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Cellular Respiration
Dr. Huq
Chapter 5
Respiration
• Overview;
– Glucose to Carbon dioxide + Water
+Energy
– C6H12O6 + O2  6CO2 + 6H2O + 38 ATP
– Glucose is highly reduced; contains energy
– Oxygen receives the electrons to form
energy
• 4 separate reactions
– Glycolysis, Transition Reaction, Krebs
Cycle, Electron Transport, Chemiosomosis
• Requires Oxygen
Chapter 5
Chapter 5
Chapter 5
Cellular Respiration
By cellular respiration the pyruvic acid molecules
are broken down completely to form three carbon
dioxide molecules, and three molecules of water.
In glycolysis, a total of four molecules of ATP are
produced, but two are used up in other steps in the
process.
Additional ATP is produced during the Krebs Cycle
and the Electron Transport Chain, resulting in a
grand total of 40 ATP molecules produced from the
breakdown of one molecule of glucose via cellular
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Cellular Respiration Steps
There are three steps in the
process of cellular respiration:
glycolysis, the Krebs cycle, and
the electron transport chain.
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Glycolysis- 10 steps
• Glucose is Phosphorylated to form
Fructose 1,6-diphosphate
• Split to form 2 Glyceraldehyde 3phosphate
• Final Products are:
– 2 Pyruvic Acid (C3H4O3)
• Compare to original glucose - C6H12O6
– 2 NADH
– 2 ATP
Chapter 5
Glycolysis
There are two important ways a cell
can harvest energy from food:
fermentation and cellular respiration.
Both start with the same first step: the
process of glycolysis which is the
breakdown or splitting of glucose (6
carbons) into two 3-carbon molecules
called pyruvic acid.
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Glycolysis
•Glycolysis happens in the cytoplasm
of cells, not in some specialized
organelle.
•Glycolysis is the one metabolic
pathway found in all living organisms.
•Glycolysis does not need oxygen as
part of any of its chemical reactions. It
serves as a first step in a variety of
both aerobic and anaerobic energyChapter 5
Kreb’s Cycle
• Figure E.3, A29
• Acetyl CoA  Carbon Dioxide
– C2H4O2 to CO2
– Energy produced/Acetyl CoA (x2 for
/Glucose)
• 3 NADH
• 1 FADH
• 1 ATP
• Metabolic Wheel
– Fats, amino acids, etc. enter or leave
– Citrate is product of first reaction
• Simmons Citrate Media
Chapter 5
In eukaryotes, the Krebs Cycle and Electron Transport
Chain occur within the mitochondria.
The pyruvic acid resulting from glycolysis is sent into the
mitochondria for these reactions to occur.
To move one molecule of pyruvic acid from the cytoplasm
into a mitochondrion “costs” the cell one molecule of ATP
(therefore two ATPs for a whole glucose), thus a net total
of 36 ATP molecules per molecule of glucose is produced in
eukaryotes as compared to only two in fermentation.
The overall reaction for cellular respiration is
C6H12O6 + 6O2
6CO2 + 6H2O (+ energy for
the cell to use for other things).
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Krebs cycle
In this cycle, discovered by Hans Krebs, the pyruvic acid
molecules are converted to CO2, and two more ATP
molecules are produced per molecule of glucose. First,
each 3-carbon pyruvic acid molecule has a CO2 broken off
and the other two carbons are transferred to a molecule
called acetyl coenzyme A, while a molecule of NADH is
formed from NAD+ for each pyruvic acid (= 2 for the
whole glucose). These acetyl CoA molecules are put into
the actual cycle, and after the coenzyme A part is released,
eventually each 2-carbon piece is broken apart into two
molecules of CO2. In the process, for each acetyl CoA that
goes into the cycle, three molecules of NADH, one molecule
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of FADH2, and one molecule of ATP are formed
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Pyruvic Acid + 2 H++ 3 O2
3 Carbon Dioxide
+ 3 H2O
+ 34 ATP
Chapter 5
Fermentation Products from Pyruvate
• Homolactic = Lactic Acid
– Yogurt, Lactobacillus
•
•
•
•
•
•
Alcohol + CO2
Propionic Acid
Butyric Acid
Acetic Acid
Succinic Acid
Butylene to Acetoin
– basis for VP Test (Vogues-Proskauer)
Chapter 5
Fermentation
Lactic acid fermentation is done by some fungi,
some bacteria, in yogurt, and sometimes by our
muscles.
Under greater exertion when the oxygen supplied
by the lungs and blood system can’t get there fast
enough to keep up with the muscles’ needs, our
muscles can switch over and do lactic acid
fermentation. In the process of lactic acid
fermentation, the 3-carbon pyruvic acid molecules
are turned into lactic acid.
Chapter 5
Fermentation Products
• Alcohol and Carbon Dioxide
– Yeast mostly
• Lactic Acid
– Humans, muscles without oxygen
– Bacteria (Lactobacillus-yogurt)
• Butyric Acid
– Rancid butter, Clostridium-gangrene
• Acetoin
– Butanediol fermentation in Klebsiella
• Propionic Acid
– Swiss Cheese
Chapter 5
Fermentation
In fermentation pyruvic acid molecules are
turned into some “waste” product, only two
ATP molecules per molecule of glucose –
against four are produced in glycolysis.
two of the most common types are lactic acid
fermentation and alcohol fermentation.
Chapter 5
Fermentation
Alcohol fermentation is done by yeast
and some kinds of bacteria. The “waste”
products of this process are ethanol and
carbon dioxide (CO2). Humans have long
taken advantage of this process in
making bread, beer, and wine. In bread
making, it is the CO2 that causes the
bread to rise.
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Transition Reaction
• Pyruvic Acid  Acetyl - Co A + CO2 +
NADH
• C 2H 4O 2
Chapter 5
The electron transport chain is a system of
electron carriers embedded into the inner
membrane of a mitochondrion. As electrons
are passed from one compound to the next in
the chain, their energy is harvested and stored
by forming ATP. For each molecule of NADH
which puts its two electrons in, approximately
three molecules of ATP are formed, and for
each molecule of FADH2, about two molecules
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of ATP are formed.
At the last step in the electron
transport chain, the “used up”
electrons, along with some “spare”
hydrogen ions are combined with
O2 (we finally got around to the
O2) to form water as a waste
product: 4e- + 4H+ + O2
2H2O.
Chapter 5
Summary of Respiration
• Aerobic Respiration
–
–
–
–
Glycolysis
Transition Rx.
Kreb’s Cycle
Electron Transport
Chain
• Anaerobic
Respiration
– Pyruvate 
• Lactic Acid
• Mixed Acids
• Alcohol + CO2
– Recycle NADH
– 2 ATP / Glucose
Chapter 5
Chapter 5