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BCH 361 EXAM PREP WITH COMPLETE SOLUTION
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BCH 361 EXAM PREP WITH COMPLETESOLUTION
The specificity of an enzyme is due to the precise interaction of the substrate with the enzyme.
This precision is a result of - =the intricate three-dimensional structure of the enzyme protein.
Enzymes are the ____ of biological systems - =catalysts
Catalysts are chemicals that - =enhance the rate of the reaction without permanently being
affected themselves
______________ whose active site can be modified by environmental signals - =allosteric
enzymes
Enzymes are characterized by their _____ and _______ and ________. - =catalytic power;
specificity to substrate; type of reaction
Enzymes are specific both in the _____ they catalyze and in their choices of _______ -
=reactions; substrate
Proteolytic enzymes catalyze the hydrolysis of _______. What is the reverse reaction? -
=hydrolysis of peptide bonds (aid in digestion and degradation of proteins).
-The reverse reaction is peptide bond formation, the forward reaction (hydrolysis) is
thermodynamically favored, but very slow without enzymes.
Enzymes speed up the rate of chemical reactions, but
Enzymes do not alter the - =free energy change ΔG of a reaction.
Oxidoreductases - =These enzymes transfer electrons between molecules. In other words,
these enzymes catalyze oxidation-reduction reactions.
,Transferases - =These enzymes transfer functional groups between molecules.
Aminotransferases are prominent in amino acid synthesis and degradation, where they shuffle
amine groups between donor and acceptor molecules.
Hydrolyases - =A hydrolyase cleaves molecules by the addition of water. Trypsin, the proteolytic
enzyme already discussed, is a hydrolyase.
Lyases - =A lyase adds atoms or functional groups to a double bond or removes them to form
double bonds.
Isomerases - =these enzymes move functional groups within a molecule
Ligases - =Ligases join two molecules at the expense of ATP hydrolysis. Ex: DNA ligase
An enzyme without its cofactor is referred to as an - =apoenzyme the complete, catalytically
active enzyme is called a holoenzyme
Cofactors can be subdivided into two groups: - =(1) small organic molecules, derived from
vitamins, called coenzymes and (2) metals. Tightly bound coenzymes are called prosthetic
(helper) groups.
Co-substrate = loosely bound
Free energy (G) is a thermodynamic property that is a measure of useful energy, or energy that
is capable of doing work. To understand how enzymes operate, we need to consider only two
thermodynamic properties of the reaction: - =(1) the free-energy difference (ΔG) between the
products and the reactants and (2) the free energy required to initiate the conversion of
reactants into products. The former determines whether the reaction will take place
spontaneously, whereas the latter determines the rate of the reaction. Enzymes affect only the
latter.
,A reaction can take place spontaneously only if - =ΔG is negative. "Spontaneously" in the
context of thermodynamics means that the reaction will take place without the input of energy
and, in fact, the reaction releases energy. Such reactions are said to be exergonic.
A reaction cannot take place spontaneously if ΔG is - =positive. An input of free energy is
required to drive such a reaction. These reactions are termed endergonic.
In a system at equilibrium, there is no net change in the concentrations of the products and
reactants, and ΔG is - =zero
The ΔG of a reaction depends only on the free energy of the products (the final state) minus -
=the free energy of the reactants (the initial state). The ΔG of a reaction is independent of the
path (or molecular mechanism) of the transformation. The mechanism of a reaction has no
effect on ΔG.
The ΔG provides no information about the rate of a reaction. - =A negative ΔG indicates that a
reaction can take place spontaneously, but it does not signify whether it will proceed at a
perceptible rate.
It is important to stress that whether the ΔG for a reaction is larger, smaller, or the same as
ΔG°′ depends on - =the concentration of the products and reactants
An enzyme cannot alter the laws of thermodynamics and consequently cannot alter - =the
equilibrium of a chemical reaction
Enzymes accelerate the attainment of equilibria but do not shift their positions. The equilibrium
position is a function only of - =the free-energy difference between reactants and products.
the transition state has one of the highest - =free energy
, The difference in free energy between the transition state and the substrate is called the -
=activation energy
enzymes function to lower the activation energy. In other words - =enzymes facilitate the
formation of the transition state
enzymes facilitate the formation of the transition state by - =lowering the activation energy
The interaction of the enzyme and substrate at the active site promotes - =the formation of the
transition state
Common features of the active site: (5 points) - =1. The active site is a three-dimensional cleft
or crevice
2. The active site takes up a small part of the total volume of an enzyme.
3. Active sites are unique micro environments.
4. Substrates are bound to enzymes by multiple weak attractions.
5. The specificity of binding depends on the precisely defined arrangement of atoms in an
active site.
The free energy released on binding is called - =binding energy
the maximal binding energy is released when - =the enzyme facilitates the formation of the
transition state
What are the two properties of enzymes that make them especially useful catalysts? - =rate
enhancement and substrate specificity
What does an apoenzyme require to become a holoenzyme? - =a cofactor
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