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					  ENERGY
METABOLISM
BIOENERGETICS

Description of energy
         in
 biological systems
Energy is the capacity to
       do work

   Forms of energy :
 Kinetic energy (heat, light)

 Potential energy (chemical)
   IMPORTANCE OF
 ENERGY METABOLISM
• Energy is a necessity in living
  systems
• Without energy, living
  systems cannot perform work
• Without energy, life does not
  exist
     The form of energy
    utilized by biological
  systems is different from
      that used by non-
     biological systems

(for example, living systems cannot utilize heat energy for
                      their activities)
Non-biological systems
may utilize heat energy
  for their activities
Heat may be used to accomplish
   work only if temperature
      differences exist
i.e. between different parts of a system

there needs to be a flow of heat from higher to lower
temperature in order for heat to be used as a source of energy
        Biological systems
         are isothermal &
    therefore does not allow
         for flow of energy
∴ heat ≠ source of energy for biological systems
Metabolism encompasses
the network of chemical
 reactions occurring in
          cells
       METABOLISM
• Consists of enzyme-catalyzed
  reactions organized into pathways

• Involved in supplying various
  requirements to the organism to
  sustain growth, replication, nutrient
  processing & activities
• Examples of
metabolic pathways
in cells


• About 500 common
metabolic reactions


• Each dot is a
molecule involved in a
metabolic pathway
The central role
of glycolysis &
the Krebs cycle
in cell
metabolism
Metabolic
reactions
known to
occur in yeast
   ALL CHEMICAL
    REACTIONS
(including reactions involved
   in energy metabolism)

OBEY THE LAWS OF
THERMODYNAMICS
ANABOLISM
   versus
CATABOLISM
Anabolism ≡ metabolic
 processes involved in
 synthesis of organic
molecules (biosynthesis)

 require energy input
Catabolism ≡ metabolic
 processes involved in
degradation of complex
      molecules

accompanied by energy
     generation
• Catabolic pathways :
degradation of complex
food molecules to simpler
molecules; energy
production

• Anabolic pathways : use
products from catabolic
pathways for biosynthesis


• Energy generated by
catabolic processes is
utilized by anabolic
processes
     TOPICS COVERED
• Bioenergetics
 (energy conversions in biological
 systems)

• Energy-generating pathways :
    glycolysis
    Krebs cycle
    respiratory chain
    ß - oxidation of fatty acids
    DISCUSSION

•Source of energy

•Energy molecule

•Free energy
  SOURCE OF ENERGY
• Organisms obtain energy from
  external sources :

    plants – energy from the sun
    other organisms – energy from food nutrients


• Organisms convert external energy
  into ATP (energy molecule)
ATP AS A SOURCE OF ENERGY

 Adenosine triphosphate :

 • contains chemical potential
 • is regarded as the cell battery
 • is the energy currency of the cell for
   instant energy to drive cellular
   activities
  SOME CELLULAR ACTIVITIES
        DRIVEN BY ATP
•  Muscle contraction
    (mechanical work)
•   Pumping of molecules across
    membranes (transport work)
•   Synthesis of macromolecules
    (chemical work)
      ATP
   CONTAINS
FREE ENERGY (G)
FREE ENERGY OF ATP IS A
   FORM OF ENERGY
USEABLE IN BIOLOGICAL
       SYSTEMS
           ATP
      CONSISTS OF
ADENINE (a nitrogenous base),
   RIBOSE (a 5-C sugar)
            &
 CHAIN OF 3 PHOSPHATE
        GROUPS
 UNSTABLE
 PHOSPHATE
 BONDS




Structure of ATP
   ATP HAS UNSTABLE
 PHOSPHATE BONDS THAT
THE CELL HYDROLYSES TO
   DRIVE ENDERGONIC
       REACTIONS
    HYDROLYSIS OF THE
TERMINAL PHOSPHATE BOND
   OF ATP PRODUCES ADP
              &
    RELEASES 30.5 kJ/mol
     OF FREE ENERGY
  (under standard conditions)
ATP
HYDROLYSIS
IS
ACCOMPANIED
BY A
CHANGE IN
FREE
ENERGY OF
–30.5 kJ/mol
Hydrolysis of ATP & ∆G°’
                      °
HOW ATP PERFORMS
     WORK :
 HYDROLYSIS OF ATP (AN
 EXERGONIC PROCESS) IS
COUPLED TO ENDERGONIC
      PROCESSES
         COUPLING OF
      ENERGY METABOLISM

              ATP
 ENERGY-                  ENERGY-
REQUIRING               GENERATING
PROCESSES     ADP        PROCESSES
              + Pi

COUPLING OF ATP HYDROLYSIS TO ENDERGONIC
PROCESSES
  ATP is continuously
regenerated by the cell :

the regeneration reaction
  is rapid & endergonic
 (the energy required comes from
        cellular respiration)
ENERGY FROM EXTERNAL SOURCES
 ARE TRANSFORMED TO GENERATE
                   ATP
• Generation of ATP involves transformations
  of energy obtained from outside the cells

