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Lecture 6

Lecture 6 Study Guide

Biological Sciences
Course Code
Mark Fitzpatrick

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Chapter 6: Enzymes
6.3 What are Enzymes?
x The reactions that occur in cells are slow and need catalysts t substances that speed up a
reaction without being permanently altered by that reaction
x Enzymes t specialized group of proteins that catalyze reactions
x Generally, reactions proceed only after the reactants receive enough energy to surpass the
activation energy requirement
x Enzymes are very specific (substrate-specific) and this specificity is determined by the 3D shape
of the enzyme
x Reactants are called substrates t they bind to the active site of the enzyme
x The binding of a substrate to the active site produces an enzyme-substrate complex held
together by one or more means
x The enzyme lowers the activation energy required, offering the reactant an easier path to take
x dZ(]voµ]o]]µu}v[ZvP]v}ZZ(}ÁvZÀµooÇ
sped up
x No difference in free energy between catalyzed and uncatalyzed reactions
6.4 How do Enzymes work?
x Enzymes orient substrates
o Bringing together atoms that will bond and bond only in that orientation
o Example: acetyl CoA and oxaloacetate to form citrate
x Enzymes can stretch the bonds in substrate molecules making them unstable
o Example: lysozyme strains and flattens the polysaccharide substrate
x Enzymes can temporarily add chemical groups to substrates
o Acid-base catalysis t the acidic or basic side chains of the amino acids forming the active
site may transfer H+ ions from the substrate (causing destabilization, and thus breaking
of the covalent bond)
o Covalent catalysis t a functional group in a side chain forms a temporary covalent bond
with a portion of the substrate
o Metal ion catalysis t metals firmly bound to side chains of the enzyme can lose or gain
electrons without detaching from the enzyme
x The active site is specific to the substrate
o The specific choice of substrate depends on a precise interlocking of molecular shapes
and interactions of chemical groups at the active site
o dZ^o}lvlÇ_u}o
x An enzyme changes shape when it binds to a substrate
o This is called induced fit
o Explains why the enzymes are so large t and what the rest of the macromolecule does
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