Enzymes Day 2
Egg in vinegar–what happened?
Why?
Explain the relationship between the structure of the active site, enzyme-
substrate specificity, and denaturation.
SL: Data-based Question on page 351 of IB Biology Course Companion Book (also do ATL Thinking Skills Assignment–will help with IA)
HL will do for homework
Metabolic Pathway
● Any chain or cycle of linked reactions catalyzed by enzymes
● Involve chain of reactions
●Interlinked and interdependent pathways
● Substrate is worked on by enzyme
○ Can have many intermediate products before end product is produced
● Also called biochemical pathways
Metabolic Pathways Can be Linear or Cyclical
In cyclic pathways, every intermediate is a product of one reaction and a substrate of
another reaction.
- Krebs Cycle and Calvin cycle are cyclic reactions (cyclic is more unusual)
- Glycolysis is linear
Some poisons can also
prevent enzymes from
working properly
Allosteric Regulation
Allosteric regulators–molecules that change the shape and activity of an
enzyme by irreversibly binding at a site on the enzyme away from the active
site–allosteric site
- Reversible non-competitive inhibition
- Allow activity of an enzyme to be regulated
- Switching between active and inactive site alters structure and
properties of the enzyme’s active site
- In some cases binding inhibits enzymes, in others it activates enzyme
Enzyme Inhibitors: Competitive Inhibitors
● Two types: Competitive and Non-competitive
● Competitive
○ Competes with the substrate for the same active site
○ Chemically similar to substrate
How would this impact the rate of reaction? How could we increase rate of reaction?
○ Maximum rate of reaction (Vmax) eventually the same as the reaction without inhibitor.
■ When substrate concentration increases rate will increase (more available substrate than inhibitor)
○ Example: Statin combines with active site of an enzyme essential in catalysing the biosynthesis of
cholesterol within the liver. Causes a reduction in production of cholesterol
■ Can be prescribed by doctors for people with high cholesterol levels
■ Reduces risk of cardiovascular disease
Nature of Science:
A lot of testing goes into the development of medicine before it is released as a
treatment. Scientists have an obligation to assess the risks associated with a
potential medicine. Hopefully there will be no harmful side effects when using a
medicine. Statins are controversial because they do have positive effects, but
also have serious side effects in some people.
Non-Competitive Inhibitors
● Non-competitive
○ Bind at a site away from the active site altering the shape of the enzyme
○ No similarity to substrate
○ Rate levels off and never reaches the same level (V max) that it would without inhibitor
○ Example Alanine stops pyruvate kinase (enzyme) from binding with phosphoenol pyruvate
to form pyruvate
■ Fewer enzyme molecules are available
How would you graph this?
Examples of Inhibitors
Enzyme Substrate Products Inhibitor Binding
Acetaldehyde Acetaldehyde Acetic Acid Disulfiram Reversible
dehydrogenase (competitive) binding to the
active site
Pyruvate Phosphoenol Pyruvate Alanine (non- Irreversible
kinase pyruvate competitive) binding to a
site away from
the active site
End-product Inhibition
● Goal: to be economical with a cell’s resources
● Also called feedback inhibition
○ Prevents cell from wasting chemical resources and energy
○ When end product is present in sufficient quantity, it can shut down the pathway
● Example: Isoleucine
○ Critical for growth, glucose transportation, and protein metabolism and for
immune system
○ An essential amino acid
○ A large presence of isoleucine inhibits the enzyme threonine deaminase
○ When isoleucine is used, it will detach from the enzyme and be used and then
more isoleucine from threonine can be produced
Isoleucine is an essential amino acid (has to be
consumed). You need to know this one.
https://www.youtube.com/watch?v=dUyxwRE8riU&list=PLU9
yzVsaZUasCqYbqtTI1vxFWg4K4Wn&index=17
Mechanism-Based Inhibition
Alexander Fleming discovered the antibiotic properties of penicillin (a mold
growing on a petri dish) in 1928
1944 produced in high enough quantities to effectively treat bacterial
infections
Penicillin and related antibiotics inhibit an enzyme called transpeptidase that
catalyzes the last step in the formation of bacterial cell walls.
- Penicillin irreversibly binds to transpeptidase
- Irreversible inhibitor–inactivates transpeptidase by by bonding to a
particular chemical group at the active site.
- Defective cell wall prevents bacterial reproduction and causes death of
bacterial cells.
Evolution
Some bacteria have become resistant to penicillin because of a mutation
that allows them to produce an enzyme called penicillinase, which attacks
the molecular structure of penicillin by breaking specific bonds
- Scientists changed structural makeup of penicillin to produce variations
not impacted by penicillinase
Now transpeptidases are beginning to mutate
Quizlet: Enzymes
Designing an
Experiment
Use IB/IA rubric
Homework for Friday: Modify
basic method (will be put on
Google Classroom) to investigate
one of these independent
variables
