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2. Cell activities 2 © Zanichelli editore 2015

3. Cell metabolism and ATP 3 © Zanichelli editore 2015

4. Cell metabolism: anabolic and catabolic reactions 4 Cell metabolism is the sum total of the reactions carried out by a cell. It involves anabolic reactions, which result in the synthesis of biomolecules and require energy, as well as catabolic reactions, which result in the degradation of biomolecules and produce energy. © Zanichelli editore 2015

5. Cells and the laws of thermodynamics 5 Cells are ordered systems and they need energy in order to function. They use the chemical energy stored in bonds between molecules of nutrients. Energy metabolism is the sum of reactions that allow cells to produce energy. © Zanichelli editore 2015 H C Chemical energy

6. ATP and energy storage 6 Cells convert chemical energy into ATP; high-energy molecules composed of adenine, ribose and three phosphate units linked together by covalent bonds. PPP Adenine Ribose Phosphate groups © Zanichelli editore 2015

7. ATP hydrolysis /1 7 ATP hydrolysis releases free energy that can be used for cell metabolism: ATP + H 2 O  ADP + P + Energy © Zanichelli editore 2015

8. ATP hydrolysis /2 8 PPP PP PiPi + ENERGY © Zanichelli editore 2015

9. ATP cycle 9 ATP molecules can be “recharged”: energy can be released and acquired in a cyclic manner. ATP ADP + P i ENERGY © Zanichelli editore 2015

10. The role of cell membranes 10 © Zanichelli editore 2015

11. Functions of biological membranes 11 Biological membranes play an important role in cell metabolism. From the functional point of view, all biological membranes: are selective filters; are flexible and dynamic; take part in metabolic processes, thanks to proteins. © Zanichelli editore 2015

12. Structure of the plasma membrane 12 Its flexible and dynamic structure is called fluid mosaic. © Zanichelli editore 2015 The plasma membrane is made up of a phospholipid bilayer with proteins immersed in it. Phospholipids have a hydrophilic head, containing a phosphate group, and two hydrophobic tails.

13. Proteins in cell membranes 13 Proteins represent around 50% of cell membranes. They can be: integral, when they cross the double layer and protrude on both sides of the membrane; peripheral, when they are associated with the internal or external side of the membrane. © Zanichelli editore 2015

14. Active and passive transport 14 Molecules can cross the membrane by two types of transport: passive transport – it is spontaneous; active transport – it requires energy from ATP. Larger molecules can be transported across the membrane by vesicles. © Zanichelli editore 2015

15. Passive transport /1 15 © Zanichelli editore 2015

16. Passive transport /2 16 In passive transport, molecules can cross the membrane by diffusion due to the concentration gradient. This process does not require energy. Simple diffusion is the movement of small and apolar molecules across the double layer of the membrane. In facilitated diffusion, polar molecules or ions cross the membrane using specific transport proteins. © Zanichelli editore

17. Osmosis and water diffusion 17 Osmosis is the movement of water across a semipermeable membrane; it is a type of diffusion. Water leaves the cell if the extracellular fluid is hypertonic (higher concentration of solutes), it enters the cell if it is hypotonic (lower concentration of solutes). © Zanichelli editore 2015

18. Active transport 18 Active transport requires energy from ATP and specific transport proteins. Transport can happen using a uniport, symport or antiport mechanism. © Zanichelli editore 2015

19. Endocytosis and exocytosis 19 In endocytosis and exocytosis, macromolecules are engulfed in transport vesicles made of membrane fragments. © Zanichelli editore 2015 endocytosis exocytosis

20. From nutrients to ATP 20 © Zanichelli editore 2015

21. Metabolic pathways 21 Energy metabolism is organized in metabolic pathways; sequences of reactions that gradually transform initial reagents into final products through a series of ordered steps. © Zanichelli editore 2015 Initial reagent Step A Step B Step C Final product

