Lecture 9- Introduction To Enzymes And Catalysis Flashcards
Delta G is positive means what?
Needs an input of energy
Delta G is negative means what?
Reaction can take place spontaneously.
Delta G provides info on the rate of a reaction. True or false?
False; Delta G provides no info on the rate of a reaction.
What is dependent upon Delta G?
The position of a reaction at equilibrium (the extent at which it will go in a certain direction).
What is activation energy? 2 answers
The minimum energy required to convert reactants to products during a collision between molecules.
Also, the energy required to position atoms for a reaction.
“The minimum energy required to convert reactants to products during a collision between molecules” is what?
Activation energy
As an overall concept, enzymes do what?
Enzymes lower the activation energy for reactions
What lowers the activation energy for reactions?
Enzymes
For delta G, when can a reaction take place spontaneously? When does it need an input of energy?
Negative; positive.
How does an enzyme lower the activation energy?
The enzymes binds tightly to one or more molecules and holds them in a precise configuration.
In addition to lowering the AE, enzymes do what?
They lower the energy barrier.
Enzymes are typically used to make or break what type of bonds?
Covalent bonds.
What is a catalyst?
A molecule or substance that can lower the AE for a reaction.
In terms of equilibrium, what CANT enzymes do?
They cannot change the equilibrium point for a reaction.
Why won’t the equilibrium position for the reaction be changed for enzymes?
They lower the AE for both the forward and backward reaction equally.
True or false: Enzymes choose to lower the AE for an unspecific type of reaction.
False; enzymes are selective and precise
For the enzyme, where do substrates bind and undergo catalysis?
At the active site?
What is the active site in the enzyme responsible for?
It is where the substrate binds and undergoes catalysis.
What is the first step in catalysis?
Substrate binding.
When is the reaction NOT limited by the binding event?
When the substrate is present at very high concentrations.
When the substrate is present at very high concentrations, what is the rate of reaction limited to?
The rate is dependent only upon how fast the enzymes can convert substrates to product (the enzyme is said to be “saturated” with substrate).
Why can enzymes find their substrates?
The molecular motions cause by heat energy within the cell are rapid.
What are the three kinds of molecular motions caused by heat energy?
Translational energy, vibrational energy, and rotation.
What is translational energy?
Movement from one place to another
“Movement from one place to another” is what?
Translational energy.
What is vibrational energy?
Rapid back and forth movement of covalently bonded atoms with respect to each other.
“Rapid back and forth movement of covalently bonded atoms with respect to each other” is what?
Vibrational energy.
Another name for translational energy?
Diffusion.
True or false: small molecule substrates of enzymes move much more rapidly than the relatively huge enzymes themselves.
True
Structurally, what is the active site for an enzyme?
A 3-D cleft or crevice formed by groups that come from different parts of the amino acid sequence.
Dose the active site take a small or large part of the total volume of an enzyme?
Small part.
What is the amino acid sequence of an enzyme responsible for?
The amino acid sequence of an enzyme is responsible for creating a “scaffold” that precisely positions the amino acids in the active site.
Is water often included in active sites.
No.
How are substrates bound to enzyme active sites?
By multiple weak interactions.
What is an induced fit?
When the active site assumes a shape that is complementary to the substrate only after the substrate is bound.
“When the active site assumes a shape that is complementary to the substrate only after the substrate is bound” is called what?
An induced fit.
Conceptually, how do enzymes accelerate reactions?
By stabilizing the transition state.
What is a transition state?
The transition state is a configuration of atoms in which they are positioned for a reaction.
In terms of free energy, does the transition state have high or low? Is is stable or not? Does it occur often?
High free energy; it is the least stable in the reaction pathway; it is seldom occurring in the reaction pathway.
Another name for the transition state?
Transient state
What is the “essence of catalysis?”
The stabilization of the transition state structure
Do enzymes have a higher affinity for the unstable transition structure or that most stable and common structure?
Enzymes have a much higher affinity for the unstable transition structure.
What happens when an enzyme bonds to the transition state structure?
When an enzyme binds to the transition state structure, this releases energy. As a consequence, it lowers the energy required to reach the transition state, and thereby lowers the AE for the reaction.
True or false: the energy of binding is used to lower the AE of the reaction.
True.
What is a coenzyme?
Small organic molecules that are found in active sites that aid catalysis.
“Small organic molecules that are found in active sites that aid catalysis” are called what?
Co-Enzymes.
