HOW ENZYMES FUNCTION © 2012 Pearson Education, Inc.

Figure 5.13A_1 Activation energy barrier Reactant Products Without enzyme Energy

What is activation energy?  The energy barrier that must be overcome before a chemical reaction can begin © 2012 Pearson Education, Inc.

How do cells overcome the energy barrier in order for a reaction to occur?  The use of ENZYMES!!!! (Catalysts) © 2012 Pearson Education, Inc.

Figure 5.13A Activation energy barrier Reactant Products Without enzyme With enzyme Reactant Products Enzyme Activation energy barrier reduced by enzyme Energy

Figure 5.13Q Reactants Products Energy Progress of the reaction a b c Which line represents an enzyme-catalyzed reaction?

What are some key features of enzyme activity?  biological catalysts that lower the E A needed for a reaction to begin,  increase the rate of a reaction without being consumed by the reaction, and  are usually proteins, although some RNA molecules can function as enzymes (ribozymes). © 2012 Pearson Education, Inc.

Animation: How Enzymes Work Right click on animation / Click play

Enzymes are very selective and specific in their activity…  The specific reactant that an enzyme acts on is called the enzyme’s substrate.  A substrate fits into a region of the enzyme called the active site.  Enzymes are specific because their active site fits only specific substrate molecules.  Tertiary structure accounts for the specificity © 2012 Pearson Education, Inc.

5.14 A specific enzyme catalyzes each cellular reaction  The following figure illustrates the catalytic cycle of an enzyme. © 2012 Pearson Education, Inc.

Figure 5.14_s1 1 Enzyme (sucrase) Active site Enzyme available with empty active site

Figure 5.14_s2 2 1 Enzyme (sucrase) Active site Enzyme available with empty active site Substrate (sucrose) Substrate binds to enzyme with induced fit

Figure 5.14_s Enzyme (sucrase) Active site Enzyme available with empty active site Substrate (sucrose) Substrate binds to enzyme with induced fit Substrate is converted to products H2OH2O

Figure 5.14_s Products are released Fructose Glucose Enzyme (sucrase) Active site Enzyme available with empty active site Substrate (sucrose) Substrate binds to enzyme with induced fit Substrate is converted to products H2OH2O

They physically position their substrates (reactants) in orientations that increase the likelihood of chemical bonds being broken or formed. They do NOT participate in the reaction, they set the stage for it! 5 How do enzymes help to lower the activation energy needed for a reaction to occur?

Explain the role of cofactors and coenzymes  Groups of atoms that bind to the enzyme for proper functioning  Organic coenzymes (vitamins) or inorganic co-factors (minerals)  Ex: DNA interaction enzymes require Zinc 2+  Ex: NAD and FAD carry electrons

Common Cofactors and Coenzymes

Table 5.UN05

How does substrate concentration affect enzyme activity?  Enzyme rate will increase and then remain constant (assuming constant amount of enzyme)

How does enzyme concentration affect enzyme activity?  Assuming that there is always substrate available…enzyme rate will increase!

How does temperature affect enzyme activity?  Temperature affects molecular motion.  Optimum temperature = maximum rate of activity  Below = slow movement  Above = denaturation

How does pH affect enzyme activity?  Optimum pH varies  Denaturation occurs both above and below optimum

Figure 8.14 Metabolic Pathways

Why is it important that metabolic pathways (enzyme activity) are regulated? Thousands of chemical reactions are occurring in cells simultaneously. Regulation of enzymes and thus reaction rates helps maintain internal homeostasis.

Figure 5.15A Substrate Enzyme Allosteric site Active site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

 Competitive inhibitors –block substrates from entering the active site and –reduce an enzyme’s productivity. © 2012 Pearson Education, Inc.

 Noncompetitive inhibitors (Allosteric Regulation) –bind to the enzyme somewhere other than the active site, –change the shape of the active site, and –prevent the substrate from binding. © 2012 Pearson Education, Inc.

5.15 Enzyme inhibitors can regulate enzyme activity in a cell  In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called feedback inhibition.  Can be positive or negative feedback © 2012 Pearson Education, Inc.

Figure 5.15B Feedback inhibition Starting molecule Product Enzyme 1 Enzyme 2 Enzyme 3 Reaction 1 Reaction 2 Reaction 3 A B C D

How can we measure enzyme activity?  Appearance of a Product  Disappearance of a substrate  Indirect Ways: Ex: Color Change, Change in Temp, Bubble formation

Figure 5.UN02 ATP cycle ATP ADP P Energy from exergonic reactions Energy for endergonic reactions