Unit 1: Biochemistry - #7 Structure and Function of Enzymes (copy)

What is an Enzyme?

• Biological catalysts that increase the speed of biochemical reactions within cells. 

• Enzymes are proteins that are NOT consumed during reactions 

• They can catalyze the same reaction repeatedly 

• Each enzyme has a unique shape, which determines which reactions it catalyzes 

Induced Fit Hypothesis

• Initially the active site is not a direct fit for the substrate 

• Just prior to substrate binding, the enzyme modifies its shape to better accommodate the substrate 

• The enzyme binds to the substrate 

• Creates an enzyme-substrate complex 

• Enzyme converts substrate into product(s)

List the factors that affect Enzyme Activity

1. Enzyme and Substrate Concentration

2. Enzyme Inhibitors

3. pH and Temperature

Enzyme and Substrate Concentration

• If excess substrate, rate of reaction becomes proportional to enzyme concentration 

• If enzyme at a constant concentration, increasing substrate concentration will only increase reaction rate to a point called saturation level 

• At this point, all enzyme molecules saturated with substrate 

What are Enzyme Inhibitors? List the two types of inhibition

• Molecules that bind to an enzyme and lowers the rate at which it catalyzes a reaction 

• Competitive and Non-Competitive

Competitive Inhibitors

• Compete with the substrate for the enzyme’s active site 

• Shape/Mimics substrate 

• Enter the enzyme’s active site and prevent the normal substrate from binding

Non-Competitive Inhibitors

• Does not compete for active site 

• Attaches to enzyme on a site other than the active site (allosteric site) 

• Causes the enzyme to change shape, so that active site looses affinity for its substrate

KEEP GOING!!

Feedback Inhibition

• A product of a reaction acts as a regulator of the reaction 

• Used by cells to control metabolic pathways involving series of reactions 

• If the product accumulates in excess, its effect as an inhibitor automatically slows or stops the enzymatic reaction that produces it.

• If the product is scarce, the inhibition is reduced, and the rate of the reaction increases.

• Product formed later in sequence allosterically inhibits the enzyme catalyzing the first reaction of the pathway 

• Each reaction catalyzed by specific enzyme 

Temperature

• As temperature increases beyond a critical point, enzymes denature 

• Every enzyme has an optimal temperature at which it works best (humans -37 C)

pH

• Enzymes have optimal pH range 

• Eg. Pepsin works best at pH of 2 in stomach, inactive in small Intestine pH of 8