BIOLOGY 101. CHAPTER 8: An Introduction to Metabolism: Energy of Life

Transcription

1 BIOLOGY 101 CHAPTER 8: An Intrductin t Metablism: Energy f Life

2 Energy f Life CONCEPTS: 8.1 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins 8.4 Enzymes speed up metablic reactins by lwering energy barriers 8.5 Regulatin f enzyme activity helps cntrl metablism Can yu describe r explain these cncepts?

3 Energy f Life 8.1 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics The sum ttal f an rganism s chemical reactins is called metablism.

4 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The chemistry f life is rganized int metablic pathways A metablic pathway begins with a specific mlecule, which is then altered in a series f defined steps t frm a specific prduct.

5 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The chemistry f life is rganized int metablic pathways A metablic pathway begins with a specific mlecule, which is then altered in a series f defined steps t frm a specific prduct. A specific enzyme catalyzes each step f the pathway. Catablic pathways release energy by breaking dwn cmplex mlecules t simpler cmpunds. The energy released by catablic pathways becmes available t d the wrk f the cell, such as ciliary beating r membrane transprt. Anablic pathways require energy derived frm catablic pathways t build cmplex mlecules frm simple nes

6 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 Organisms transfrm energy Energy is the capacity t cause change. In everyday life, sme frms f energy can be used t d wrk that is, t mve matter against ppsing frces, such as gravity and frictin. Energy exists in varius frms, and cells transfrm energy frm ne type t anther.

7 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 Organisms transfrm energy Kinetic energy is the energy assciated with the relative mtin f bjects. Objects in mtin can perfrm wrk by imparting mtin t ther matter. Wrk = t mve matter (r cause change) against ppsing frces Thermal energy is kinetic energy assciated with the randm mvement f atms r mlecules. Heat is caused by thermal energy Mechanical Energy is derived frm particles in mtin Electrical Energy exists in the frm f membrane ptentials that exist in cells

8 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 Organisms transfrm energy Ptential energy is the energy that matter pssesses because f its lcatin r structure. Water behind a dam pssesses energy because f its altitude abve sea level. Mlecules pssess energy because f the arrangement f electrns in the bnds between their atms. Chemical energy is a term used by bilgists t refer t the ptential energy available fr release in a chemical reactin.

9 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics Organisms are pen systems: They absrb energy light r chemical energy in the frm f rganic mlecules and release heat and metablic waste prducts, such as urea r CO 2, t their surrundings. Tw laws f thermdynamics gvern energy transfrmatins in rganisms and all ther cllectins f matter

10 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics The first law f thermdynamics states that the energy f the universe is cnstant: Energy can be transferred and transfrmed, but it cannt be created r destryed. The first law is als knwn as the principle f cnservatin f energy. Plants d nt prduce energy; they transfrm light energy t chemical energy

11 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics Energy transfers and transfrmatins make the universe mre disrdered due t the lss f usable energy. Entrpy is a measure f disrder r randmness: The mre randm a cllectin f matter, the greater its entrpy

12 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics The secnd law f thermdynamics states: Every energy transfer r transfrmatin increases the entrpy f the universe. Althugh rder can increase lcally (as in a cell), there is an unstppable trend tward randmizatin f the universe.

13 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics Fr a prcess t ccur n its wn, withut utside help in the frm f energy input, it must increase the entrpy f the universe A spntaneus prcess is ne that is energetically favrable. A prcess that cannt ccur n its wn is said t be nnspntaneus: it will happen nly if energy is added t the system.

14 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics Living systems increase the entrpy f their surrundings, even thugh they create rdered structures frm less rdered starting materials.

15 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.1 The energy transfrmatins f life are subject t tw laws f thermdynamics Over evlutinary time, cmplex rganisms have evlved frm simpler nes. This increase in rganizatin des nt vilate the secnd law f thermdynamics. The entrpy f a particular system, such as an rganism, may decrease as lng as the ttal entrpy f the universe the system plus its surrundings increases. Cells are pen systems, bth receiving and distributing energy and mlecules Organisms are islands f lw entrpy in an increasingly randm universe Can yu explain this statement?

