2. Chapter 8: Metabolism

3. Metabolism Metabolism – all of the chemical reactions in an organism - A metabolic pathway begins with a specific molecule and ends with a product - Each step is catalyzed by a specific enzyme

4. Examples  dehydration synthesis (synthesis)  hydrolysis (digestion) + H2OH2O + H2OH2O enzyme

5. Enzyme 1Enzyme 2Enzyme 3 D CB A Reaction 1Reaction 3Reaction 2 Starting molecule Product

6. Catabolic pathways release energy by breaking down complex molecules into simpler compounds (ex: digestion) - Ex: Cellular Respiration Anabolic pathways consume energy to build complex molecules from simpler ones - The synthesis of protein from amino acids is an example of anabolism Catabolic and Anabolic Pathways

7. Forms of Energy Energy is the capacity to do work - Kinetic energy is energy associated with motion - Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules - Potential energy is energy that matter possesses because of its location or structure - Chemical energy is potential energy available for release in a chemical reaction * Energy can be converted from one form into another Describe the E transformations that occur when you climb to the top of a stairway

8. Flow of energy through life Life is built on chemical reactions –transforming energy from one form to another organic molecules  ATP & organic molecules sun solar energy  ATP & organic molecules

9. Energy Transformation Thermodynamics is the study of energy transformations –1 st law of thermodynamics = conservation of energy Energy of universe is constant, energy CAN be transferred and transformed, but NOT created/destroyed –2 nd law of thermodynamics Every energy transfer or transformation increases the entropy (disorder or randomness) in universe

10. (a) First law of thermodynamics (b) Second law of thermodynamics Chemical energy Heat CO 2 H2OH2O +

11. Exergonic and Endergonic Reactions in Metabolism An exergonic reaction releases free energy An endergonic reaction absorbs free energy from its surroundings Cells manage energy resources and do work by energy coupling EXERGONIC REACTIONS DRIVE ENDERGONIC REACTIONS

12. Energy & life Organisms require energy to live –where does that energy come from? coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) ++ energy + + digestion synthesis

13. ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work: –Chemical –Transport –Mechanical To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one Most energy coupling in cells is mediated by ATP

14. The Structure and Hydrolysis of ATP ATP (Adenosine tri phosphate) is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups Phosphate groups Ribose Adenine

15. The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis (unstable bonds) 3 Things happen: WRITE THIS DOWN 1.A phosphate group is removed 2.ATP becomes ADP 3.Energy is released (exergonic reaction)

16. Inorganic phosphate Energy Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) P P P PP P + + H2OH2O i

17. How ATP Performs Work The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction

18. ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant The recipient molecule is now phosphorylated

19. Fig. 8-11 (b) Mechanical work: ATP binds noncovalently to motor proteins, then is hydrolyzed Membrane protein P i ADP + P Solute Solute transported P i VesicleCytoskeletal track Motor protein Protein moved (a) Transport work: ATP phosphorylates transport proteins ATP

20. The Regeneration of ATP ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP) The energy to phosphorylate ADP comes from catabolic reactions in the cell

21. Fig. 8-12 P i ADP + Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) ATP + H2OH2O

22. Enzymes speed up metabolic reactions by lowering energy barriers A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction An enzyme is a catalytic protein The reactant that an enzyme acts on is called the enzyme’s substrate The enzyme binds to its substrate, forming an enzyme-substrate complex The active site is the region on the enzyme where the substrate binds

23. The Activation Energy Barrier The initial energy needed to start a chemical reaction is called the activation energy (E A ) Enzymes catalyze reactions by lowering the E A barrier Enzymes do not affect the change in free energy (∆G); instead, they speed up reactions that would occur eventually

24. Activation energy Breaking down large molecules requires an initial input of energy –activation energy –large biomolecules are stable –must absorb energy to break bonds energy cellulose CO 2 + H 2 O + heat

25. Progress of the reaction Products Reactants ∆G is unaffected by enzyme Course of reaction without enzyme Free energy E A without enzyme E A with enzyme is lower Course of reaction with enzyme

26. Properties of enzymes Reaction specific –each enzyme works with a specific substrate chemical fit between active site & substrate –H bonds & ionic bonds Not consumed in reaction –single enzyme molecule can catalyze thousands or more reactions per second enzymes unaffected by the reaction Affected by cellular conditions –any condition that affects protein structure temperature, pH, salinity

27. Induced fit model More accurate model of enzyme action –3-D structure of enzyme fits substrate –substrate binding cause enzyme to change shape leading to a tighter fit “conformational change” bring chemical groups in position to catalyze reaction

28. Substrate Specificity of Enzymes Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

29. Fig. 8-16 Substrate Active site Enzyme Enzyme-substrate complex (b)(a)

30. Factors Affecting Enzyme Function Enzyme concentration Substrate concentration Temperature pH Salinity Activators Inhibitors catalase

31. Cofactors Cofactors are nonprotein enzyme helpers - Cofactors may be inorganic (zinc, iron, copper) OR… An organic cofactor is called a coenzyme - Coenzymes include vitamins

32. Enzyme Inhibitors Competitive inhibitors bind to the active site of an enzyme, competing with the substrate Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective Examples of inhibitors include toxins, poisons, pesticides, and antibiotics

33. Competitive Inhibitor Inhibitor & substrate “compete” for active site –penicillin blocks enzyme bacteria use to build cell walls –disulfiram (Antabuse) treats chronic alcoholism blocks enzyme that breaks down alcohol severe hangover & vomiting 5-10 minutes after drinking

34. Allosteric Regulation of Enzymes Allosteric regulation may either inhibit or stimulate an enzyme’s activity Allosteric regulation occurs when a regulatory molecule binds to a protein at one site (not active site) –This binding changes shape of enzyme

35. Non-Competitive Inhibitor Inhibitor binds to site other than active site –allosteric inhibitor binds to allosteric site –causes enzyme to change shape conformational change active site is no longer functional binding site –keeps enzyme inactive –some anti-cancer drugs inhibit enzymes involved in DNA synthesis stop DNA production stop division of more cancer cells –cyanide poisoning irreversible inhibitor of Cytochrome C, an enzyme in cellular respiration stops production of ATP

36. Feedback Inhibition In feedback inhibition, the end product of a metabolic pathway shuts down the pathway Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed