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Chapter 7 Cellular Respiration Notes
Section 1 – Glycolysis and Fermentation
Harvesting Chemical Energy:
 Cellular respiration is a biochemical pathway which allows cells to make ATP by breaking down organic
molecules such as glucose
 Autotrophs like plants, and heterotrophs like humans both go through cellular respiration
o Autotrophs produce glucose through the process of photosynthesis
o Heterotrophs obtain glucose through eating
Overview of Cellular Respiration:
 Divided into 2 stages:
o Glycolysis
 Glucose is converted into 2 molecules of pyruvic acid (a 3-carbon compound); this produces a
small amount of ATP and NADH (an electron carrier); it is an anaerobic process
o Aerobic respiration
 Pyruvic acid is broken down into NADH is used to produce a large amount of ATP
o Overall equation for cellular respiration:
o C6H12O6 + 6O2 6CO2 + 6H2O + ATP
Stages of Glycolysis: Occurs in the cytoplasm of the cell
1. 2 phosphate groups are added to glucose – uses 2 molecules of ATP
2. The new 6-carbon compound is split into 2 3-carbon compounds called G3P
3. Each G3P becomes oxidized and has another phosphate group added to it; the oxidation of G3P is accompanied
by the reduction of 2 molecules of NAD+ (nicotinamide adenine dinucleotide) to NADH
4. The 4 phosphate groups are removed from the molecules of G3P
5. This results in 2 molecules of pyruvic acid
6. The 4 removed phosphate groups combine with 4 molecules of ADP to produce 4 ATP
7. Since 2 were used in step 1, the net gain of ATP is 2
 In anaerobic conditions (without oxygen) some cells can convert pyruvic acid from glycolysis into other
compounds and regenerate NAD+ (which keeps glycolysis going)
 Two types of fermentation:
 Lactic Acid Fermentation:
o Pyruvic acid is converted into lactic acid and NAD + is regenerated
o Lactic acid fermentation is used in the manufacturing of many dairy products like yogurt and cheese
o Lactic acid fermentation also occurs in your muscle cells during strenuous exercise; as oxygen is used up,
cells will switch over to using fermentation to regenerate NAD+, this causes a build-up of lactic acid in
your muscle cells  muscle fatigue and burning
o Breathe heavier and faster to bring more oxygen into your cells and remove the lactic acid
 Alcoholic Fermentation:
o Some plant cells and yeasts use alcoholic fermentation to convert pyruvic acid into ethyl alcohol and to
regenerate NAD+
o A molecule of carbon dioxide is removed and released as a gas, the resulting 2 carbon compound is then
utilized to produce ethanol (ethyl alcohol)
o Used in the wine and beer making industries
o Used in baking  yeast will ferment the glucose present in the dough, causing CO2 to be released,
which is what causes dough to rise, and there to be air bubbles in bread
Section 2 – Aerobic Respiration
Overview of Aerobic Respiration:
 Two sets of reactions occur after glycolysis – the Kreb’s Cycle and the Electron Transport Chain
 Both processes are necessary for the complete breakdown of glucose that was started in glycolysis
 Need to harvest the maximum amount of energy from each molecule of glucose
 The Kreb’s cycle produces NADH which is used in the ETC to produce ATP
 In eukaryotic cells, these reactions occur inside the mitochondria (glycolysis occurs in the cytosol)
 The mitochondria is an organelle that has a smooth outer membrane and a highly folded inner membrane
 The folds of the inner membrane are called cristae; the space between the inner and outer membranes is called
the mitochondrial matrix
Steps of the Kreb’s Cycle: Biochemical pathway that breaks down acetyl CoA and produces CO2, H atoms and ATP
 Before the Kreb’s cycle begins, one molecule of pyruvate (from glycolysis) enters the mitochondrial matrix and
reacts with a compound called co-enzyme A ; the resulting compound is called acetyl Co-A
o This reaction releases CO2 and produces NADH
1. Acetyl Co-A (2 carbons) combines with a 4-carbon molecule called oxaloacetic acid to produce a 6-carbon
molecule called citric acid; this step regenerates CoA so that the linking reaction can continue
2. Citric acid loses one carbon atom and a hydrogen atom – the carbon atom combines with oxygen to be released
as CO2 and the hydrogen atom is used to make NADH
3. The resulting 5-carbon compound from step 2 also loses one carbon atom and one hydrogen atom; the carbon
atom combines with oxygen to be released as CO2 and the hydrogen atom is used to make NADH; a molecule of
ATP is also generated at this step
4. The resulting 4-carbon compound from step 3 releases a hydrogen atom to form another 4-carbon compound;
the hydrogen atom is used to produce a molecule of FADH2 (similar to NADH)
5. The resulting 4-carbon compound from step 4 releases a hydrogen atom to form oxaloacetic acid which is
needed to keep the Kreb’s cycle going. The hydrogen atom is used to make NADH
One glucose molecule produces 2 molecules of pyruvate from glycolysis; one molecule of pyruvate is utilized per
“turn” of the Kreb’s cycle; multiply each product by 2 to get the net result
Net products of the Kreb’s Cycle (per 1 glucose molecule; per 2 pyruvate molecules)
o 4 molecules of CO2 – given off as waste
o 2 molecules of ATP – used to keep the Kreb’s cycle going
o 6 NADH – used in the ETC
o 2 FADH2 – used in the ETC
The Electron Transport Chain
 A series of molecules that are embedded in the inner mitochondrial membrane that transfers electrons; NADH
and FADH2 release H protons and electrons which provide the energy to produces ATP
Steps of the ETC
1. NADH and FADH2 from the Krebs cycle each give up Hydrogen atoms – the electrons are passed from one
molecule to another in the ETC, and the protons are pumped into the space between the inner and outer
mitochondrial membranes
2. As the electrons are passed down the ETC, the lose energy – that energy is used to pump the protons into the
space; this causes a high concentration of protons to build up in the space between the inner and outer
mitochondrial membrane
3. The high concentration of protons provides the energy needed to produce ATP
4. Oxygen is the final electron acceptor of the ETC – if no oxygen is present, the ETC would not be able to pass any
more electrons, and the chain would build up – like a traffic jam