EnzymesOrganic Catalysts

Enzymes are Proteins!• Proteins contain the elements: C, H, O, N• The monomers of proteins are Amino acids

• Facilitate or catalyze chemical reactions in cells– Speed them up– By lowering the activation energy (the energy needed to start the reaction)

– W/O enzymes, chemical reactions would occur too slowly at the temperatures found in organisms to sustain life processes

Characteristics of Enzymes

A Catalyst Analogy*

• You are at the American Museum of Natural History (because you are a science nerd and like to look at Dinosaur Bones

• You need to get to Babo (because you are a big fan of Iron Chef)

• What are your transportation options?

*Analogy provided thanks to Ms.Walker

• You can walk…• If you walk like a New Yorker – about 1 block a minute – you would walk over 80 blocks – so an hour and 20 minutes.

• Longer if you walk like a Livingston High School student on their way to class

• You can take the C from 81st to West 4th St

• Once the train arrives – about 15-17 minutes.

• Less time if you can transfer to the A

A Catalyst Analogy*

*Analogy provided thanks to Ms.Walker

The train is the “enzyme” that catalyzes your transportation

*Analogy provided thanks to Ms.Walker

• 3D shape (tertiary or quaternary) confers specificity to the substrate upon which it binds to facilitate the reaction

• Many enzymes are named after the substrate on which they act and end in

–ase • Sucrase (enzyme) acts upon sucrose (substrate)

Characteristics of Enzymes

• Substrate = Reactant Molecule

• Active site= specific binding site on the enzyme for the substrate to bind to

Lock and Key Model

An exact fit between enzyme and substrate; The enzyme works with one specific

substrate

Induced Fit ModelEnzyme can react with similar substrate molecules to produce the same product; The active site of enzyme undergoes shape change

How Enzymes WorkEnzymes bind to the substrate and weaken the chemical bonds, so less energy is needed for

the reaction to proceed

Factors that affect Enzymes

• Enzymes are affected by their environment• There are optimal conditions for every enzyme

• Optimal conditions = optimal performance• Deviations= Denaturization = Loss of Function– Substrate & Enzyme Concentration– Higher temperatures– Changes in salt concentrations & pH

Substrate Concentration

• Enzymes must “bump into” substrate molecules

• More substrate =more collisions =more enzymes being used=more activity

• At some point activity levels off because all possible enzymes are already in use

Enzyme Concentration

• Again, enzymes must “bump into” substrate molecules

• More enzymes= more collisions = more activity

• At some point all substrates are being broken down and so increasing enzymes no longer increases activity

pH• Every enzyme has an “optimal” pH– a pH at which the enzyme functions most effectively

• Most enzymes in the human body work best between pH 6-8 (near neutral)

Temperature• Every enzyme has an

optimal temperature• Most enzymes in the

human body work best between 35-40˚C (near normal body temps)

• Increase in Temp = increase in molecular collisions = increase in enzyme activity

• However, this only hold true to a point!– Too much heat can denature

the protein and slow activity down or cause loss of function

Energy and Chemical Reactions

What is Energy?• Energy– The ability to do work

• Potential– Stored Energy– Chemical Energy = potential energy of molecules

• Kinetic– Energy of doing work (motion)– Heat

• Energy associated with the movement of molecules

Life Depends on Energy Conversion

Thermodynamics =The study of energy conversions• Two laws govern energy conversion:– First Law of Thermodynamics• The law of energy conservation• Energy can be transferred and transformed, but not created or destroyed

– Second Law of Thermodynamics• Energy conversions reduce order (increase disorder)• Amount of disorder = Entropy

Chemical Reactions• Chemical reactions are involved when energy conversions occur– Atoms are rearranged– Law of Conservation of Matter– Matter is neither created nor destroyed

• The sum of all chemical reactions in an organism– Metabolism

• Chemical reactions either store or release energy

Endothermic and Exothermic ReactionsChemical reactions either store or release energy

• Endergonic Reactions = Endothermic Reactions– Store energy– Yield products high in potential energy– Photosynthesis

• Exergonic Reactions = Exothermic Reactions– Release energy– Potential energy is high in the reactants– Cellular Respiration

Comparing Endothermic and Exothermic

ReactionsExothermic Reaction Endothermic Reactions

Net release of energy as products are formed (often in the form of light or heat)

Net input of energy needed as products are formed

Reactants have more PE than products Reactants have less PE than products

Reactants are less stable than the products

Reactants are more stable than the products

Less energy is needed to start reaction than is released as products are formed

More activations energy is needed than energy released as products form

Includes Cell Respiration and Hydrolysis Includes Photosynthesis and Synthesis

Coupled Reactions

• Many reactions use the energy released from exothermic reactions to drive or fuel endothermic reactions

• These are called “Coupled Reactions”– ATP Regeneration is the main example in cells• The usable energy released by most exothermic reactions is stored in ATP• The energy used in most endothermic reactions comes from ATP

Cellular work is sustained because ATP is a renewable resource that cells can

regenerate