Chapter 8 Introduction to Metabolism

1. Chapter 8Introduction to Metabolism

2. Think Tank Question… Using the concepts of energy, entropy, and metabolism answer the following: Does the concept of evolution violate the 2nd law of thermodynamics? Explain.

3. Metabolism • Metabolism is the sum of all of the chemical reactions in a biological organism • A metabolic pathway is a series of defined steps resulting in a certain product, each step catalyzed by an enzyme • Catabolic pathway – release energy by breaking down complex molecules into simpler compounds; energetically “downhill”; example – cellular respiration • Anabolic pathway – consume energy to build complicated molecules from simple ones; energetically “uphill”; example - photosynthesis • The energy released from a catabolic pathway is stored and used to complete an anabolic pathway

4. Energy • Energy – the capacity to cause change or do work • Kinetic energy – energy of motion • Potential energy – stored energy, the energy in an object currently not moving

5. Thermodynamics • Thermodynamics – the study of energy transformations that occur in a collection of matter • 1st law – energy can be transferred and transformed, but cannot be created or destroyed • 2nd law – every energy transfer or transformation increases the entropy of the universe • Entropy is a measure of randomness or disorder in the universe • Disorder = randomness caused by the thermal motion of particles; the energy is so dispersed it is unusable.

6. Back to the tank… • Does evolution violate the 2nd law??? • NOPE. • The construction of complex molecules (metabolism) generates disorder. • Life requires as constant input of energy to maintain order.

7. The Laws of Thermodynamics

8. Free Energy • Free energy – the energy available to do work • ΔG = ΔH - T ΔS ; the Gibbs-Helmholtz equation • ΔG = the change in free energy, the maximum amount of usable energy that can be harvested • ΔH = enthalpy or total energy in biological systems • T = temperature in Kelvin • ΔS = change in entropy • Significance • Indicates the maximum energy available to do work • Indicates whether a reaction will occur spontaneously or not • At equilibrium ΔG = 0

9. Exergonic Chemical products have less free energy than the reactants Energetically downhill Spontaneous Loses free energy ΔG is negative - ΔG is the max amount of work the reaction can perform Endergonic Products have more free energy than reactants Energetically uphill Non-spontaneous Requires energy ΔG is positive + ΔG is the minimum amount of work required to drive the reaction Reaction types

11. Applying Concepts… • The table shows some reactions and the absolute values of their associated free energy changes (ΔG). • For each reaction, would you expect ΔG to be positive or negative? • Which reactions will be spontaneous? Explain your answers.

12. Cellular Work • ATP powers cellular work by coupling exergonic and endergonic reactions • Cell conducts 3 main types of work: mechanical, transport, and chemical • ATP – Adenosine triphosphate

13. ATP Hydrolysis • Breaking of the bonds between phosphate groups • ATP + H2O  ADP + Pi • ΔG = -7.3 kcal/mol or -30.5 kJ/mol (under standard conditions

14. Energy Coupling Example

15. How ATP Performs Work

16. Regeneration of ATP • Organisms at work are constantly using ATP, but ATP can be regenerated with the addition of a phosphate to ADP • Requires energy; ΔG = +7.3 kcal/mol or +30.5 kJ/mol

17. Enzymes • Enzyme – biological catalysts or catalytic protein (a chemical agent that speeds up a reaction without being consumed by the reaction) • All reactions require an initial investment of energy for starting a reaction called the activation energy (EA) • Enzymes reduce this activation energy

18. How Enzymes Work

19. Induced Fit Model • Substrate – enzyme reactant • Active site – pocket or groove on enzyme that binds to substrate • Enzyme substrate complex – enzyme flexes and molds to the shape of the substrate

20. Induced Fit Model

21. Enzyme Specificity • Enzymes function in a very specific range of environmental conditions including temperature and pH • Some enzymes require ions or other molecule partners: • Cofactors– inorganic nonprotein helpers, ex: zinc, iron, copper • Coenzymes – organic cofactors, ex: vitamins

22. Enzyme Inhibitors • Competitive inhibitors – block active site, direct competition with substrate • Noncompetitive inhibitors – bind away from the active site, not in direct competition with substrate

23. AllostericRegulation • Allosteric regulation can be described as any case in which a protein’s function at one site is affected by the binding of a regulatory molecule to a separate site • Activation, inhibition, and cooperativity

24. Feedback Inhibition • In feedback inhibition a metabolic pathway is switched off by the binding of its end product to an enzyme that acts early in the pathway

25. Applying Concepts… The Scenario: • In the boy’s locker room a bacteria is found growing on some old socks made of a synthetic polymer. • You make a protein extract from the bacteria and isolate the probable enzyme that can cleave the monomers from the polymer. • You also synthesize a dipeptideglycine-glycine to test as a possible inhibitor of the enzyme.

26. Applying Concepts… • Explain the results of each experiment. • How do you think the dipeptide works? How would you test your hypothesis?