Transcript Chapter 4 Enzymes and Energy

Chapter 4 - Enzymes and Energy
• Most enzymes are proteins with diverse
structure.
• Enzymes are chemical catalysts that:
– Increase the rate of a reaction.
– Are not permanently altered or used up by the
reaction.
– Do not change the nature of the reaction.
enzyme animation
– Reduce the required amount of activation
energy required to initiate the reaction.
• Many enzymes work by orienting molecules so that
they can better contact each other.
• Each type of enzyme has has a highly-ordered,
characteristic 3-dimensional shape (conformation).
• Ridges, grooves, and pockets lined with specific
amino acids.
• Pockets active in catalyzing a reaction are called the
active sites of the enzyme.
• The molecule affected by the enzyme is the
substrate.
• Substrates have specific shapes to fit into
the active sites (lock-and-key model):
• Better fit may be induced (induced-fit
model):
• Enzyme undergoes structural change.
• Enzyme names end with suffix “-ase.”
– Enzymes may be named according to their
mode of action, e.g. kinase.
• May specify both the substrate of the enzyme and
job category.
– Enzymes may be named for the substrate, e.g.
lipase, maltase.
• Different organs may make different
enzymes (isoenzymes) that have the same
activity.
– Differences in structure do not affect the active
sites.
• Enzyme activity can be affected by several
factors:
– Changes in pH and/or temperature may
denature the enzyme. These changes may break
the H bonds stabilizing the molecule.
– Small molecules or ions called cofactors alter
the shape of the active site and/or is needed for
the substrate to bind with the active site, e.g.
Ca++.
– Certain organic molecules called coenzymes
are needed to transport small molecules or ions
(especially H+) from one enzyme to another.
– Increasing the substrate concentration will
increase the reaction rate.
• Law of Mass Action – the principle that reversible
reactions will be forced in the direction where the
concentration is lowest.
H20 + C02
H2C03
• A metabolic pathway is a sequence of
enzymatic reactions that results in a final
product.
– Metabolic pathways are frequently regulated by
inhibition. End-product inhibition occurs when
one product binds with the enzyme and
prevents it from binding with the substrate. The
product may bind with the enzyme at the
allosteric site. This is negative feedback.
inhibition animation
• Competitive inhibition occurs when some
other molecule (similar to the substrate)
binds with the enzyme. This prevents the
substrate from participating in any
metabolic pathway. This is typically how
poisons work.
Living organisms require the constant
expenditure of energy to maintain their
complex structures and processes. Central
to life processes are chemical reactions that
are coupled, so that the energy released by
on reaction is incorporated into the products
of another reaction = Bioenergetics
• Exergonic reactions – give off energy
• Endergonic reactions – take up energy
• Reduction – gain e- or H+
• Oxidation – lose e- or H+
• Reducing agent – donates e- or H+ to
another molecule
• Oxidizing agent – accepts e- or H+ from
another molecule