Dissimilation Reactions and Energy Release

Coupling of Cellular Reactions

            Free energy change--energy liberated or used during Rx

                        negative value--release energy--exergonic

                        positive value--require energy—endergonic

            Exergonic reactions “drive” endergonic reactions

                        coupling reactions

                        use of common reactant

                                    energy rich or high energy transfer compounds


                                                            ATP-energy currency

                                                                        direct transfer to ATP

                                                                        indirect transfer to ATP

Oxidation and Energy Production

            Oxidation--loss of electrons--dehydrogenations

            Reduction--gain of electrons

            Oxidant (oxidizing agent) accept electrons and are reduced

            Reductant (reducing agent) donate electrons and are oxidized

            Oxidation-reduction system

                        Electrons may be transferred from O / R system to another

                                    electromotive potential

                                                differences in elec. pot. is free energy

                                                            ATP created if large free energy

                                                            Heat created if small free energy

Energy production by Anaerobic Processes

            Heterotrophic bacteria us CHO’s, fatty acids, & amino acids

            Glycolytic pathway (aerobic and anaerobic)

                        Aerobic--electron transport

                        Anaerobic--pyruvic acid to lactic acid or EtOH

            Pentose phosphate pathway

                        Formation of hexose monophosphates

                        Formation fo pentose monophosphates--nucleotide syn.

                        “Shunt” of glycolysis

            Fermentation--Anaerobes (organic e- acceptors / donors)

                        No ATP fromed by small free energy releases

                        Pyruvic acid “hub” of CHO fermentation

            Electron transport chain (oxidative phosphorylation)

                        NAD--nictinamide adenine dinucleotide

                        FAD--flavin adenine dinucleotide

                        FMN--flavin mononucleotide

            Tricarboxylic acid cycle (TCA)--Kreb’s or Citric acid cycle

                        Amphibolic--anabolic and catabolic reactions

Energy Yields in Aerobic Respiration



Catabolism of Lipids

            Difficult to catabolize due to solubility

Catabolism of Proteins--proteases / peptidases

            Carbon skeleton enters TCA via:

                        acetyl-CoA, a-ketoglutaric acid, succinic acid,

fumaric acid or oxaloacetic acid

Anaerobic Respiration in some Bacteria

            Nitrates may be substituted for oxygen as final e- acceptor

Energy Production by Photosynthesis

            Requirements:   1) ATP and 2) reducing agent (water)

            Cyanobacteria, plants, algaes--chlorophyll

            Green and purple bacteria—bacteriochlorophyll

            Cyclic Photophosphorylation

                        e- excited from bacteriochlorophyll

                                    cycles through e- transport systems

                                    e- returns to bacteriochlorophyll

            Non-cyclic Photophosphorylation

                        e- excited in Photosystem II is replaced

                                    photolysis (water)

                        NADP+ is reduced (final e- acceptor)

            Mechanism of ATP Synthesis

                        Chemiosmotic hypothesis—1961  Peter Mitchell—Nobel 1978

                                    Transmembranous proton movement

                                    pH gradient

                                    electric potential gradient (promotive force)

                                    hydrogen ion reentry transported membranous transport

                                                adenosine triphosphotase

                                    energy of reentry “drives” ATP synthesis

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