Microbiology Exam Prep V3

The ability of a virus to infect an organism is regulated by multiple factors, including the host species, the type of cells it can infect, the availability of an attachment site, and the presence of cell factors necessary for replication. All of these factors play a role in determining whether a virus can successfully infect an organism.

Antibodies actually have two binding sites, one at the end of each arm of the "Y". Each binding site consists of a specific region called the antigen-binding fragment (Fab), which is responsible for binding to antigens. Therefore, the correct answer is false.

Mycoplasma lacks a cell wall. This is because Mycoplasma is a type of bacteria that belongs to the class Mollicutes, which are known for their lack of a rigid cell wall. Instead, Mycoplasma has a flexible cell membrane that allows it to take on different shapes and sizes. This lack of a cell wall makes Mycoplasma more susceptible to osmotic pressure and antibiotics that target cell wall synthesis.

IgG is the most common type of antibody found in the serum. It plays a crucial role in the immune system by providing long-term protection against infections. IgG antibodies are able to cross the placenta, providing passive immunity to newborns. They also help in opsonization, neutralization of toxins, and activation of complement system. IgG antibodies are produced in response to a wide range of pathogens and are involved in both primary and secondary immune responses.

An enveloped virus acquires its envelope during the release phase of its life cycle. After the virus has replicated inside the host cell, it needs to exit the cell in order to infect other cells. During the release phase, the virus buds off from the host cell, taking a portion of the host cell's membrane with it. This membrane becomes the envelope of the virus, which is essential for its ability to infect new cells.

Antigenic peptides that are presented by antigen presenting cells are called epitopes. Epitopes are specific regions on an antigen that are recognized by the immune system. They are responsible for eliciting an immune response and can bind to antibodies or T cell receptors. Antigen presenting cells, such as dendritic cells, macrophages, and B cells, present these epitopes to T cells to initiate an immune response. Fc fragments and secretory fragments are not directly involved in antigen presentation, and antibodies are molecules produced by B cells in response to an antigen.

A photosynthetic cell that lacks a nucleus would be placed in the group Bacteria. This is because bacteria are prokaryotes, which are organisms that lack a nucleus and other membrane-bound organelles. They have a simpler structure compared to eukaryotes, such as the cells found in Animalia, Fungi, and Plantae. Bacteria are capable of photosynthesis through various mechanisms, such as using pigments like chlorophyll or bacteriochlorophyll to capture light energy and convert it into chemical energy.

A viroid is a naked infectious piece of RNA. Unlike a complete infectious virus particle, which consists of both nucleic acid and a protein capsid, a viroid lacks a protein coat and is composed solely of RNA. Viroids are smaller and simpler than viruses, and they can cause diseases in plants by interfering with the normal functioning of the host cell. Their ability to replicate and spread within plants without a protein coat makes them unique and distinct from viruses.

Bacillus subtilis is expected to be most resistant to high temperatures because it is a spore-forming bacterium. Spore formation is a survival mechanism that allows certain bacteria to enter a dormant state and withstand harsh conditions such as high temperatures. This ability to form spores makes Bacillus subtilis more resistant to heat compared to the other bacteria listed, which do not have the same capability.

The antigen-binding site of an antibody molecule is composed of the variable domains of one light and one heavy chain. These variable domains contain the hypervariable regions, also known as the complementarity-determining regions (CDRs), which are responsible for binding to specific antigens. The light chains and constant domains of the light and heavy chains are not directly involved in antigen binding. Therefore, the correct answer is the variable domains of one light and one heavy chain.

Opsonisation is a process in which antibodies bind to antigens, marking them for ingestion by phagocytes. This interaction between antibodies and Fc receptors on phagocytes enhances the efficiency of phagocytosis. Opsonisation plays a crucial role in resisting and fighting bacterial infections. It is particularly effective when mediated by several subclasses of IgG antibodies. Therefore, all of the statements mentioned in the options are correct and contribute to the explanation of opsonisation.

The given correct answer is "viruses multiply inside living cells using viral mRNA, tRNA and ribosomes." This statement is not true because viruses do not have their own mRNA, tRNA, or ribosomes. Instead, they rely on the host cell's machinery to replicate and produce new viral particles. Viruses inject their genetic material into a host cell, and then hijack the cell's machinery to produce viral proteins and replicate their genetic material.

