Bioenergetics

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Bioenergetics

• The Flow of Energy in the Cell

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Living Versus Nonliving

• Living cells/organisms maintain order.

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Life Has 4 Essential
Requirements

• Molecules that provide basic building blocks
• Chemical catalysts (enzymes)
• Information that guide activities
• Energy to drive reactions and processes
  necessary for life

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Nonliving Versus Living
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Maintenance of Order

• How do cells maintain or create order?

Energy
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Energy

• Capacity to cause change capacity to do work
  the ability to rearrange matter.
• Kinetic energy of motion
• Examples
• Heat (random movement of molecules)
• Light (movement of photons)
• Potential stored energy or energy of position
• Example
• Chemical energy (energy due to structure)

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Flow of Energy through Biosphere
Against concentration, electrical gradient
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Ultimate Fate of All Energy.

• Is to become randomized in the biosphere as
  increased entropy.
• Energy flows from nuclear fusion of sun to
  eventual sink, the entropy of the universe.
• Every process of reaction that occurs in the
  universe leads to greater entropy.

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Forms of Energy

• Kinetic
• associated with motion
• Heat (thermal energy)
• kinetic energy of random movement of atoms or
  molecules
• Potential
• energy that matter possesses because of its
  location or structure
• Chemical
• potential energy available for release in a
  chemical reaction

Energy can be converted from one form to another
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Energetics

• Is there a great divide between the living and
  the nonliving?
• No, according to Erwin Schrödinger
• Both obey same laws of chemistry physics
• Thermodynamics laws and principles that govern
  flow of energy.

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The Laws of Energy Transformation

• Closed system
• isolated from its surroundings (liquid in a
  thermos)
• Open system
• energy and matter can be transferred between the
  system and its surroundings
• Organisms are open systems

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Closed System
System Surroundings Universe
surroundings
system
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Open System

• Energy is transferred to or from the surroundings.

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1st Law of Thermodynamics
The law of conservation of energy

• Energy can be transferred or transformed but
  cannot be created or destroyed.

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1st Law of Thermodynamics

• During any reaction the total amount of E that
  leaves the system the E that enters the system
  minus E that is stored within system.
• ?E difference in internal energy of the system
  before the reaction (E1) and after the reaction
  (E2)

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Meaning of ?E

• ?E E2 E1
• ?E E products E reactants
• Change in enthalpy, H (heat content)
• H E PV
• ?H ?E ?(PV) PV 0
• ?H H products H reactants
• ?H Neg (endothermic), Positive (exothermic)

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2nd Law of Thermodynamics

• Every energy transfer or transformation increases
  entropy of the universe.

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Does life violate 2nd law?

• NO!
• Life forms are open systems.
• Energy from complex molecules ? simple molecules
  used to maintain order.
• Heat generated ? entropy of surroundings.

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What the First Law Means

• 1st Law Energy is conserved whenever a process
  or reaction occursall energy that goes into a
  system must either be stored within the system or
  released again to the surroundings.
• ? H measures how much total enthalpy of a system
  would change if a given process occurs (calories)

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What the 2nd Law Means

• In every chemical or physical change, the
  universe always tends toward greater disorder or
  randomness
• Allows prediction in what direction a reaction
  will proceed, how much energy will be released
• Thermodynamic spontaneity whether a reaction
  can go (but not will go)

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2nd Law Allows a Prediction
Greater Entropy ? S

• Of whether to what extent a process will occur

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2nd Law of Thermodynamics
Less Entropy ?S
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Free Energy

• Free energy of a living system
• energy that can do work when temperature and
  pressure are uniform
• ?G - change in free energy during a process
• ?H - change in enthalpy, or change in total
  energy
• ?S - change in entropy

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Measures of Thermodynamic Spontaneity

• Changes in Entropy ?S
• Universe vs system
• Changes in Free Energy ?G
• Measures spontaneity of a reaction for a system
  based on properties of the system
• ?H ?G T?S
• ?G ?H - T?S
• Every spontaneous reaction has a decrease in free
  energy of the system

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Free Energy, Stability, and Equilibrium

• Free energy
• measure of a systems instability, its tendency
  to change to a more stable state
• decreases during a spontaneous change
• stability of a system increases
• Equilibrium - state of maximum stability
• A process is spontaneous and can perform work
  only when it is moving toward equilibrium

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Exergonic and Endergonic Reactions in Metabolism

• Exergonic reaction
• proceeds with a net release of free energy
• spontaneous
• Endergonic reaction
• absorbs free energy from its surroundings
• nonspontaneous

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DG (Change in Free Energy)

• DG is convenient way to measure the amount of
  disorder created in the universe when a chemical
  reaction takes place.

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Energy Profiles
DG Gproducts - Greactants
Exergonic Reaction (Spontaneous)
Endergonic Reaction (Non-spontaneous)
transition state
transition state
Free energy ?
EA
EA
products
DG gt 0
reactants
DG lt 0
products
reactants
Progress of reaction ?
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What if DG 0?

• Reaction has reached chemical equilibrium.

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Dependence of ?G on Numerical Values of ?H and
the Terms (?T?S)
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Change in G for Oxidation, Synthesis of Glucose
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Relationship Between Keq DG
(DG 0)
Keq
Pure A
Pure B
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DG

• Free energy change under standard conditions
• indicates pH 7.0
• indicates
• products reactants 1.0M (except water)
• Temperature 25C 298K
• Pressure 1 atmosphere
• Useful way to compare reactions.

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DG

• Under standards conditions, all of these
  reactions will proceed to right.

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Relating DG to DG
R 1.987 cal/molK (gas constant) T
temperature in Kelvin
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Energy Coupling
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Reaction coupling
The entire process is negative (energy release)
Figure 2-51
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Energy Cycle
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• Activated Carrier Molecules Are Essential for
  Biosynthesis

• Oxidation of food leads to
• energy release
• need temporary storage before
• using it for biosynthesis
• Special activated carrier molecules
• Store energy in easily inter-changeable forms
• transferable chemical groups
• high-energy electrons
• -ATP
• NADH
• NADPH

Figure 2-55
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Activated Carriers
Store energy as readily transferable group
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• ATP Is the Most Widely Used Activated Carrier
  Molecule

• ATP (adenosine triphosphate) is the cells energy
  shuttle
• ATP is composed of
• ribose (a sugar),
• adenine (nitrogenous base),
• and 3 phosphate groups
• The bonds between the phosphate groups of ATPs
  tail can be broken by hydrolysis
• Energy is released from ATP when the terminal
  phosphate bond is broken

Figure 2-57
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Chapter 2

• NADH and NADPH Are Important Electron Carriers

• -Oxidation-reduction reactions
• Carry high-energy electrons
• and hydrogen atoms
• NAD and NADP
• Each pick a packet of energy
• 2 high-energy electrons proton H
• Get reduced to NADH (catabolic reactions)and
  NADPH (anabolic reactions)

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Spontaneity Revisited

• True or false?
• A spontaneous chemical reaction will
  automatically take place.
• False.
• Example Dissolve sucrose in water. Is the
  sucrose hydrolyzed to yield glucose and fructose?

• Why is this concept important to living organisms?