Chapter 11: Enzymatic Catalysis Flashcards
General function of enzymes?
Living systems are shaped by an enormous variety of biochemical reactions, nearly all of which are mediated by a series of remarkable biological catalysts known as enzymes.
They accelerate the rate of a reaction of a million or more by decreasing the activation energy
what is activation energy
activation energy is the amount of energy that must be inputted into our reaction to overcome that energy barrier to basically reach that transition state and transform the reactants to the product
Certain species of RNA molecules known as ? also have enzymatic activity. These include ribosomal RNA, which catalyzes the formation of peptide bonds between amino acids during protein synthesis. I
ribozymes
In what ways do enzymes differ from ordinary chemical catalysts?
- Higher reaction rates - The rates of enzymatically catalyzed reactions are typically 10 6 to 10 12 times greater than those of the corresponding uncatalyzed reactions (Table 11-1) and are at least several orders of magnitude greater
- Milder reaction conditions - Enzymatically catalyzed reactions occur under relatively mild conditions: temperatures below 100°C, atmospheric pressure, and nearly neutral pH. In contrast, efficient chemical catalysis often requires elevated temperatures and pressures as well as extremes of pH.
3.Greater reaction specificity - Enzymes have a vastly greater degree of specificity with respect to the identities of both their substrates (reactants) and their products than do chemical catalysts; that is, enzymatic reactions rarely have side products. - Capacity for regulation - The catalytic activities of many enzymes vary in response to the concentrations of substances other than their substrates. The mechanisms of these regulatory processes include allosteric control, covalent modification of enzymes, and variation of the amounts of enzymes synthesized.
What are the seven major classes of enzymes?
- Oxidoreductases - catalyze oxidation-reduction reactions (gives products a charge)
- Transferases - move functional groups between molecules
- Hydrolases - cleave bonds with the addition of water
- Lyases - remove atoms to form double bonds or add atoms to form double bonds
- Isomerases - move functional groups within a molecules
- Ligases - join two molecules at the expense of ATP (DNA)
- Translocases - transport other biomolecules, usually across a cell membrane
Which class of enzymes catalyze each of the following reactions?
The unique physical and chemical properties of the active site limit an enzyme’s activity to specific substrates and reactions. How do enzymes bind to substrates what kind of interactions
through non-covalent interactions, VDW, electrostatic, H-bonds, hydrophobic interactions
what is a catalyst?
a catalyst is something that lowers the activation energy of a reaction, and enzymes catalyze biochemical reaction
what is an enzyme? What is the active site? What factors influence an enzyme’s substrate specificity?
every enzyme has a specific substrate, and the enzyme recognizes its substrate with extremely high specificity, activates the enzyme’s function.
-there is a specific area on the enzyme that the substrate will bind to which is called the active site.
-The substrate will bind to the active site because it has just the right shape and composition to do so, meaning it is the right size but it also has functional groups that make favorable electrostatic interactions known as geometric and electronic complimentary.
with certain key residues in the active site of the enzyme, whether those are van der Waals interactions, hydrogen bonds, or any other interaction of this type.
Induced fit? what is lock and key model
The substrate might fit into the active site as is or it might cause an induced fit, where the enzyme changes shape slightly once the substrate is inside
substrate and enzyme fit perfectly
Enzymatic activity is always stereospecific, meaning ?
Enzymes are highly specific both in binding chiral substrates and in catalyzing their reactions. This stereospecificity arises because enzymes, by virtue of their inherent chirality (proteins consist of only L-amino acids), form asymmetric active sites.
that if a substrate can exist as two mirror images, only one of those forms will fit into the active site of the enzyme.
first step in enzymatic catalysis ?
enzymes bring substrate together to form an enzyme-substrate complex on a particular region of the enzyme called the active site , this interaction promotes the formation of the transition state
enzymes do not interact with their substrates like a lock and key, rather?
the enzyme changes shape upon substrate binding, called induced fit
Why do enzymes need cofactors? What are the two main classes?
Some need cofactors to work completely. Enzymes are less suitable for catalyzing oxidation–reduction reactions and many types of group-transfer processes. . This is some other thing that must also bind to the enzyme before it can operate on the substrate. Although enzymes catalyze such reactions, they can do so only in association with small cofactors, which essentially act as the enzymes’ “chemical teeth”
1. Metal ions such as copper, iron, and zinc
2. Coenzymes which are organic molecules derived form vitamins
types of coenzyme
-cosubstrate-binds and unbinds/temporarily binds
-prosthetic group-always binds with covalent bond such as heme
Holoenzyme? Apoenzyme?
Holoenzyme-An enzyme with its cofactor
Apoenzyme-Without the cofactor
apoenzyme (inactive) + cofactor ⇌ holoenzyme (active)
Coenzymes Must Be Regenerated.
Coenzymes are chemically changed by the enzymatic reactions in which they participate. In order to complete the catalytic cycle, the coenzyme must return to its original state.
An enzyme provides a lower-energy pathway from substrate to product but does not affect ?
the overall free energy change for the reaction.
Enzymes catalyze reactions by facilitating a reaction pathway with lower activation free energy, ΔG‡ , which is the free energy required to reach the transition state, the point of highest free energy in the reaction.
activation energy?
- is the amount of energy that must be added to transform the reactant into product
the energy required to form the transition state
the transition state?
The point of highest free energy in which the reactants are partially converted to products.
ΔG ‡ is the?the greater the value of ΔG ‡, the faster or slower? what does it determine
free energy of activation,the free energy required to reach the transition state
free energy gap between reactants and transition state
rate determining step
the greater the value of ΔG ‡, the slower the reaction rate.
free energy of the reaction? ΔG?
the gap between reactants and products, measure if energy capable of doing work
ΔG is the change in free energy when reaction occurs
free energy change information?ΔG What does it provide information on
ΔG < 0 = spontaneous, exergonic : when a reaction occurs without the input of energy
ΔG > 0 = not spontaneous, endergonic : reaction will not occur
ΔG = 0 reaction is at equilibrium, no net change in amount of reactant or product
the ΔG of a reaction depends only on the free energy difference between reactants and products and provides no info about the rate of the reaction
provides info on spontaneity but not rate
enzymes do not alter what, what do they alter
the ΔG of a reaction/reactio equilibrium
alter reaction rate
Enzymes do not change the energy of the products and reactants.
can only decrease activation energy to increase rate of reaction.
An enzyme cannot alter ΔGreaction; it can only decrease ΔG ‡to allow the reaction to more quickly approach equilibrium (where the rates of the forward and reverse reactions are equal) than it would in the absence of a catalyst.
