Enzymes, Nonenzymatic Protein Function, and Protein Analysis

MCAT Prep: Biochemistry Part 2

enzymes

catalyst; lower the activation energy necessary for reactions. They do not alter the free energy (ΔG) or enthalpy (ΔH) change that accompanies the reaction nor the final equilibrium position

rate (kinetics)

Enzymes change the __________ at which equilibrium is reached.

Ligases

are responsible for joining two large biomolecules, often of the same type

Isomerases

catalyze the interconversion of isomers, including both constitutional and stereoisomers

Lyases

catalyze cleavage without the addition of water and without the transfer of electrons. The reverse reaction (synthesis) is usually more biologically important

Hydrolases

catalyzes cleavage with the addition of water

Oxidoreductases

catalyze oxidation-reduction reactions that involve the transfer of electrons

Transferases

move a functional group from one molecule to another molecule

saturation kinetics

as substrate concentration increases, the reaction rate also increases until a maximum value is reached

v = (vmax [S])/(Km + [S])

Michaelis-Menten equation

[S] = Km

At one-half vmax

Michaelis-Menten

sigmoidal

Cooperative enzymes show a ________ curve.

Lineweaver-Burk

kcat = (vmax)/([enzyme])

equation for the turnover number for an enzyme

(kcat)/(Km)

catalytic efficiency equation

Competitive

Binding site: active site

Impact on Km: increases

Impact on vmax: no change

Noncompetitive

Binding site: allosteric site

Impact on Km: no change

Impact on vmax: decreases

Mixed

Binding site: allosteric site

Impact on Km: increases or decreases

Impact on vmax: decreases

Uncompetitive

Binding site: enzyme-substrate complex

Impact on Km: decreases

Impact on vmax: decreases

Polyacrylamide gel electrophoresis (PAGE)

proteins migrate through porous matrix according to size and charge

Native PAGE

is used to analyze the protein in folded state

SDS-PAGE

uses detergent to break all noncovalent interactions and analyzes the unfolded state

Reducing

_________ reagents can be used to break covalent disulfide bonds.

Structural proteins

generally fibrous. Include collage, elastin, keratin, actin, and tubulin

Motor proteins

capable of force generation through a conformational change. Include myosin, kinesin, and dynein

Cell adhesion molecules (CAM)

bind cells to other cells or surfaces. Include cadherins, integrins, and selectins

Ion channels

can be used for regulating ion flow into or out of a cell. There are three main types: ungated channels, voltage-gated channels, and ligand-gated channels

Enzyme-linked receptors

participate in cell signaling through extracellular ligand binding and initiation of second messenger cascades

G protein-coupled receptors

have a membrane-bound protein associated with a trimeric G protein. They also initiate second messenger systems