CELL RESPIRATION Energetic Metabolism
Think back to the beginning of class. We discussed the role of the producers (Plants, Algae (Green Protista) and
Cyanobacteria) and Consumers (all organisms that eat other organisms and can not make their own food. The
formation (synthesis) and breakdown (hydrolysis) of glucose in the ecosystems represents a part of the Carbon
cycle. It is represented in this figure in which Photosynthesis produces Glucose and O 2 while Cell Respiration is the
process by which Glucose is broken down into CO2 and H2O.
Nutrition is the process by which an organism takes in and uses food.. Take a look at 3 of the 4 food groups that we
take into our diets. Only Nucleic Acids are missing. They are each digested at some point in the Glucose
Metabolizing Pathway.
Metabolism is the sum total of all chemical reactions that occur in living systems. Two major metabolic pathways in
living systems are Cell Respiration and Photosynthesis
In living systems, Cell Respiration is the source of energy for cell work. Cells use energy to grow, reproduce, to
move, to transport substances, for certain chemical reaction and to make more energy.
Photosynthesis: is the metabolic pathway in Plants, green protista and prokaryotes that converts raw materials into
sugars. Cell Respiration: is the metabolic pathway that converts sugars (carbohydrates) to carbon dioxide and water.
All organisms utilize sugars to make energy (ATP).This is the unbalanced equation for Cell Respiration
(Glucose)
C6H1206
(Oxygen)
+
6O2
(Carbon Dioxide)
 
6CO2
This reaction is coupled to the formation of ATP
ADP+ Pi ATP
(Water)
+
6H20
The complete break down of glucose occurs in three stages each stage happens in a specific area of the cell and
organelle.
1.
Glycolysis: occurs in the cytoplasm (common to all organisms) with or without O 2 (anaerobic)
a. Splits glucose, a 6 carbon compound, (C6) in half to 2 (3 carbon compounds) pyruvate (C3)
b. makes 4 ATP, and 2 NADH per glucose molecule. Because glycolysis uses 2 ATP, there is a net
gain of 2ATP
2.
Kreb Cycle: occurs in the matrix of the mitochondria only in the presence of oxygen (aerobic)
a. breaks pyruvate down completely to carbon dioxide (CO 2) (complete oxidation)
b. produces 2 ATP
reduces NAD to NADH and FADH to FADH2 (coenzymes). Overall 8 NADH and 2 FADH2
c.
d. the Kreb Cycle works only when O2 is present
3.
Electron transport Chain: occurs in the cristae membranes of mitochondria
a. moves e- in the form of H+ down a chain or redox proteins in steps that involve a drop in energy
b. results in the production of a high potential energy H + gradient
c. e- delivered to the ETC from NADH will produce 3ATP while those from FADH 2 will produce
2ATP
d. Oxygen is the final electron acceptor and it becomes reduced to water. ATP are produced only if
O2 is available
e. Heat is released, this is the heat used to maintain body temperature and to facilitate chemical
reactions in the body. This is also an example of the second law of thermodynamics…. The Law
of Entropy.
NAD+ and FADH both are hydrogen carrier. When they are reduced they carry H + to the chain of redox proteins
embedded in the Cristae membranes of the mitochondria. As the redox protein alternate between reduction/oxidation
they dam up H ions forming a concentration gradient. The gradient of H ions will provide the energy needed to link
the third phosphate group to the ADP molecule. Three ATP molecules are produced per NADH and
2ATPperFADH2. The complete breakdown of Glucose to CO2 using the three phases of cell respiration can
produce between 32-38 molecules of ATP.
Study this Figure of the mitochondria to know where in the cell. Each of the three Stages occurs. Remember that
glycolysis occurs in the cytoplasm and will not be in the picture of the mitochondria.
In Cell Respiration and in Photosynthesis ATP is generated by two mechanisms
1. Substrate level phosphorylation does not involve an electron transport chain nor membranes with redox
proteins. It simply involves the transfer of a phosphate group from one molecule to an ADP molecule with
the aide of an enzyme.
2. Chemiosmosis (oxidative or photophosphorylation) involves ETC, the protein ATP synthase and the
dissipation of a H+ gradient.
Poisons interrupt Cell Respiration
1. Cyanide and CO block the transport of e- to oxygen
2. Oligomycin the antifungal antibiotic blocks passage of H+ ions through the ATP synthase molecule
3. Uncouplers DNP, dinitrophenol, causes the cristae to leak H+ ions so that the gradient is not
maintained and chemiosmosis does not occur
Fermentation is a biologically and commercially valuable chemical process. Yeast cells grown in the absence of
oxygen (anaerobically produce ethanol and carbon dioxide). Ethanol is a component of beer and wine. Yeast added
to bread dough cause the breads to rise due to the production of carbon dioxide gas. Redox reactions are coupled.
An oxidation depends on a reduction. The interruption of one limits the other from happening. Glycolysis reduces
NAD to NADH and makes ATP in the process. During Anaerobic respiration a cell is dependent on Glycolysis for
ATP. If NADH remains reduced Glycolysis stalls. Fermentation not only produces ethanol, CO 2 or lactic acid but it
also (most importantly) oxidizes NADH to NAD and glycolysis and the production of ATP can resume.
In the Absence of oxygen Fermentation occurs. Fermentation occurs in the cytoplasm.
There are 2 types of Fermentation:
Lactic Acid Fermentation Pyruvate  Lactic Acid (NADH is oxidized)
Alcohol (ethanol) Fermentation Pyruvate  Ethanol (NADH is oxidized) and CO2
Respiration is an exergonic process. While some energy is used during glycolysis, there is a net gain in energy upon
its completion. It is a physiologically important for all organisms because of its influence on cell pH. One end
product of cell respiration is carbon dioxide. When carbon dioxide dissolves in water it forms carbonic acid
(H2CO3). This is a weak acid and it dissociates into the carbonic ion and a proton. The pH is lower and the solution
becomes acidic.
CO2 + H2O  H2CO3  H2CO3 + H+
In animals: CO2 levels regulate respiratory rates
In plants CO2 affects mineral uptake from the soil.
All organisms use respiration for the production of ATP and heat.
The ATPrepresents only 40% of the energy in glucose
Plants and animals convert fatty acids into acetyl CoA. Acetyl CoA is metabolized to CO using the Kreb Cycle and
ATP is derived by the ETC.
Plants obtain oxygen in both their leaves (via stomata) and in their roots. Anoxia is no oxygen, lack of oxygen stops
the Kreb Cycle and ETC. Hypoxia is Low Oxygen it slows down cell respiration. Soils become Hypoxic when they
are flooded . This causes a plant to shift its metabolism to fermentation in an effort to produce ATP via glycolysis.
Increased O2 or Sugars will speed up the rate of the reaction. The rate of cell respiration can be measured by
measuring the production of the end products which include CO 2 and H20, Heat and ATP