The enzyme-linked immunosorbent assay (ELISA) and western blot are used to analyze proteins. Antibodies are utilized in both assays to detect and quantify the protein of interest. Electrophoresis is specifically employed in western blots. On the other hand, the polymerase chain reaction (PCR) is used to amplify DNA. In prokaryotes, antibiotics in the tetracycline family hinder protein synthesis by binding to and obstructing the A site of the small (30S) ribosomal subunit. Tetracycline has a specific interaction with the 16S ribosomal RNA (rRNA) component of the 30S subunit, thereby inhibiting translation initiation. It's important to note that eukaryotes lack 16S rRNA and instead possess 18S rRNA in their small (40S) subunit, which does not bind tetracycline.

Moving on to Case 3, a deficiency in vitamin C (ascorbic acid) impacts collagen synthesis. Vitamin C acts as a coenzyme in the hydroxylation of proline and lysine during collagen synthesis, which is a fibrous protein found in the extracellular matrix. Additionally, vitamin C serves as a coenzyme for duodenal cytochrome b (Dcytb), which is responsible for reducing dietary iron from the ferric (Fe3+) to the ferrous (Fe2+) form. This reduction is necessary for iron absorption through the divalent metal transporter (DMT) in enterocytes. A deficiency in vitamin C impairs dietary iron uptake and leads to a type of anemia called microcytic, hypochromic anemia. It's important to note that vitamin C is a water-soluble vitamin and is not stored in the body. Furthermore, the cross-linking of collagen by lysyl oxidase requires copper, not vitamin C.

Moving on to the next answer, an inability to absorb vitamin B12 results in pernicious anemia. The most common cause of this absorption issue is a decrease in the production of intrinsic factor (IF) by the parietal cells of the stomach. Vitamin D and A, when complexed with their receptors, have the ability to bind to DNA and modify gene expression. Thiamine (vitamin B1) acts as a coenzyme in the oxidative decarboxylation of pyruvate and αketoglutarate, playing a crucial role in energy metabolism in most cells. Methotrexate, on the other hand, inhibits dihydrofolate reductase, the enzyme responsible for reducing dihydrofolate to tetrahydrofolate (THF), which is the active coenzyme form of folate. This inhibition results in reduced availability of THF. Pyridoxine (vitamin B6) in the form of pyridoxal phosphate serves as a coenzyme for most reactions involving amino acids. It's worth noting that tetrahydrobiopterin is required by aromatic amino acid hydroxylases and nitric oxide synthases. Nutritional anemias are characterized by either increased red blood cell (RBC) size (folate and B12 deficiencies) or decreased RBC size (iron and vitamin C deficiencies). In hemolytic anemias, such as those seen in glucose 6-phosphate dehydrogenase and pyruvate kinase deficiencies, as well as sickle cell anemia, RBC size is typically normal while RBC number is decreased.

Lastly, in Case 4, the symptoms experienced, including rapid heart rate, headache, and sweating, are associated with a condition called pheochromocytoma.
Answer = B. The enzyme-linked immunosorbent assay (ELISA) and western blot are used to analyze proteins. Each makes use of antibodies to detect and quantify the protein of interest. It is western blots that utilize electrophoresis. The polymerase chain reaction (PCR) is used to amplify DNA. Antibiotics in the tetracycline family inhibit protein synthesis by binding to and blocking the A site of the small (30S) ribosomal subunit in prokaryotes. Tetracycline specifically interacts with the 16S ribosomal RNA (rRNA) component of the 30S subunit, inhibiting translation initiation. Eukaryotes do not contain 16S rRNA. Their small (40S) subunit contains 18S rRNA, which does not bind tetracycline.
Case 3: Blood on the Toothbrush with Vitamin C Deficiency
Answer = C. Vitamin C (ascorbic acid) functions as a coenzyme in the hydroxylation of proline and lysine in the synthesis of collagen, a fibrous protein of the extracellular matrix. Vitamin C is also the coenzyme for duodenal cytochrome b (Dcytb) that reduces dietary iron from the ferric (Fe3+) to the ferrous (Fe2+) form that is required for absorption via the divalent metal transporter (DMT) of enterocytes (see figure below). With a deficiency of vitamin C, uptake of dietary iron is impaired and results in a microcytic, hypochromic anemia. As a water-soluble vitamin, vitamin C is not stored. Cross-linking of collagen by lysyl oxidase requires copper, not vitamin C.
Answer = A. An inability to absorb vitamin B12 leads to pernicious anemia and is most commonly caused by decreased production of intrinsic factor (IF) by the parietal cells of the stomach (see figure at right). Vitamins D and A, in complex with their receptors, bind to DNA and alter gene expression. Thiamine (vitamin B1) is a coenzyme in the oxidative decarboxylation of pyruvate and αketoglutarate and, therefore, is important in energy metabolism in most cells. Methotrexate inhibits dihydrofolate reductase, the enzyme that reduces dihydrofolate to tetrahydrofolate (THF), the functional coenzyme form of folate. This results in decreased availability of THF. It is pyridoxine (vitamin B6) as pyridoxal phosphate that is the coenzyme for most reactions involving amino acids. [Note: Tetrahydrobiopterin is required by aromatic amino acid hydroxylases and nitric oxide synthases.] Nutritional anemias are characterized by either increased red blood cell (RBC) size (folate and B12 deficiencies) or decreased RBC size (iron and vitamin C deficiencies). In hemolytic anemias, such as is seen in glucose 6-phosphate dehydrogenase and pyruvate kinase deficiencies and in sickle cell anemia, RBC size typically is normal, and RBC number is decreased.
Case 4: Rapid Heart Rate, Headache, and Sweating with a Pheochromocytoma