Cellular Metabolism

1. Cellular Metabolism Including Cellular Respiration and Photosynthesis

2. Energy • Energy the capacity to do work. • Comes in different forms: Chemical, thermal, light, and mechanical • Two types of energy: • Kinetic Energy: is the energy of moving objects; it is energy in use • Potential Energy: is stored energy; energy that has potential to do the work.

3. Continue… • A molecule stores potential energy until it is released in the kinetic form of chemical or thermal (heat) energy. • Free energy: the sum of potential and kinetic energy • The amount of energy that could be used to power other chemical reactions.

4. Oxidation-Reduction Reaction • Transfer energy between molecules in the form of electrons. • The molecules that loses an electron is oxidized, while the molecule that gains an electron is reduced. • Example: NADH is a common energy carrier within cells. In the equation below, through a chemical reaction with hydrogen (2H), NAD+ is oxidized to NADH, while hydrogen is reduced to hydrogen ions (H+). In the process, the reverse direction, with NADH being reduced to NAD+ and hydrogen ion becoming oxidized to hydrogen • NAD+ +2H NADH + H+

5. Endergonic Reactions • Store energy within a molecule because the reactants have less free energy than the products. • These reactions require energy input • Example: The production of glucose from carbon dioxide (CO2) and water (H2O) is an endergonic reaction because it requires energy input. Because energy is expended in the process, this reaction cannot occur in the reserve direction. • 6CO2 + 6H2O + energy  C6H12O6 +6O2

6. Exergonic Reactions • Release energy, leaving the reactants with more free energy than the product • Example: The breakdown of glucose into carbon dioxide (CO2) and water (H20) is exergonic reaction because it results in the release of energy. Because this reaction releases energy, it cannot occur in the reverse directions C6H12O6 (glucose) + 6 O2 6CO2 +6H2O +energy

7. Continue… • Cells often use the energy released from exergonic reactions to power endergonic reactions; these are called coupled reactions. Exergonic Reactions Endergonic Reactions

8. ATP • Adenosine triphosphate, is referred to as the “the energy of the cell” (cell energy) because it powers most of the reactions that take place in a cell. • ATP consist of • Ribose, an adenine (a type of nucleotide) • Chain of three phosphate groups • The bonds that link the second and third phosphate group can be broken down to produce ADP (adenosine diphosphate), a free phosphate group (P), and a substantial amount of energy used for endergonic reactions. ATP  ADP + P + energy Example: The human body uses, on average, one kilogram of ATP every hour

9. Enzymes • Exergonic reactions require a small initial input of energy, called activation energy, before the reaction can proceed. • Enzyme are proteins that lower the activation energy of a reaction. • Active Site of an enzyme binds with the reactants (substrate) and either changes them in some way or simply brings them in closer proximity to one another.

10. Continue… • Chemical reactions do not use up or change the enzyme. • Once the reaction has taken place, the product is released, and the enzyme is free to catalyze other reactions.

11. Enzyme Inhibitors • The presence of other molecules may inhibit an enzyme, or prevent it from functioning. Inhibitions can occur in two ways: • Competitive inhibition: occurs when the inhibitor binds with the active site of an enzyme. With the active site already occupied, the enzyme cannot bind with the substrate. • Noncompetitive inhibition: occurs when the inhibitor binds with an allosteric site (any site other than the active site) and changes the shape of the enzyme so that it no longer bonds with the substrate.

12. Continue… • Example: Inhibitors are often used as drugs, in many cases to prevent detrimental reactions in an organism. Aspirin, for instance, inhibits the enzymes that causes pain and inflammation. However, inhibitors can also be poisonous. Cyanide is a lethal toxin because it competitively inhibits cytochromecoxidase, an enzyme involved with cellular respiration.

13. Cellular Respiration • Organisms must obtain their own energy from the environment, usually in the form of food and solar radiation. • The process of converting energy into a form that can be used by cells is called cellular metabolism. • Two methods of cellular metabolisms: • Cellular respiration and Photosynthesis

14. Continue… • Cellular respiration converts the energy found in food molecules, especially glucose, to the more useable form of ATP. • 36 ATP can be produced from a single molecule of Glucose Cellular Respiration Equation C6H12O6 + 6O2 +ADP + P  6CO2 + 6H20 + ATP • Energy transfer is not efficient for organisms Cellular respiration only 40% energy in glucose is converted to ATP.

