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Energy and Matter - Madison Public Schools

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									Energy and
Metabolism
• Thermodynamics – branch of
  chemistry dealing with
  changes in energy
• This applies to the study of
  biology since laws of
  chemistry apply to events
  within cells
          Flow of Energy

Energy: capacity to do work
  - work: activity involving a force and
  movement in the direction of the
  force
  -kinetic energy: energy of motion
  -potential energy: stored energy
Energy can take many forms:
 mechanical       electric current
 heat             light
 chemical
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 1 g of
 water by 1 C
            o



1 kilocalorie (kcal) = 1000 calories
Redox Reactions - Potential energy
 stored in chemical bonds can be
 transferred from one molecule to
 another through electrons

oxidation: loss of electrons
reduction: gain of electrons
redox reactions are coupled to
 each other
  Energy Source for Living
         Systems
• What do you think the source
  of energy for living systems on
  Earth is?
   Energy Source for Living
          Systems
• The ultimate energy source for
  living systems on Earth is the Sun
• Sunlight energy is captured by
  plants, algae and some bacteria
  during the process called
  photosynthesis
• Photosynthesis is a process that uses
  sunlight energy to combine water and
  carbon dioxide (small molecules) into
  sugars (larger, more complex
  molecules)
   –Inorganic carbon is converted to
    organic form
   –Chemical energy is stored in the
    bonds of the sugars (potential
    energy or kinetic energy?)
    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
• During each energy conversion,
  some energy is released into the
  environment as heat – measured as
  the random motion of molecules

• Energy flows through biological
  systems in one direction – energy
  from the Sun replaces energy
  dissipated as heat
   Laws of Thermodynamics
Second Law of Thermodynamics:
 disorder/entropy is always
 increasing (disorder is more likely
 than order)

entropy: disorder in the universe
• Disorder happens spontaneously

• Order/organization requires
  energy
Free energy (G): the energy
 available to do work (break bonds
 and form new bonds)
  enthalpy (H): energy contained in a
  molecule’s chemical bonds
free energy = enthalpy – (entropy x
  temp.)
              G = H – ST

Note: T = temp expressed in Kelvin scale
• Chemical reactions can create changes
  in free energy:
             DG = DH - T DS

• When products contain more free energy
  than reactants, energy is required and
  DG is positive
• When reactants contain more free energy
  than products, energy is released and
  DG is negative
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
  endergonic




 exergonic
(spontaneous)
Most reactions require an input of
 some energy to get started
activation energy: extra energy needed
 to get a reaction started
 -destabilizes existing chemical bonds
 -required for endergonic and
 exergonic reactions
• Exergonic reaction rates depend on
  the activation energy required for
  the reaction to begin
   – The larger the activation energy
     is, the slower the reaction
     proceeds
      • Fewer molecules reach that
        critical energy level required to
        start the reaction
Exergonic reaction rates can be
  increased in two ways:
• Increasing the energy of
  reacting molecules – adding
  heat
• Use a catalyst to lower the
  activation energy
catalysts: substances that lower the
 activation energy of a reaction

catalysis: the process of influencing
 chemical bonds in a way that lowers
 the activation energy required to
 start a reaction
    ATP = adenosine triphosphate
• ATP structure:
  – ribose, a 5-carbon sugar
  – adenine
  – three phosphates
• ATP stores energy in the bonds
  between phosphates
• Phosphates are highly negative:
  - the phosphates repel each other
  - energy is required to keep the
  phosphates bound to each other
  - energy is released when the bond
  between two phosphates is broken
When the bond between phosphates is
 broken:
         ATP            ADP + Pi
           energy is released

ADP = adenosine diphosphate
Pi = inorganic phosphate
This reaction is reversible
• The energy released when ATP is
  broken down to ADP and Pi , and can
  be used to power endergonic
  reactions

• The energy released from an
  exergonic reaction can be used to
  fuel the production of ATP from
  ADP + Pi
  Back to exergonic reactions
Remember -exergonic reaction
  rates can be increased in two
  ways:
• Increasing the energy of
  reacting molecules – adding
  heat
• Use a catalyst to lower the
  activation energy
             Enzymes
Enzymes: molecules that catalyze
  reactions in living cells
--lower the activation energy
  required for a reaction
-are not changed or consumed by the
  reaction so they are available to
  catalyze the same reaction again
  and again
- most are proteins*
NOTE: Not all catalysts are protein
 enzymes
• Some reactions involving RNA
  molecules are actually catalyzed by
  the RNA itself
   – ribozymes: RNA with catalysis
     abilities
    • Speed reaction rates
    • Substrate specific
  – ribosomes are ribozymes
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 (enzyme-
 substrate complex)
• Sometimes several enzymes
  catalyzing different steps of a
  reaction sequence in assemblies
  called multienzyme complexes
Multienzyme complexes offer three
 significant advantages:

1. The product of one reaction can be
  directly delivered to the next
  enzyme – increased rate of
  sequential reactions - no lag
  associated with frequency of
  enzyme/substrate collisions
2. The possibility of unwanted side
  reactions is eliminated since the
  substrate is in contact with the
  multienzyme complex throughout
  the sequence of reactions
3. The sequence of reactions that
  take place within the multienzyme
  complex can be controlled as a unit
        Enzyme Function
• Enzyme function is affected by its
  environment
• Factors that can change an enzyme’s
  3-dimensional shape can also change
  its function
1. Temperature
  -enzyme activity may be increased
  with increasing temp, up to the
  optimum
  -temperatures too far above the
  optimum can denature the enzyme,
  destroying its function
2. pH – most enzymes function
 best at pH values ranging from
 6 to 8
3. Regulatory molecules
- Inhibitors are molecules that bind
 to an enzyme and decrease enzyme
 activity
3. Regulatory molecules
- Inhibitors are molecules that bind
 to an enzyme and decrease enzyme
 activity
    -competitive inhibitors compete
    with the substrate for binding to
    the same active site
3. Regulatory molecules
- Inhibitors are molecules that bind
 to an enzyme and decrease enzyme
 activity
    -competitive inhibitors compete
    with the substrate for binding to
    the same active site
    -noncompetitive inhibitors bind
    to sites other than the enzyme’s
    active site
Definition:
Allosteric = relating to a change in
 the shape and activity of an
 enzyme that results from
 combination with another
 substance at a point other than
 the chemically active site
      More About Enzymes

Allosteric enzymes exist in either an
  active or inactive state
-possess an allosteric site where
  molecules other than the substrate
  bind
-allosteric inhibitors: substances
 that bind to the allosteric site to
 inactivate the enzyme
-allosteric activators: substances
 that bind to the allosteric site to
 activate the enzyme
           Metabolism
Metabolism: all chemical reactions
 occurring in an organism

  – Anabolism: chemical reactions
    that expend energy (energy added
    – endergonic or exergonic???) to
    make new chemical bonds – build
    more complex molecules
Photosynthesis is anabolic
– Catabolism: chemical reactions
  that harvest energy (energy
  released – endergonic or
  exergonic???) when bonds are
  broken – break down complex
  molecules
Cellular Respiration is catabolic
During chemical reactions, 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

OR…
-coenzymes: nonprotein organic
  molecules, often used as an
  electron donors or acceptors in
  redox reactions
…transport energy, along with the
  electrons, from one enzyme to
  another
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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