• Solar energy & energy obtained from food
  nutrients need to be transformed into a form
  useable by the cells

• Energy transformations obey the first &
  second laws of thermodynamics
LAWS OF THERMODYNAMICS
• Physical law describing basic characteristics of energy
  (quantity & application)

• Obeyed by chemical & biochemical reactions

• Thermodynamics allows one to predict:

       i.     the direction in which a process will proceed
       ii.    the extent to which the process will occur

• Thermodynamic concepts need to be understood to
  understand metabolism
      FIRST LAW OF
THERMODYNAMICS / LAW OF
  ENERGY CONSERVATION
The first law of thermodynamics states that the
quantity of energy in a system is fixed

i.   Energy can neither be created nor destroyed


ii. Energy may be transferred or transformed
    from one form to another
 RELATIONSHIP BETWEEN THE
FIRST LAW & LIVING PROCESSES

Photosynthesis: light energy     chemical energy
                               (organic molecule)

      conversion / transformation of energy

   Respiration: chemical energy (sugar)

   Chemical energy (ATP        work energy + heat

            conservation of energy
     SECOND LAW OF THERMODYNAMICS /
        LAW OF MASS ORGANIZATION

The second law of thermodynamics states that events in
       the universe lead to randomness & disorder

• Introduces the concept of entropy (S)

             entropy = measure of randomness & disorder

• Every process increases the entropy of the universe S
  ( ∆S = Send – Sstart = positive value)
Progression from an ordered
  to a disordered state is a
    spontaneous process

 (the reverse progression
 requires input of energy)
ATP CONTAINS FREE ENERGY
• Free energy (G) ATP ≡ a form of energy
  useable in biological systems

• ATP hydrolysis is accompanied by a free
  energy change of −30.5 kJ/mol

• ATP is continuously used & formed
  (adults require ≈40 kg ATP per day and
  the requirement increases with exercise
  or strenuous activity)
         ATP GENERATION
• ATP is a product of aerobic & anaerobic
  metabolism

• To generate ATP:

  plants − solar energy transduction (conversion)
  other organisms − oxidation of food nutrients

• ATP regeneration in cells is rapid
  (> one million ATP molecules used and
  generated per second)
      COUPLING OF ENERGY
  - REQUIRING & - GENERATING
          PROCESSES
• Energy - requiring & - generating processes are
  coupled via ATP

• ATP is generated by catabolic processes
  (degradation of food nutrients)

• ATP is utilized in anabolic processes
  (biosynthesis)
       BIOENERGETICS
• Bioenergetics ≡ a phenomena
  describing energy conversions
  (transductions) in living organisms

• Energy conversion is necessary to
  sustain cellular activities

• Living organisms generate ATP from
  oxidation of food nutrients
  Thermodynamic analysis

          of living cells


(even though molecules in cells appear
   to be more ordered, heat energy
 produced causes molecules in the cell
  environment to be disordered and
        entropy S to increase)
                      Ordered state in the cell when
                      energy is obtained from food
The cell & its        nutrients but heat released in the
environment in a      oxidation process into the
disordered state      surrounding increases the
(entropy S is high)   entropy
More examples of processes
 with increase in entropy
 More
ordered




  Less
ordered
Less ordered




   More
  ordered
                  FREE ENERGY
• The first & second laws of thermodynamics indicate that
  the energy of the universe is constant but the entropy
  continues to increase. Taken together:

                 ∆H = ∆G + T∆S
                            ∆

                             rearrangement

      ∆G = ∆H – T∆S (Gibbs free energy equation)
                 ∆
 Tenaga suatu sistem terbahagi kepada
tenaga yang boleh diguna & tidak boleh
            diguna oleh sel

          ∆H = ∆G + T∆S
                     ∆

                    penyusunan semula

          ∆G = ∆H – T∆S
                     ∆

      (persamaan tenaga bebas Gibbs)
      GIBBS FREE ENERGY EQUATION
                     ∆G = ∆H - T∆S
                                ∆
• Relates enthalpy (H), entropy (S) & free energy (G)

• Provides a measure of the spontaneity of a particular
  process:

      i. − ve ∆G indicates a spontaneous (exergonic)
         process which releases energy

      ii. + ve ∆G indicates a non-spontaneous (endergonic)
          process which requires input of energy to occur
GX < GY




GX > GY
   CHANGE IN FREE ENERGY ∆G AS AN
     INDICATOR OF SPONTANEITY
• Negative ∆G         from a state of higher energy to a
  state of lower energy
  (spontaneous, release of energy, exergonic)

• Positive ∆G         from a state of lower energy to a
  state of higher energy
  (non-spontaneous, requires input of energy,
  endergonic)

• G = part of the total energy content of a system
  available for work
  ∴ ∆G = maximum amount of energy for use
FREE ENERGY CHANGE UNDER
   STANDARD CONDITIONS
• For the reaction reactant              product:
                       absolute T (oK)
               gas constant


          ∆G = ∆G0 + RT In [ product ]
                            [ reactant ]


