ENZYME ACTION Flashcards
*What is an enzyme ? Provide an example of an important reaction that requires an enzyme (CO2)
Enzyme- protein catalyst that speeds up a reaction
When water reacts with CO2, the enzyme carbonic anhydrase (one of fastest enzymes) allow reaction to occur and produce carbonic acid in red blood cells. (OH-O=C-OH).
What are substrates?
the reactants in an enzyme catalyzed reaction.
What is the function of Proteolytic enzymes? Provide examples of these proteolytic enzymes and discuss their specificity.
Proteolytic enzymes- catalyze hydrolysis of peptide bonds (break peptide bond by adding H2O and form Carboxyl and amino groups)
Ex: Trypsin and Papain have different degrees of specificity.
Trypsin- specific to catalyze hydrolysis on Lysine or Arginine residues
Papain- not as specific. will cleave any peptide bond (papaya plant)
Thrombin- more specific than trypsin; ONLY catalyze on ARG-GLY bonds. used in blood clotting.
What are the six major classes of enzymes?
- Oxidoreducatase- oxid-reduc reactions (transfer e-)
- Transferases -move fcn groups between molecules
- Hydrolases- cleave bonds with adding H2O
- Lyases- remove atoms to form double bonds/add to db.
- Isomerases- move fcn groups within molecule
- Ligases- join two molecules using ATP
What are cofactors? what are the two types? What are prosthetic groups?
Cofactors- small molecules that some enzymes require for activity. Can be coenzymes (derived from Vitamins) and metals Ex: FAD, NAD+; Zn, K+
Prosthetic groups- tightly bound coenzymes.
Distinguish between holoenzyme and apoenzyme
Holoenzyme- enzyme with cofactor
Apoenzyme- enzyme without a cofactor (inactive)
What are the thermodynamic properties of a reaction
- free energy difference (delta G) between reactants and products determines whether reactions occur spontaneously.
- energy required to initiate conversion of reactant to products determines the rate of reaction (how enzymes involve)
*What is Free energy (G)? How does delta G apply to enzymes?
measure of energy that is capable of doing work. enzymes do not alter change in free energy (delta G)
distinguish between exergonic and endergonic reactions. which is spontaneous? What is the sign of delta G?
Exergonic reactions- reaction that will occur spontaneously (w/out input of energy), Delta G is negative.
Endergonic reactions- reaction will NOT occur spontaneous (need an input of energy to drive reaction) Delta G is positive
Describe what occurs when Delta G= 0
when Delta G=0, the reaction is at equilibrium. There is not net change in concentrations of reactants and products. Reaction has stopped.
What kind of info does delta G depend on? What does it not depend on?
Delta G depends only on free energy difference between reactants and products.
Does NOT have info on how reaction occurs, or rate of reaction
What happens when the pka is less than pH?
the compound will be protonated and there will be more of reactant present.
What does the pka tell you? What other info does this provide?
tells you pH that the chemical group needs to be to accept or donate an proton. Hence it lets you know how acidic or basic a group is.
Describe the relationship between acidity and pka.
the lower the pka, the stronger the acid and greater the ability to donate protons (vice versa)
What is Delta G ?
The change in free energy when a reaction occurs.
*What is Delta G^o? What does it tell you?
The standard free energy change of reaction (change in energy of reaction under standard conditoins). The special conditions for reaction when concentrations of reactants and products are each 1 molar, pH of 7.
*What is the free energy change equation? what do the symbols represent?
Delta G= Delta G^o + RT ln [ C ] [ D ]/ [ A ] [B ]
R- gas constant, T- Kelvins.
How does standard free energy change relate to equilibrium constant (K’eq)
At equilibrium, delta G= 0, making energy equation 0= delta G^o + RT ln [ C ] [ D ]/ [ A ] [B ] which = Delta G^o = -RT ln [ C ] [ D ]/ [ A ] [B ].
k equilibrium constant for reaction under standard conditions:
K’eq= [ C ] [ D ]/ [ A ] [B ] and can be substituted for concentration of products and reactants in free energy change equation.
So K’eq= e^-delta G/RT (RT = 2.47)
How do exergonic and endergonic reactions relate to equilibrium?
The more exergonic a reaction, the LARGER the keq.
The more endergonic a reaction, smaller the keq.
What determines the differences between Delta G and Delta G^o?
Delta G can be larger than, smaller or equal to delta G^o depending on concentrations of reactions.
*How does standard free energy change (Delta G^o) relate to keq? in terms of products vs substrate?
The larger the standard free energy change, the smaller the keq, and you will have more substrate than products.
smaller the G^o, larger keq and more products than substrate.
What Factor from free energy change equation is criteria for spontaneity of reaction?
Delta G only (not standard free energy)
*What is equilibrium? What determines this reaction equilibrium?
Equilibrium- when there is no net change in concentration of products and reactants, delta G =0.
only determined by the free energy difference between the products and reactants.
enzymes do not change equilibrium.
*What is the transition state in a reaction? What facilitates forming of transition state?
The point in the middle of reaction that is after the substrate but has not yet become product.
transition state X^$- has double dagger sign.
Enzymes facilitates this.
*What is the activation energy?
Energy required to form the transition state from substrate (delta G$) (delta G$= Gx^$ - Gs)
How do enzymes affect the transition state?
Enzymes will reduce the energy needed to form transition state (Activation energy) and allow the reaction to go faster.
*What is the first step of Enzyme catalysis?
forming the enzyme- substrate complex
What promotes the transition state?
the interaction of the enzyme and substrates at the active site. (enzyme and S come together to form ES complex at active site)
Describe features of the active site on enzymes.
- 3D cleft or crevice created by amino acids from different parts of primary structure
- constitutes a small portion of enzyme volume
- sites create microenvironments.
- multiple weak interactions (noncovalent) between enzyme and substrate interactions
- enzyme specificity depends on molecular architecture (shape) of active site.
How do enzymes interact with their substrates? What is this type of interaction called.
Enzyme will change shape upon substrate binding to active site on enzyme.
INDUCED FIT
(enzyme and substrate, NOT lock and key)
*What is the binding energy in a reaction? When is binding energy highest?
The free energy released from interaction between enzyme and substrate.
binding energy highest when enzyme interacts with transition state, and will thus facilitate formation of transition state.
What is the stability of istate and why?
least stable because it has the highest free energy in reaction compared to substrate and products.
What is the essence of catalysis?
to stabilize the transition state?
What happens to reaction when activation energy is lower?
Activation energy lower, more molecules have enough energy to reach transition state, and you’ll make products faster.
*What are transition state analogs? How are they useful?
compounds that resemble transition state of reaction but are not actually acted upon by enzyme. They serve as inhibitors for enzyme catalyzed reactions since they can bind so tightly to an enzyme even more than substrate.
What are abyzymes?
Antibodies that serves as enzymes and recognize transition states.
