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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

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

22. 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

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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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