Summary of Section 5.5 ;))

-=Enzymes=-

Enzymes and Activation Energy

-to start a chemical reaction:

-it is necessary to weaken chemical bonds in reactant molecules

-this requires for the molecules to absorb energy

activation energy-minimum amount of energy required to start up a chemical reaction

-one way to provide activation energy: heat up the mixture of molecules

-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, including reactions that destroy the cell's structures

-instead, cellular reactions depend on the assistance of catalysts

catalysts: compounds that speed up chemical reactions

enzymes

definition-specialized proteins that are main catalysts of chemical reactions in organisms

-provide a way for reactions to occur at cell's normal temperature

-doesn't supply activation energy to the reacting molecules

BUT

-lowers the energy requirement barrier so that the reaction can proceed at normal cell temperature

-each enzyme catalyzes a specific kind of chemical reaction

-at any moment's of a cell's life, the specific enzymes that are present and active determine which reactions occur

How do enzymes work?

-the shape of each enzyme fits the shape of the particular reactant molecules

substrate-a specific reactant acted upon by an enzyme 

active site-region of an enzyme into which a particular substrate fits

-the fit between substrate and enzyme is not rigid

-as the substrate enters, the active site changes slightly which fits the substrate more comfortably

-this places certain function groups of the active site in position to catalyze the reaction

-the tighter grip may also bend the substrate which bends its bonds

Another way that an enzyme can lower activation energy

-by accepting two substrates into adjacent sites

-holding the reactant together helps them to react more easily

So...

enzymes can catalyze the formation of larger molecules into smaller molecules 

-an enzyme's structure and shape is essential to its function

also...

-an enzyme's shape is sensitive to changes in its surrounding environment

So....

-factors of pH and temperature can greatly affect: 

-how well an enzyme works

-or if it can work at all

this is one reason why cells can only survive within certain conditions

Concept Check:

1.Explain the role of activation energy in a reaction. How does an enzyme affect activation energy?

The activation energy activates the reactants and triggers the chemical reaction. An enzyme lowers the activation energy to a normal temperature. 

2.Describe how a substrate interacts with an enzyme. 

A substrate enters into the active site of the enzyme, the active site changes shape slightly to fit the substrate more snugly. Then the substrate is converted into products.