Transcript Enzyme Notes

Chapter 8.1, 8.2, 8.4, 8.5

metabolism is the process of breaking
down and creating molecules necessary
for life
◦ each step in this process is driven by an
enzyme which directs the speed of the
reaction (enzymes are proteins!)
 catabolic--breakdown molecules
 cellular respiration
 anabolic--build molecules
 protein synthesis

energy is the capacity to cause change
◦ kinetic (heat) vs. potential (chemical)

thermodynamics = energy transformations
◦ 1st law (matter cannot be created or destroyed,
only change form)
◦ 2nd law (energy transfer increases the entropy of
the universe)
 spontaneous reactions vs. reactions that need
energy

free energy--identifies if a reaction
requires energy to proceed
◦ higher free energy = unstable
 does not require outside energy for the
reaction to happen (spontaneous)
 exergonic reaction (negative delta G)
 does not imply that it happens fast!
◦ lower free energy = stable
 requires outside energy for the reaction to
proceed (nonspontaneous)
 endergonic reaction (positive delta G)

Lower energy barriers for the reaction to
happen at an increased rate (catalyst); not
used up during the reaction
◦ activation energy (energy required to get
reaction going)
 based on how difficult it is to break the chemical
bonds
◦ speed up reactions that would occur anyway

substrate (reactant an enzyme acts on)
◦ enzyme binds to substrate, forming enzymesubstrate complex
◦ each enzyme has a specific substrate (results
from unique sequence of amino acids)

active site (region of enzyme where substrate
binds)
◦ when this occurs, the shape of the enzyme
changes which enhances the reaction

Rate in which enzyme converts substrate to product
is determined by...
◦ the initial concentration of the substrate (or
enzyme)
 more substrate molecules that are available the
more frequently they access active site.
 limited by the enzyme concentration
(saturated when rate of reaction is determined
by how often substrate can move into active
site)
◦ general environmental factors
 temperature, pH, and other chemicals
 each enzyme has optimal environment
depending on the organism and where it needs
to work

competitive inhibition
◦ reduce the productivity of
enzymes by blocking
substrate from entering
active site
◦ overcome by increasing
concentration of substrate

noncompetitive inhibition
◦ impede reactions by binding
to another part of the
enzyme, thus changing the
shape of the active site and
making it less effective
◦ **often pesticides,
antibiotics, and toxins are
inhibitors

enzymes need to be told when and where to
be active so only necessary reactions are
occurring
◦ Allosteric regulation
 protein function changed by binding of
another molecule
 has active (activator binds) and
inactive (inhibitor binds) forms
 “Chemical on/off switch”
◦ feedback inhibition
 end product of reaction binds to enzyme
causing inhibition, thus slowing the
reaction down