We need them for the “chemistry of life”

The last time you exercised you used lots of oxygen to liberate energy from food molecules like sugars and lipids.  You used that energy to make ATP that was then used to power your muscle contractions.  Every step in this required the help of our little molecular friends the enzymes (remember cellular respiration from your basic Biology class?  Cells get their energy needs met through a complicated series of enzymatic pathways–  also known as metabolic pathways).

Enzymes are biological catalysts (usually made of protein) that are usually very specific to the particular chemical reaction that they speed up or allow to happen.

What’s a catalyst you say!!!   A catalyst is a substance that speeds up a chemical reaction by lowering the activation energy of that reaction– but these catalysts don’t get used up in the reaction…  so, they can do it again and again.

What’s is activation energy you say!!!   I say go look it up!!!!  Let’s just say that enzymes allow many needed chemical reactions to occur inside of us and also allow our bodies to control those reactions so that they happen when we need them to.


The Major Parts of an Enzyme: Active Site and Allosteric Site

  • Every enzyme has what is called an active site.  This is the part of the enzyme that interacts directly with the chemicals involved in the reaction.  The active site has a specific 3 dimensional structure that allows for this interaction  (Another example of anatomy and physiology).
  • Many enzymes also have an allosteric site.  This is a site other than the active site that certain chemicals can bind to and effect the activity of the enzyme (basically, when the chemical binds to the allosteric site the shape of the active site changes leading to an increase or decrease in the activity of the enzyme).
    • Allosteric inhibition:  a chemical has bound to the allosteric site and caused the enzyme to become less effective.
    • Allosteric activation:  a chemical has bound the the allosteric site and caused the enzyme to become more effective.

What is a Metabolic Pathway?

A metabolic pathway is basically a series of enzyme mediated reactions that lead to the production of some important molecule.  Example:  Cellular respiration involves several enzymes in a step by step pathway that ultimately takes the energy from a food molecule and uses it to generate ATP molecules.


Why do We Care?

We care about enzymes for a few fundamental reasons– beyond the fact that we can’t live without them.

  • Genetic Diseases:  One reason we care is that they are the source of several genetic diseases.  If the gene for a specific enzyme is mutated so that we don’t get the right amount of the enzyme made we will have a disease (because too little or too much of some product will be made).
  • Drugs:  Another reason we care is that we can use drugs that interfere in various ways with enzyme function.  One example drug is ibuprofen, an anti-inflammatory drug or NSAID.  When you take an NSAID it helps to decrease inflammation by inhibiting the activity of an enzyme who’s job is to help produce signaling molecules involved with in inflammation (specifically they inhibit cyclooxygenase enzymes that catalyze one of the reactions needed to make prostaglandins).  Other drugs that interfere with enzymes include some drugs for blood pressure and some antibiotics.
  • Poisons:  Many poisons also interfere with enzyme function.  Cyanide for example interferes with one of the enzymes involved in cellular respiration.  Too much cyanide and our body can’t make the ATP needed to stay alive.


Enzyme Images and Explanations

(click on images for larger version)

enzyme diagram with words

enzyme diagram with numbers

Label explanations (for the above image with numbers):

  1.   Enzyme and substrate:  The substrate is the molecule(s) that will undergo some kind of chemical reaction.  (in the above example there is only one molecule involved as a substrate, but there may be more substrates depending on the enzyme).
  2. Enzyme substrate complex:  In this part of the image the substrate has bound to the active site of the enzyme and the chemical reaction is starting to happen.
  3. Enzyme and products: In this part of the image the reaction is over, the substrate has undergone a chemical reaction and become product(s).  Note that the enzyme is unchanged in the reaction… another substrate molecule can now bind and the process can repeat again and again (until we run out of substrate).
  4. Active site:  This is the site on the enzyme that interacts with substrate.  The active site has a specific shape that fits the substrate just right.  In fact it appears that the active site changes shape as the substrate binds…  it also changes shape as it catalyzes the reaction.
  5. Allosteric site:  This is a site different from the active site where other chemicals can interact with the enzyme and alter its activity (inhibit the enzyme or activate it).

******Both the active site and the allosteric site are potential targets for drug therapies!!

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