Introduction to Enzymes Flashcards
What are enzymes?
Biological catalysts
How do enzymes work?
By lowering the activation energy required for a chemical reaction by stabilising the transition state
What is rate enhancement calculated by?
Catalysed rate/uncatalyzed rate
What is the clinical importance of enzymes?
Looking at specific diseases
Using them for diagnosis
Looking at drug therapy
Basic research
If the substrate concentration increases, what also increases?
Reaction velocity
How dower measure enzyme activity?
Measured by increasing the substrate concentration and measuring the accumulation of products over time
What is enzyme activity dependent on?
How rapidly it can process a substrate
What is the maximum velocity a reaction can go to? denoted by?
Vmax
How do we gain more information about the activity of an enzyme?
Using Lineweaver-Burke plot
Putting [S} and Vo under 1
What is Km?
Used along with Vmax to measure enzyme activity
What does Km equal?
The substrate concentration that is required to reach half of maximum velocity
What is the usefulness of a lower Km?
Can work in lower concentration
How do we measure Km?
-1/Km is equal to the x intercept
What are enzymes inhibitors?
Chemicals that interfere with enzyme reactions
What are the two types of enzyme inhibitors?
Irreversible or reversible
What are irreversible inhibitors?
They react with the enzyme and form a covalent bond adduct with the protein
What is the main function of diisopropyl fluorophosphate and what inhibition does it use? (DIPF)
Inhibition of acetylcholinesterase
Irreversible
What is AChE?
An enzyme that degrades the neurotransmitter acetylcholine into choline and acetic acid
What classification does DIPF come under?
Organophosphates
Describe the inhibition by aspirin?
Irreversible
- Aspirin acetylates the alpha-amino group of the terminal serine of the enzyme forming a covalent bond
What competitive inhibition?
Where a drug will compete with the substrate for the active site of the enzyme
How do competitive inhibitor alter the kinetics of an enzyme?
You can achieve Vmax but will require more substrate ie Km
What is allosteric inhibition?
Bind to another area of the enzyme, changing the structure and stopping the substrate binding in the active site
What is graphical effect of allosteric inhibition?
Vmax decreases
Km often (but not always) increases
What are the two types of allosteric inhibition?
Mixed and non-competitive
What is the graphical effect of mixed allosteric inhibition?
Vmax decreases due to inhibtion
Km increases as substrate affinity is reduced
What is the graphical effect of non-competitive inhibition?
Vmax decreases due to reduced efficiency of the reaction
Km is unchanged
Example of allosteric inhibition
Phosphofructokinase is inhibited when ATP has high levels due to it having two binding sites, one active and one inhibiting
Example of competitive inhibition
Sulphonamides starve bacteria of essential folic acid by occupying the enzymes that would be binding to 4-aminobenzoic acid as they have a similar structure
Why is anti-freeze poisonous?
It is converted from ethylene glycol into oxalate by alcohol dehydrogenase
How do we treat anti-freeze poison?
Inducing a near-fatal dose of ethanol
Ethanol then competes with ethylene glycol for alcohol dehydrogenase so slows down reaction
