Enzymes: the proteins in our body
that get the chemical reactions
necessary of life done
Human catalase
Review: the basics of a chemical
reaction
A+B
C
Reactants
Products
Energy
To be effective and save energy, cells rely on proteins (the ‘workers’ of the cell) to
bring down the “cost” of this reaction. These proteins are also known as enzymes!
All enzymes are proteins but not all proteins
are enzymes!
• Serve to reduce the activation energy required to make a chemical
reaction go!
• ** Do you remember this?**
To costly for the cell
to get the job done alone!
It needs help!
It needs an enzyme!
Types of Enzymes
Anabolic example: Making ATP
Catabolic example:
Breaking up
macromolecules
Enzymes are catalysts!
– enzymes bind specifically to a
molecule and stress the bonds
to make the reaction more likely
to proceed
– active site is a site on the
surface of the enzyme that
binds to a reactant
– the site on the reactant where
the enzyme binds is called the
binding site
Fig. 6.4.b
Exergonic reaction: energy is released as a
product of the reaction
Activation
energy
Fig. 6.4.c
Enzymes reduce the activation energy and
certain catalyzed reactions will have energy
release as a byproduct
uncatalyzed
Catalyzed reactions will
occur at a faster rate bc
the amount of activation
energy required to initiate
the reaction
catalyzed
Activation
energy
Chemical reactions and catalysis
Quick overview: How an enzyme works!
The “lock and key” mechanism!
• Brings the right substrates together in the right orientation to get the
reaction done!
Fig. 6.5
Lock and Key Mechanism and enzyme specificity
Enzymes selectively recognize proper substrates over other molecules
Specificity is controlled by structure – the unique fit of substrate with enzyme
controls electivity for substrate and the product yield
Substrate binding to the active site induces a conformational change in the
active site
More on how enzymes work:
• In most cases substrates are held in the active site by weak
interactions
• Catalyze the conversion of substrate to product
• A single enzyme molecule can catalyze thousands or more
reactions a second
• Enzymes are unaffected by the reaction and are reusable
• Each enzyme is unique based on its 3-D
structure. It has a specific chemical reaction it
will participate in.
Human glyoxalase
carbonic anhydrase II
These enzymes have unique active sites, different substrates and catalyze difference reactions!
What effects an enzyme’s function?
• Temperature and pH affect enzyme activity
– enzymes function within an optimum temperature range
• when temperature increases, the shape of the enzyme changes
due to unfolding of the protein chains
– enzymes function within an optimal pH range
• the shape of enzymes is also affected by pH
• most enzymes work best within a pH range of 6 - 8
– exceptions are stomach enzymes that function in acidic ranges
pH
scale
1
6
7
8
14
Fig. 6.8
Effects of temperature on the function of an
enzyme
Pepsin is an enzyme that is released by the chief cells in the stomach and that
degrades food proteins into peptides.
Trypsin is a serine protease found in the digestive system of many vertebrates,
where it hydrolyses proteins.Trypsin is produced in the pancreas
Fig. 6.8
The effects of pH on the function of an enzyme
Pepsin
Trypsin
How a cell regulates (uses) an enzyme
• Feedback inhibition is a form of enzyme inhibition where the product of a reaction
acts as a repressor
– competitive inhibition
• the inhibitor competes with the substrate for the active site
• blocks the active site so that it cannot bind substrate
– non-competitive inhibition
• the inhibitor binds to the allosteric site and changes the shape of the active
site so that no substrate can bind
Fig. 6.10
Competitive and Non-competitive inhibition
Allosteric Regulation: can inhibit or
activate
Fig. 6.7
Biochemical pathways: the product of one
enzyme reaction acts as the substrate for
the next reaction
We can design drugs which mimic natural enzyme
inhibitors to treat disease and enzyme misfunction
• HIV is treated with many different types of enzyme inhibitors