Human Biology (Enzyme Activity) Flashcards
What is an enzyme?
Organic biological catalysts, that speed up reactions in the body without changing their form.
How do enzymes work (in relation to the activation energy)?
By decreasing the activation energy (which is the energy required to start the reaction), and allow chemical reactions to occur at a suitable rate.
What model is used to describe enzyme activity
Lock and Key Model:
Suggests that an enzyme’s function depends on its shape. That an enzyme as it attaches to its substrate is like a lock and key fitting together.
The shape of the enzyme’s active site (the site at which the substrate binds to the enzyme), is complementary to the shape of the substrate, and every enzyme is specific to its substrate.
After the reaction has occurred, the substrate no longer fits onto the active site and escapes into the surrounding medium, leaving the enzyme free to work with other substrates.
What are the parts involved in Enzyme activity?
Substrate: The reacting substance that the enzyme acts on.
Active Site: The point where the enzyme and substrate bind.
Enzyme-substrate complex: Result of the enzyme being attached to the substrate. (At the active site).
State the process of enzyme activity?
- The substrate binds to the enzyme at the active site and forms an enzyme-substrate complex.
- The substrate is either joined together into 1 piece (Anabolism), or is broken down (Catabolism).
- The shape of the substrate now has changed depending on the reaction that occurred, and no longer is able to fit into the active site.
- As the enzyme has not changed shape and the product is no longer complementary, the enzyme can work on another substrate and repeat the process.
Factors affecting enzyme activity?
- Temperature
- pH
- Enzyme Concentration
- Substrate Concentration
- Inhibitors
- Cofactors and Co-enzymes
How does temperature affect enzyme activity?
As the temperature increases, the enzyme activity increases, because there is a rise in heat which is a rise in the movement of particles. This occurs until the optimal point at ~ 40° at which the temperature continues rising and the enzyme is becoming overheated. The enzyme begins to denature and changes shape making it no longer complementary to the substrate reducing enzyme activity, which will result in the death of the cell.
pH and enzyme activity
Enzymes are pH sensitive, meaning that they will work only within a certain range of pH levels.
Extreme pH levels will result in the denaturing of the enzyme which will cause the active site to no longer be complementary to the substrate and reduce enzyme activity.
How does enzyme concentration affect enzymatic activity?
As the concentration of enzyme increases the rate of reaction increases, assuming the reaction is not limited by other factors.
Substrate concentration and enzyme activity
As the concentration of substrate increases, the rate of enzyme action increases to a maximum limiting value which occurs when the amount of enzyme becomes a limiting factor. When there is more substrate than enzyme, and every enzyme is in use this is known as ‘saturation’. Conversely, if there the products are not removed, then it will be harder for the enzyme and substrate to meet reducing enzyme activity.
Co-factors and co-enzymes
Cofactors are inorganic molecules that help make the fit between enzyme and substrate.
e.g. Calcium and Magnesium
Coenzymes are organic molecules that aid in the process of enzyme activity.
e.g. Vitamin A and Vitamin B
More cofactors and co-enzymes increase enzyme activity.
Inhibitors
Inhibitors are poisons that try to compete for the active site and stop substrates from attaching, or they try to completely block the active site.
Examples of competitive inhibitors: sulfonamide drugs
Examples of blockage inhibitors: Arsenic, DDT, Lead, Cyanide
What is saturation?
When there is more substrate than enzyme, and every enzyme is in use this is known as ‘saturation’.
