2.5 Enzymes

KEY CONCEPT Enzymes 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 an enzyme 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 an enzyme at certain places called active sites.

The enzyme brings substrates together and weakens their bonds.

The catalyzed reaction forms a product that is released from 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 Enzymes

!  Inhibitors also can prevent enzymes from working properly Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site.

Enzyme Competitive inhibitor

Substrate

2.5 Enzymes

!  Inhibitors continued… Noncompetitive inhibitors: Inhibitors that 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 active site altered

Noncompetitive Inhibitor

Substrate

2.5 Enzymes

2.5 Enzymes

2.5 Enzymes

2.5 Enzymes

2.5 Enzymes