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.
