Question

The U.S. Centers for Disease Control and Prevention (CDC) recommends that anyone who might have been exposed to anthrax begin treatment with the antibiotic ciprofloxacin, a DNA-synthesis inhibitor. For ciprofloxacin to be useful, it must work a. exclusively against telomerase b. exclusively against bacterial DNA synthesis proteins c. exclusively against eukaryotic DNA synthesis proteins d. against both bacterial and eukaryotic DNA synthesis proteins

Short answer

The correct answer is (b). Ciprofloxacin works exclusively against bacterial DNA synthesis proteins, enabling it to target the bacteria causing anthrax without affecting eukaryotic cells.

Step-by-step solution

Understand the terms

Telomerase is an enzyme that adds DNA sequence repeats to the ends of chromosomes, preventing them from getting shorter during replication. Telomerase is found in eukaryotes (organisms with cells containing a nucleus surrounded by a membrane). Bacterial DNA synthesis proteins are the proteins involved in the process of replicating DNA in bacteria. Eukaryotic DNA synthesis proteins are the proteins involved in the process of replicating DNA in eukaryotic organisms.

Analyse the options based on ciprofloxacin's mechanism of action

Ciprofloxacin is a DNA-synthesis inhibitor. This means it must interfere with the replication process of DNA. a. exclusively against telomerase - If ciprofloxacin worked exclusively against telomerase, it would only target eukaryotic cells, not bacteria. Since anthrax is a bacterial infection, this option is incorrect. b. exclusively against bacterial DNA synthesis proteins - If ciprofloxacin worked exclusively against bacterial DNA synthesis proteins, it would target the bacteria causing anthrax, without affecting eukaryotic cells. This is the desired outcome for an antibiotic, so this option seems promising. c. exclusively against eukaryotic DNA synthesis proteins - If ciprofloxacin worked exclusively against eukaryotic DNA synthesis proteins, it would be harmful to the infected person's cells, not the bacteria causing the infection. This option is incorrect. d. against both bacterial and eukaryotic DNA synthesis proteins - If ciprofloxacin targeted both bacterial and eukaryotic DNA synthesis proteins, it would harm both the infected person's cells and the bacteria. Since the goal of an antibiotic is to target the bacteria without harming the person's cells, this option is incorrect.

Conclusion

Based on our analysis, option (b) is correct. Ciprofloxacin works exclusively against bacterial DNA synthesis proteins, allowing it to target and eliminate the bacteria causing anthrax, without affecting eukaryotic cells.

Key concepts

Ciprofloxacin Mechanism of Action

Ciprofloxacin, a potent antibiotic, plays a critical role in treating bacterial infections like anthrax. It belongs to a class of antibiotics known as fluoroquinolones and its primary function is to impede bacterial DNA synthesis. Ciprofloxacin exerts its effect by targeting an enzyme called DNA gyrase (bacterial topoisomerase II), which is essential for supercoiling and uncoiling DNA strands during replication and transcription.

By inhibiting this enzyme, ciprofloxacin prevents the bacteria from replicating its DNA, thereby halting cell division and leading to the death of the bacterial cell. Importantly, this mechanism is specific to bacteria, which is why option (b) exclusively against bacterial DNA synthesis proteins is the correct answer in the context of the exercise. Human cells do not contain DNA gyrase; hence, ciprofloxacin selectively targets bacteria without harming the host's (human) cells.

Another enzyme affected by ciprofloxacin is topoisomerase IV which is involved in chromosome segregation during bacterial cell division. The dual action on both DNA gyrase and topoisomerase IV makes ciprofloxacin a highly effective antibacterial agent.

Antibiotics in Bacterial Infections

Antibiotics are the cornerstone treatment for bacterial infections. They function by interfering with various bacterial processes to inhibit growth or kill bacteria. Some antibiotics, like ciprofloxacin, are bactericidal, as they directly lead to bacterial death. Others are bacteriostatic, wherein they merely inhibit the growth and replication of bacteria, allowing the immune system to clear the infection.

The choice of antibiotic depends on the type of bacteria, the site of infection, and the patient's health condition. It is important to use antibiotics specifically targeting the causative agent of an infection to avoid unnecessary damage to the body’s normal flora and to minimize the risk of antibiotic resistance. Resistance occurs when bacteria evolve mechanisms to withstand the effects of antibiotics, rendering them ineffective.

This emphasizes the need for targeted therapy, as seen with ciprofloxacin's mechanism of action which is designed to affect only bacterial cells by blocking their ability to synthesize DNA, thereby treating the infection effectively while minimizing harm to the host organism.

Telomerase Function

Telomerase is a crucial enzyme predominantly active in germ cells, stem cells, and some cancer cells. It has a unique function in extending the protective caps of chromosomes called telomeres. These telomeres consist of repetitive DNA sequences and are crucial for maintaining chromosome integrity and stability during cell division.

Every time a cell divides, its telomeres become shorter, which eventually leads to cell aging and death when the telomeres reach a critically short length. Telomerase counters this process by adding telomeric DNA to the ends of chromosomes, thus providing them with a kind of 'renewable resource' that allows cells to continue dividing beyond their normal limit.

This perpetuation of telomere length is particularly important in cells that need to divide frequently or indefinitely. Inhibiting telomerase has been a point of interest in cancer treatment as cancer cells often rely on this enzyme to maintain their immortality. However, in the context of bacterial infections, targeting telomerase would be inappropriate as bacteria do not possess telomeres or telomerase. They replicate their DNA through a circular chromosome, which does not require telomere maintenance.