Enzymes and Energy

1
Chapter 8

• Enzymes and Energy

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Enzymes
3
Enzymes

• - Proteins.
• - Allow chemical rxns to occur at body temp.
• - CATALYSTS

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Enzymes

• CATALYSTS
• - are themselves unchanged at the end of the rxn.
• - do not change the final result of the rxn,
  rather they...
• increase the rate of a rxn by lowering the
  activation energy.
• Activation energy amount required to initiate
  the rxn

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Enzymes
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Enzymes

• SUBSTRATES
• - reactants of the rxn.
• - changed by the rxn, into products.

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Enzymes

• Conformation shape of the enzyme tertiary or
  quaternary structure.
• Active sites pockets of the enyzme which
  specifically bind the substrates.

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Enzymes

• Substrates
• can be one or two different molecules, typically.

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Enzymes
10
Enzymes-catalytic cycle
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Enzyme names

• - ase
• - function in the name (i.e. DNA polymerase).

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Enzymes

• Activation energy (EA)
• Often a reaction requires a temporary change into
  an unstable state.

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Enzymes
14
Enzymes
15
Enzymes
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Enzymes

• Enzymes only change the rate of a reaction. They
  dont change the overall ?G, or what the
  substrates and products actually are.

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Enzymes

• Induced fit
• Sometimes once the substrate binds, the enzymes
  active site changes a little so it works even
  better!

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Enzymes-induced fit
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Enzymes

• Enzyme-substrate complex
• Enzyme bound to substrate.

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Enzymes

• Often enzymes can catalyze 1000 substrates/sec!

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Enzymes

• - Rate of the rxn measured by the rate of
  generation of the products.
• Factors which can affect the rate
• - temperature
• - pH
• - concentration of cofactors or coenzymes
• - concentration of active enzyme
• - concentration of substrate
• - inhibitory effects of products.

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Temperature

• Enzymes are well-suited to the temperature of
  their organisms!
• E.g Human enzymes peak at body temp. (37o C)
• Rate of rxn increases as temp. increases,
  untilslightly above body temperature the
  reaction rate decreases as enzymes denature.

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pH

• Enzymes usually work in a narrow pH range.
• pH optimum pH at which each enzyme exhibits
  peak activity.
• this reflects the pH in which the enzyme needs to
  function.

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Cofactors and Coenzymes

• Needed for the activity of certain enzymes.
• Cofactor
• Metals, ions
• often for conformational change of active site.
• help bind the substrate
• Coenzyme
• often derived from vitamins

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Active enzyme concentration

• Transcription then translation makes enzymes.
• - Concentration of ACTIVE enzymes is important.

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Active enzyme concentration

• - Enzymes may be produced in an inactive form
  then modified to be active (usually when they
  reach a different location), by chemical
  modifications, clipping small pieces, association
  with other proteins (quaternary), pH.
• - Phosphorylation/dephosphorylation common
  post-translational modification (performed by
  enzymes called kinases or phosphatases).

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Substrate Concentration

• - At a specific enzyme, rate of product
  formation increases as the substrate increases.
• Plateau of maximum rate occurs when enzyme is
  saturated.
• All the active sites are fully occupied, at all
  times.
• - Additional substrate does not not increase
  reaction rate.

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Substrate concentration

• Some enzymatic reactions are reversible.
• Both forward and backward reactions are catalyzed
  by same enzyme.
• H20 C02 H2C03
• Law of mass action
• Reversible reactions will be driven from the side
  of the equation where concentration is higher to
  side where concentration is lower.

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Substrate concentration

• Enzymes move reactions towards equilibrium

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Substrate concentration

• Removal of products can drive an enzymatic
  reaction in a certain direction!
• Many enzymatic reactions participate in
  multi-step metabolic pathways.

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Metabolic Pathways

• Sequence of enzymatic reactions that begins with
  initial substrate, progresses through
  intermediates and ends with a final product.

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Metabolic Pathways

• Usually webs of pathways!
• Branch points more affinity of substrate for
  enzyme 3 or enzyme 10?

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End-Product Inhibition
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End-Product Inhibition
Enz12
Enz11
Enz10
X
Y
Z
A
B
C
Enz2
Enz1
D
E
F
Enz3
Enz4
Enz5

• Aka negative feedback inhibition, or feedback
  inhibition
• - One of the final products in a divergent
  pathway inhibits the activity of a branch-point
  enzyme.
• -prevents accumulation of final product.
• - can result in shift to alternate pathway.

