Nokea
Why did Barry Marshall drink a pure culture of Helicobacter pylori?
- A. To demonstrate the H. pylori is the cause of gastric cancer
- B. To demonstrate an association between H. pylori infection and gastric ulcers
- C. To demonstrate that gastric ulcers are caused by stress rather than bacterial
- D. A and B are both correct
Correct Answer: B
Rationale: Barry Marshall drank a pure culture of H. pylori to demonstrate an association between H. pylori infection and gastric ulcers. This is because he wanted to prove the theory that the bacteria is a primary cause of stomach ulcers, contradicting the prevailing belief at the time. Choice A is incorrect because the direct link between H. pylori and gastric cancer was not the primary focus of his experiment. Choice C is incorrect as his goal was to show the bacterial link to ulcers, not to disprove stress as a factor. Choice D is incorrect because only choice B accurately reflects his intended purpose.
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What is the consequence of granzyme entering a target cell?
- A. Neutralization of toxins
- B. Activation of apoptosis pathways
- C. Inhibition of cytokine secretion
- D. Promotion of antigen presentation
Correct Answer: B
Rationale: Granzyme entering a target cell activates apoptosis pathways by inducing cell death. Firstly, granzyme activates caspases leading to cell death. Secondly, it triggers DNA fragmentation and cell shrinkage. Lastly, it enhances membrane blebbing and apoptotic body formation. The other choices are incorrect because granzyme does not neutralize toxins, inhibit cytokine secretion, or promote antigen presentation within a target cell.
Multi-photon microscopy has proved to be an invaluable tool for the evaluation of the dynamics of immune responses in vivo. The following is a list of observations derived from intra-vital microscopy. Identify the incorrect statement.
- A. T cells make stable and prolonged contacts with APC presenting the specific antigen in the paracortex
- B. In the absence of antigens B cells move at the same speed and randomly in follicles
- C. In the presence of infection specific B cells quickly direct themselves towards the source of antigen
- D. Dendritic cells move rapidly through the germinal centre during an immune response
Correct Answer: D
Rationale: The correct answer is D because dendritic cells do not typically move rapidly through the germinal center during an immune response. Dendritic cells usually interact with T cells in the paracortex to present antigens, and they are not known to migrate rapidly through the germinal center.
A: This statement is correct as T cells do make stable and prolonged contacts with APCs in the paracortex during immune responses.
B: This statement is incorrect as B cells do not move at the same speed and randomly in follicles in the absence of antigens. They respond to signals and cues in the microenvironment.
C: This statement is correct as specific B cells can quickly direct themselves towards the source of antigen during an infection.
In summary, choice D is incorrect because dendritic cells do not move rapidly through the germinal center during an immune response, while the other choices accurately describe behaviors of immune cells during immune responses.
Which of the following nucleotide triplets best represents a codon?
- A. a triplet in the same reading frame as an upstream AUG.
- B. a triplet separated spatially from other triplets.
- C. a sequence in tRNA at the 3' end.
- D. a triplet that has no corresponding amino acid.
Correct Answer: A
Rationale: The correct answer is A because a codon is a triplet of nucleotides in mRNA that corresponds to a specific amino acid during protein synthesis. To be a codon, the triplet must be in the same reading frame as the start codon (AUG) to maintain the correct reading of the genetic code. Choice B is incorrect because codons are typically consecutive in mRNA. Choice C is incorrect as tRNA sequences are not codons. Choice D is incorrect because all codons correspond to specific amino acids.
Why is smallpox considered a factor that greatly helped European explorers to defeat the Native populations of the Americas (e.g. Mexico)?
- A. When the Europeans arrived there was an ongoing smallpox epidemic in the Americas that weakened the ability of the Natives to fight back
- B. The Native populations used a form of vaccination against smallpox that was often lethal and therefore they lost more lives.
- C. Smallpox was introduced in Mexico by the European explorers therefore the Native population had no immunity to it and the disease spread rapidly
- D. Both A and B are correct
Correct Answer: C
Rationale: The correct answer is C because smallpox was indeed introduced to the Americas by European explorers, leading to devastating effects on the Native populations who had no immunity. This weakened the Natives' ability to fight back against the Europeans. Option A is incorrect as there was no ongoing smallpox epidemic in the Americas before the arrival of the Europeans. Option B is also incorrect as there is no evidence that the Native populations used a lethal form of vaccination against smallpox. Option D is incorrect as only option C accurately explains the impact of smallpox on the Native populations in relation to European conquest.
Which of the following is not usually observed in severe Covid-19 cases?
- A. Prompt and sustained production of type I Interferon
- B. Autoantibodies
- C. A delayed CD4 T cell response
- D. Elevated levels of inflammatory cytokines
Correct Answer: A
Rationale: Step-by-step rationale:
1. In severe Covid-19 cases, there is usually a dysregulated immune response.
2. Type I Interferon plays a crucial role in early antiviral defense.
3. However, in severe cases, there is often a blunted or delayed response of type I Interferon.
4. This delayed response contributes to viral persistence and hyperinflammation.
5. Therefore, the prompt and sustained production of type I Interferon is not usually observed in severe Covid-19 cases.
Summary:
- Choice A is correct as the prompt and sustained production of type I Interferon is not typically observed in severe Covid-19 cases.
- Choices B, C, and D are incorrect as autoantibodies, a delayed CD4 T cell response, and elevated levels of inflammatory cytokines are commonly observed in severe Covid-19 cases.