Enzymes Lecture 3

Front 1

What is the equation for Kapp

Back 1

Kapp = Km (1 + [I] / Ki)

Front 2

For biological reactions that require 2 substrates what are the three general catergories of them?

Back 2

1. Ordered - substrates must bind in a certain order for the reaction to go forward, products will come off in a certain order as well.
2. random - either substrate can bind in any order, does not mater
3. Ping pong - one substrate binds, and a product is released, another substrate binds and the 2nd product is releases. In the middle you get a chemical modified enzymne.

Front 3

there are the 4 general mechanisms that enzymes use to facilitate catalysis.
what is Catalysis by Proximity?

Back 3

here the active site assembles the substrates in close proximity within bond forming distance of one another. the higher the [S] the greater the chance that the S will occupy the active site in close proxmitiy to enhance catalysis

Front 4

there are the 4 general mechanisms that enzymes use to facilitate catalysis.
What is catalysis by strain?

Back 4

Enzymes that catalyze lytic reactions breaking a covalent bond bind
its substrate at the active site in a strained position so that the conformation of the substrate
at the active site places the targeted covalent bond in a thermodynamically unfavorable
position so that it will undergo cleavage.

Front 5

there are the 4 general mechanisms that enzymes use to facilitate catalysis.
What is acid base catalysis?
What is an example?

Back 5

the ionizable functional group at the active site contribute to catalysis by serving as acids or bases.

An example is a reaction mediated by pepsin (an aspartic protease). this enzyme has both a active site which serves as a base (proton acceptor) and an acid (which serves as a proton donor).

Front 6

there are the 4 general mechanisms that enzymes use to facilitate catalysis.
What is covalent catalysis?
What is an example?

Back 6

involves the foramtion of a transient covalent bond between an active site residue of the enzyme and one or mroe substrates. Often follows a ping pong reaction type.

An example is Chymotrypsin - which forms the active site from Asp-102, his-57 and Ser -195. Ser-195 forms a transient covalent intermediate with the substrate. Here you get a modified enzyme thing in the middle.

Front 7

Allosteric Enzymes.
Do they fit the michaelis model?
what kind of curve do they give?
what kind of structure do they have? How many subunits?

Back 7

they do not fit the michaelis menten model.
on a velocity vs [S] plot they give a sigmodial shape -> this indicates an allosteric enzyme.
they have a quaternary structure wit multiple subunits..

Front 8

What is the allosteric site?

Back 8

the allosteric site is where the allosteric inhibitor binds

Front 9

what is the equation that describes V and the sigmoidal behavoir. What is n? What does it have to be?

Back 9

V = Vmax * S^n / Km^n * S^n; n is the hill coefficient. it has be greater than 1 to be an allosteric enzyme. it denotes the number of substrate binding sites present on the enyzme.

Front 10

What is the difference between Homotrophic and heterotropic

Back 10

when the effector is the substrate it is homotropic; when the effector is not the substrate it is heterotropic

Front 11

What is the difference between k-class effectors and V-class effectors?

Back 11

K-Class - alters Km but not Vmax - binds at an allosteric site which then affects the affinity of the substrate binding

V-class effectors; alters Vmax but not Km.

Front 12

Look at the following example:
PFK-1 is an allosteric enzyme.
F6P + ATP -> F1,6BP + ADP

of the following things which are inhibitors and which are stimulators? Citrate, F2,6BP, ATP and AMP

Back 12

Inhibitors - Citrate and ATP
for atp; at lower concentrations it is a substrate at higher concentrations it is an inhibitor

Stimulators - F26BP, and AMP.

Front 13

Another example of an allosteric enzyme is Aspartate transcarbamoylase. How does this one work?

Back 13

it creates CTP which is an allosteric heterotropic negative modulator

Front 14

Enzymes are covalent modified. What is the most common modification? What are some of the other forms of modification?

Back 14

the most common modification is phosphorylation and dephosphorylation of Serine, Threonine and or tyrosine.
THis may activate orr inhibit enzymatic activity.
other forms of modification are methylation, adenylylation, ADPRibosylation.

Front 15

what is an isozyme? Will it have different delta G, what about Km, Vmax, Ki, Kcat

Back 15

an isozyme is an enzyme that exists in more than one molecular form. i.e. 2 different molecules help catalyze the same reaction

same delta G, different Kcat, Km, Vmax, Ki.