Enzymes: Biological Catalysts

Substrate: The Molecules that will undergo the reaction.
An enzyme lowers the activation energy required for new bonds to form: How? -bringing two substrates together in the correct orientation. -or by stressing particular chemical bonds of a substrate
Enzymes are not changed or consumes in reactions and therefore can be used over and over again.
Enzyme names usually end in “–ase”
Thousands of different kinds of enzymes are known, each catalyzing one or a few specific chemical reactions
1. Different types of cells contain different sets of enzymes, and this difference contributes to structural and functional variations among cell types
Most Enzymes:
1. Have one or more pockets or clefts, called active sites , on their surface
  1. Substrates bind to the enzyme at these active sites--> formi an enzyme–substrate complex.
    1. What Happens?
      1. A substrate molecule fits precisely into an active site, the amino acid side groups of the enzyme end up very close to certain bonds of the substrate and these side groups interact chemically with the substrate, usually stressing or distorting a particular bond and consequently lowering the activation energy needed to break the bond
Can form: Multienzyme Complexes
1. =Several enzymes catalyzing different steps in a sequence of reactions.
2. Noncovalently bonded
Nonprotein Enzymes
1. RNA molecules catalyzed in cells by RNA itself
  1. Ribozymes=
    1. Perform Intramolecular and Intermolecular catalysis.
Increasing the temperature of an uncatalyzed reaction increases its rate because the additional heat increases random molecular movement.
1. The rate of an enzyme-catalyzed reaction also increases with temperature, but only up to a point called the optimum temperature
  1. Higher? Protein denatures.
Characteristics:
Inhibitors and Activators
1. Inhibitor: A substance that binds to an enzyme and decreases its activity
  1. Competitive Inhibitor:
    1. Competes with the substrate for the same active site, occupying the active site and thus preventing substrates from binding
  2. Noncompetitive Inhibitor:
    1. Binds to the enzyme in a location other than the active site, changing the shape of the enzyme and making it unable to bind to the substrate
    2. Most noncompetitive inhibitors bind to a specific portion of the enzyme called an Allosteric site.
      1. A substance that binds to an allosteric site and reduces enzyme activity is called an allosteric inhibitor
2. (Allosteric) Activator: binds to allosteric sites to keep an enzyme in its active configuration, thereby increasing enzyme activity
Cofactors
1. Metal ions that are often found in the active site participating directly in catalysis.=
2. When the cofactor is a nonprotein organic molecule, it is called a coenzyme
3. In numerous oxidation–reduction reactions that are catalyzed by enzymes, the electrons pass in pairs from the active site of the enzyme to a coenzyme that serves as the electron acceptor. The coenzyme then transfers the electrons to a different enzyme, which releases them (and the energy they bear) to the substrates in another reaction. Often, the electrons combine with protons (H+) to form hydrogen atoms. In this way, coenzymes shuttle energy in the form of hydrogen atoms from one enzyme to another in a cell.

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Enzymes: Biological Catalysts

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