Enzymes Review Day
Biology, Sixth Edition
Chapter 6, Energy and Metabolism
“gonic” Reactions
• Reactions that require energy input are called endergonic
•
if they need heat, they are endothermic
• If a reaction releases energy it is exergonic
•
if the energy is released as heat, it’s exothermic.
ATP
• Adenosine triphosphate
• It is a nucleotide
• 3 parts
– Nitrogen base (adenine)
– Ribose (5C sugar)
– 3 phosphate groups
• Energy of ATP is in these
bonds
• Hydrolysis (adding water)
breaks this bond making ADP
+ Pi
– This is called phosphorylation
Biology, Sixth Edition
Chapter
Energy Released by the Hydrolysis of ATP is Coupled
to Other Reactions
Biology, Sixth Edition
Chapter
NAD+ / NADH &
Oxidation / Reduction Reactions
• Reduction is the addition of electrons.
–
–
–
–
Results in increased energy content
Very common in metabolism
e.g., NAD+
NADH
e.g., FAD
FADH2
• Oxidation is the loss of electrons.
– e.g., NADH
NAD+
– e.g., FADH2
FAD
– Oxidation and reduction are often coupled
as redox reactions.
Biology, Sixth Edition
Chapter
Enzymes Lower EA
Activation energy (Ea) is the energy required to
break the bonds to begin the reaction
Biology, Sixth Edition
Chapter
Catalase
• Example of an enzyme (all enzymes end in
ASE)
• Is found in all living things
• Used to break down toxins in the body
• For example, Catalase breaks down hydrogen
peroxide in the body (it is a byproduct of
metabolism)
3.4 Notes!
• Having too little of an enzyme or having too
much of an enzyme can have major
consequences
– Sucrase (lack of it causes diarrhea, cramps &
possibly slower growth in kids)
– Too much of an enzyme is wasteful for the cell
• So in order to maintain homeostasis, we need
to regulate enzymes!
Inhibitors
• Chemicals
• Some naturally occur in cells (can regulate
metabolism)
• Others are made in laboratories (used to treat
diseases)
• Inhibitors bind to enzymes, which has an
effect on the function of an enzyme.
Competitive Inhibition
• Inhibitor binds to the
active site of an
enzyme
• Induced fit occurs and
enzyme is unable to
bind to substrate.
• Reversible
– When inhibitor is in
low amounts, it will
leave the active site
and then the
substrate can bind.
Allosteric inhibition
• Inhibitor binds to an alternate site on the
enzyme (not the active site), called the allosteric
site.
• Still changes shape of enzyme, so substrate
cannot bind to active site
• Also called noncompetitive inhibition
What can affect an enzyme?
• pH
• Temperature
• All enzymes have optimal conditions for
optimal performance
• Remember enzymes are proteins, so if the
tertiary level is changed, the enzyme loses its
function