Biology of Cells
Which of the "clinically relevant" microbes does NOT have a cellular structure?
Viruses
Which two main structures characterize a Gram-negative cell wall?
A thin layer of peptidoglycan and a second plasma membrane called the outer membrane.
What are the two functions of hyphae in a fungal mycelium, and how do they differ in location?
Vegetative hyphae (most of the mycelium) for anchoring and absorbing nutrients; aerial hyphae (above the mycelium) for reproduction.
How do Giardia trophozoites cause disease in the intestine?
They grow and reproduce, damaging the intestinal wall, which causes diarrhea, nausea, and abdominal pain.
Why is the mosquito considered the definitive host for Plasmodium, even though replication happens in other hosts?
Because Plasmodium parasites can only perform sexual reproduction in mosquitos.
All cells, both prokaryotic and eukaryotic, share which four common structures?
Plasma membrane, cytoplasm, ribosomes, chromosome(s)
Name three functions of bacterial cell walls.
Providing cell shape, protecting against physical damage, and allowing bacteria to stick to cells.
What are fungal spores, and what is their general function?
Fungal spores are the products of reproduction in fungi; their general function is to disperse (spread out) and grow new fungal organisms.
What is the difference between a definitive host and an intermediate host for a parasite?
A definitive host is the organism in which the parasite can fully mature and reproduce by sexual reproduction, while an intermediate host is the organism in which the parasite is immature or unable to reproduce by sexual reproduction.
What are the characteristic cyclical symptoms of uncomplicated malaria?
Flu-like symptoms with cyclical fever, chills, and profuse sweating. These cyclical symptoms correspond with the death of red blood cells in each cycle of parasite replication in the red blood cell stage (which takes 12-72 hours).
How do prokaryotic and eukaryotic cells compare in terms of their external structures?
Prokaryotes have several different types of external structures for movement, protection, attachment, and genetic transfer, while eukaryotes have only a few, usually for cell movement
What is a biofilm, and what are the sticky molecules within it called?
An entire community of microbes that stick to surfaces; the sticky molecules are called Extracellular Polymeric Substances (EPS).
What are the two types of yeasts, and how do they differ regarding pathogenicity?
True yeasts (non-pathogenic, always yeast form) and Dimorphic yeasts (pathogenic, can switch between mold and yeast forms).
What is a "latent infection" and how does Toxoplasma cause it in humans?
A dormant infection inside the human body; after a brief infection, the immune system forces the Toxoplasma parasite to form dormant tissue cysts, which can remain dormant for decades.
What happens during the Red Blood Cell Stage of Plasmodium infection in humans?
Parasites from the liver infect red blood cells and replicate by cell division. Infected red blood cells fill up with parasites and eventually burst, releasing more parasites into the blood. Some newly made parasites reinfect more red blood cells, and some develop into gametocytes that can infect the next mosquito host.
If a drug were designed to prevent the formation of "supercoiled" DNA by inhibiting the twisting process, would this drug likely have a greater impact on bacterial cells or human cells, and why?
It would have a greater impact on bacterial cells because their single, circular chromosome must be extensively supercoiled to fit within the nucleoid.
Where is Staphylococcus epidermidis (Staph epi) normally found, and why is its presence there a concern for medical devices?
It's part of the normal microbiota on human skin; it can contaminate implanted medical devices and form antibiotic-resistant biofilms inside the body.
Where are Candida yeasts normally found in the body, and why are they considered opportunistic pathogens?
Candida can be found in the "healthy microbes" (normal microbiota) of the skin, mouth, intestinal, urinary, and vaginal tracts; they are opportunistic pathogens because if the normal physiological balance in these places is thrown off, Candida will overgrow and cause infections.
What is "cysticercosis," and what can happen if it affects the brain and spine (neurocysticercosis)?
Cysticercosis occurs in an atypical tapeworm life cycle when humans directly ingest tapeworm eggs. The eggs hatch into larvae, which form cysticerci in muscles, eyes, and brain. Neurocysticercosis (in brain/spine) can be severe, causing headaches, brain swelling, and epileptic seizures.
What is the typical treatment for malaria, and why is a combination of two drugs often used?
Artemisinin combination therapy (ACT), which uses a combination of two anti-parasitic drugs. Multiple medications attack the parasite's life cycle at multiple points, making the treatment more effective and reducing the development of microbial resistance.
A new antibiotic is being developed that specifically targets and binds to 70S ribosomes, blocking protein synthesis. Why would this antibiotic be effective against bacterial infections but generally safe for human cells and eukaryotic microbes like fungi?
Because human cells and eukaryotic microbes have 80S ribosomes, which have subtle structural differences preventing the antibiotic from binding, while bacterial cells have 70S ribosomes that are targeted.
A hospital needs to ensure all surgical instruments are free of Clostridium species, which are known to form endospores. Why would simple disinfection with water-based cleaners or even boiling the instruments be insufficient to achieve sterility in this case?
Endospores are highly resistant, dormant structures that cannot be killed by disinfection; they require sterilization methods like autoclaving or strong chemical agents to destroy their protective layers.
You are tasked with cleaning a laboratory bench contaminated with both fungal spores and bacterial endospores. You use a standard, relatively mild disinfectant. Which type of spore would you expect to be more likely to survive this treatment, why?
Bacterial endospores, because they are much tougher and more resistant than fungal spores.
In regions with poor sanitation, children often acquire hookworm infections. Describe the unusual route by which hookworm larvae typically enter the human body from contaminated soil, and explain why "Ground itch" is an early sign of infection.
Larvae in contaminated soil penetrate the skin (most often via bare feet), then migrate through the body, eventually reaching the intestine; "Ground itch" is caused by the itching and redness of the skin where larvae penetrate.
Malaria is prevalent in tropical and subtropical regions but is rarely found in colder or drier climates. Explain two biological factors related to the Plasmodium parasite's life cycle and its mosquito host that account for this geographical distribution.
Mosquitoes require pools of standing water to reproduce, and Plasmodium requires temperatures above 68-70 degrees F for sexual reproduction in mosquitos, thus cold and/or dry climates do not support parasite growth.