Summary of 5.5

CONCEPT 5.5: Enzymes are proteins that speed up specific reactions in cells.


Key Terms:

activation energy -- minimum amount of energy required to trigger a chemical reaction
catalyst -- compounds that speed up chemical reactions
enzyme -- the main catalysts of chemical reactions in organisms are specialized proteins
substrate -- a specific reactant acted upon by an enzyme
active site -- the substrate of its into a particular region of the enzyme


Summary:

Enzymes and Activation Energy
* to start a chemical reaction
- need to weaken chemical bonds in the reactant molecules first
--requires molecules absorb energy
--- "start-up" energy for chemical reaction - activation energy
* heat up the mixture of molecules - providing activation energy
- hotter molecules may collide with enough energy to weaken bonds
- cooler molecules collide with less energy
* heating up a cell would cause many unnecessary reactions to occur at once
- cellular reactions depend of the assistance of catalysts
-- main catalysts of chemical reactions in organisms are enzymes
* enzymes doesn't supply activation energy to the reacting molecules
- lowers the energy requirement barrier so that the reaction can proceed at normal cell temperatures
* figure 5-15: enzyme lowers the wall so that frogs have enough energy to reach the other side.


Concept:

1. Explain the role of activation energy in a reaction. How does an enzyme affect activation energy?
Activation energy is a "start-up" energy for starting a chemical reaction. Enzymes affect on activation energy when a cell got heat up and cause many unnecessary reactions to occur at once, including reactions that destroy the cell's delicate structures.


2. Describe how a substrate interacts with an enzyme.
The fit between substrate and enzyme is not rigid. When the substrate enter the enzyme, active site changes shape sligthly which makes fitting substrate more fitly.