Respiration & secondary metabolism of plants

I.             Overview

                A.            Photosynthesis (energy & CO₂ fixation) - chloroplasts

                B.            Respiratory & secondary metabolism

                                1.             Glycolysis - cytoplasm

                                2.             Krebs (Citric acid cycle) - mitochondrion

                                3.             Electron transport & oxidative phosphorylation - mitochondrion

II.            Glycolysis [glucose and fructose from Calvin cycle (photosynthesis)]

                A.            Glucose - glucose-6-p - fructose-6-p - fructose 1,6-dp - PGAL (=DHAP) - 1,3-dp-glycerate - 3-p-glycerate - 2-p-glycerate - phosphoenolpyruvate - pyruvate

                B.            Initial step(s) - energy requiring (2 ATP)

                C.            Subsequent steps

                                1.             Two - substrate-level phosphorylations (4 ATP)

                                2.             One - reduction of NAD to NADH (2 NADH)

                D.            Yield - 2 ATP & 2 NADH

                E.            Final product - 2 pyruvates

III.          Alternatives after glycolysis

                A.            Lactic acid - 2 ATP (no NADH) ... intense muscle activity (little O₂ available)

                B.            Ethanol - 2 ATP (no NADH) ... fermentation

                C.            Krebs Cycle - (2 ATP) and oxidative phosphorylation (32 ATP)

IV.          Krebs Cycle - mitochondrial matrix

                A.            [pyruvate - acetyl CoA] - citrate - isocitrate - alpha-ketoglutarate - succinyl CoA - succinate - fumarate - malate - oxaloacetate - w/acetyl CoA - citrate

                B.            Initial step(s) - pyruvate converted to acetyl CoA [CO₂ emission and NADH production] - acetyl CoA combines with oxaloacetate (4 carbon) to form citrate (6 carbon)

                C.            All steps from pyruvate to CO₂

                                1.             Cycle (two trips) - 2 GTP (2 ATP), 8 NADH, and 2 FADH₂

                D.            Final product - 6 CO₂

V.            Electron transport system & oxidative phosphorylation - inner mitochondrial membrane

                A.            Convert NADH & FADH₂ to ATP

                                1.             NADH (glycolysis) = 2 ATP -            4 ATP

                                2.             NADH (Krebs) = 3 ATP      -             24 ATP

                                3.             FADH₂ (Krebs) = 2 ATP     -             4 ATP

                B.            How is it done?  H⁺ gradient (opposite of chloroplast)

                                1.             NADH & FADH₂ give up H⁺ to outer compartment (High outside)

                                2.             H⁺ is then pumped back in and ATP is produced

                C.            Net yield of ATP

                                1.             From oxidative phosphorylation - 32 ATP

                                2.             Substrate level phosphorylation - 4 ATP

                                3.             TOTAL............................ 36 ATP

VI.          Secondary metabolism

                A.            From glycolysis & Krebs

                                1.             Fats, glycerol, fatty acids, amino acids, & proteins

                                                a)            Example:  Carbohydrate - (ribose) - nucleic acid

                                                b)            Example:  Amino acid - (glycine) - hemoglobin

                                                c)             Example:  Amino acid - (glutamate) - chlorophyll

                                                                                                       

                                               C₆H₁₂O₆ + 6O₂ + 36 ADP + 36 Pi ===> 6CO₂ + 36 ATP + 6H₂O