Enzymes Flashcards
Enzymes are _____ proteins with a specific _____ structure held together by ________ bonds, __________ _______, ______ bonds and _____________ interactions
Globular, tertiary, hydrogen, disulphide bridges, ionic, hydrophobic
What does “enzymes act as biological catalysts” mean?
They speed up the rate of metabolic reactions by lowering the activation energy
Where can enzymes work?
Inside our cells (intracellular) or outside our cells (extra cellular)
What are the 2 ways enzymes can catalyse metabolic reactions?
Anabolic reactions (a for adding) eg making a disaccharide
Catabolic reactions (c for cutting) eg breaking down a disaccaride
What are the 2 main models for enzyme action?
Lock and key model
Induced fit model
Describe how the lock and key model works
- The substrate molecule fits into the active site of the enzyme molecule like a key fitting into a lock as they are complementary shapes.
- This forms the enzyme substrate complex.
- The product is then formed.
- As it no longer fits into the active site it is released
Describe how the induced fit model works
- The substrate and the active site of the enzyme are not complementary shapes
- When a substrate molecule binds to the active site, the active site changes shape and fits itself around the substrate
- This places a strain on the substrate molecule and distorts a particular bond, lowering the active energy required to break the bond
- The products are formed and leave the active site which then returns to its original shape
What is an example of an induced fit enzyme?
Lysozyme
How does the enzyme lysozyme help to kill bacteria?
It catalyses the hydrolysis of sugars in the peptidoglycan cell walls. Cell walls are weakened. Water moves into the bacteria by osmosis causing them to burst. Found in secretions eg tears, saliva, human milk and in lysosomes.
State and explain the 3 properties of enzymes
- Specific due to sequence of amino acids that make up their active site
- Fast acting with very high turnover number They convert many molecules of substrate per unit time
- Soluble as hydrophilic R groups are found on the outside of the molecule
Describe and explain enzyme controlled reaction graphs
Pages 5 and 6 of notebook
What are the 5 factors that can affect the rate of an enzyme controlled reaction?
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
- Inhibitors
Describe the effect of increasing temperature on enzyme action
- Low temp - rate of reaction is low as enzymes and substrate molecules have low kinetic energy
- Increasing temp up to optimum - increases rate of reaction as enzyme and substrate molecules have more kinetic energy increasing the chance of successful collisions. More enzyme substrate complexes are formed
- Above optimum - rate of reaction decreases as molecules have more kinetic energy. Increasing vibrations begin to break hydrogen bonds, changing the tertiary structure of the enzyme which alters the shape of the active site so it is no longer complementary to substrate so less enzyme substrate complexes can form.
At very high temperatures - rate of reactions falls to 0 as enzymes are denatured. Active site is permanently distorted by irreversible breaking of hydrogen bonds. No enzyme substrate complexes can form as substrate and active site no longer complementary shapes
What may happen if there is an extreme change in the pH?
It may alter the electrostatic charge on the side chains of the amino acids. The active site and the substrate may both have the same charge and the enzyme will repel the substrate.
Why would you add a buffer to an enzyme controlled reaction?
To maintain a constant pH
