United State Medical Licensing Examination (Step 1) Set 12

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 as a result of the airway infection. Additionally, he suffers from gastrointestinal (GI) and nutritional abnormalities that include biliary cirrhosis, meconium ileus, and pancreatic insufficency. The symptoms are classical for which of the following disorders?

Acetyl-CoA enhances the rate of gluconeogenesis by acting as an allosteric activator of which of the following enzymes?

You are studying the effects of a compound on the respiratory activity of isolated mitochondria. Your experiments demonstrate that oxygen consumption is normal when pyruvate and malate are added. Oxygen consumption is also seen to be normal when succinate is added. However, you find that the production of ATP is severely impaired in the presence of pyruvate/malate or succinate when the compound is added to the reaction. These results most closely resemble the effects that would be seen by the addition of which of the following inhibitors of oxidative phosphorylation?

The bacterial lac operon is controlled by both glucose and lactose levels. Which of the following conditions would result in the greatest level of transcription from the lac operon?

The term "genomic imprinting" refers to the phenomenon of gene expression dependence on the mode of inheritence. A typical example of this phenomenon is the control of the expression of the growth factor IGF- II. Genomic imprinting, termed "epigenesis," is defined by which of the following?

The process of RNA editing leads to sequence changes that are not reflective of the genetic information contained within the gene for an edited RNA. RNA editing occurs through the action of specific nucleotide deaminases that change either adenine to inosine or cytidine to uridine. These nucleotide changes can affect the coding or splicing capacity of the RNA. Which of the following proteins is an important example of the result of RNA editing?

Carnitine, a zwitterionic compound derived from lysine, is involved in fatty acid metabolism and is required at which two points in the transport of fatty acids from the cytoplasm to the mitochondria (see below figure)?

When the body becomes acidotic, the liver and the kidneys play central roles in reactions designed to reduce the proton level (i.e., increase the pH) of the circulation. Which of the following constitutes the hepatic reaction occuring during periods of acidosis?

The occurrence of Type II diabetes (NIDDM) in adolescent females can lead to the development of polycystic ovarian syndrome (PCOS). PCOS is the result of follicular atresis and ovulatory dysfunction brought about by a hyperandrogenic microenvironment in the ovary. Which of the following statements reflects the underlying cause of the hyperandrogenic state in females with NIDDM?

A 15-year-old boy has been diagnosed with retinitis pigmentosa, peripheral polyneuropathy, and cerebellar ataxia. Analysis of his cerebrospinal fluid indicated a high protein content but no elevation of cell number. A telling clinical finding was a high level of serum phytanic acid. These findings are indicative of which of the following disorders?