1. Mr. Safford’s Biological Sciences

2.  All enzymes are globular proteins thus spherical in shape  Control biochemical reactions in cells  They have the suffix "-ase"

3.  Intracellular enzymes are found inside the cell  Extracellular enzymes act outside the cell (e.g. digestive enzymes)  Enzymes are catalysts → speed up chemical reactions  Reduce activation energy required to start a reaction between molecules  Substrate molecules (reactants) are converted into products  Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action)  Enzymes catalyze a reaction at max. rate at an optimum state

6.  Lock and key theory  Only one substrate (key) can fit into the enzyme's active site (lock)  Both structures have a unique shape  Enzyme is not used (reusable) up in the reaction (unlike substrates)

8.  Let’s See it in Action! Let’s See it in Action!

9. 1. Changes in pH  Affect attraction between substrate and enzyme  Ionic bonds can break and change shape → enzyme is denatured  Charges on amino acids can change → Enzyme Substrate complex cannot form  Optimum pH (enzymes work best)  pH 7 for intracellular enzymes  Acidic range (pH 1-6) in the stomach for digestive enzymes (pepsin)  Alkaline range (pH 8-14) in oral cavity (amylase)

10. 2. Temperature Increased Temperature  Increases speed of molecular movement → increased chances of molecular collisions → more ES complexes  Enzymes have optimum temp. for their action (usually 37°C in humans)  Just above ≈42°C, enzyme is denatured due to the breaking Hydrogen bonds and higher temps. break covalent bonds  Denaturation -the loss of appropriate structure rendering the enzyme inactive.  Shape is changed → active site can't be used, ever again

12. Decreased Temperature  Enzymes become less and less active, due to reductions in speed of molecular movement  Below freezing point  Inactivated, not denatured  Regain their function when returning to normal temperature

13.  A typical graph of rate against temperature might look like this:

14. 3. Concentrations of Substrate and Enzyme

15. 4. The presence of inhibitors  Enzyme inhibitors are substances which alter the catalytic action of the enzyme and consequently slow down, or in some cases, stop catalysis.  three common types of enzyme inhibition –  Competitive-compete for active site  Non-competitive- bind to enzyme somewhere other than the active site and change the active site