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Chapter 5: Protein Structure and Function

The quaternary structure of a given protein is defined by which of the following?

A. linear order of the amino acids

B. ordered organization of secondary structures within the protein

C. organization of super-secondary structures within the protein

D. overall structure resulting from association of domains within the protein

E. structure resulting from the interactions between multiple polypeptide chains

Answer E: Quaternary structure is the protein structure resulting from the interaction of at least 2 protein subunits in the functional protein.

In an enzyme with a critical glutamic acid residue (Glu, E) in the active site, which of the following amino acid substitutions would be expected to have the least effect on enzyme activity?

A. Arg

B. Asp

C. Lys

D. Ser

E. Tyr

Answer B: Since glutamic acid is a negatively charged amino acid at physiological pH, any other negatively charged amino acid, such as aspartic acid, could potentially be substituted without significant loss of enzyme activity.

A 12-year-old boy has suffered from chronic sinopulmonary disease including persistent infection of the airway with Pseudomonas aeruginosa. He has constant and chronic sputum production because of the airway infection. Additionally, he suffers from gastrointestinal (GI) and nutritional abnormalities that include biliary cirrhosis, meconium ileus, and pancreatic insufficiency. The symptoms are classical for which of the following disorders?

A. congenital adrenal hyperplasia

B. cystic fibrosis

C. renal Fanconi syndrome

D. sickle cell anemia

E. Tay-Sachs disease

Answer B: Cystic fibrosis results from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). The disease is characterized by abnormal transport of chloride and sodium across an epithelium, leading to thick, viscous mucus secretions. This mucus builds up in the breathing passages of the lungs, as well as in the pancreas and intestines. Difficulty breathing is the most serious symptom and results from frequent lung infections, particularly with P. aeruginosa. The secretions in the pancreas block the exocrine movement of the digestive enzymes into the duodenum and result in irreversible damage to the pancreas. The lack of digestive enzymes leads to difficulty in absorbing nutrients with their subsequent excretion ...

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