General Information Enzymes Flashcards
An ______________ is a protein or in some cases a RNA catalysts that acts upon a substrate (S).
Enzyme (E)
The ___________ is the region of the enzyme where a substrate binds and catalysis occurs.
Active site
In order to function properly, many enzymes contain ________ such as Mg2+, Zn2+, Fe2+ or ________ such as biotin, NAD+, FAD+, coenzyme A.
Cofactors
Coenzymes
Cofactors are generally ________ and coenzymes are generally ________.
Inorganic
Organic
When an enzyme is bound to it cofactor, it is called a ______________.
Holoenzyme
When the enzyme lacks its cofactor, it is called a _____________.
Apoenzyme
Enzymes specifcally bind a substrate or several similar substrates via _____________________________.
Non-covalent interactions
An enzyme is said to be _______________________ to the substrate with regards to shape, charge distribution, stereochemistry, etc.
Structurally complementary
There are two models for enzyme-substrate interactions. What are they?
Lock and key hypothesis
Induced fit hypothesis
In the ____________________ hypothesis, proposed by FIscher in 1894, the enzyme is a ______ and the substrate is a _______. Only the correctly sized _____ (substrate) can fit into the ________________ (active site) of the _______ (enzyme)
Lock and key
Lock
Key
Key
Key hole
Lock
In the lock and key hypothesis, the enzyme is ______________ complementary to the substrate.
Perfectly complementary
In the _____________________ hypothesis proposed by Koshland in 1958, the enzyme undergoes a conformational change upon binding with the substrate. The active site is ____________.
Induced fit
Flexible
What makes enzymes different from other catalysts?
- They are soluble in water
- They can operate under mild temperatures and pHs
- They are very specific for their substrates
- They engage in no side reactions
- They produce only one enantiomer as product
- They have great catalytic power
Enzymes catalyze reactions up to _________ times the original rate
1016/17
What do all catalysts do?
Lower the activation energy (Ea = ∆G‡)
How is the activation energy of a reaction related to the speed of a reaction?
High Ea = Slow rate
Low Ea = High rate
What is the Arrhenius equation?
It describes the relationship between ∆G‡ and k, the rate of the reaction
The relationship between ∆G‡ and k is _________ and ______________ related.
Inversely
Exponentially
The rate or k of a reaction decreases with lower ∆G‡ because the Arrhenius equation shows that k is inversely and exponentially related to ∆G‡.
A catalyst does NOT make a reaction more or less spontaneous, it only affects the _______ of the reaction.
Rate
A catalyst does not affect the thermodynamics of a reaction, only the _________ of a reaction.
Kinetics
Be familiar with an energy diagram for a reaction.
The first class of enzymes is _______________, which catalyzes electron transfer reactions, and an example is alcohol dehydrogenase.
Oxidoreductase
The second class of enzymes is ______________, which catalyzes group transfer reactions, and DNA polymerase is an example of one.
Transferase
The third class of enzymes is ___________________, which catalyzes hydrolysis reactions, and examples include chymotrypsin and RNase A.
Hydrolyase
The fourth class of enzymes is ____________, which catalyzes cleavage reactions or eliminations, and carbonic anhydrase is an example.
Lyase
The fifth class of enzyme is ______________, which catalyzes the transfer of groups within a molecule to yield isomers, and phosphohexose isomerase is an example.
Isomerase
The sixth and last class of enzymes is _____, which catalyzes the formation of covalent bonds by condensation reactions and ATP, and aminoacyl-tRNA synthetase is an example.
Ligase
There are four mechanisms in which an enzyme can catalyze a reaction. What are they?
- Electrostatic catalysis
- Proximity and orientation effects
- General acid/base catalysis
- Covalent or nucleophilic catalysis
_______________ catalysis involves charged groups in an active site that help stabilize the transition-state; the active sites are generally hydrophobic and exclude water, thereby enabling the reaction to occur at a low dielectric constant, which increases the strength of charged interactions.
Electrostatic
In electrostatic catalysis, pKa values can ______________ from tabulated values.
Differ greatly
An example of electrostatic catalysis discussed in class is the deprotonation of aspartate. When in the presence of ___________, a positively charged amino acid, aspartate is ______________ (more or less) likely to deprotonate, thereby _____________ the pKa.
Lysine
More likely
Lowering
In proximity and orientation effects, the enzyme brings the catalytic groups together, holding the enzyme and substrate in ______________________ thereby freezing _______________ and _____________ motion of the substrate and catalytic groups.
Proper orientation
Translational
Rotational