16 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly Hw can we determine which reactins ccur spntaneusly and which nes require an input f energy? The cncept f free energy (symblized by the letter G) is useful fr measuring the spntaneity f a system. G stands fr Gibbs Free Energy

17 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly Free energy (G) is the prtin f a system s energy that can perfrm wrk when temperature and pressure are unifrm thrughut the system, as in a living cell. The key t understanding Free Energy (G), is that it is cmpsed f the energy that can actually d wrk, as well as energy lst in reactins due t heat lss r entrpy

18 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly The change in free energy, G, can be calculated fr any specific chemical reactin by applying the fllwing equatin: G = H T S Change in Free Energy = Change in Enthalpy (Temperature (K)) (Change in Entrpy) In this equatin: H symblizes the change in the system s enthalpy (in bilgical systems, equivalent t ttal energy (r ttal heat cntent f the system) S is the change (lss) in the system s entrpy; and T is the abslute temperature in Kelvin (K) units (K = C + 273)

19 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly The change in free energy, G, can be calculated fr any specific chemical reactin by applying the fllwing equatin: G = H T S Change in Free Energy = Change in Enthalpy (Temperature (K)) (Change in Entrpy) In this equatin: H symblizes the change in the system s enthalpy (in bilgical systems, equivalent t ttal energy (r ttal heat cntent f the system) S is the change (lss) in the system s entrpy; and T is the abslute temperature in Kelvin (K) units (K = C + 273)

20 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly The change in free energy, G, can be calculated fr any specific chemical reactin by applying the fllwing equatin: G = H T S Enthalpy wuld equal G, but it is missing energy lst t heat and entrpy Free Energy is smewhat theretical, in that it des nt take entrpy and heat-lss int accunt Enthalpy measures the usable energy cntent f the system

21 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly WHY IS THE CHANGE IN ENTROPY SUBTRACTED IF IT IS A POSITIVE VALUE? This is explained by understanding that in spntaneus reactins, the change in free energy is NEGATIVE 1. This means the cmbinatin f enthalpy change and entrpy change must bth be negative. 2. Because the 2 nd Law f Thermdynamics says the change in entrpy must be psitive, it needs t be subtracted

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25 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly G must have a negative value ( G < 0) in rder fr a prcess t be spntaneus. In ther wrds, every spntaneus prcess decreases the system s free energy, and prcesses that have psitive r zer G are never spntaneus Because it has less free energy, the system in its final state is less likely t change and is therefre mre stable than it was previusly Spntaneus reactins that release energy are called exergnic, while thse that are nnspntaneus (requiring energy) are called endergnic

26 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly A system at equilibrium is at maximum stability. In a chemical reactin at equilibrium, the rates f frward and backward reactins are equal, and there is n change in the relative cncentratins f prducts r reactants. At equilibrium, G = 0, and the system can d n wrk.

27 Energy f Life 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly A prcess is spntaneus and can perfrm wrk nly when it is mving tward equilibrium. Mvements away frm equilibrium are nnspntaneus and will have a psitive G

28 Energy f Life 8.2 Chemical reactins can be classified as either exergnic r endergnic An exergnic reactin prceeds with a net release f free energy; G is negative. The magnitude f G fr an exergnic reactin is the maximum amunt f wrk the reactin can perfrm. An endergnic reactin is ne that absrbs free energy frm its surrundings. Endergnic reactins stre energy in mlecules; G is psitive. Endergnic reactins are nnspntaneus

29 Energy f Life 8.2 Chemical reactins can be classified as either exergnic r endergnic An endergnic reactin is ne that absrbs free energy frm its surrundings. Endergnic reactins stre energy in mlecules; G is psitive. Endergnic reactins are nnspntaneus, and the magnitude f G is the quantity f energy required t drive the reactin

30 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins A cell des three main kinds f wrk: 1. Chemical wrk, pushing endergnic reactins such as the synthesis f plymers frm mnmers; 2. Transprt wrk, pumping substances acrss membranes against the directin f spntaneus mvement; 3. Mechanical wrk, such as the beating f cilia, cntractin f muscle cells, and mvement f chrmsmes during cellular reprductin This is what - G can accmplish in cells

31 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins S if wrk is dne inside cells Where des the energy t pwer endergnic reactins cme frm?

