Enzyme Models and Factors Affecting Enzyme Activity

Similar components to the lock and key model but with a slight difference in mechanism.
Components:
- Enzyme
- Substrate
- Active site
- Enzyme-substrate complex
- Products
The active site can shift to improve the contact between the enzyme and substrate.
Process: Connect → Shift → Reaction → Release.
Involves a slight change in the enzyme to optimize the reaction.

A coenzyme is a helper molecule.
Components:
- Enzyme
- Substrates
- Active sites
- Enzyme-substrate complex
- Products
- Coenzyme
The coenzyme fits into the active site, which alters the shape of the active site to facilitate the reaction.
Coenzymes do not have an active site themselves.
Like enzymes, coenzymes are reusable.
Most vitamins function as coenzymes.
Minerals often act as cofactors that work with enzymes outside the active site.

Several factors can influence enzyme activity, including temperature, pH, and heavy metals.

Increased temperature generally increases the reaction rate until the enzyme becomes denatured.
The reaction rate doubles for every 10 degrees Celsius increase.
Lower temperatures do not destroy enzymes but slow down their reactivity.
Optimum temperature for human enzymes is around 37 degrees Celsius.
High temperatures can denature the enzyme (above 40-42 degrees Celsius).

Enzyme Concentration:
- Increasing enzyme concentration increases the rate of reaction because more active sites are available.
Substrate Concentration:
- Increasing substrate concentration increases the reaction rate until all active sites are fully loaded.
- When all active sites are occupied, the enzyme is saturated, and the reaction rate plateaus.
- Adding more substrate increases the rate only if active sites are available.
- Adding more enzyme can increase the reaction rate even when the substrate concentration is high and the enzyme is saturated.

Each enzyme has a specific pH zone in which it functions optimally.
Enzymes denature if the pH is outside of their optimal zone.
- Pepsin (stomach enzyme) has an optimum pH of 1-2.5 (acidic environment).
- Trypsin (small intestine enzyme) has an optimum pH of 8-8.5 (slightly alkaline environment).
Optimal pH refers to the pH at which the enzyme's activity is at its peak.

Coenzymes are non-protein helpers that assist the catalytic activity of an enzyme.
They do not have an active site of their own.
They fit in the active site of the enzyme, similar to the substrate.
Coenzymes are not destroyed during the reaction and are reusable.
Most coenzymes are vitamins, while most cofactors are minerals.
Cofactors bind outside the active site.
Adding cofactors or coenzymes makes more active sites readily available, enhancing the enzyme's reactivity.
Coenzymes inside the active site make the enzyme more effective, while cofactors outside the active site make the activation site more responsive.

Inhibitors prevent or block enzyme function.
Competitive Inhibitors:
- Compete with the substrate for the active site of the enzyme.
- Similar in structure to the substrate.
- May be products of other reactions that regulate the reaction rate.
- Some, like heavy metals, can be toxins that harm organisms.
- Adding a competitive inhibitor decreases the reaction rate.
- Can be reversible or irreversible.
- Irreversible inhibitors can destroy the active site.
Noncompetitive Inhibitors:
- Bind to a location outside the active site.
- Change the shape of the active site, preventing substrate binding.
Examples of Inhibitors:
- Pesticides (e.g., DDT) inhibit key enzymes in the nervous system.
- Penicillin blocks the active site of an enzyme used by bacteria to make cell walls.
- Antibiotics, drugs, insecticides, herbicides, toxins, and chemical warfare agents often function by inhibiting enzymes.

Adding acid to trypsin lowers the pH, decreasing the reaction rate.
Restoring the pH brings the reaction rate back up.
Lowering the temperature slows down the reaction.
Warming the temperature back up restores the reaction rate.
Temperatures exceeding 45 degrees Celsius typically result in full denaturation.

Enzymes are highly specific to the reactions they catalyze.
Each chemical reaction is catalyzed by a unique enzyme.
- Amylase works on starch.
- Lipase acts on fats.
A gene is the code for a polypeptide, and an enzyme is a tertiary polypeptide.

Enzymes work in a series of steps called metabolic pathways because they are highly specific.
A different enzyme is required for each step.
Cellular respiration is a complex metabolic process requiring many enzymes.

A substrate reacts with an enzyme to produce a product.
That product then becomes a substrate for another enzyme, creating a new product.
Example: Pyruvate → Acetaldehyde → Ethanol, each with a specific enzyme.
- Pyruvate joins with pyruvate decarboxylase, which cuts off a carboxyl group.
- Alcohol dehydrogenase removes or adds a hydrogen to yield ethanol.
A series of enzyme-catalyzed reactions leads to a final product.
Some pathways have multiple branches.
Once a product is made, it can become a substrate for multiple different pathways.

An experiment investigates enzyme activity with a test tube containing substrate solution w and enzyme solutions one, two, and three.
- w + Enzyme 1 → x
- x + Enzyme 2 → y
- x + Enzyme 3 → z
Ways to Increase Production of Product y:
- Add more enzyme two.
- Add more w (to produce more x, which will react with enzyme two to produce more y).
- Add more x (if available).
- Add more enzyme one (to produce more x).
- Ensure pH and temperature are optimal.
- Add necessary coenzymes or cofactors.
- Add a competitive inhibitor to block enzyme three, forcing the pathway to proceed through enzyme two.
If Product y is not formed, but Product z is, an inhibitor was added, which blocked enzyme two without affecting enzymes one or three.