CELL RESPIRATION Energetic Metabolism
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 system these Cell Respiration is the source of energy for cell work.
Cell Respiration: is the metabolic pathway that converts sugars (carbohydrates) to carbon dioxide and water. All
organisms utilize sugars to make energy (ATP)
Eq: Glucose + Oxygen  Carbon Dioxide + Water
Photosynthesis: is the metabolic pathway in Plants, green protista and prokaryotes that converts raw materials into
sugars.
Cell Respiration has three stages
1.
Glycolysis: occurs in the cytoplasm (common to all organisms) with or without O2 (anaerobic)
a. Splits glucose (C6) in half to pyruvate (C3)
b. makes 2 ATP and 2 NADH per glucose molecule
2.
Kreb Cycle: occurs in the matrix of the mitochondria only in the presence of oxygen (aerobic)
a. breaks pyruvate down to carbon dioxide (CO2) (complete oxidation)
b. produces 2 ATP
c. reduces NAD to NADH and FADH to FADH2 (coenzymes). Overall 6 NADH and @ FADH2
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. Net energy production for the ETC is 32 ATP for each glucose
d. Oxygen is the final electron acceptor 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.
NAD+ and FADH both are hydrogen carrier, it helps to carry H + to the chain of redox proteins embedded in the
Cristae membranes of the mitochondria. 3ATP molecules are produced per NADH and 2ATPperFADH2. The
estimated theoretical max number of ATP produced is between 32-38.
ATP is generated by two mechanisms
1. Substrate level phosphorylation. Involves no electron transport chain or membrains. It simply involves the
transfer of a phosphate group 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
In the Absence of oxygen Fermentation occurs. Fermentation occurs in the cytoplasm. There are 2 types:
Lactic Acid Fermentation
Pyruvate  Lactic Acid (NADH is oxidized)
Alcohol (ethanol) Fermentation Pyruvate  Ethanol (NADH is oxidized)