Unit 4 - Enzymes Flashcards
What is an enzyme?
Biological catalyst
What is the role of enzymes?
To speed up chemical reactions
What are virtually all enzymes made of?
Proteins
What do most enzymes have associated with them?
Co-factors
What is the difference between enzymes and chemical catalysts?
Enzymes are very specific in the substrates that they will use
- active site only accepts certain molecules
Chemical catalysts are not specific
How can inhibition of an enzyme be used to halt a particular reaction?
Interferes with a metabolic process
- can be used to treat a disease or infection
Give an example of how inhibition of a human enzyme can be used to treat a metabolic disease
Inhibition of angiotensin converting enzyme (ACE) can be used to treat high blood pressure
Give an example of how inhibition of a pathogen enzyme can be used to treat an infection
Inhibition of bacterial cell wall enzyme can be used to treat bacterial infections
What factors are important in a drug?
Toxicity - inhibition of related enzymes or enzymes involved in other processes Bioavailability Penetration across membranes Clearance from the body - low half life Non-specific binding to other macromolecules Degredation - e.g. by the liver
What are the six major types of enzyme classification?
Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases
What are the two types of enzyme inhibition?
Reversible
Irreversible
Describe reversible inhibition of enzymes
Rapid dissociation of the enzyme-inhibitor complex when the inhibitor is removed
Describe irreversible inhibition of enzymes
Very slow dissociation of the enzyme-inhibitor complex
- often there is covalent attachment of the inhibitor to the enzyme
What types of reversible inhibition are there?
Competitive inhibition - most common - direct competition Non-competitive inhibition - binds at different site - rare Uncompetitive inhibition - very rare!
Describe competitive inhibition
The inhibitor almost always binds to the same active site as the substrate
The enzyme can bind the inhibitor or the substrate but not both at the same time
- competitive!
Usually the inhibitor is closely related to the substrate
- structurally
How can competitive inhibition be overcome?
Increasing concentration of substrate
- related to how tightly bound the enzyme-substrate complex is
What is plotted to determine important kinetic data from easily measurable parameters?
Lineweaver-Burk plot
What effect does a competitive inhibitor have on a Lineweaver-Burk plot?
The steepness of the line increases relative to the control
Vmax remains unchanged
Km is increased
What effect does increasing concentration of substrate have on non-competitive inhibition?
No effect
What is allosteric inhibition?
Binding of inhibitor at site other than the enzyme active site
What does binding of an inhibitor at an allosteric site cause?
Conformational change to enzyme reducing binding between enzyme and substrate
Give an example of an allosteric inhibitor
Non-nucleoside Reverse Transcriptase Inhibitors for HIV Infection
What is a reverse transcriptase enzyme?
Replicative enzyme of HIV
- converts viral RNA to double stranded DNA
What effect does a non-competitive inhibitor have on a Lineweaver-Burk plot?
As non-competitive inhibitor concentration against a control experiment show an increase in gradient compared to with the origin at the x-axis intercept
Increased Y intercept same x axis point
Vmax is reduced
Km remains the same as no affect on affinity
What is uncompetitive inhibition?
Inhibitor binds to the enzyme substrate complex but not to the enzyme
