6-1 MECHANISTIC CHEMISTRY
Introduction

Mechanisms of enzyme-catalyzed reactions have been devised using…
o
_______________ experiments
o protein _______________ studies
o studies of _______________ model reactions

Extraordinary catalytic ability of enzymes results from simple _______________ and
_______________ properties, including the _______________ and proper
_______________ of reactants in the active sites of enzymes.

_______________, _______________, and _______________ have contributed to the
understanding of enzyme mechanisms.
Mechanisms

A detailed description of the _______________, __________ and even
_______________ events that occur during a reaction.

Lab techniques include…
o _______________ labeled reactants that can be used to trace the path of
individual atoms
o kinetic techniques measure the changes in the chemical __________ of a reactant
or solvent during the reaction
o studying _______________ changes that give a 3D view of the process

Mechanistic information about the reactants and intermediates must be coordinated with
the ___-___ structure of the enzyme.

The movement of _______________ is represented by __________, and is the key to
understanding enzymatic reactions.
Nucleophilic Substitution

Nucleophiles and electrophiles are ionic intermediates:
o Electron-rich: _______________ (has a __________ charge or lone pairs)
o Electron-poor: _______________

During nucleophilic substitution, _______________ usually attack _______________
with their lone pairs, called nucleophilic _______________.
o For example:
o The dissociation of the tetrahedral intermediate (displacement of the leaving
group) is the rate-determining step:
R=k[
]
o Therefore, there is one reactant molecule in the rds, making it an _____
mechanism.
o Serine proteases use _____ mechanisms.

Another version of nucleophilic attack involves the making and breaking of two covalent
bonds in the transition state:
o The formation of the transition state is the rds:
R=k[
][
]
o Therefore, there are two reactant molecules in the rds, making it an _____
mechanism.
Cleavage Reactions

Covalent bonds can be cleaved in two ways:
o Both electrons stay with one atom. For example…

_______________ formation:

_______________ formation:
o One electron remains with each product. For example…

__________-_______________ formation:

This is not very common in biochemistry.
Oxidation – Reduction Reactions

Redox reactions are the central to the supply of biological __________.
o Oxidation: __________ of electrons. Causes the _______________ of the other
reactant, so it is known as the _______________ agent (__________ electrons).
o Reduction: __________ of electrons. Causes the _______________ of the other
reactant, so it is known as the _______________ agent (__________ electrons).

Examples:
o _______________ catalyze redox reactions.
o _______________, or the removal of hydrogen, is the most common form of
biological oxidation, and is catalyzed by _______________.