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End-Product Inhibition
Enz12
Enz11
Enz10
X
Y
Z
A
B
C
Enz2
Enz1
D
E
F
Enz3
Enz4
Enz5

• How
• - allosteric inhibition product binds (not to
  active site), conformation changes, active site
  doesnt work.

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Inhibition of enzymes

• Competitive inhibition
• molecule binds to active site, competiting with
  substrate
• can reverse the inhibition by adding more
  substrate

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Inhibition of enzymes
Substrate binds
Competitive inhibition
Noncompetitive inhibition
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Inhibition of enzymes

• Non competitive inhibition
• - inhibitor binds elsewhere on the enzyme (not to
  the active site)
• aka allosteric inhibition
• cannot reverse it by adding more substrate

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Inhibition of enzymes

• Allosteric regulation
• Allosteric binding of a molecule can
• - inhibit the enzyme or
• - activate the enzyme

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Inhibition of enzymes

• Allosteric activation
• - cooperativity happens in a multisubunit
  enzyme, when the first substrate binds and locks
  the enzyme into its active form

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Inhibition of enzymes
Substrate
Inactive form
Stabilized active form
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Enzymes

• Enzymes that need to work together in a pathway
  are usually found in the same location in a cell.

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Inborn Errors of Metabolism
Enz12
Enz11
Enz10
X
Y
Z
A
B
C
Enz2
Enz1
D
E
F
Enz3
Enz4
Enz5

• - Inherited defect in the gene for an enzyme.
• - This can result in an accumulation of
  intermediate products, and a deficiency in final
  product.

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ENERGY
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RXNS
ENDERGONIC requires energy (enters!)
- gathers energy! EXERGONIC energy is
produced (exits!) - gives energy!

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Endergonic Reactions
C
D

High EnergyProducts
Low EnergyReactants
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ENERGY

• Metabolism all the chemical rxns of an organism
• Catabolism release energy (usually breakdown of
  molecules), exergonic rxns
• Anabolism require input of energy (usually
  synthesis of molecules), endergonic rxns

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ENERGY

• Bioenergetics study of energy flow through
  organisms

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ENERGY

• Kinectic energy energy associated with movement
• Potential energy energy associated with location
  or structure
• - includes chemical energy

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ENERGY
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ENERGY

• Thermodynamics physics study of energy
  transformations in a system
• closed system not in contact with its
  surroundings
• open system includes organisms

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ENERGY

• 1st law of thermodynamics
• Energy can be transformed, but it cannot be
  created or destroyed.
• 2nd law of thermodynamics
• Energy transformations increase entropy (degree
  of disorganization of a system).

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ENERGY
Heat
co2

H2O
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ENERGY

• Free energy (energy in organized state) can be
  used to do work.
• ?G measure the change in free energy

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ENERGY

• Because of the second law of thermodynamics
• - ?G means reaction will occur spontaneously,
  and is exergonic (products have less energy)
• ?G means reaction will occur only with an input
  of energy, and is endergonic (products have more
  energy)

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(a) Exergonic reaction energy released
Products
Amount of energy released (?Ggt0)
Energy
Free energy
Reactants
Progress of the reaction
(b) Endergonic reaction energy required
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ENERGY
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ENERGY
ATP is the universal energy carrier of
life. Follow the ATP.
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ATP
ADP
ATP
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Synthesis of ATP endergonic

energy

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Breakdown of ATP  exergonic
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ATP

• ?G 7.3 kcal/mol

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ATP

• Energy released from the hydrolysis of ATP is
  used for the synthesis of other molecules through
  coupled reactions.

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ATP

• ATP can attach one of its phosphates
  (phosphorylate) to another molecule.
• The phosphorylated molecule is less stable, and
  usually undergoes a conformational change that
  performs work.

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ATP

• Phosphorylation of ADP produces ATP, and is often
  coupled with catabolism.
• So
• ATP powers anabolism.
• Catabolism generates ATP.

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ATP

• Phosphorylation of ADP produces ATP, and is often
  coupled with catabolism.
• So
• ATP powers anabolism.
• Catabolism generates ATP.

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ATP
ATP synthesis from ADP Pi requires energy
ATP hydrolysis to ADP Pi yields energy
ATP
Energy from catabolism (exergonic, energy
yielding processes)
Energy for cellular work (endergonic,
energy- consuming processes)
ADP Pi
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ATP

• A working muscle cell can recycle its entire ATP
  pool in one minute!
• Thats 10 million ATPs used per sec!