Energy and Metabolism

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Energy and Metabolism

• Chapter 6

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Flow of Energy

• Energy the capacity to do work
• -kinetic energy the energy of motion
• -potential energy stored energy
• Energy can take many forms
• mechanical electric current
• heat light

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Flow of Energy

• Most forms of energy can be converted to heat
  energy.
• Heat energy is measured in kilocalories.
• One calorie the amount of heat required to
  raise the temp of water by 1oC
• 1 kilocalorie (kcal) 1000 calories

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Flow of Energy

• Potential energy stored in chemical bonds can be
  transferred from one molecule to another by way
  of electrons.
• oxidation loss of electrons
• reduction gain of electrons
• redox reactions are coupled to each other.

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Laws of Thermodynamics

• First Law of Thermodynamics energy cannot be
  created or destroyed
• -energy can only be converted from one form to
  another
• For example
• sunlight energy chemical energy
• photosynthesis

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Laws of Thermodynamics

• Second Law of Thermodynamics disorder is more
  likely than order
• entropy disorder in the universe
• The 2nd Law of Thermodynamics states that entropy
  is always increasing.

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Laws of Thermodynamics

• Free energy the energy available to do work
• -denoted by the symbol G (Gibbs free energy)
• enthalpy energy contained in a molecules
  chemical bonds
• free energy enthalpy (entropy x temp.)
• G H - TS

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Laws of Thermodynamics

• Chemical reactions can create changes in free
  energy
• DG DH - T DS
• When products contain more free energy than
  reactants DG is positive.
• When reactants contain more free energy than
  products DG is negative.

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Laws of Thermodynamics

• Chemical reactions can be described by the
  transfer of energy that occurs
• endergonic reaction a reaction requiring an
  input of energy
• - DG is positive
• exergonic reaction a reaction that releases free
  energy
• - DG is negative

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Laws of Thermodynamics

• Most reactions require some energy to get
  started.
• activation energy extra energy needed to get a
  reaction started
• -destabilizes existing chemical bonds
• -required even for exergonic reactions
• catalysts substances that lower the activation
  energy of a reaction

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Energy Currency of Cells

• ATP adenosine triphosphate
• -the energy currency of cells
• ATP structure
• -ribose, a 5-carbon sugar
• -adenine
• -three phosphates

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Energy Currency of Cells

• ATP stores energy in the bonds between
  phosphates.
• Phosphates are highly negative, therefore
• -the phosphates repel each other
• -much energy is required to keep the phosphates
  bound to each other
• -much energy is released when the bond between
  two phosphates is broken

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Energy Currency of Cells

• When the bond between phosphates is broken
• ATP ADP Pi
• energy is released
• ADP adenosine diphosphate
• Pi inorganic phosphate
• This reaction is reversible.

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Energy Currency of Cells

• The energy released when ATP is broken down to
  ADP can be used to fuel endergonic reactions.
• The energy released from an exergonic reaction
  can be used to fuel the production of ATP from
  ADP Pi.

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Enzymes

• Enzymes molecules that catalyze reactions in
  living cells
• -most are proteins
• -lower the activation energy required for a
  reaction
• -are not changed or consumed by the reaction

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Enzymes

• Enzymes interact with substrates.
• substrate molecule that will undergo a reaction
• active site region of the enzyme that binds to
  the substrate
• Binding of an enzyme to a substrate causes the
  enzyme to change shape, producing a better
  induced fit between the molecules.

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Enzymes

• Multienzyme complexes offer certain advantages
• 1. The product of one reaction can be directly
  delivered to the next enzyme.
• 2. The possibility of unwanted side reactions is
  eliminated.
• 3. All of the reactions can be controlled as a
  unit.

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Enzymes

• Not all enzymes are proteins.
• Certain reactions involving RNA molecules are
  catalyzed by the RNA itself.
• ribozymes RNA with enzymatic abilities
• For example, the ribosome is a ribozyme.

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Enzymes

• Enzyme function is affected by its environment.
• Factors that can change an enzymes 3-dimensional
  shape can change its function.
• -for example, pH, temperature, regulatory
  molecules

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Enzymes

• Temperature
• -enzyme activity may be increased with increasing
  temp, up to the temp optimum
• -temperatures too far above the temp optimum can
  denature the enzyme, destroying its function
• pH most enzymes prefer pH values from 6 to 8.

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Enzymes

• Inhibitors are molecules that bind to an enzyme
  to decrease enzyme activity.
• -competitive inhibitors compete with the
  substrate for binding to the same active site
• -noncompetitive inhibitors bind to sites other
  than the enzymes active site

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Enzymes

• Allosteric enzymes exist in either an active or
  inactive state.
• -possess an allosteric site where molecules other
  than the substrate bind
• -allosteric inhibitors bind to the allosteric
  site to inactivate the enzyme
• allosteric activators bind to the allosteric site
  to activate the enzyme

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Metabolism

• Metabolism all chemical reactions occurring in
  an organism
• Anabolism chemical reactions that expend energy
  to make new chemical bonds
• Catabolism chemical reactions that harvest
  energy when bonds are broken

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Metabolism

• Some enzymes require additional molecules for
  proper enzymatic activity.
• These molecules could be
• -cofactors usually metal ions, found in the
  active site participating in catalysis
• -coenzymes nonprotein organic molecules, often
  used as an electron donor or acceptor in a redox
  reaction

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Metabolism

• Biochemical pathways are a series of reactions in
  which the product of one reaction becomes the
  substrate for the next reaction.
• Biochemical pathways are often regulated by
  feedback inhibition in which the end product of
  the pathway is an allosteric inhibitor of an
  earlier enzyme in the pathway.

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