Enzymes & their function SBI4U Biology

What is an enzyme? A specialized protein Act as a biological catalysts Catalysts speed up chemical reactions, without taking part in them. (not a reactant). Reusable: after they catalyze one reaction, they can catalyze another.

Reactions & Energy Chemical reactions only occur if the reactants have enough energy to collide, combine & react. It takes energy to break or make chemical bonds in molecules. This minimum required energy is called the Activation Energy. If molecules can’t achieve Activation Energy, no reaction occurs.

Reactions & Energy An enzyme makes it easier for reactions to occur; they stress the bonds, making them weaker & more likely to break. If Activation Energy is like the ‘You Must Be This Tall to Ride’ sign, Enzymes are simply making that line lower.

Reactions & Energy Sometimes you’re not tall enough to ride, while other times you’re too tall!

Activation Energy

Activation Energy

Enzymes as proteins Large molecules with complex structure 1o  4o Structure Creates pits & grooves on surface that smaller molecules, called substrates, can fit in. One main site is called the Active Site. This is where the reaction will occur.

Example of an Enzyme: Active Site Substrate must be the correct shape to fit here.

Lock & Key Model: Induced Fit Model: Enzymes will only react with a substrate that fits correctly, like a lock & key. Induced Fit Model: Unlike a lock & key, the enzyme changes shape slightly to ‘grip’ the substrate better. This conformational change puts stress on the substrate’s bonds, making them easier to break.

Enzyme Action: ENZYME + SUBSTRATE (ENZYME-SUBSTRATE COMPLEX) ENZYME + PRODUCTS

Controlling enzymes: Active Site for Substrate The complex shape of enzymes allows for another site, the Allosteric Site, to play a role in controlling function. Active Site for Substrate Allosteric Site + inhibitor = closed Active Site Allosteric Site + activator = more open Active Site Allosteric Site for Inhibitor or Activator

Controlling enzymes: A more open Active site makes reactions more likely; closed Active sites slow or prevent reactions.

Controlling enzymes: Sometimes a molecule similar in shape to the substrate tries to bind to the enzyme… it ‘competes’ for the Active site, but can’t react. This is Competitive Inhibition. This is like putting the wrong key in a lock: it might fit, but it won’t unlock because it’s not 100% correct in shape.

Controlling enzymes: Enzymes can also regulate their own activity through Feedback Inhibition. In a chain of enzymatic reactions, the final product can attach to the enzyme & shut down the active site, stopping further reactions.

Naming Enzymes Pancreatic Lipase! Old System: -in ending New System: -ase ending. Rule: (Name of Substrate + -ase ending) i.e. Lipid  Lipase i.e. Protein  Protease Alternatively: (Function + -ase ending) i.e. Dehydration reaction  Dehydrase enzyme Pancreatic Lipase!

Sources &Uses of Enzymes: Dairy products Tanning leather Biodegradable plastics Bioethanol Dietary supplements Some enzyme-rich foods include papaya, pineapple, mango, pepper, & tomato. Medical therapy