An Introduction to Enzymes Ms. Gaynor AP Biology https://www.youtube.com/watch?v=vTQybDgweiE

ENZYMES Enzymes are catalytic proteins A catalyst Is a chemical agent that speeds up a reaction without being consumed by the reaction http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

Chemical Reaction Every chemical reaction between molecules Involves both bond breaking and bond forming Figure 8.13 H2O H HO OH O CH2OH Sucrase Sucrose Glucose Fructose C12H22O11 C6H12O6 +

Catabolic vs. Anabolic Reactions CATABOLIC (an exergonic reaction) Reactions that BREAK down LARGE molecules into smaller ones Think: “C” for cut apart (make smaller) RELEASE ENERGY POLYMER  MONOMER Ex: Cellular Respiration (glucose  O2 + ATP) ANABOLIC (an endogonic reaction) Reactions that PUT TOGETHER down SMALL molecules into LARGER ones Think: “A” for add together (make bigger) ABSORBS/NEEDS ENERGY MONOMER  POLYMER Ex: Photosynthesis (sun + CO2 + H2O  Glucose)

EXERGONIC vs. ENDERGONIC Exergonic reaction RELEASE ENERGY (exits) Do NOT need extra energy  occurs spontaneously OCCUR SLOWLY!!! Endogonic reaction ABSORBS/NEEDS ENERGY (INTO) Will NOT happen without ENERGY input NOT SPONTANEOUS!

Activation Energy, EA initial (starting) amount of energy needed to start a chemical reaction Amount of energy needed to “PUSH” reactants over a barrier Determines the RATE of the reaction Proportional to difficulty of breaking bonds All reactions require energy of activation (EA) ENZYMES Lowers the EA barrier so that chemical reactions can more quickly.

The energy profile for a reaction (net release of energy) Uphill= EA required to start reaction. Downhill = the loss of energy by molecules in reaction. DG is the difference in energy of products and reactants. http://www.stolaf.edu/people/giannini/flashanimat/enzymes/transition%20state.swf The energy profile for a reaction (net release of energy) Free energy Progress of the reaction ∆G < O EA A B C D Reactants Transition state Products

Unaffected by enzyme

Substrate Specificity of Enzymes The substrate Is the reactant an enzyme acts on The enzyme Binds to its substrate, forming an enzyme-substrate complex

NOTE: Oxygen gas(O2) forms BUBBLES ENZYME SUBSTRATE (REACTANT) PRODUCTS

Most enzyme-substrate interactions  result of weak bonds. The active site Is the region on the enzyme where the substrate binds Figure 8.16 Substrate Active site Enzyme (a) Most enzyme-substrate interactions  result of weak bonds.

20 Different Amino Acids Proteins (ex: enzymes) are made up of amino acids sequences (orders) Each amino acid has different functional groups (R groups)

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

 Involves carboxyl and amino groups Makes covalent peptide bonds btw amino acids  Involves carboxyl and amino groups Makes hydrogen bonds btw carboxyl and amino groups  Involves R groups Makes hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic or Van Der Waals interactions btw available R groups  Involves R groups Same as tertiary structure http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein%20structure.swf

Induced fit of a substrate “tight” fit  creates a “microenvironment” Enzyme binds to substrate better using amino acid R groups Weakens bonds  gets to transition state faster Figure 8.16 (b) Enzyme- substrate complex http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf

Enzyme is RECYCLED!!Never used up or destroyed

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 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

What factors denature proteins? Denaturation = take away (or lower) the function of protein pH Salt concentration Temperature

Why does pH denature proteins? In either excess H+ or excess OH- ions, protein's shape is altered Active site is distorted/blocked  alters ionic bonds that contribute to its functional shape Enzyme cannot catalyze reactions at all or as well + H+ ( pH)  in acids - +/- +/-

Why does SALT [ ] denature proteins? REMEMBER: SALTS are IONIC COMPOUNDS!!! THEY HAVE +/- ions In either excess + or excess - ions, protein's shape is altered R-groups/side chains of amino acids  distorted/blocked by affecting ionic bonding Enzyme cannot catalyze reactions at b/c it forms a precipice Less salt= R groups form extra bonds with each other More salt= disrupt R groups from normal bonding patterns

Why does TEMPERATURE denature proteins? Kinetic energy changes with temperature Atoms move differently and affects the bonding patterns that hold the protein together A higher temperature generally results in increase activity b/c molecular motion increases resulting in more molecular collisions If, however, temp rises above a certain point, the heat will denature  molecules move too fast and can’t H-bond Cold temp’s SLOW DOWN or stop activityb/c molecular motion decrease

[Enzymes] http://www.sumanasinc.com/webcontent/animations/content/proteinstructure.html Denaturation and eggs

[SUBSTRATE] ALSO EFFECTS ENZYME ACTIVITY If [ ] of enzyme is constant… at lower [substrate]  [substrate]= limiting factor As [substrate] increases, RATE of enzyme activity also increases However, at very high [substrate]  enzymes become saturated with substrate and a higher concentration of substrate does NOTHING to increase the reaction rate All the enzymes are already in use

Cofactors Cofactors Are non-protein enzyme helpers Bind to active site to enhance enzymatic rxns Cofactors may be inorganic metals such as zinc, iron, or copper. Coenzymes Are organic cofactors Coenzymes example= vitamins

Enzyme Inhibition Competitive inhibitors Non-competitive inhibitors mimic the substrate and compete for the active site. Non-competitive inhibitors bind to the enzyme away from the active site, and indirectly cause a change in the active site (i.e.-changing the function) https://www.youtube.com/watch?v=PILzvT3spCQ https://www.youtube.com/watch?v=VQVPlmzf-iY

Enzyme Inhibitors

Allosteric Enzymes A specific type of enzyme https://www.youtube.com/watch?v=d5fDEUhjo-M A specific type of enzyme Helps regulate cell processes Can change their conformational shape Have 2 states (ACTIVE vs. INACTIVE)

Allosteric Enzymes

Stabilized active form Cooperativity Is a form of allosteric regulation that can amplify enzyme activity Figure 8.20 Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation. Substrate Inactive form Stabilized active form (b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate. https://www.youtube.com/watch?v=fyww37XOrXo

Cooperativity