22. The role of NAD in metabolism 22 The molecule NAD is a co-enzyme that intervenes in many metabolic pathways. It exists in two forms: NAD + and NADH. In the presence of hydrogen and an electron donor, NAD + becomes NADH which contains more energy. NAD + NADH + H + acquires e – loses e – RH 2 R R’ R’H 2 © Zanichelli editore 2015

23. The most common nutrient is glucose 23 The most common nutrient for obtaining energy is glucose. C 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 O + Energy The breakdown of the molecule occurs in two phases: glycolysis and cellular respiration. © Zanichelli editore

24. Glycolysis is a universal metabolic pathway 24 Glycolysis occurs in cytoplasm and transforms glucose into 2 molecules of pyruvate, producing 2 molecules of ATP and 2 of NADH. © Zanichelli editore 2015 glucose (C 6 H 12 O 6 ) 2 pyruvate (C 3 H 4 O 3 ) 2 ATP 4 ATP 2 NADH

25. Cell respiration /1 25 Cell respiration takes place in the mitochondria and uses O 2 molecules as electron acceptors. © Zanichelli editore 2015 Its preparatory phase is called pyruvate oxidation which degrades pyruvate to CO 2 to produce acetyl-CoA. P YRUVATE OXIDATION 2 pyruvate (C 3 H 4 O 3 ) 2 CoA 2 CO 2 2 NADH 2 acetyl-CoA (CH 3 CO-S-CoA) 2 NAD +

26. Cell respiration /2 26 © Zanichelli editore 2015 The second phase of cell respiration is the Krebs cycle, which degrades acetyl-CoA to CO 2 to produce electron carriers (NADH and FADH 2 ) and ATP. K REBS CYCLE 2 acetyl-CoA (CH 3 CO-S-CoA) 4 CO 2 2 ATP 6 NADH 2 FADH 2 6 NAD + 2 FAD

27. Cell respiration /3 27 © Zanichelli editore 2015 The final step of cell respiration is the electron transport chain: it oxidizes carriers and produces H 2 O and ATP. E LECTRON TRANSPORT CHAIN 10 NADH + 2 FADH 2 6 O 2 6 H 2 O 28 ATP 10 NAD + 2 FAD

28. Fermentation 28 In the absence of oxygen, fermentation occurs, which regenerates NAD + from NADH, by an alternative path. © Zanichelli editore 2015 Fermentation is used by anaerobic organisms (for example Lactobacillus bulgaricus or yeasts) and by muscle cells during intense exercise.

29. Solar energy and the production of nutrients 29 © Zanichelli editore 2015

30. Autotrophs produce glucose 30 Autotrophs produce glucose from inorganic molecules and an external energy source - usually the Sun. The most important process used by autotrophs is photosynthesis, done by plants, algae and cyanobacteria. Photosynthesis transforms CO 2 and H 2 O into glucose and oxygen: 6 CO 2 + 6 H 2 O + Energy  C 6 H 12 O 6 + 6 O 2 © Zanichelli editore 2015

31. Photosynthesis: different phases /1 31 The process of photosynthesis can be divided into two major phases: during the light-dependent reactions, chlorophyll and other photosynthetic pigments capture energy from the Sun and use it to produce ATP and NADPH; in the light-independent reactions (or Calvin cycle), the high-energy molecules are used to fix carbon and transform CO 2 in sugars. © Zanichelli editore 2015

32. Photosynthesis: different phases /1 32 © Zanichelli editore 2015

33. Photosynthesis takes place in the chloroplasts /1 33 In the thylakoids inside the chloroplasts there are molecules of chlorophyll. They are necessary to transfer electrons from water to NADPH during the light-dependent phase. Calvin cycle occurs in the stroma - the synthesis phase in which carbon is fixed in sugars. © Zanichelli editore 2015

34. Photosynthesis takes place in the chloroplasts /2 34 © Zanichelli editore 2015