Mitochondria Are Semiautonomous Organelles

The breakdown of sucrose to pyruvate releases less than 25 of the total energy in sucrose the remaining energy is stored in the two molecules of pyruvate. The next two stages of respiration (the citric acid cycle and oxidative phosphorylation i.e., electron transport coupled to ATP synthesis) take place within an organelle enclosed by a double membrane, the mitochondrion (plural mitochondria). In electron micrographs, plant mitochondria whether in situ or in vitro usually look spherical or...

Different Tissues and Organs Respire at Different Rates

A useful rule of thumb is that the greater the overall metabolic activity of a given tissue, the higher its respiration rate. Developing buds usually show very high rates of respiration (on a dry-weight basis), and respiration rates of vegetative tissues usually decrease from the point of growth (e.g., the leaf tip in dicotyledons and the leaf base in monocotyledons) to more differentiated regions. A well-studied example is the growing barley leaf (Thompson et al. 1998). In mature vegetative...

Overview Of Plant Respiration

Aerobic (oxygen-requiring) respiration is common to nearly all eukary-otic organisms, and in its broad outlines, the respiratory process in plants is similar to that found in animals and lower eukaryotes. However, some specific aspects of plant respiration distinguish it from its animal counterpart. Aerobic respiration is the biological process by which reduced organic compounds are mobilized and subsequently oxidized in a controlled manner. During respiration, free energy is released and...

Respiration Is Tightly Coupled to Other Pathways

Glycolysis, the pentose phosphate pathway, and the citric acid cycle are linked to several other important metabolic pathways, some of which will be covered in greater detail in Chapter 13. The respiratory pathways are central to the production of a wide variety of plant metabolites, including amino acids, lipids and related compounds, isoprenoids, and porphyrins (Figure 11.13). Indeed, much of the reduced carbon that is metabolized by glycolysis and the citric acid cycle is diverted to...

Fermentation Does Not Liberate All the Energy Available in Each Sugar Molecule

Before we leave the topic of glycolysis, we need to consider the efficiency of fermentation. Efficiency is defined here as the energy conserved as ATP relative to the energy potentially available in a molecule of sucrose. The standard free-energy change AG0' for the complete oxidation of sucrose is -5760 kJ mol-1 1380 kcal mol-1 . The value of AG0' for the synthesis of ATP is 32 kJ mol-1 7.7 kcal mol-1 . However, under the nonstandard conditions that normally exist in both mammalian and plant...

Aerobic Respiration Yields about 60 Molecules of ATP per Molecule of Sucrose

The complete oxidation of a sucrose molecule leads to the net formation of 8 molecules of ATP by substrate-level phosphoryla-tion 4 during glycolysis and 4 in the citric acid cycle 4 molecules of NADH in the cytosol 16 molecules of NADH plus 4 molecules of FADH2 via succinate dehydrogenase in the mitochondrial matrix On the basis of theoretical ADP O values see Table 11.1 , a total of approximately 52 molecules of ATP will be generated Uptake of pyruvate in exchange for a hydroxy ion is...

Storage Lipids Are Converted into Carbohydrates in Germinating Seeds

Metabolization Seed Storage Cycle

After germinating, oil-containing seeds metabolize stored triacylglycerols by converting lipids to sucrose. Plants are not able to transport fats from the endosperm to the root and shoot tissues of the germinating seedling, so they must convert stored lipids to a more mobile form of carbon, generally sucrose. This process involves several steps that are located in different cellular compartments oleosomes, gly-oxysomes, mitochondria, and cytosol. Overview Lipids to sucrose. The conversion of...