Download 8.4 Enzymes speed up metabolic reactions by

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Spontaneous chemical reactions occur
without a need for outside energy but
may be very slow
Free energy: ΔG
Catalyst: a chemical agent that speeds up
a reaction without being consumed by
the reaction
Enzyme: a catalytic protein
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AB + CD
AC + BD
(SPONTANEOUS EXERGONIC)
Every chemical reaction
between molecules
involves bond breaking
and bond forming
Free energy of
activation, or activation
energy (EA): initial
investment of energy to
start the reaction
Transition state: the
summit where the
reactants are in an
unstable condition
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Enzymes are proteins which are biological
catalysts
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Speed up reactions by lowering the EA barrier
Heat denatures proteins and kills cells and it
would speed up ALL reactions, so organisms need
alternative- catalysis
 Enzymes catalyze reactions
by lowering the EA barrier,
Enabling the reactant molecules
to absorb enough energy to
reach the transition state
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Substrate: the reactant an enzyme acts on
Enzyme-substrate complex: formed by an
enzyme binding to its substrate
Enzymes +
Substrate(s)
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Enzyme-substrate
complex
Enzyme + Product(s)
Enzymes=proteins=macromolecules
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Active site: the restricted region of the enzyme
molecule that binds to the substrate
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a pocket on the surface of the protein
Induced fit: when the enzyme changes shape
slightly so that the active site fits more snugly
around the substance
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Brings chemical groups of the active site into
positions that enhance their ability to catalyze the
chemical reaction
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In most enzymatic reactions, substrate binds to
active site and is held there by weak
interactions
Side chains (R groups) of a few of the amino
acids that make up the active site catalyze the
conversion of substrate to product
Product departs
Repeats
Most metabolic reactions are reversible and an
enzyme can catalyze both forwards and
backwards
The active site can lower an EA barrier by
orienting substrates correctly, straining their
bonds, providing a favorable
microenvironment, and covalently bonding
with a substrate
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Each enzyme has an optimal temperature and
pH (6-8)
Cofactors: nonprotein helpers for catalytic
activity required by many enzymes
coenzyme: if the cofactor is an organic
molecule
http://www.youtube.com/watch?v=5eBzLgleVL8
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Inhibitors reduce enzyme function
If done by covalent bonds the effects are
irreversible.
Most are weaker bonds making them reversible
Competitive inhibitor: binds to active site,
reduces productivity of enzymes by blocking
substrates from entering active sites
- can be overcome increase [ ] of the substrate
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Noncompetitive inhibitor: impede reactions
by binding to different site on enzyme
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Allosteric regulation: any case where a protein’s
function at one site is affected by the binding of a
regulatory molecule to a separate site
- results in either inhibition or stimulation of
activity
Cooperativity: mechanism that amplifies the
response of enzymes to substrates
Feedback inhibition: a metabolic pathway is
switched off by the inhibitory binding of its end
product to an enzyme that acts early in the
pathway
Ex: thermostat
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Some enzymes are grouped into complexes
Some are transported into membranes
Others are contained inside organelles
Metabolism (intersecting set of chemical
pathways characteristic of life)= choreographed
interplay of thousands of different kinds of
cellular molecules
http://www.youtube.com/watch?v=2N-ydg4J4tA
http://www.youtube.com/watch?v=M5bftq-W2aY
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http://www.uic.edu/classes/bios/bios100/lec
turesf04am/lect04.htm
http://www.youtube.com/watch?v=5eBzLgle
VL8
http://www.youtube.com/watch?v=2Nydg4J4tA
http://courses.washington.edu/conj/protein/
proregulate.htm
http://bio1152.nicerweb.com/Locked/media/
ch08/