Chapter 5: Section 0 (Protein Function)

What are five functions of Globular Proteins?

• Transport of ions and molecules

• Storage of ions and molecules

• Muscle contractions

• Biological catalysis

• Defense against pathogens

What is a Ligand?

A molecule that binds to a protein

What is the binding site (active site)?

A region in the protein where the ligand binds

What types of interactions occur when a ligand binds to a protein?

• Hydrogen bonding

• Hydrophobic Effect

• Van der Waals

• Electrostatic interactions

What is the Equilibrium Constant?

The ratio between the concentrations of products and the concentrations of reactants at equilibrium

What is the Rate Constant?

A proportionality number that connects the rate of chemical reaction (speed of a chemical reaction) at a given temperature to the concentrations of the reactants or to the products of the reaction

What is the reaction type of the Equilibrium Constant?

A reaction that does not change with time

What reaction type is the Rate Constant?

A reaction that changes with time

What is Equilibrium Association Constant (Ka)?

The function of the concentration of the bound ligand complex (PL) divided by unbound protein (P)

What increases the Equilibrium Association Constant (Ka)?

When more ligand is bounded

What is another way the association rate constant (Ka) be described?

Ka = (ka/kd)

What is the Dissociation Rate Constant (Kd)

How much a protein can bind

What does the fraction of bound sites depend on?

The free ligand concentration and dissociation constant (Kd)

What does a lower Kd mean?

Tight binding

What can explain the high specificity of proteins for specific ligands?

Complementarity of the binding site and the ligand

What are some of the complementarity conditions of the binding site and the ligand?

• Size

• Shape

• Charge

• Hydrophobic/Hydrophilic character

What is the Lock-and-Key Model

Assumes that the complementary surfaces are preformed

What is the Induced Fit Model?

Conformation changes may occur upon ligand binding. Both the ligand and the protein change their conformations

What does the induced fit allow?

• Allows for tighter binding of the ligand

• Allows for high affinity for different ligands