32 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins Cells manage their energy resurces t d this wrk by energy cupling, using an exergnic prcess t drive an endergnic ne. ATP is respnsible fr mediating mst energy cupling in cells, and in mst cases it acts as the immediate surce f energy that pwers cellular wrk ATP is the energetic link between Exergnic and Endergnic reactins!

33 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins Cells manage their energy resurces t d this wrk by energy cupling, using an exergnic prcess t drive an endergnic ne. ATP is respnsible fr mediating mst energy cupling in cells, and in mst cases it acts as the immediate surce f energy that pwers cellular wrk The frmatin f Glutamine is nt spntaneus (+3.4 G)

34 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins Cells manage their energy resurces t d this wrk by energy cupling, using an exergnic prcess t drive an endergnic ne. ATP is respnsible fr mediating mst energy cupling in cells, and in mst cases it acts as the immediate surce f energy that pwers cellular wrk The frmatin f Glutamine is nt spntaneus (+3.4 G) Phsphrylatin by ATP decreases G by -7.3 G ATP brings the reactin t -3.9 G

35 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins Cells manage their energy resurces t d this wrk by energy cupling, using an exergnic prcess t drive an endergnic ne. ATP is respnsible fr mediating mst energy cupling in cells, and in mst cases it acts as the immediate surce f energy that pwers cellular wrk The frmatin f Glutamine is nt spntaneus (+3.4 G) Phsphrylatin by ATP decreases system by -7.3 G ATP brings the reactin t -3.9 G

36 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins Cells manage their energy resurces t d this wrk by energy cupling, using an exergnic prcess t drive an endergnic ne. ATP is respnsible fr mediating mst energy cupling in cells, and in mst cases it acts as the immediate surce f energy that pwers cellular wrk Thrugh energy cupling, ATP can take an endergnic reactin and make it exergnic!

37 Energetic Cupling by ATP Why des adding ATP change the system by -7.3kcal/ml?

38 Energetic Cupling by ATP Why des adding ATP change the system by -7.3kcal/ml?

39 Energetic Cupling by ATP Why des adding ATP change the system by -7.3kcal/ml? This is the energy resulting frm the hydrlysis f ATP t ADP + Pi (which is exergnic yielding -7.3Kcal/ml) There are 2 reactins ccurring here, ne yielding G f +3.4 Kcal/ml, and anther yielding G f -7.3Kcal/ml

40 Energetic Cupling by ATP Why des adding ATP change the system by -7.3kcal/ml?

41 Energetic Cupling by ATP Why des adding ATP change the system by -7.3kcal/ml?

42 Energy f Life 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins Cells manage their energy resurces t d this wrk by energy cupling, using an exergnic prcess t drive an endergnic ne. ATP is respnsible fr mediating mst energy cupling in cells, and in mst cases it acts as the immediate surce f energy that pwers cellular wrk Thrugh energy cupling, ATP can take an endergnic reactin and make it exergnic!

43 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins 8.3 ATP mediates mst energy cupling in cells Under standard cnditins, G = -7.3 kcal/ml

44 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins 8.3 ATP mediates mst energy cupling in cells Althugh the phsphate bnds f ATP are smetimes referred t as high-energy phsphate bnds, these are actually fairly weak cvalent bnds. The release f energy during the hydrlysis f ATP cmes frm the chemical change t a state f lwer free energy change, nt frm the phsphate bnds themselves. Why des the hydrlysis f ATP yield s much energy? Each f the three phsphate grups has a negative charge. These three like charges are crwded tgether, and their mutual repulsin cntributes t the instability f this regin f the ATP mlecule. The triphsphate tail f ATP is the chemical equivalent f a cmpressed spring.

45 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Spntaneus chemical reactins may ccur s slwly as t be imperceptible. The hydrlysis f table sugar (sucrse) t glucse and fructse is exergnic, with G = 7 kcal/ml. Despite this, a slutin f sucrse disslved in sterile water may sit fr years at rm temperature with n appreciable hydrlysis. If a small amunt f the enzyme, sucrase, is added t a slutin f sugar, all the sucrse is hydrlyzed within secnds

46 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers An enzyme is a macrmlecule that acts as a catalyst, a chemical agent that speeds up the rate f a reactin withut being cnsumed by the reactin. Enzymes are generally prteins (exceptin f ribzymes) Every chemical reactin invlves bnd breaking and bnd frming.

