Block 9 Prokaryot Strategy In Lab Diag MCQ

CD8 T-cells are responsible for intracellular pathogens. Intracellular pathogens cause the cell to express MHC I

The correct answer is the sizes and number of the rRNA components. Eukaryotic ribosomes are larger and more complex than prokaryotic ribosomes. Eukaryotes have a 60S and a 40S subunit, while prokaryotes have a 50S and a 30S subunit. Additionally, eukaryotic ribosomes have more rRNA molecules compared to prokaryotic ribosomes. This size and number difference allows eukaryotic ribosomes to perform more intricate and specialized functions in protein synthesis.

Mycobacterium tuberculosis is an acid-fast organism, which means it has a unique cell wall composition that is resistant to the staining process used in the Gram stain. Therefore, it would not retain the crystal violet stain or the counterstain, resulting in no staining.

The role of alcohol in the Gram stain reaction is to dissolve lipids. This allows the crystal violet, which is the primary stain, to wash out of Gram-negative cells. Gram-negative cells have a thinner peptidoglycan layer in their cell wall, which is not able to retain the crystal violet stain as effectively as Gram-positive cells. By dissolving the lipids, the alcohol helps to remove the crystal violet from the Gram-negative cells, resulting in their decolorization.

The human cytomegalovirus US3 glycoprotein binds and retains major histocompatibility complex class I molecules in the endoplasmic reticulum of infected cells. This will affect somatic cell-mediated antigen presentation to activated CD8+ cells. The major histocompatibility complex class I molecules are responsible for presenting antigens to CD8+ cells, which triggers an immune response against infected cells. Therefore, by binding and retaining these molecules, the US3 glycoprotein inhibits the presentation of antigens to CD8+ cells, compromising the immune function of somatic cell-mediated antigen presentation to activated CD8+ cells.

The correct answer explains that Gram-positive bacteria stain blue/purple during the Gram Stain process because the peptidoglycan in their cell wall irreversibly binds to the application of crystal violet after the application of the mordant (iodine). This binding forms a complex that is not easily washed away, allowing the bacteria to retain the crystal violet stain and appear blue/purple under a microscope.

MHC class II molecules are found mostly on B cells, dendritic cells, and macrophages. This is in contrast to MHC class I molecules, which are found on all nucleated cells. MHC class II molecules are responsible for presenting antigens to CD4+ T cells, whereas MHC class I molecules present antigens to CD8+ T cells. Therefore, the major difference between MHC class II and MHC class I molecules lies in their distribution on different cell types and their role in antigen presentation to different types of T cells.

The plating factor is calculated by multiplying the count of a plate with the dilution. In this case, the count of the plate is 70 colonies and the dilution is 10^-5. Therefore, the plating factor is 70 x 10^-5 = 7.0 x 10^-4. Since Section C is labeled as the plating factor, it is the correct answer.

Bacteria might produce adhesins to counteract the host defense mechanism of ciliated epithelial cells. Ciliated epithelial cells have hair-like projections called cilia that help in moving mucus and trapped bacteria out of the respiratory tract. By producing adhesins, bacteria can attach to these ciliated cells and avoid being swept away, allowing them to establish an infection.

Lysozyme works by cleaving bonds between the NAG and NAM sugars, which are components of the peptidoglycan cell wall in bacteria. This cleavage weakens the cell wall and ultimately leads to the lysis of the bacterial cell.

Nocardia asteroides is the most structurally similar to the causative agent of tuberculosis. Nocardia asteroides is a Gram-positive bacterium that belongs to the same order (Actinomycetales) as Mycobacterium tuberculosis, the causative agent of tuberculosis. Both Nocardia asteroides and Mycobacterium tuberculosis are acid-fast bacteria and share similar cell wall structures, including the presence of mycolic acids. This similarity in cell wall composition and staining properties makes Nocardia asteroides the most structurally similar to Mycobacterium tuberculosis among the given options.

A human dendritic cell would typically express six different MHC class I molecules. MHC class I molecules are highly diverse and play a crucial role in presenting antigens to T cells. They are encoded by a group of genes called the human leukocyte antigen (HLA) complex. Each individual has multiple variants of MHC class I genes, resulting in a diverse repertoire of MHC class I molecules. Dendritic cells are professional antigen-presenting cells and have the ability to capture and present a wide range of antigens. Thus, they express multiple MHC class I molecules to ensure efficient presentation of diverse antigens to T cells.

Expression of antigens that are not found on other self tissues is least likely to enable tumor cells to evade the host immune system. This is because the immune system is more likely to recognize and target cells that express antigens that are not found on self tissues. By expressing antigens that are not found on other self tissues, tumor cells are more likely to be recognized as foreign by the immune system, leading to an immune response against the tumor cells. In contrast, down regulation of MHC Class I, failure to express B7, production of immunosuppressive cytokines like TGFP, and shedding of membrane antigens can all contribute to tumor cells evading the host immune system.

Serological testing for patient's antibodies against the organism would best confirm that the patient is infected with Mycoplasma pneumoniae. Serological testing detects the presence of specific antibodies produced by the patient's immune system in response to the infection. This method is effective because it can detect past or current infections, even when the organism is no longer present in the patient's sputum. Other methods like Gram stain, acid-fast stain, examination of wet prep, and culture in cell lines may not be as reliable for confirming the presence of Mycoplasma pneumoniae.

The correct answer is N-acetytglucosamine. Both the peptidoglycan and lipid A biosynthetic pathways require N-acetytglucosamine as a component. Peptidoglycan is a major component of the bacterial cell wall and is composed of N-acetylmuramic acid and N-acetytglucosamine. Lipid A is a component of lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria and also contains N-acetytglucosamine. Therefore, N-acetytglucosamine is essential for the synthesis of both peptidoglycan and lipid A.