Bioenergetics and Biochemical Reaction Types

1. bioenergetics is the study of the balance between energy intake in the form of food and energy utilization by organisms for life-sustaining processes- tissue synthesis, osmoregulation, digestion, respiration, reproduction, locomotion, etc. Bioenergetics and Biochemical Reaction Types Photosynthetic autotrophs Heterotrophs

2. Autotrophs Use CO2 as sole carbon source Photoautotrophs: Energy from sunlight (photosynthesis) Chemoautotrophs: Energy from oxidation of inorganic compounds e.g.,Fe ++-----> Fe+++ Heterotrophs: Use combined forms of carbon (sugars) for energy

3. The measurement of energy requires converting it from one form to another • The basic unit of energy is the calorie • international unit: the joule - 1.0 joule = 0.239 calories or 1 calorie = 4.184 joule • Energy content of a substance • Gross energy represents the energy present in dry matter (DM)- Energy Laws of Thermodynamics 1. Conservation of energy. Energy may change form or be transported but cannot be created or destroyed. 2. Entropy. In all natural processes, the entropy of the universe increases.

4. Animals are not engines and can’t use heat to perform work • Cells are isothermal (Const temp and pressure) • Cells obtain their energy from chemical bonds, • Free energy G- amt of energy capable of work at const temp and pressure • Enthalpy H-Heat content of the system. • Entropy S- expression of randomness in the system- • DG=DH-TDS • DG’o = -RTlnK’eq(Std free energy change of a reaction) (pH7, 25C, 1M reactant/product, 1Atm)

5. Std free energy change DG’o tells us direction of a reaction and how far it will go to reach equilibrium WHEN Initial conc of reactant and product is 1M, pH is 7, temp is 25C, pressure is 1Atm. DG’o is a constant for that reaction ACTUAL CHANGE A+B <-----> C+D DG = DG’o + RTln [C][D] [A][B] A---->B DG’o = +13.8 kJ/mol B---->C DG’o =-30.5 kJ/mol A---->C Sum= -16.7 kJ/mol (reaction is spontaneous because the two are coupled) Std versus actual

6. Keq and DGo ATP+H2O---->ADP+ Pi -7.3Kcal/mol ATP+H2O---->AMP+PPi -10.9Kcal/mol PPi+H2O---->2Pi -4.6Kcal/mol

7. Energy transduction in cells are via chemical reactions- bond formation/breakage Covalent bonds share electrons Homolytic cleavage- each atom leaves the bond with on electron Heterolytic cleavage-one atom retains both electrons Nucleophiles-groups rich in and capable of donating electron (attracted to nucleus) Electrophile- group deficient in electron (attracted to electron) Review Non-bonded electrons (dots) are moved in direction of arrows

8. Carbonyl

9. Chemical reaction that occur during metabolism Carbonyl bonds play a key role in C-C bond formation and breakage Rearrangements in electrons Grp transfer- transfer of acyl/phosphoryl from one nucleophile to another Biological oxidation (loss of electron)-Oxidation releases energy. Every oxidation is accompanied by a reduction (electron acceptor acquires electrons removed by oxidation).

10. Metabolism= Catabolism and Anabolism

11. Converge and Diverge Catabolism • Generate ATP • Generate building blocks for biosynthesis Anabolism • Utilize energy • Generate biomolecules Different enzymes mediate catabolic and anabolic pathways. Catabolic and anabolic pathways employ different enzymes which are regulated separately Some key steps in each pathway are unidirectional

12. Themes Allosteric regulation- metabolic intermediate (ATP) Synthesis/degradation of enzyme Control enzyme levels Covalent Modification of enzyme- Phosphorylation (integrated via growth factors/hormones) Compartmentalization •One way to allow reciprocal regulation of catabolic and anabolic processes •Cytosol Vs mitochondria Specialization of organs • Regulation in higher eukaryotes • Organs have different metabolic roles Liver = gluconeogenesis (glucose) Muscle = glycolysis Availability of substrate-(intracellular conc of substrate is often below Km of enzyme- rate is proportional to substrate conc)

13. Glucose

14. (Liver) Glycogen (liver muscle) Glucose Amino acids Hexose shunt (every cell) Glycolysis (every cell) Gluconeogenesis (every cell) NADPH Pyruvate AcetylCoA Fatty acids (liver, adipose)

15. ATP ATP ATP Heterotrophic cells obtain free energy from catabolism of nutrients forming ATP Hydrolysis of ATP has a high negative DG- -30.5kJ/mol. This means that ATP has a strong tendency to transfer terminal phosphate to water. ATP hydrolysis in water only produces heat In cells ATP hydrolysis involves covalent participation of ATP. ATP provides energy by grp transfer (Substrate Level Phosphorylation). ATP hydrolysis is exogermic (negative DG). This is coupled with endogermic (positive DG) reactions in cells allowing these reactions to proceed. Some processes do involve direct ATP hydrolysis providing energy that changes protein conformation producing mechanical motion

16. High energy bond Why is ATP PO4 bond high energy bond? It is not breaking of bond - it is difference in free energy between reactant and product. ATP + H2O <-------> ADP + Pi DGo’ = -30.5 kJ/mol Why does ATP have strong tendency to transfer its terminal phosphate? Electrostatic repulsion Resonance stabilization- Hydration-

17. Oxidation and Reduction Fatty acids are more energy rich compared to glucose because carbon in fatty acids is more reduced Reduced High energy Oxidized Low energy Oxidation - loss of electrons Reduction - gain of electrons Electrons can be transferred from one mol to another directly as an electron (one electron) as hydrogen atoms (one proton + one electron) as hydride ion (:H-) (two electron) (NAD) direct combination with oxygen In aerobic organisms Oxidation of carbon (loss of electrons from carbon) is used to generate ATP The final acceptor of electrons is oxygen producing CO2

18. Oxidation Biological Oxidation Involves loss of electrons from carbon In cells Carbon (or another atom like nitrogen) exists in a range of oxidation states because: Carbon shares electrons with another atom (Oxygen, nitrogen, sulphur, hydrogen) The more electronegative atom “OWNS” the bonded electrons it shares C O C N C C C H In the C-O bond, the C has partially lost the electron and has undergone oxidation In the C-N bond, the C has partially lost the electron and has also undergone oxidation even when no oxygen is involved! Electron is not Fully transferred

19. Conjugate redox pairs AH2 <--------> A + 2e- + 2H+ (redox pair) B+2e- + 2H+ <-----> BH2 (redox pair) Two conjugate redox pairs together in soln- electron transfer from electron donor of one pair to electron acceptor of another pair AH2 + B <-----> A + BH2 AH2 + NAD+ -----> A + NADH + H+ Electron donating mol is called reducing agent Electron accepting mol is called oxidising agent (In a buffer you have proton donor <---------> proton acceptor+ H+)

20. Overview Cytosol Mitochondria H2O Electron Transport chain Krebs cycle AcetylCoA Glucose Glycolysis O2 CO2 NADH FADH ATP ATP

22. Glycolysis and Anaerobic respiration Lactate 4ADP 2NAD 2ATP Muscle Glucose 2 Pyruvate Krebs Yeast 2ADP 2NADH 4ATP CO2 Acetaldehyde Ethanol

23. Krebs cycle 3NAD 3NADH ADP Acetyl CoA Pyruvate 3 CO2 ATP FADH2 FAD

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