Nokea
Terminal deoxynucleotidyl transferase catalyzed reactions produce fragments with
- A. poly A or poly C tails
- B. poly C tails
- C. poly A tails
- D. poly A or poly T tail
Correct Answer: A
Rationale: Terminal deoxynucleotidyl transferase (TdT) adds nucleotides to the 3' end of DNA fragments in a template-independent manner. This results in the production of fragments with poly A or poly C tails. TdT does not add poly T tails, making option D incorrect. It also does not specifically add only poly C tails (option B) or poly A tails (option C). The addition of poly A or poly C tails by TdT is essential for techniques like DNA sequencing and PCR, where these tails are utilized for downstream applications.
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The best treatment for mononucleosis is:
- A. Antibiotics.
- B. Physical therapy.
- C. NSAIDs.
- D. Rest and fluids.
Correct Answer: D
Rationale: Mononucleosis is caused by a viral infection, so antibiotics are ineffective. Rest and fluids are the most effective treatments as they support the body's immune response and help manage symptoms like fatigue and dehydration.
What is the primary role of Helper T cells in the immune response?
- A. Killing infected host cells
- B. Producing antibodies
- C. Secreting cytokines to activate other immune cells
- D. Suppressing immune responses
Correct Answer: C
Rationale: Helper T cells primarily secrete cytokines to activate other immune cells. This is crucial for coordinating and amplifying the immune response. They do not kill infected host cells (A), as that is the role of cytotoxic T cells. Producing antibodies (B) is the function of B cells. Suppressing immune responses (D) is the role of regulatory T cells, not Helper T cells.
Protease inhibitors interfere with
- A. Release of new viral particles from infected cells
- B. Processing of gp160
- C. Proviral stage
- D. Reverse transcription of viral RNA into DNA
Correct Answer: D
Rationale: Protease inhibitors interfere with the final step in HIV replication, which is the cleavage of the polyprotein into individual functional proteins. Inhibiting protease prevents the formation of mature infectious viral particles. This step occurs after reverse transcription of viral RNA into DNA, making choice D the correct answer. Choices A, B, and C are incorrect because protease inhibitors do not affect the release of new viral particles, processing of gp160, or the proviral stage of HIV replication.
With respect to vaccination against a particular infectious disease 'herd immunity' refers to:
- A. The total number of people who are immunized in a given population
- B. The protection offered to non-immunized people when high rates of immunization prevent the pathogen from spreading
- C. The percentage of people who generate a protective response to the vaccine
- D. The tendency of people to choose to be vaccinated if close contacts (friends and family) have been vaccinated
Correct Answer: B
Rationale: The correct answer is B. Herd immunity refers to the protection offered to non-immunized individuals when a high percentage of the population is immunized, preventing the pathogen from spreading easily. This is because when a large portion of the population is immune to a disease, it creates a barrier that reduces the overall transmission of the pathogen, thus protecting those who are not vaccinated or cannot be vaccinated.
Choice A is incorrect because herd immunity is not solely about the total number of immunized individuals, but rather about the impact on the entire population. Choice C is incorrect as it refers to the efficacy of the vaccine in generating a protective response, not the concept of herd immunity. Choice D is incorrect as it relates to social influence rather than the collective protection provided by high rates of immunization.
In mice, mutations of which of the following genes cause the 'scurfy' phenotype (scaly skin and multiple autoimmune disorders)?
- A. FOXP3
- B. AIRE
- C. NFkB
- D. IRF
Correct Answer: A
Rationale: Rationale:
1. FOXP3 gene encodes a transcription factor crucial for regulatory T cells function.
2. Mutations in FOXP3 lead to dysfunctional regulatory T cells, causing autoimmune disorders.
3. Scurfy phenotype matches the symptoms of autoimmune disorders seen with FOXP3 mutations.
Summary:
- B (AIRE): AIRE mutations cause autoimmune polyendocrine syndrome, not scurfy phenotype.
- C (NFkB): NFkB is a transcription factor involved in immune response but not linked to scurfy phenotype.
- D (IRF): IRF is a regulator of interferon signaling, not directly associated with scurfy phenotype.