• ∆G0 is the change in free energy under in vitro
  standard conditions (25oC, 1 atm, 1M)
     ∆ Go      ∆Go’ for biochemical reactions


In vitro standard conditions = 25oC, 1 atm, 1M
In vivo standard conditions = 25oC, 1 atm, [H+] = 10−7 M


• ∆G = ∆G0 + RT In [ product ] @ std conditions
                    [ reactant ]            in vitro

• ∆G = ∆G0’ + RT In [ product ] @ std conditions
                     [ reactant ]             in vivo
         ∆G = 0 AT EQUILIBRIUM

For the reaction reactant      product @ equilibrium:


• ∆G = ∆G0’ + RT In [ product ] @ std conditions
                     [ reactant ]         in vivo
  becomes;


• ∆G0’ = − RT In [ product ]@ equilibrium
                  [reactant ]@ equilibrium
     [ product ]@ equilibrium = Keq
     [ reactant ]@ equilibrium

For the reaction reactant      product @ equilibrium:


• ∆G0’ = − RT In [ product ]@ equilibrium
                  [ reactant ]@ equilibrium
becomes;

• ∆G0’ = − RT ln Keq = − 2.303 RT log Keq
  Keq is determined by letting in vitro reaction reach
  equilibrium & determining [ product ]
  & [ reactant ] @ equilibrium


• ∆G0’ may be calculated if Keq is known

• Negative ∆G0’ value indicates that @ 25oC, 1 atm, [H+]
  = 10−7 M (in vivo std conditions), formation of product
  is favored
                 Calculation of ∆G0’
For the reaction : glu-1-phosphate       glu-6-phosphate
catalyzed by phosphoglucomutase:

[glu-6-phosphate ] = [glu-1-phosphate ] = 20 mM
@ start & allowed to reach equilibrium

          [glu-6-phosphate ]@ equilibrium = 19 mM
          [glu-1-phosphate ]@ equilibrium = 1 mM
          ∴ Keq= 19 mM = 19
                  1 mM

   ∆G0’ = − 2.303 RT log 19 = − 7.3 kJ mol−1
    For the reaction A + B                  C + D:

Negative ∆G0’ value indicates direction of rxn. :
Zero ∆G0’ value indicates rxn is at equilibrium:
Positive ∆G0’ value indicates direction of rxn. :


  Example: for glu-1-phosphate            glu-6- phosphate
  ∆Go’ = − 7.3 kJ mol−1

  • Direction of reaction:
  • Favors formation of glu-6-fosfat
  • Exergonic
    ∆G0’ FOR ATP HYDROLYSIS

     ATP + H2O                       ADP + Pi
          Keq = [ ADP][Pi ] = 2.23 X 105
                  [ATP]

∆G0’ = − 2.303 RT log Keq
    ∆G0’ = − 2.303 (8.31 J) (298oK) log 2.23 X 105
                        moloK
         = − 30.5 kJ
               mol
       ∆G FOR ATP HYDROLYSIS

      ∆G = ∆Go’ + RT 2.303 log [ ADP][Pi ]
                               [ ATP ]

In liver cells @ 37 oC, pH 7.0:

[ADP] = 1.35 mM; [Pi] = 4.65 mM; [ATP] = 4.0 mM

∆G = − 30.5 X 103 + 2.303 (8.31 J) (310oK) log 1.57 X 10−3
                           moloK
  = − 47.13 kJ
        mol
 ∆G FOR ATP HYDROLYSIS CELLS IS
    MORE NEGATIVE THAN ∆Go’


• ATP hydrolysis in liver cells releases energy
  ( - 47.13 kJ/mol)


• ATP is an energy molecule in biological
  systems
   ENDERGONIC REACTIONS ARE COUPLED TO
      EXERGONIC REACTIONS TO OCCUR



Glucose + Pi    G6P + H2O    ∆Go’ = + 13.8 kJ/mol
ATP + H2O       ADP + Pi      ∆Go’ = − 30.5
  kJ/mol


Glucose + ATP   G6P + ADP   ∆Go’ = − 16.7 kJ/mol
       OVERALL ∆Go’ OF A PATHWAY IS THE
         OVERALL SUM OF ∆Go’ FOR EACH
        INDIVIDUAL REACTION INVOLVED

           A         B             ∆Go’1
           B         C             ∆Go’2
           A         C             ∆Go’1 + ∆Go’2


• A thermodynamically-unfavorable reaction will occur
  when coupled to exergonic reaction as long as the value
  ∆Go’ overall is − ve
RELATIONSHIP BETWEEN Keq & ∆G0’

  Keq      ∆Go’
  0.001    17.1
                   @ Keq <1.0, ∆G0’
  0.01     11.4    becomes increasingly
                   positive (endergonic)
  0.1      5.7
  1.0      0.0      @ Keq = 1.0, ∆G0’ = 0
  10.0     −5.7
  100.0    −11.4     @ Keq > 1.0, ∆G0’
                     becomes increasingly
  1000.0   −17.1     negative (exergonic)