Enzymes Lecture #8

Chemical Reactions Every chemical reaction Involves both bond breaking and bond forming Initial amount of energy to start reaction = activation energy (EA) REACTANTS PRODUCTS Figure 8.13 H2O H HO OH O CH2OH Sucrase Sucrose Glucose Fructose C12H22O11 C6H12O6 +

What is an ENZYME? Enzymes are proteins Also known as a catalyst speeds up a chemical reaction Lower the amount of energy needed to start a reaction https://www.youtube.com/watch?v=qgVFkRn8f10

Enzymes Are specific for what they will catalyze Are Reusable End in –ase -Sucrase -Lactase -Maltase

How do enzymes Work? Enzymes work by weakening bonds which lowers activation energy

ENZYMES LOWERS THE AMOUNT OF ACTIVATION ENERGY NEEDED  INCREASES SPEED OF REACTION

Progress of the reaction Transition state = bonds in substrates (reactants) are WEAKENED and about to break Free energy Progress of the reaction ∆G < O EA A B C D Reactants Transition state Products Enzymes help “weaken” bonds FASTER  TRANSITION STATE REACHED FASTER!!!

Enzyme Vocabulary The substrate Is the reactant an enzyme acts on The enzyme binds to its substrate, forming an enzyme-substrate complex Enzyme Substrate Joins

Is the region on the enzyme where the substrate binds The active site Is the region on the enzyme where the substrate binds Enzyme Substrate Active Site C B

Substrate Active site Enzyme Figure 8.16 Substrate Active site Enzyme (a)

Induced fit of a substrate “tight” fit  helps weaken bonds FASTER in substrate(s) Weakens bonds  gets to transition state faster http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf

Remember… Proteins (ex: enzymes) are made up of DIFFERENT amino acids sequences (orders) Each amino acid has different functional groups (R groups) Different R groups in active site allow enzyme to bind different substrates

R groups = red POLAR w/ Charges (+ or -) HYDROPHILIC POLAR with NO Charges HYDROPHILIC Non polar HYDROPHOBIC

Enzyme is RECYCLED!!Never used up or destroyed

What Affects Enzyme Activity? Two factors: 1. Environmental Conditions 2. Enzyme Inhibitors

EFFECTS OF TEMPERATURE & pH 1. Environmental Conditions EFFECTS OF TEMPERATURE & pH Enzymes have an optimal temperature and pH in which it can function Figure 8.18 Optimal temperature for enzyme of thermophilic Rate of reaction 20 40 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes typical human enzyme (heat-tolerant) bacteria

(b) Optimal pH for two enzymes 1. Environmental Conditions Enzymes have an optimal pH in which it can function Figure 8.18 Rate of reaction (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) 1 2 3 4 5 6 7 8 9

Denaturation = take away (or lower) the function of protein 1. Environmental Conditions What can destroy enzymes? Denaturation = take away (or lower) the function of protein pH Salt concentration Temperature

Why does pH denature proteins? Excess H+ or excess OH- ions, protein's shape is altered Active site is blocked  enzyme CAN’T bind its substrate Enzyme cannot complete reactions at all or as well H+ H+ H+

Why do salts denature proteins? Excess + or - ions, protein's shape is altered… remember salts are made of ions bonded together! Active site is blocked  enzyme CAN’T bind its substrate Enzyme cannot complete reactions at all or as well Na+ Na+ Cl+

Why does TEMPERATURE denature proteins? Kinetic energy (energy of motion) changes Atoms move differently and bonding in protein is disrupted Higher temperatures = more movement/kinetic energy Atoms in protein move too fast and can’t bond together (ACTIVE SITE IS DESTROYED!) Cold temp’s SLOW DOWN or stop activity because molecular motion decrease

Two examples of Enzyme Inhibitors: Competitive Inhibitors Noncompetitive Inhibitors

2. Enzyme Inhibitors a. Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Substrate Competitive inhibitor

2. Enzyme Inhibitors b. Noncompetitive inhibitors: do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site. Enzyme Substrate Noncompetitive Inhibitor active site altered

Enzyme Inhibitors Ex: Poison/toxins or drugs Competitive inhibitor Noncompetitive inhibitor Enzyme Inhibitors Ex: Poison/toxins or drugs

Let’s Practice… Products Substrate (reactant) Active site Enzyme

Let’s Practice…True/False _______ Enzymes interact with specific substrates _______ Enzymes speed up reactions _______ Boiling temperature will increase the rate of reaction ______ Enzymes increase activation energy _______ Changing the pH will not change the rate of reaction _______ Freezing an enzyme will decrease the rate of reaction True True False False False True