47 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers The initial investment f energy fr starting a reactin is the free energy f activatin, r activatin energy (E A ). Activatin energy is the amunt f energy necessary t push the reactants ver an energy barrier s that the dwnhill part f the reactin can begin. E A is ften supplied in the frm f thermal energy that the reactant mlecules absrb frm the surrundings. This accelerates the reactant mlecules, which then cllide mre ften with mre frce making the breakage f bnds mre likely. When reactants reach E A, they are in an unstable transitin state

48 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers The initial investment f energy fr starting a reactin is the free energy f activatin, r activatin energy (E A ). Activatin Energy is critical t life because it keeps exergnic reactins frm running ut f cntrl This means that sme input f energy (r lwering f E A ) is required fr reactins t prceed it is a regulating device

49 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Fr sme prcesses, EA is nt high, and the thermal energy prvided by rm temperature is sufficient fr many reactants t reach the transitin state In mst cases, EA is high enugh that the transitin state is rarely reached and the reactin hardly prceeds at all. In these cases, the reactin will ccur at a nticeable rate nly if the reactants are heated.

50 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Hw are the barriers fr selected reactins surmunted t allw cells t carry ut the prcesses f life? Heat wuld speed up all reactins, nt just thse that are needed. Excessive Heat als denatures prteins and can kill cells

51 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Enzymes speed reactins by lwering E A. The transitin state can then be reached even at mderate temperatures.

52 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Enzymes speed reactins by lwering E A. The transitin state can then be reached even at mderate temperatures.

53 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Enzymes speed reactins by lwering E A. The transitin state can then be reached even at mderate temperatures. Enzymes d nt change G; they hasten reactins that wuld ccur eventually. Because enzymes are s selective, they determine which chemical prcesses will ccur at any time.

54 Energy f Life 8.4 Enzymes speed up metablic reactins by lwering energy barriers Enzymes speed reactins by lwering E A. The transitin state can then be reached even at mderate temperatures. Enzymes d nt change G; they hasten reactins that wuld ccur eventually. Because enzymes are s selective, they determine which chemical prcesses will ccur at any time. Hw Enzymes Wrk [VIDEO]

55 Enzymes speed up metablic reactins by lwering energy barriers 8.4 Enzymes are substrate specific The reactant that an enzyme acts n is the substrate. The enzyme binds t a substrate, r substrates, frming an enzyme-substrate cmplex.

56 Enzymes speed up metablic reactins by lwering energy barriers 8.4 Enzymes are substrate specific The reactant that an enzyme acts n is the substrate. The enzyme binds t a substrate, r substrates, frming an enzyme-substrate cmplex. While the enzyme and substrate are bund, the catalytic actin f the enzyme cnverts the substrate t the prduct r prducts.

57 Enzymes speed up metablic reactins by lwering energy barriers 8.4 Enzymes are substrate specific The reactant that an enzyme acts n is the substrate. The enzyme binds t a substrate, r substrates, frming an enzyme-substrate cmplex. While the enzyme and substrate are bund, the catalytic actin f the enzyme cnverts the substrate t the prduct r prducts. Prducts are then released

58 Enzymes speed up metablic reactins by lwering energy barriers 8.4 Enzymes are substrate specific The reactant that an enzyme acts n is the substrate. The enzyme binds t a substrate, r substrates, frming an enzyme-substrate cmplex. While the enzyme and substrate are bund, the catalytic actin f the enzyme cnverts the substrate t the prduct r prducts. Prducts are then released The enzyme is then available fr new substrates

59 Enzymes speed up metablic reactins by lwering energy barriers 8.4 Enzymes are substrate specific Only a restricted regin f the enzyme binds t the substrate. The active site f an enzyme is typically a pcket r grve n the surface f the prtein where catalysis ccurs. The active site is usually frmed by nly a few amin acids. The rest f the prtein mlecule prvides a framewrk that determines the cnfiguratin f the active site.

