Chapter 5 Biochemistry

The interactions of ligands with proteins

• are relatively nonspecific.

• are relatively rare in biological systems.

• are usually irreversible.

• are usually transient

• usually result in the inactivation of the proteins.

A prosthetic group of a protein is a non-protein structure that is:

• A) a ligand of the protein.

• B) a part of the secondary structure of the protein.

• C) a substrate of the protein.

• D) permanently associated with the protein.

• E) transiently bound to the protein.

When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are

occupied by:

• one O atom and one amino acid atom.

• one O2 molecule and one amino acid atom.

• one O2 molecule and one heme atom.

• two O atoms.

• E) two O2 molecules.

In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the

fraction of binding sites occupied can best be described as:

• hyperbolic

• linear with a negative slope.

• linear with a positive slope.

• random.

• sigmoidal

Which of the following statements about protein-ligand binding is correct?

• A) The Ka is equal to the concentration of ligand when all of the binding sites are occupied.

• B) The Ka is independent of such conditions as salt concentration and pH.

• C) The larger the Ka (association constant), the weaker the affinity.

• D) The larger the Ka, the faster is the binding.

• E) The larger the Ka, the smaller the Kd (dissociation constant).

Myoglobin and the subunits of hemoglobin have:

• A) no obvious structural relationship.

  
  

• B) very different primary and tertiary structures.

  
  

• C) very similar primary and tertiary structures.

  
  

• D) very similar primary structures, but different tertiary structures.

  
  

• E) very similar tertiary structures, but different primary structures.

  
  

An allosteric interaction between a ligand and a protein is one in which:

• A) binding of a molecule to a binding site affects binding of additional molecules to the same site.

  
  

• B) binding of a molecule to a binding site affects binding properties of another site on the protein.

  
  

• C) binding of the ligand to the protein is covalent.

  
  

• D) multiple molecules of the same ligand can bind to the same binding site.

  
  

• E) two different ligands can bind to the same binding site.

  
  

In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by:

• A) Fe2+ binding.

  
  

• B) heme binding.

  
  

• C) oxygen binding.

  
  

• D) subunit association.

  
  

• E) subunit dissociation.

  
  

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?

• A) It binds at a distance from the heme groups of hemoglobin.

  
  

• B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.

  
  

• C) It increases the affinity of hemoglobin for oxygen.

  
  

• D) It is an allosteric modulator.

  
  

• E) It is normally found associated with the hemoglobin extracted from red blood cells.

  
  

Which of the following is not correct concerning cooperative binding of a ligand to a protein?

• A) It is usually a form of allosteric interaction.

  
  

• B) It is usually associated with proteins with multiple subunits.

  
  

• C) It rarely occurs in enzymes.

  
  

• D) It results in a nonlinear Hill Plot.

  
  

• E) It results in a sigmoidal binding curve.