I: Energy in Cells: An Overview II: Cellular Respiration (Gylcolysis, Kreb’s Cycle, Electron Transport), and Fermentation Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5 th ed., Singh-Cundy and Cain, Textbook, 2012.)

Learning Objectives 1.Discuss the transformation of energy. 2.Describe metabolism, anabolic and catabolic feactions. 3.Explain how redox reactions are involved in energy exchanges. 4.Compare the reactants, products and energy yield of the 3 stages of cellular respiration (glycolysis, kreb’s cycle, & electron transport). 5.Explain the role of electron transport chain in cellular respiration. 6.Describe fermentation of lactic acid and alcohol. 7.Explain how the human body uses energy.

Overview 1 st Law of Thermodynamics: Potential (stored) energy is neither created or destroyed It can be transferred and transformed to other forms (chemical, electrical, mechanical, light, or heat). Cells transform energy to perform work ATP is the primary energy currency of cells Potential Energy in Food Is Converted to Kinetic Energy in a Hummingbird’s Body

Metabolism Sum of all chemical reactions ____ reaction is the process of building of complex (large) molecules from simple molecules; requires energy (endergonic) ____ reaction is the process of breaking down complex molecules into simple molecules; releases energy (exergonic) a. Catabolic b. Anabolic c. oxidation d. reduction

Energy is usually liberated from the ATP molecule to do work in the cell by a reaction that removes one of the phosphate-oxygen groups, leaving adenosine diphosphate (ADP). When the ATP converts to ADP, the ATP is said to be spent. Then the ADP is usually immediately recycled in the mitochondria where it is recharged and comes out again as ATP

Figure 5.12A_s2 ADP: Adenosine Diphosphate P P P Energy H2OH2O Hydrolysis Ribose Adenine P P P Phosphate group ATP:Adenosine Triphosphate

Energy transfer/transformation increases entropy (measure of disorder/degree of randomness) Living cells maintain order through continual input of energy.

Redox Reactions Redox reactions - transfer of electrons (negative charge) during chemical reactions, releases energy stored in organic molecules Oxidation - loss of electrons (LEO) Reduction - gain of electrons (GER)

Figure 6.5A Glucose  Heat C 6 H 12 O 6 O2O2 CO 2 H2OH2O ATP Loss of hydrogen atoms (becomes oxidized) Gain of hydrogen atoms (becomes reduced) p. 91 The transfer of H to O, make water (reduced) and yield energy (ATP)

Enzymes are often arranged in the cell in ways that facilitate the orderly series of chemical reactions

Figure 6.5C Controlled release of energy for synthesis of ATP NADH NAD  HH HH O2O2 H2OH2O ATP Electron transport chain 2 1 In cellular respiration, electrons fall down an energy staircase and finally reduce O 2.

Other carriers of Electrons NAD (Nicotinamide Adenine Dinucleotide)- NAD+ (oxidized); NADH + H (reduced) NADPH (Nicotinamide Adenine Dinucleotide Phosphate FAD (Flavin Adenine Dinucleotide)

Uses of ATP (energy) 1.Mechanical Work= ___ 2.Transport work= ___ 3.Conduction of impulses= ___ 4.Chemical Work= ___ a.Generate electricity in nerve b.Movement (muscle contraction) or locomotion c.Biosynthesis of complex molecules during active growth, repair, and replaced damaged molecules d.Active transport of solute across cell membrane

Fig. 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energy ATP Harvesting Chemical Energy

Cellular Respiration Process of harvesting energy from glucose to generate ATP. 3 stages: 1. Glycolysis 2. Citric Acid (krebs) Cycle 3. Oxidative Phosphorylation (electron transport & chemiosmosis) Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration; powered by redox reactions A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

Glycolysis Occur in the cytoplasm. Does not require oxygen Breakdown of glucose into 2 molecules of ______, and produces a net of ____ ATP and _____ NADH

Formation of Acetyl CoA In the presence of O2, pyruvate enter the mitochondia Before the krebs cycle can begin, 2 Pyruvates are converted into 2 AcetylCoA (C2) Produced 2 AcetylCoA and 2 NADH

Krebs (Citric Acid) Cycle Occurs in mitochondrial matrix; requires oxygen Acetyl CoA enters the Krebs cycle Joins a 4 carbon molecule to produce citrate (C6) Cycle twice to produced 4 Co 2, 2 FADH 2, 6 NADH, and 2 ATP

Oxidative Phosphorylation Final stage of cellular respiration; occurs in mitochondrial membrane (eukaryotes) or plasma membrane (prokaryotes) Involves Electron Transport Chain and Chemiosmosis NADH and FADH2 (energy carriers) shuttle electrons through the ETC to O2, final electron acceptor; and form H2O, as waste product. ATP synthase uses the exergonic flow of H + to drive phosphorylation of ATP; this is chemiosmosis, the use of energy in a H + gradient to drive cellular work Produce 34 ATP

Fig Protein complex of electron carriers H+H+ H+H+ H+H+ Cyt c Q    VV FADH 2 FAD NAD + NADH (carrying electrons from food) Electron transport chain 2 H / 2 O 2 H2OH2O ADP + P i Chemiosmosis Oxidative phosphorylation H+H+ H+H+ ATP synthase ATP 21

Cellular Respiration In summary: gylcolysis - 2 ATP Kreb’s Cycle - 2 ATP Oxidative Phosphorylation - 34 ATP Total ATP

Fermentation Occurs in the ________ of oxygen (anaerobic); uses phosphorylation to generate ATP Fermentation consists of glycolysis plus reactions that regenerate NAD +, which can be reused by glycolysis Two common types are ______fermentation and ______ fermentation Alcohol fermentation by yeast, release CO2 gas

Fig. 9-18a 2 ADP + 2 P i 2 ATP GlucoseGlycolysis 2 Pyruvate 2 NADH2 NAD H + CO 2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 Final electron acceptor

Fermentation In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO 2 Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O 2 is scarce

Fig. 9-18b Glucose 2 ADP + 2 P i 2 ATP Glycolysis 2 NAD + 2 NADH + 2 H + 2 Pyruvate 2 Lactate (b) Lactic acid fermentation Final electron acceptor

Compare Cellular (Aerobic) Respiration and Fermentation (Anaerobic) Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate The processes have different final electron acceptors: O 2 in cellular respiration and an organic molecule (such as pyruvate or acetaldehyde) in fermentation Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration

Homework 1. Define terms: Metabolism, catabolism, anabolism, aerobic (cellular) respiration, fermentation, oxidation, reduction, glycolysis, chemiosmosis, 2. Describe briefly the 3 stages of cellular respirations (glycolysis, kreb cycle, and oxidative phosphorylation) noting its reactants and final products. 3. Discuss at least 3 ways how we use energy (ATP) for cellular functions. 4. Describe the 2 types of fermentation. 5. Distinguish between obligate and facultative anaerobes. 6. What are the electron carriers (donors) in electron transport? 7. What is the final electron acceptor and waste product in cellular respiration? 8. What intermediate molecule is needed to proceed to Kreb’s cycle?