2.5 Enzymes

KEY CONCEPTEnzymes are catalysts for chemical reactions in living things.

2.5 Enzymes

A catalyst lowers activation energy.

• Catalysts are substances that speed up chemical reactions.– decrease activation energy– increase reaction rate

2.5 Enzymes

Enzymes allow chemical reactions to occur under tightly controlled conditions.

• Enzymes are catalysts in living things.– Enzymes are needed for almost all processes.

– Most enzymes are proteins.– Most enzyme names end in –ase– Enzymes are specific for what they catalyze:

Ex. Sucrase- breaks down sucrose

Lipase- breaks down lipids

Protease- ?

2.5 Enzymes

• An enzyme’s structure allows only certain reactants to bind to the enzyme.

– substrates– active site

substrates (reactants)

enzyme

Substrates bind to anenzyme at certain places called active sites.

2.5 Enzymes

1. An enzyme and a substrate are in the same area.

2. The enzyme grabs onto the substrate with a special area called the active site The active site is a specially shaped area of the enzyme that fits around the substrate. The active site is the keyhole of the lock.

3. Chemical reaction takes place

4. The enzyme lets go. Big idea. When the enzyme lets go, it returns to normal, ready to do another reaction. The substrate is no longer the same. The substrate is now called the product.

2.5 Enzymes

• The lock-and-key model helps illustrate how enzymes function.

– substrates brought together– bonds in substrates weakened

Substrates bind to anenzyme at certain places called active sites.

The enzyme bringssubstrates together and weakens their bonds.

The catalyzed reaction formsa product that is releasedfrom the enzyme.

2.5 Enzymes

Induced Fit Model vs. Lock and Key Model

• Induced Fit Model claims that substrate binding slightly changes the shape of the enzyme.

2.5 Enzymes

• An enzyme’s function depends on its structure. If the shape of the active site is changed, the enzyme no longer functions.

– Enzymes function best in a small range of conditions.– Changes in temperature and pH can break hydrogen

bonds which changes the enzyme’s shape.

– Inhibitors also effect the way enzymes work

2.5 EnzymesInhibitors also can prevent Inhibitors also can prevent enzymes from working enzymes from working properlyproperlyCompetitive Competitive inhibitorsinhibitors:: are chemicals that resembleresemble an enzymeenzyme’’s normal s normal substrate substrate and competecompete with it for the active siteactive site. EnzymeCompetitive inhibitor

Substrate

2.5 Enzymes

Inhibitors continued…Inhibitors continued…Noncompetitive inhibitorsNoncompetitive inhibitors::Inhibitors that do not enter the do not enter the

active siteactive site, but bind to another bind to another part part of the enzymeenzyme causing the enzymeenzyme to change its shapechange its shape, which in turn alters the active alters the active sitesite.

Enzymeactive site altered

NoncompetitiveInhibitor

Substrate

2.5 Enzymes

2.5 Enzymes

2.5 Enzymes

2.5 Enzymes

2.5 Enzymes