Enzymes Flashcards
What are enzymes?
Enzymes are tertiary globular proteins and biological catalysts that lower activation energy. They increase the ROR.
How are enzymes specified?
It’s a feature of the tertiary structure, which is held together by hydrogen, ionic and sometimes disulfide bonds. This determines the shape and electrostatic charges of the active site.
Describe the lock & key model
The active site is fixed and doesn’t change shape. It does not wrap around the substrate as it already fits it and is complementary before binding.
Explain the induced fit model
This occurs when the correct substrate is present but the active site is somewhat altered. The enzyme is flexible and moulds itself around the substrate. The AS allows 2 molecules to come close together, making a reaction more likely.
What is the effect of substrate concentration?
For a given concentration of enzymes, increasing the substrate will increase the ROR until max rate. The ROR initially increases as collisions are more likely, but it then levels out as all AS are occupied by substrate molecules and now ROR is limited by the time required for product to be formed by ESC. Only way to increase ROR is to add more enzymes.
What is the effect of temperature?
- Increases ROR to maximum constant as collisions are more likely due to more kinetic energy.
- More ESC formed
- Increasing above optimum temperature denatures enzymes and alters tertiary structure and AS.
- Slows down reaction as substrates can’t really bind to AS.
- Denaturation above 50c is usually permanent.
What is the effect of pH?
- Denatures enzyme if not its optimum pH.
- Breaks hydrogen and ionic bonds
- Alters tertiary structure and AS so substrates can’t bind.
What does a competitive inhibitor do?
They compete with the substrate to bind with the AS. Has a similar structure to the substrate and decreases ROR as less ESC are formed. Can be reduced by addition of more substrate.
What does a non-competitive inhibitor do?
Attaches to the allosteric site and alters the tertiary structure and AS. The substrate can’t attach/ if it does no product is formed. Doesn’t have a similar structure to substrate. Can’t be reduced by addition of more substrates, decreases ROR. The amount of inhibition is dependant on concentration of inhibitor present.
