Deep-Sea Firefly Squid
(Watasenia scintillans)
Anglerfish
Cookiecutter shark
(Isistius brasiliensis)
Firefly
Ch 5—Introduction
Turning on the Lights to Be Invisible
 Bioluminescence the production and emission of light by a living organism.


bios =“living”
lumen = “light”
 Three components needed for a bioluminescent reaction:



Oxygen
Luciferin, a molecular substrate
Luciferase, an enzyme
Intro continued…
 Purpose of bioluminescence:
 Camouflage
 Attraction of mates or prey
 Repulsion of predators
 Communication
 Key point:
 Bioluminescence is one example of how living things put energy to
work by means of enzyme controlled chemical reactions!
C. How Enzymes Function
5.14-5.16
 5.14 Enzymes speed up the cell’s chemical reactions
Page 84
 Energy of activation- (EA) the amount of energy needed to
push the reactants over an energy barrier so that the
chemical reaction can begin.
 Enzymes- proteins that function as biological catalysts,
increasing the rate of reaction
 they lower the EA barrier
5.15
Page 84
 As a protein, an enzyme has a unique 3-D shape.
 This shape determines which chemical reaction the enzyme will
catalyze.
 Substrate- a specific reactant that an enzymes acts on.
 Active site- a region of the enzyme where the substrate locks in.
 Induced fit- a change in shape of the active site when a substrate
binds to the enzyme.
 Enzymes are specific because their active sites fit specific substrate
molecules.
 Think of a lock and key!
How do Enzymes Work?
• Enzymes bind to
specific reactant
molecules.
• The shape of each
enzyme fits the shape
of only one particular
reactant molecule.
• substrate: a specific
reactant acted upon by
an enzyme.
• active site: the region of
the enzyme where the
substrate binds
Continued…
• The substrate binds to an enzyme at an
active site (like a lock and key)
• The enzyme—substrate interaction lowers
the activation energy required for the
reaction to occur.
The role of enzymes
• They can join (reactants) substrates to
form a larger molecules (products)
• They can help break down large
molecules into smaller ones.
• So enzymes are involved in both
dehydration and hydrolysis reactions.
THE
CATALYTIC
CYCLE OF AN
ENZYME
5.16
Page 85
 Inhibitors- a chemical that interferes with an enzymes
activity.
 Competitive inhibitor- resembles the enzyme’s
normal substrate and competes for the active site.
 Result: reduces the enzymes productivity
Enzyme inhibition continued…
 Noncompetitive inhibitor- does not enter the active
site; it binds to the enzyme somewhere else.
 Result: changes the overall shape of the enzyme so that
the active site no longer fits the substrate
Enzyme Inhibition as regulators of metabolism
 Most chemical reactions are organized into metabolic
pathways:
 a molecule is altered in a series of steps, each catalyzed by a
specific enzyme, to form a final product.
 If a cell is producing more of that product than it needs, the
product may act as an inhibitor of one of the enzymes early
in the pathway.
 Feedback inhibition- inhibition whereby a metabolic
reaction is blocked by its own products.

This is one of the most important mechanisms that regulate
metabolism!
Feedback Inhibition