Chemotaxis refers to the movement of bacteria in response to chemical gradients in their environment. When bacteria exhibit chemotaxis, they are capable of detecting and moving towards an attractant, such as a nutrient or favorable condition. Therefore, the correct answer is that bacteria move towards an attractant.

The secondary immune response refers to the immune response that occurs upon re-exposure to a previously encountered pathogen. It is characterized by a more rapid onset compared to the primary response, as the immune system has already been primed and is ready to respond. The secondary response also reaches higher maximum levels of immune activity, as the immune system has a memory of the pathogen and can mount a stronger and more efficient response. Additionally, the secondary response displays a more acute rise in immune activity over time, with a steeper slope, compared to the primary response. Finally, the secondary response is often able to prevent disease by effectively eliminating the pathogen before it can cause significant harm. Therefore, all of the above statements are true regarding the secondary immune response.

Humoral immunity refers to the immune response mediated by soluble antibodies, which are proteins produced by B cells. These antibodies circulate in the blood and lymphatic system, targeting and neutralizing pathogens or foreign substances. This type of immunity is distinct from cellular immunity, which involves T cells directly attacking infected cells. Therefore, the correct answer is "immunity involving soluble antibodies."

Rickettsias require an arthropod for transmission, which means they rely on arthropods like ticks, fleas, or lice to spread from one host to another. This is in contrast to chlamydias, which do not require an arthropod for transmission. The other options, being gram-negative and intracellular parasites, are characteristics that both rickettsias and chlamydias share, so they do not differentiate between the two. Therefore, the correct answer is that rickettsias require an arthropod for transmission.

IgA is an immunoglobulin that is primarily found in secretions such as tears, saliva, mucus, and breast milk. It plays a crucial role in mucosal immunity by preventing pathogens from entering the body through these secretions. Unlike other immunoglobulins, IgA cannot cross the placenta, which means it does not provide passive immunity to the fetus. While it is one of the first antibodies secreted in response to antigen stimulation, it is not the very first antibody produced. Therefore, the correct answer is that IgA is found in secretions.

The statement "they are used for penetration" is not true about spikes. Spikes are protein structures on the surface of viruses that are used for attachment and entry into host cells, but they do not directly penetrate the host cell. Instead, they facilitate the fusion of the viral envelope with the host cell membrane, allowing the virus to enter the cell.

Clostridium is a genus of bacteria that is known for its ability to form endospores. Endospores are a dormant and highly resistant form of the bacteria that allows it to survive in harsh conditions. The other options listed in the question, such as mycobacteria, gram-negative aerobic cocci, and anaerobic gram-negative rods, do not accurately describe the characteristics of Clostridium. Therefore, the correct answer is endospore-forming cocci.

If both organisms are gram-positive, it indicates that they have a similar cell wall structure, which suggests a closer evolutionary relationship. Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, which differentiates them from gram-negative bacteria. This similarity in cell wall composition suggests that these organisms may have a common ancestor and are therefore more closely related.

In a DNA-virus infection, the host animal cell supplies all the necessary components for viral replication except DNA polymerase. DNA polymerase is an enzyme responsible for synthesizing new DNA strands during replication. The host cell's RNA polymerase is used by the virus to transcribe its genetic material, nucleotides are used as building blocks for DNA synthesis, and tRNA is involved in protein synthesis. However, the virus must bring its own DNA polymerase in order to replicate its DNA.

The most conclusive evidence that viruses cause cancers is provided by cancer following the injection of cell-free filtrates. This suggests that the filtrates contain a virus that is capable of causing cancer in the injected individuals. This direct link between injecting the filtrates and the development of cancer provides strong evidence of the role of viruses in causing cancer. Other options such as finding oncogenes in viruses, the presence of antibodies against viruses in cancer patients, treating cancer with antibodies, and some liver cancer patients having had hepatitis, may also suggest a potential association between viruses and cancer, but they do not provide as direct and conclusive evidence as the injection of cell-free filtrates.