15. Continue • Cellular respiration occurs in four stages: 1- Glycolysis 2- Oxidation of pyruvate 3- Kreb Cycle 4- Electron Transport Chain

16. Glycolysis • Takes place in the cytoplasm (cytosol) • Converts glucose to two molecules of pyruvate, the compound from which energy will be extracted in the Kreb Cycle. • Produces 2 ATP and 2 NADH (energy carrying molecule). Water is also released in this reaction.

17. Glycolysis Diagram

18. Oxidation of Pyruvate • The two molecules of pyruvate are oxidized and transformed into molecules of acetyl CoA. • Takes place in mitochondria • Also produces one molecule of NADH • Releases CO2

19. Kreb Cycle • Takes place in matrix of the mitochondria • Processes each acetyl CoA to produce 3 NADH, 1 FADH2, and 1 ATP for a total of 6 NADH, 2 FADH2, 2 ATP per glucose. • Carbon dioxide is also released in this reaction.

20. Diagram of Kreb Cycle Mnemonic Device Kreb Cycle (order) Can Intelligent Karen Solve Some Foreign Mafia Operations?

21. Oxidative Phosphorylation • After the Kreb Cycle, large amount of ATP produced from NADH (produces 3 ATP) and FADH2 (produces 2 ATP) • Requires the presence of oxygen in the mitochondria

22. Electron Transport Chain • Is series of molecules embedded in the inner membrane of the mitochondria • The 10 NADH and 2 FADH2 (Produced from previous stages) power the production of the final 32 ATP • Chemiosmosis: coupling of the movement of electrons down the electron transport chain with the formation of ATP. • Coupled Reaction: A reaction that uses the product of one reaction as part of another reaction.

23. Steps of the Electron Transport Chain • 1- Electron carriers NADH and FADH2 shuttle electrons to the inner mitochondrial membrane. • 2- NADH and FADH2 donate their electrons to the first in a series of membrane proteins. Each protein uses the energy in the electron to pump H+ into the intermembrane space of the mitochondrion before passing the electron the next carrier. The final electron receptor is O2, which combines with two protons, H+ to form water

24. Continue… • 3- By pumping H+ into the intermembrane space, the electron transport chain sets up a high concentration gradient. H+ flows down gradient through the ATP synthase, a membrane protein that catalyzes the production of ATP from ADP.  Chemiosmosis Oxidative phosphorylation

25. Summary of Cellular Respiration

26. Fermentation • Eukaryotic cells can produce ATP through fermentation. • Fermentation is much less efficient than the four stages of cellular respiration, but allows ATP to produce when oxygen is not available • Begins with glycolysis producing only 2 ATP. • All other stages cannot be completed without oxygen.

27. Continue… • Two types of fermentation: • 1- Alcoholic Fermentation: Pyruvic acid is converted to ethanol. • Used by fungi and some plants • Used to make beer, wine, and bread • 2- Lactic Acid Fermentation: Pyruvic acid is converted to lactate. • Lactic acid fermentation is used by animals and bacteria • Muscle Cramps (occurs when over exercise your muscles) • Sour Cream and buttermilk Example: The sour taste of sourdough comes from the lactic acid produced by the fermentation of bacteria

28. Photosynthesis • Plants, some protists, and bacteria, create food molecules (sugars) from carbon dioxide and solar energy through the process of photosynthesis. • Equation for photosynthesis: 6CO2 + 6H2O  C6H12O6 + 6O2 Light

29. Players of Photosynthesis • Organelle: Chloroplast • Chloroplast is divded into inner and outer portion of the organelle • Stroma: inner fluid portion • Thylakoid: Green disk membrane system (first stage of photosynthesis occurs) • Grana: Flatten channels and disk (thylakoid) arranged in stacks Thylakoid Grana Stroma

30. Continue… • Autotroph: Organisms that is self-nourishing. • Heterotroph: organisms that must consume food. • Bundle Sheath cells: Cells that are tightly wrapped around the veins of a leaf. Site of the Calvin Cycle in C4 plants • Mesophyll: interior leaf • Mesophyll Cells: contains many chloroplast and host the majority of photosynthesis • Photolysis: process by which water is broken up by an enzyme into hydrogen ions and oxygen atoms. Occurs in the light dependent reaction

31. Continue… • Photophosphorylation: process by which ATP is produced during light-dependent reaction of photosynthesis • Photorespiration: process by which oxygen competes with carbon dioxide and attaches to RuBP. Plants that experience this has a lower capacity of growth. • Photosystem: cluster of light-trapping pigments involved in photosynthesis. Photosystem I and Photosystem II are two most important.