60 Enzymes speed up metablic reactins by lwering energy barriers 8.4 Enzymes are substrate specific The specificity f an enzyme is due t the fit between the active site and the substrate The active site is nt a rigid receptacle fr the substrate. As the substrate enters the active site, interactins between the chemical grups n the substrate and thse n the side chains f the amin acids that frm the active site cause the enzyme t change shape slightly. This change leads t an induced fit that brings the chemical grups f the active site int psitin t catalyze the reactin.

61 Enzymes speed up metablic reactins by lwering energy barriers 8.4 A cell s physical and chemical envirnment affects enzyme activity The activity f an enzyme is affected by general envirnmental cnditins, such as temperature and ph. Each enzyme wrks best at certain ptimal cnditins, which favr the mst active cnfrmatin fr the enzyme mlecule.

62 Enzymes speed up metablic reactins by lwering energy barriers 8.4 A cell s physical and chemical envirnment affects enzyme activity Temperature has a majr impact n reactin rate. As temperature increases, cllisins between substrates and active sites ccur mre frequently as mlecules mve mre rapidly. As temperature increases further, thermal agitatin begins t disrupt the weak bnds that stabilize the prtein s active cnfrmatin, and the prtein denatures Each enzyme has an ptimal temperature that allws the greatest number f mlecular cllisins and the fastest cnversin f the reactants t prduct mlecules. Mst human enzymes have ptimal temperatures f abut C

63 Enzymes speed up metablic reactins by lwering energy barriers 8.4 A cell s physical and chemical envirnment affects enzyme activity Temperature has a majr impact n reactin rate. As temperature increases, cllisins between substrates and active sites ccur mre frequently as mlecules mve mre rapidly. As temperature increases further, thermal agitatin begins t disrupt the weak bnds that stabilize the prtein s active cnfrmatin, and the prtein denatures There is a delicate balance between an enzyme s ptimal temperature and increasing thermal energy t much T much heat will denature prteins!

64 Enzymes speed up metablic reactins by lwering energy barriers 8.4 A cell s physical and chemical envirnment affects enzyme activity Maintenance f the active cnfrmatin f the enzyme requires a particular ph. This ptimal ph falls between ph 6 8 fr mst enzymes. Hwever, digestive enzymes in the stmach are designed t wrk best at ph 2, whereas thse in the intestine have an ptimal ph f 8.

65 Enzymes speed up metablic reactins by lwering energy barriers 8.4 A cell s physical and chemical envirnment affects enzyme activity Many enzymes require nnprtein helpers, called cfactrs, fr catalytic activity Cfactrs bind permanently r reversibly t the enzyme. Sme inrganic cfactrs are zinc, irn, and cpper in inic frm. Organic cfactrs are called cenzymes. Mst vitamins are cenzymes r the raw materials frm which cenzymes are made

66 Regulatin f enzyme activity helps cntrl metablism 8.5 Metablic cntrl ften depends n allsteric regulatin In enzymes with multiple catalytic subunits, binding by a substrate mlecule t ne active site in a multisubunit enzyme triggers a shape change in all the subunits. This mechanism, called cperativity, amplifies the respnse f enzymes t substrates, priming the enzyme t accept additinal substrates. Cperativity is cnsidered t be allsteric regulatin because binding f the substrate t ne active site affects catalysis in a different active site.

67 Regulatin f enzyme activity helps cntrl metablism 8.5 Metablic cntrl ften depends n allsteric regulatin The vertebrate xygen-transprt prtein hemglbin is nt an enzyme, but is a classic example f cperativity. Hemglbin is made up f fur subunits, each with an xygen-binding site. The binding f an xygen mlecule t each binding site increases the affinity fr xygen f the remaining binding sites. Under cnditins f lw xygen, as in xygen-deprived tissues, hemglbin is less likely t bind xygen and releases it where it is needed. When xygen is at higher levels, as in the lungs r gills, the prtein has a greater affinity fr xygen as mre binding sites are filled.

68 Energy f Life CONCEPTS: (Review) 8.1 An rganism's metablism transfrms matter and energy, subject t the laws f thermdynamics 8.2 The free-energy change f a reactin tells us whether r nt the reactin ccurs spntaneusly 8.3 ATP pwers cellular wrk by cupling exergnic reactins t endergnic reactins 8.4 Enzymes speed up metablic reactins by lwering energy barriers 8.5 Regulatin f enzyme activity helps cntrl metablism Can yu describe r explain these prcesses?