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Immagini e concetti della biologia Sylvia S. Mader Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

B1 - Energy metabolism Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

ATP and Photosynthesis Adenosine triphosphate is ancient and universal. All living organisms produce or use ATP to do work. Photosynthesizers are autotrophs (protists, cyanobacteria, plants, algae and mosses) that produce their own food. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Photosynthesis Photosynthesis converts visible light (the portion of electromagnetic radiation) from the sun into chemical energy. The most used pigments (light-absorbing molecules) in photosynthesis are: Chlorophyll a Chlorophyll b Carotenoids Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Chloroplasts Chloroplasts carry out photosynthesis. CO2 enters the leaf through small pores called stomata. CO2 O2 stoma chloroplast Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Chloroplasts Chlorophyll and other pigments within the thylakoid membranes absorb solar energy. Conversion of CO2 to carbohydrates occurs in the stroma. thylakoid membranes stroma granum inner membrane outer membrane Chloroplast Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Chloroplasts In the thylakoid membranes, pigment complexes absorb solar energy which excites electrons (e-). Energized e- pass through an electron transport chain (ETC) where they release energy for ATP production. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Photosynthesis is a redox Photosynthesis is a reduction-oxidation reaction (redox) where CO2 is reduced and H2O is oxidized, resulting in carbohydrate and oxygen. During photosynthesis the coenzyme NADP+ is the e- acceptor and is reduced to NADPH. NADP+ + 2e- + H+ NADPH Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

O2 comes from the water Isotope-based experiments proved that the oxygen produced during photosynthesis comes from the water rather that from CO2. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Photosynthesis reactions Light reactions: occur in the thylakoid membranes during the day when light is available. Calvin cycle reactions: enzymatic reactions that reduce CO2 to a carbohydrate in the stroma. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Light reactions During the light-dependent reactions, e- move from photosystem II (PS II) down an ETC to the photosystem I (PS I). Here the e- is re-energized and passes to NADP+ that reduces to NADPH. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The thylakoid membranes By chemiosmosis NADP reductase passes e- to NADP+ and NADPH results. H+ flows down gradient through ATP synthase complex, where ADP binds to phosphate group and ATP is produced. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Calvin cycle During the light-independent reactions, the Calvin cycle uses ATP and NADPH to produce carbohydrates. During this process CO2 is fixed and then reduced. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Calvin cycle The Calvin cycle includes three steps. CO2 fixation: the enzyme RuBP carboxylase fixes CO2 to RuBP, producing a C6 molecule that immediately splits into two C3 molecules (3PG). CO2 reduction: each 3PG is reduced to a glyceraldehyde 3-phosphate (G3P) molecule. RuBP regeneration: G3P molecules are used to regenerate RuBP. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Carbohydrates and other molecules In plants carbohydrates (G3P) are used to synthesize other important organic molecules as fructose, sucrose and starch. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Leafs colors in fall Fall temperatures cause leaves to change the color. Less sunlight in fall means not as much solar energy to rebuild chlorophyll, which disintegrates, leaving yellow and orange pigments visible. In some plants, as maples, pigments accumulate in acid vacuoles, leading to brilliant red color. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Deforestation and global warming Destroying tropical rain forests increases the concentration of CO2 emissions in the atmosphere. CO2 is a powerful green house gas. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration Cellular respiration is a redox reaction that requires O2 and produces energy. Glucose is oxidized to CO2, while O2 is reduced to water. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration Coenzymes NAD+ and FAD remove hydrogen atoms (e- and H+) from glucose. NAD+ + 2e- + H+ NADH FAD + 2e- + 2H+ FADH2 Slow release of energy at the ETC allows it to be captured for ATP production. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Glycolysis Glucose breakdown starts with glycolysis, that occurs in the cytoplasm and is an anaerobic process. Pyruvate is the final product of the glycolysis and it can follow two pathways: Cellular respiration (aerobic pathway) Fermentation (anaerobic pathway) Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Glycolysis Cellular respiration has three phases: Preparatory reaction Citric acid cycle Electron transport chain (ETC) Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Glycolysis Glycolysis starts with an energy-investment phase during which 2 ATP molecules are consumed to produce two C3 molecules (glyceraldehyde 3-phosphate). Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Glycolysis The second step is an energy-harvesting phase with the synthesis of four ATP molecules. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Glycolysis 2 ATP molecules are consumed 4 ATP molecules are produced The net gain is 2 ATP molecules 2 NADH molecules are produced Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The mitochondrion Apart from the preparatory reaction, all cellular respiration reactions (citric acid cycle and ETC) occur in the mitochondrion. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Two NADH and two CO2 molecules are also produced. Cellular respiration The preparatory reaction occurs before the citric acid cycle. Here the pyruvate molecule reacts with Coenzyme A (CoA) and is converted into acetyl CoA (C2 molecule). Two NADH and two CO2 molecules are also produced. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

NADH and FADH2 are produced as CO2 is released. Cellular respiration The citric acid cycle (or Krebs cycle) starts when the two acetyl CoA molecules enter the matrix of the mitochondrion. One ATP molecule per cycle (two per glucose) results. NADH and FADH2 are produced as CO2 is released. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration The Electron transport chain occurs in the mitochondrial cristae and stores much energy in ATP molecules. Electrons are carried by the coenzymes NADH and FADH2. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration The ETC is composed of proteins embedded in the membrane. Electrons pass through the proteins and the energy is captured and used to form ATP. O2 is the final acceptor of electrons and is reduced to water. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Cellular respiration Protein complexes form the ETC. As e- move through the ETC, H+ are pumped to the intermembrane space and create an H+ gradient. As H+ flow down the gradient, ATP is synthesized from ADP + P through chemiosmosis. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Total ATP production Complete oxidation of one glucose molecule produces a total of 36 ATP molecules. 2 ATP in the cytoplasm (glycolysis) 2 ATP from the Citric acid cycle 32-34 ATP from the ETC and chemiosmosis Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Fermentation Fermentation is an alternative metabolic pathway when oxygen is in short supply. Depending on the organisms, after glycolysis two types of fermentation can occur: Lactic acid fermentation (the pyruvate is reduced to lactate) Alcoholic fermentation (the pyruvate is reduced to alcohol and CO2) Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Fermentation Fermentation results in a net gain of only 2 ATP molecules, but provides a quick burst of energy for short-term activities. Yeast fermentation is used to prepare bread and alcohol; bacterial fermentation is used to produce yogurt, sour cream, cheese, pickles and vinegar. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Metabolic pathways Metabolism includes catabolism (break down of molecules) and anabolism (synthesis of molecules). Carbohydrates, fats and proteins can be all catabolized to produce ATP. Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018