentation (microorganisms, muscles)
i. Pyruvic acid + NADH + H+  3-C lactic acid + NAD+
ii. Cheese, buttermilk, yogurt, sour cream, etc…
iii. Acid buildup in muscles  fatigue, pain, cramps  liver  pyruvic acid
II. Aerobic respiration
A. Two major stages (Krebs cycle & electron transport chain)
B. Krebs cycle (aka “citric acid cycle”)
1. Location
a. Eukaryotic mitochondrial matrix (space inside the inner membrane of mitochondrion)
b. Prokaryotic cell membrane
2. Pyruvic acid diffuses across mitochondria’s double membrane into the matrix.
3. Pyruvic acid reacts with coenzyme A to form acetyl coenzyme A + CO2 as NAD+ is reduced
4. Acetyl CoA enters Krebs cycle, joins with oxaloacetic acid to form citric acid & CoA leaves
a. In 4 enzymatic steps 2CO2, 3NADH, 1ATP, & 1 FADH2 are generated per acetyl CoA
i. FAD (flavin adenine dinucleotide) reduced to FADH2 as it carries electrons too
ii. Each FADH2 helps generate 2 ATPs later in the electron transport chain.
iii. The 2-C acetyl group does not yield CO2 in its first run through the cycle
b. Process is amphibolic (both anabolic & catabolic)
i. Intermediates serve as precursors for nucleotides, amino acids, carbohydrates
c. Series of redox reactions
i. Citric acid is oxidized as NAD+ is reduced in the 2nd step, for example.
C. Electron Transport Chain & Chemiosmosis
1. Location
a. Eukaryotes: mitochondrial cristae (folds of inner membrane)
b. Prokaryotes: plasma membrane
2. Series of molecules that transfer electrons from one molecule to another
3. When NADH & FADH2 release their H atoms, electrons from these are at high energy levels
a. Molecules of the electron transport chain accept and transport these electrons.
b. Energy lost in transport provides energy to pump protons (H+) from the matrix
c. A high H+ concentration gradient forms between the inner & outer membranes
d. An electrical gradient is also created due to the (+) charge of H+s
4. The concentration & electrical gradients drive the synthesis of ATP by chemiosmosis
a. ATP synthase, embedded in the inner membrane, is responsible for ATP formation.
b. O2 is the final electron acceptor and so allows the transport chain to keep moving ec. O2 + 4 e- + 4 H+  2 H2O
d. Process is conserved from photosynthesis
III. Efficiency of cellular respiration
A. Glycolysis
1. 686 kcal/ glucose molecule
2. Two ATPs net @ 7 kcal used/ATP formed
3. (2 ATP x 7 kcal/ATP) / 686kcal/ glucose x 100% = 2 %
B. Krebs cycle
1. Two ATPs net  14 kcal/ 686 kcal = 2%
C. Electron transport chair
1. 3 ATP/ NADH x 10 NADH/ glucose = 30 ATP
2. 2 ATP/ FADH2 x 2 FADH2/ glucose = 4 ATP
D. Final Yield
1. 2 ATP/ glycolysis + 2 ATP/ Krebs + 34 ATP/ electron transport chain = 38 ATP
2. (38 ATP/ glucose)(7 kcal/ ATP) / 686 kcal/ glucose x 100% = 39 %
IV. Summary
A. Glycolysis reactions in detail
** glucose + ATP  glucose-6-phosphate + ADP  fructose-6-phosphate + ATP  fructose-1,6-diphosphate
(cleavage)  D-glyceraldehyde-3-phosophate (G3P) x 2 (oxidative phosphorylation/ NAD+  NADH) 
1,3-diphosphoglycerate (x2)  (ADPATP) 3-phoshoglycerate (3PG)
B. Bare bones of reactions
1. Glucose <via glycolysis>  2 Pyruvic acids + 2 ATP + 2 NADH
2. {Pyruvic acid + NAD+  Acetyl CoA + CO2 + NADH} x 2
3. {Acetyl CoA <via Krebs cycle>  ATP + FADH2 + 3 NADH} x 2
4. (2 NADH x 3 ATP/NADH) + (2 NADH x 3 ATP/NADH) + (6 NADH x 3 ATP/NADH) +
(2 FADH2 x 2 ATP/FADH2) = 34 ATP <via electron transport chain>
C. Net Reaction
a. C6H12O6 + 6O2  6 CO2 + 6 H2O + 38 ATP (energy)
b. Cellular respiration also provides key essential precursors for macromolecule synthesis.
i. ~ 10 essential amino acids can be derived from Krebs cycle intermediates.
ii. Nucleotides essential for nucleic acid synthesis can be derived from Krebs cycle.