Energy, ATP, and Enzymes

Energy - the ability to do work, that is, to move matter against opposing forces such as gravity and friction

Thermodynamics - the study of energy transformation

Free Energy - the portion of a system's energy that can perform work Exergonic Reaction - a process with a net release of free energy Endergonic Reaction - a process which absorbs free energy from the surroundings Energy Coupling - the use of an exergonic process to drive an endergonic process Types of Cellular Work

Useful and much more detailed links

ATP - Power To Drive Cellular Work

ATP - Adenosine triphosphate - a close relative to Adenine, a nucleotide found in DNA.

Enzymes and Chemical Reactions

Catalyst -  a chemical agent that changes the state of a reaction without being consumed in the reaction
Substrate - reactants in an enzyme-catalyzed reaction
Intermediates - compounds formed between initial reactants & products (i.e. enzyme-substrate complex)
Products - products
Cofactors- helpers for enzymes (carry e-)
Energy Carriers - sources of quick energy (ATP)

Enzymes are protein catalysts

How Energy Relates to Reactions

Any reaction requires some energy to overcome the activation energy barrier

Enzymes are Substrate Specific

Enzyme Activity Animation

Active Site, Lock and Key, and Induced Fit Animation

The Catalytic Cycle of an Enzyme

A Cell's Physical and Chemical Environment Affect Enzyme Activity

Most Enzymes are Regulated

Competitive Inhibition

  • Active sites are specific - only the substrates can fit... usually
  • Sometimes, usually simply due to some accident of molecular geometry, other molecules not involved in the reaction can fit into the active site an enzyme
  • When this other molecule is present, it can interfere with substrate binding, slowing down the reaction rate
  • This is known as competative inhibition - the other molecule is "competing" for space on the active site

Allosteric Regulation

  • Regulatory molecules (ligands) may bind to a location other than the active site
  • This other binding site is known as the allosteric site
  • Binding of a ligand to the allosteric site changes the shape of the enzyme
    • If the shape change makes the active site available (i.e. turns the enzyme on), this is known as allosteric activation
    • If the shape change makes the active site unavailable (i.e. turns the enzyme off), then this is known as allosteric deactivation or non-competative inhibition
  • Many, if not most, enzymes are allosterically regulated

The Control of Metabolism

In many cases, the molecules that naturally regulate enzyme activity behave like reversible noncompetitive inhibitors


Feedback Inhibition in the Regulation of Threonine Deaminase