Monday, October 27, 2008

Chapter 8 Enzymes

Section 8.4 Enzymes
Catalysts: are substance that can change the rate of a reaction without being altered themselves in the process.
Enzymes are proteins that are biological catalysts.

  • Enzymes= speed up reactions by lowering amount of energy needed for reaction to occur. * NO ENERGY IS ADDED
  • Protein with a specific sites.
- Have active sites
  • Both catabolic (polymer) & anabolic (monomer)

  • Enzymes can be recycled and re-used
The activation energy of a reaction is the amount of energy it takes to start s reaction (amount of energy it takes to break bonds or reactant). The reactant that the enzyme acts on is called the substrate.

Structure of Enzyme
Enzyme has an active site where the substrate binds.

  • The enzyme and substrate form a complex called enzyme- substrate complex, which is then converted into products. The products are released from the enzyme.
- Products are the result of substrates binding to the enzyme.
-Ex. If the substrate binds in one piece then the result could be two products or if the substrate is in two pieces then the product could be one. (This is a simple example).

Each Enzyme has an optimal temperature and pH
There are some substances that inhibit the actions of enzymes.

  • Competitive inhibitors: are reversible inhibitors that compete with the substrate for the active site on the enzyme.

  • Noncompetitive inhibitors: bind to other site on the enzyme (not the active site)

- Result of binds is that it changes the shape of enzyme= preventing substrate or competitive inhibitor from binding.

* Competitive and Noncompetitive can NEVER work together to take over an enzyme.

Section 8.5 Regulation of enzyme activity help control metabolism
Many enzymes regulators bind to an allosteric site (specific site) on the enzyme away from the active site.

  • Bound= either stimulate or inhibit enzyme activity.
Cooperativity: is the binding of one substrate molecule, which can stimulate the binding or activity at other active sites.
  • This mechanism amplifies the response of enzymes to substrates.
In feedback inhibition, the end product of a metabolic pathway allosterically inhibits the enzyme for a previous step in the pathway.

is the immediate source of energy that drives most cellular work.
  • The 3 main kinds of work are:
  1. Mechanical work

  • Examples:

- Muscle contractions
- Movement of chromosomes during cellular reproduction.

2. Transport work

  • Examples:

- Pumping of substances across the membrane

3.Chemical work.

  • Examples:

- Pushing of endergonic reactions

- Synthesis of polymers from monomers

* All enzymes are proteins but all proteins are not enzymes.

Multiple choice questions

1. Which of the following characteristics are not associated with allosteric regulation of an enzyme's activity?
a. A mimic of the substrate competes for the active site.
b. A naturally occurring molecule stabilizes a catalytically active conformation.
c. Regulatory molecules bind to a site remote from the active site.
d. Inhibitors and activators may compete with one another.
e. The enzyme usually has a quaternary structure.

2. If an enzyme has been inhibited noncompetitive,
a. The delta G for the reaction it catalyzes will always be negative.
b. The active site will be occupied by the inhibitor molecule.
c. Raising substrate concentration will increase inhibition.
d. More energy will be necessary to initiate the reaction.
e. The inhibitor molecule may be chemically unrelated to the substrate.

3. The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs?
a.The allosteric inhibitor binds to the active site, preventing the substrate from binding.
b.The allosteric inhibitor causes free energy change of the reaction to increase.
c.The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.
d.The allosteric inhibitor lowers the temperature of the active site.
e.The allosteric inhibitor binds to the substrate and prevents it from binding at the active site.


1.a, 2.e, 3.c

Created by Alyssa Hamilton

No comments: