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Enzymes (Chapter 6) Notes
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Metabolism the total of the chemical reactions in an
organism
Catabolism breaking down
o Cellular respirations Anabolism building up
o Photosynthesis
Metabolism = catabolism + anabolism
Laws of Thermodynamics
o 1st Law energy can be transferred but neither created nor
destroyed
o 2nd Law transfers of energy increase entropy (disorder)
Free energy
o Like potential energy
o Symbolized by letter G
o
Is energy available to do worko Changes that occur in a reaction
are
delta G
o Spontaneous
System becomes more stable
Delta G is less than zero
The released free energy can
be harnessed to do work
Delta G = Gfinal Gstarting
o Spontaneous delta G = - (energy never released)
o Non-spontaneous delta G = + (energy must be added)
Reactions are either:o Exergonic release energy, spontaneous,
loss of free energy, - delta G
(think respiration)
o Endergonic absorbs energy non-spontaneous, gain of free
energy,
+deltaG (think photosynthesis)
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delta G of zero
o found in systems at equilibrium
o can do no work
o Cells at metabolic equilibrium is dead
o Disequilibrium is maintained because living things are open
systemso Fuel sources in (high in free energy) and waste is out
(low in free energy)
Energy Coupling
o Living things tie the release of free energy by some molecules
(like
glucose) to the gain of free energy of other molecules
o ATP couples exergonic and endergonic reactions
Cellular Work
o Mechanical
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o Transport
o Chemical
ATP adenosine triphosphate (picture)
Purina double dog chow; Pure as gold (purine: adenine,
guanine)
ATP Hydrolysis
o Non spontaneous (picture) If ATP were directly hydrolyzed in
the cell, it would just release heat
If, however, the hydrolysis is coupled with a transfer of a
phosphate froup to
another molecule, more of the energy can be used
The molecule is said to be phosphorylated
ATP Cycle
o
o Energy used to phosphorylate ADP is released in catabolic
reactions
o ATP couples the cells energy yielding processed to
energy-consuming
processes
Reaction Profile
o
o 1. Need a collision of sufficient impact and correct
orientation
productive collision
o 2. Bonds distort
o 3. New products are more stable lower free energy
o 4. Before they can react they much climb the activation energy
hill
Enzyme Action
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o Enzymes dont change deltaG, they lower the activation energy
needed
o
Enzymes and Catalysts
o Biochemical reactions require enzymes to speed up and control
reaction
rateso Catalyst chemical agent that accelerates a reaction
without being
permanently changed in the process so it can be reused
o Enzyme proteins which are biological catalysts
Enzyme Characteristics
o Most enzymes are proteins
o They lower activation energy
o Do NOT change deltaG
o Act on a substrate (thing getting broken apart)
o Are selective and specific
o
Commonly named with ase endingo Work because of their shape,
destroy shape, destroy enzyme function
o Have an active site where substrate fits
o Can be controlled
Enzyme Induced Fit
o
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Catalytic Cycle
o
o Substrate binds to active site
o Forms enzyme-substrate complex due to chemical
interactions
o Induced fit side chains of a few amino acids catalyze the
reaction
o Product departs enzyme resumes original shape
Enzyme Rap
o Enzyme Structures one of a kind
o 3-D shape will let it bind
o Enzyme-structure is not snug
o Induced fit provides a hug
o Most are protein dont you knowo Amino acid r groups show
o Specific is the site that active
o Only one thing is reactive
o A groove we see as the active site
o Substrates come and fit here tight
o Catalytic cycle is the enzyme way
o Fit, fill, hug, release all day
SIP SAC
o Structure
o Induced fito Protein
o Specific
o Active site
o Catalytic cycle
Enzyme Regulation
o Is affected by many different things
Environmental conditions (pH, temperature, ionic
concentration)
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Cofactors
Non-protein helpers needed for catalysis by many enzymes
May be permanently bound to the active site
May bind at the same time as the substrate
Some cofactors are inorganic like metal
Organic cofactors are called coenzymes and are oftenvitamins or
derived from vitamins
Enzyme Inhibitors
Competitive
Non-competitive
Allosteric site interactions
Activators
Inhibitors
o GRAPHS ON TEST!!!!
Enzyme Inhibition
o If the enzyme attaches covalently it is usually irreversible,
weak bonds are
usually reversible
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o
o Competitive
Compete for the active site
Similar to normal substrate
Reduces productivity active sites are busy
If reversible increasing substrate concentration will
overcome
inhibitor
o Non-competitive
Bind to a part of the enzyme away from the active site
Causes shape change which inactivates or reduces activity
Allosteric Regulation
o Inhibition and Activation are important in enzyme control
o Most regulating molecules bind to an Allosteric site, a
receptor site
different from the active site
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o
o Allosteric inhibitors are a type of non-competitive
inhibitor
o Inhibitors and activators are attached by weak bonds and are
affected by
concentration
o The activator and the inhibitor may be similar enough in shape
to compete
for the Allosteric site making concentration the driving factor
for whetheror not a reaction proceeds
o Most enzymes with allosteric sites are made of two or more
polypeptide
chains. The allosteric site is usually found where the subunits
join
Enzyme Cooperativity
o Seen when an enzyme has two or more subunits
o Amplifies the response of enzymes to the substrate
o One substrate molecule stabilizes the enzyme to accept
additional
substrate
Feedback Inhibition
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o
o Common way metabolism is controlled
o Metabolic pathway is turned off by its end product
o The end product inhibits an enzyme in the pathway
One Practical Use of Enzymes
o Use of lactase in production of lactose-free milk
1. Most humans born with the enzyme lactase that digest
lactose
2. Production of lactase is gradually lost as people age (in
many
people)
3. When milk products are consumed, bacteria feast on the
lactoseleading to cramping, gas and diarrhea
4. Lactase can be added to milk products to pre-digest the
lactose
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