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2 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Sylvia S. Mader Immagini e concetti della biologia

3 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 B1 - Photosynthesis and cellular respiration

4 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

5 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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

6 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Chloroplasts Chloroplasts carry out photosynthesis. CO 2 enters the leaf through small pores called stomata. CO 2 O2O2 stoma chloroplast

7 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Chloroplasts Chlorophyll and other pigments within the thylakoid membranes absorb solar energy. Conversion of CO 2 to carbohydrates occurs in the stroma. thylakoid membranes stroma granum inner membrane outer membrane Chloroplast

8 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

9 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Photosynthesis is a redox Photosynthesis is a reduction-oxidation reaction (redox) where CO 2 is reduced and H 2 O 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

10 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 O 2 comes from the water Isotope-based experiments proved that the oxygen produced during photosynthesis comes from the water rather that from CO 2.

11 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Photosynthesis reactions Light reactions: occur in the thylakoid membranes during the day when light is available. Calvin cycle reactions: enzymatic reactions that reduce CO 2 to a carbohydrate in the stroma.

12 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

13 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

14 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Calvin cycle During the light-independent reactions, the Calvin cycle uses ATP and NADPH to produce carbohydrates. During this process CO 2 is fixed and then reduced.

15 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Calvin cycle The Calvin cycle includes three steps. 1.CO 2 fixation: the enzyme RuBP carboxylase fixes CO 2 to RuBP, producing a C 6 molecule that immediately splits into two C 3 molecules (3PG). 2.CO 2 reduction: each 3PG is reduced to a glyceraldehyde 3-phosphate (G3P) molecule. 3.RuBP regeneration: G3P molecules are used to regenerate RuBP.

16 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Carbohydrates and other molecules In plants carbohydrates (G3P) are used to synthesize other important organic molecules as fructose, sucrose and starch.

17 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

18 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Deforestation and global warming Destroying tropical rain forests increases the concentration of CO 2 emissions in the atmosphere. CO 2 is a powerful green house gas.

19 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cellular respiration Cellular respiration is a redox reaction that requires O 2 and produces energy. Glucose is oxidized to CO 2, while O 2 is reduced to water.

20 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cellular respiration Coenzymes NAD + and FAD remove hydrogen atoms (e - and H + ) from glucose. Slow release of energy at the ETC allows it to be captured for ATP production. NAD + + 2e - + H + NADH FAD + 2e - + 2H + FADH 2

21 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cellular respiration

22 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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: 1.Cellular respiration (aerobic pathway) 1.Fermentation (anaerobic pathway)

23 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Glycolysis Cellular respiration has three phases: Preparatory reaction Citric acid cycle Electron transport chain (ETC)

24 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Glycolysis Glycolysis starts with an energy-investment phase during which 2 ATP molecules are consumed to produce two C 3 molecules (Glyceraldehyde 3-phosphate).

25 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Glycolysis The second step is an energy-harvesting phase with the synthesis of four ATP molecules.

26 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Glycolysis 2 ATP molecules are consumed 4 ATP molecules are produced The net gain is 2 ATP molecules 2 NADH molecules are produced

27 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The mitochondrion Apart from the preparatory reaction, all cellular respiration reactions (citric acid cycle and ETC) occur in the mitochondrion.

28 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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 (C 2 molecule). Two NADH and two CO 2 molecules are also produced.

29 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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 FADH 2 are produced as CO 2 is released.

30 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cellular respiration

31 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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 FADH 2.

32 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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. O 2 is the final acceptor of electrons and is reduced to water.

33 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

34 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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 ATP from the ETC and chemiosmosis

35 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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 CO 2 )

36 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.

37 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 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.