1. Cell Biology: Enzymes Lesson 2 – Factors Affecting Enzyme Activity ( Inquiry into Life pg. 106-109 )

2. Today’s Objectives  Analyze the roles of enzymes in biochemical reactions, including:  Apply knowledge of proteins to explain the effects on enzyme activity of pH, temperature, substrate concentration, enzyme concentration, competitive inhibitors, and non-competitive inhibitors including heavy metals

3. Factors Affecting Enzyme Activity  There are several factors that have an effect on enzyme activity, such as:  1) pH  2) Temperature  3) Substrate concentration  4) Enzyme concentration  5) Competitive inhibition  6) Non-competitive inhibition (ex: heavy metals)

4. 1) pH  Each enzyme operates best at a preferred pH level  Any other pH affects tertiary structure and slows down reactions  Tertiary structure: remember, enzymes are proteins!  Too much of a change in pH stops the reaction  Why?  Recall the tertiary structure of proteins:

5. Tertiary Structure Bonds between amino acids on the polypeptide help maintain the protein’s shape: Hydrogen bonds + electrostatic interactions = “Salt bridges”

6. 1) pH  Since salt bridges depend on ionic charges for their bonding power, anything which neutralizes such a charge will destroy the salt bridge and make the folded structure of the enzyme (protein) less stable  If an enzyme’s normal shape is destroyed, it is said to be “denatured” and is no longer able to combine efficiently with its substrate  An increase of pH will take an H+ from an NH3+ group and neutralize its charge.  A decrease in pH will put an H+ on a COO- and neutralize its charge  This means that each enzyme has an optimum pH which its folded (active) structure its most stable.  It has its maximum catalytic power at that pH  Animation Animation

7. 2) Temperature  Cold temperature slows down enzymatic reactions  Warm temperatures up to around 40 ° C will speed up reactions  High temperatures will denature enzymes and cause reactions to stop  If we increase the temperature of the solution the enzymes are operating in, we will typically see an increase in the reaction rate until a point is reached at which the enzyme starts to unfold  This is a result of breaking hydrophobic bonds and salt bridges between R-groups of the protein as the increase in temperature causes the enzyme’s structure to “wiggle” around  Animation Animation

8. 3) Substrate concentration  The more concentration of substrate, the greater the rate of reaction  If we do a series of experiments where we maintain the same enzyme concentration, but increase the substrate concentration each time, we find that the reaction rate increases as we increase the substrate concentration…..  But eventually a maximum reaction rate will be reached

9. 3) Substrate concentration  Eventually, adding substrate will not increase the reaction rate any further  At this point, we say that the enzyme is saturated  To increase the rate again, we would need to add more enzyme

10. 4) Enzyme concentration  Adding more enzymes will increase the rate of reaction  More catalyst means a faster reaction, so the reaction rate increases  Reaction rate is basically “how much substrate reacts in a particular amount of time” (usually per second)

11. 5) Competitive Inhibition  Some molecules are shaped like a substrate and compete with the substrate for the enzyme’s active site  Example: carbon monoxide (CO) competes with Oxygen (O 2 )

12. 5) Competitive Inhibition  Since some of the enzymes get bonded to the “wrong” substrate (competitive inhibitor), the amount of “correct” product is reduced  Sometimes these molecules bond temporarily with the enzyme, but sometimes they bond permanently  When this happens, the enzyme is rendered useless  If too many important enzymes are inactivated, the organism may die

13. 5) Competitive Inhibition  A molecule which fits into an enzyme’s active site, but doesn’t react with anything there, is called a competitive inhibitor  If this molecule (an inhibitor) is in the active site, a substrate molecule can’t get in, and that particular enzyme molecule is inactive until the inhibitor falls off

14. 6) Non-competitive inhibition  Certain molecules can bond with parts of enzymes (other than the active site) and cause them to change shape (denature)  This bonding is called non- competitive inhibition  Example: Heavy Metals such as Pb 2+ (lead) or Hg 2+ (mercury)

15. 6) Non-competitive inhibition  A molecule that bonds to an enzyme (other than in the active site), causing the enzyme to change it’s shape is called a non-competitive inhibitor  Once the enzyme changes shape, it is inactive (no products can form)  When the molecule bonds to the enzyme, the folding of the enzyme changes a little bit, and the active site is distorted in a way which makes it a less effective catalyst Inhibitor Animation