32. Continue… • Pigment: a molecule that absorbs light of a particular wavelength. Pigments include carotenoids (orange), phycobilins, and chlorophyll • Rubisco: an enzyme that catalyzes the first step of the Calvin Cycle in C3 plants • Stomata: Structure through which CO2 enters a plant and water vapor and O2 leave • Transpiration: natural process by which plants lose H2O via evaporation of leaves

33. Light Dependent Reactions • Convert solar energy into ATP and NADPH, the reduced form of the electron receptor, NADP+. • During these reactions, water is split, leaving oxygen as a waste product. • Why is oxygen considered to be a waste product? • These reactions take place in photosystem in the choloroplast.

34. Continue… • Photosystems comprise cluster of molecules composed of light-absorbing pigments and a reaction center, which includes a primary electron acceptor and two chlorophyll a pigment molecules. • There are two photosystems work sequentially, with light first being absorbed by photosytem II and later by photosystem I

35. Steps to light dependent reactions • 1- Photosystem II absorbs solar energy in the form of light. • 2- The solar energy excites electrons in the reaction center of photosystem II, which the n enter an electron transport chain. These electrons originate from the splitting of water, which produces free electrons and O2 • 3- As electrons pass down the electron transport chain, protons are pumped into the thylakoid membrane space of the chloroplast. Protons diffuse out of the thylakoid membrane space through an ATP synthase, creating ATP.

36. ATP and NADPH made in the light dependent reaction Continue… • 4- Photosystem I accepts electrons from the electron transport chain and uses light energy to excite the electrons further.

37. Cellular Respiration and Light Dependent Reaction • Cellular respiration and light dependent reactions of photosynthesis use similar processes to produce ATP. • Scientist believe that the electron transport chain used in cellular respiration may have evolved from the transport system used in photosynthesis.

38. Calvin Cycle • Uses ATP and NADPH from the light-dependent reaction to convert CO2 into sugar that the plant can use. • CO2 is obtained through the stomata. • Carbon fixation: incorporates the CO2 into organic molecules • The incorporation is completed by the energy rich enzyme rubisco (ribulosebiphosphatecarboxylase (RuBP)), a protein made during light-dependent reaction of photosynthesis . Abundant in leaves

39. Continue… • CO2 is split into: • 3 carbon molecule PGA (3-phosphoglycerate) • Converts PGA into 3-carbon sugar molecule glyceraldehyde 3-phosphate • Used to make glucose and sucrose • The production of a single 3-carbon sugar molecule require 3 CO2, 9 ATP, 6 NADPH

40. Calvin Cycle Diagram

41. Photorespiration • When the enzyme rubisco incorporates oxygen, rather than CO2, into organic molecules, plants create energy through the process of photorespiration. • Occurs most in arid regions where plants must close their stomata to prevent water loss to the air. • The results in a buildup of oxygen levels in the leaf, which makes rubisco more likely to bind with the oxygen. • Detrimental to plants because it consumes more ATP to produce each 3-carbon sugar. • Three different categories this type of method: C3 pathway, CAM pathway, and C4 pathway

42. C3 Plants • Found in areas with moderate temperature and above amount of rainfall • Exacerbated in Hot arid climates, where the rate of photosrespiration increases as the temperature goes up. • Consequently C3 plants are rarely found in these climates • Located in the temperate zones • Examples: Wheat, barley, and sugar beets

43. C4 Plants • Use the enzyme PEP carboxylase to fix CO2 in the mesophyll cells of their chloroplast. • The fixed CO2 is then shuttled to specialized structures known as bundle-sheath cells, where it is released and incorporated into the Calvin Cycle. • Energetically expensive, but limits photorespiration by allowing high concentration CO2 to build up in the bundle-sheath cells • Examples: Corn and sugar cane are common in warm environments

44. CAM Plants(Crassulacean acid metabolism) • Plants reduce photorespiration and conserve water by opening their stomata only at night. • CO2 enters through the stomata and is fixed into organic acids, which are then stored in the cell’s vacuole . • During the day, the acids break down to yield high levels of CO2 for use in the Calvin cycle • Common in dry environments • Examples: Pineapples and cacti