Enzymes and
Metabolism
Metabolism
The sum of all rxns that occur within a cell
 Rxns either require or produce ATP
 Rxns that occur within a cell are regulated
by the production of specific enzymes
(proteins coded by DNA)

Metabolic Pathway

Series of linked rxns, requiring many
enzymes
Enzyme 1
Enzyme 2
Enzyme 3
ABCD
Substrate
Product
Substrate
Product
Substrate
Product
Thyroid Gland

Produces thyroxin (hormone) that functions
to:
 Increase metabolic rate
 Stimulate all cells (no target organ)
 Stimulate production of enzyme that breaks
down glucose and release NRG
 More glucose is broken down
 More NRG is utilized
 Increase O2 consumption
 Increase heart rate
Cellular Respiration
Glucose + O2  CO2 + H2O + ATP

Glucose breakdown is exergonic as it creates
ATP for use within cells
Characteristics of Enzymes
1.
2.
3.
4.
5.
Enzyme combine briefly with substrate during
rxn
Enzymes are released unchanged
Enzymes are specific
Enzymes are saturated by high [substrate]
Enzymes are pH and temperature sensitive
Characteristics of Enzyme con’t
6. Enzymes contain protein & non-protein
groups called:
Substrate
Cofactor/coenzyme (nonprotein part)
Apoenzyme (protein
part)
Active Site – area on enzyme where
substrate binds on to
Enzyme Inhibition
Competitive Inhibiton
Uncreative molecule that resembles the
substrate combines with active site of
enzyme
 Block access of normal substrate so rxn
rate slows down

Non-competitive Inhibitors
Inhibitors that bind to enzyme outside of
active site (ex. Poisons, toxins)
AKA: Allosteric Inhibitors – bind to site
other than active site, resulting in a shape
change of enzyme  enzyme = no
function

Substrate
Active site
Allosteric inhibitor
Allosteric site
enzyme
Changed the shape
of active site
How is homeostasis maintained?
How do cells control the level of
activity of enzymes within the
cell?
Feedback Inhibition (Negative
Feedback) Competitive Inhibition
When product is in abundance in cell, it
binds to the active site of the enzyme,
competing for space with the substrate.
Rxn rate decreases.
 Non-permanent binding – when the
[product] is lowered, the product leaves
active site to allow more substrate to bind.
In this way, the [product] stays within a
certain range

Feedback Inhibition (Negative
Feedback) Non-Competitive Inhibition

Within metabolic pathway, the end
product can also bind to an allosteric site
of the first enzyme in the pathway. This
binding causes a change in the enzyme's
shape and it can no longer function,
decreasing the rxn rate
D Binds to E1 therefore entire rxn stops
A  B  C D
E1
E2
E3
Internet Video
Enzyme Review
Enzyme Song
Provincial Questions
What is structure Y?
A. a product
B. a reactant
C. an active site
D. an enzyme-substrate complex
Competitive inhibitors bind to which
structure?
A. W
B. X
C. Y
D. Z
The changes shown in the diagram cause the rate of an
enzyme-catalyzed reaction to decrease because
A. the enzyme denatures the substrate.
B. the substrate cannot bind to the active site.
C. the coenzyme is unable to bind to the substrate.
D. the enzyme can no longer increase the activation
energy.
Which of the following describes the
function of an enzyme?
A. It speeds up a chemical reaction.
B. It increases the available substrate.
C. It increases the activation energy of a
reaction.
D. It contributes atoms to facilitate a
chemical reaction.