Nokea
Which part of an antibody determines its antigen specificity?
- A. Fc fragment
- B. Fab region
- C. Heavy chain constant region
- D. Light chain constant region
Correct Answer: B
Rationale: The correct answer is B: Fab region. The Fab region of an antibody contains the antigen-binding site, where specific interactions with antigens occur. This region is formed by the variable regions of both the heavy and light chains. The Fc fragment (choice A) is responsible for effector functions, not antigen specificity. The heavy chain constant region (choice C) and light chain constant region (choice D) are not involved in antigen binding, but rather provide structural support and determine the antibody class. Therefore, the Fab region is crucial for antigen specificity due to its variable regions that directly interact with antigens.
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Identify the correct statement(s). In prokaryotes:
- A. Translation begins after transcription is finished.
- B. Messenger RNA is not co-linear with the DNA template.
- C. 5s, 16s, and 28s ribosomal RNA's are present.
- D. 50s and 30s ribosomal subunits are necessary for protein synthesis.
Correct Answer: d
Rationale: The correct answer is D because in prokaryotes, 50s and 30s ribosomal subunits combine to form the 70s ribosome, which is necessary for protein synthesis. Firstly, ribosomes are composed of two subunits, and in prokaryotes, these are the 50s and 30s subunits. Secondly, these subunits come together during translation to form the functional ribosome. Therefore, these ribosomal subunits are indeed necessary for protein synthesis in prokaryotes.
A: Incorrect. Translation can begin before transcription is finished in prokaryotes due to their lack of a nuclear membrane.
B: Incorrect. Messenger RNA in prokaryotes is co-linear with the DNA template as they do not undergo RNA splicing like eukaryotes.
C: Incorrect. In prokaryotes, the ribosomal RNA present is the 16s, 23s, and 5s, not 28s.
The MMR (Measles, MUMPs, Rubella) vaccine has been the object of controversy after a report (lately declared fraudulent) of an association with development of:
- A. Multiple sclerosis
- B. Autism
- C. Encephalitis
- D. Epilepsy
Correct Answer: B
Rationale: The correct answer is B: Autism. The controversy surrounding the MMR vaccine and autism emerged from a fraudulent report that falsely claimed a link between the two. Numerous scientific studies have since debunked this association, confirming the safety of the MMR vaccine. Autism is a neurodevelopmental disorder with a complex etiology, involving genetic and environmental factors, but not vaccines. Choices A, C, and D are incorrect as there is no proven causal link between the MMR vaccine and multiple sclerosis, encephalitis, or epilepsy.
What is the primary advantage of Toll-like receptors (TLRs)?
- A. They are highly specific to individual pathogens
- B. They recognize common molecular patterns shared by groups of microbes
- C. They activate B cell antibody production
- D. They require antigen presentation to function
Correct Answer: B
Rationale: The correct answer is B because Toll-like receptors (TLRs) recognize common molecular patterns shared by groups of microbes, allowing for rapid detection of a wide range of pathogens. This recognition triggers immune responses without the need for prior exposure to the specific pathogen. The other choices are incorrect because:
A: TLRs are not highly specific to individual pathogens but rather recognize common patterns.
C: TLRs do not directly activate B cell antibody production; they initiate immune responses by activating various immune cells.
D: TLRs do not require antigen presentation to function; they directly recognize microbial patterns.
Which characteristics are seen with acute transplant rejection (select all that apply)?
- A. Treatment is supportive
- B. Only occurs with transplanted kidneys
- C. Organ must be removed when it occurs
- D. The recipient’s T cytotoxic lymphocytes attack the foreign organ
Correct Answer: D
Rationale: Acute transplant rejection involves the recipient's T cytotoxic lymphocytes attacking the transplanted organ, requiring immunosuppressive therapy.
Virulence factors can be transferred from pathogenic to non-pathogenic bacterial strains that are part of the normal flora. An example of a commensal bacterial species that has turned into a pathogenic strain is:
- A. E. coli 0157:H7
- B. M. tuberculosis
- C. Group A S. pyogenes
- D. All opportunistic bacterial species
Correct Answer: A
Rationale: The correct answer is A: E. coli 0157:H7. This strain of E. coli has acquired virulence factors that allow it to cause severe illness in humans, such as bloody diarrhea and kidney failure. The transformation of E. coli from a commensal to a pathogenic strain is well-documented. In contrast, choices B and C involve species that are inherently pathogenic and not commensal. Choice D is too broad and includes a wide range of bacterial species that do not necessarily originate from the normal flora. Therefore, E. coli 0157:H7 is the best example of a commensal bacterium that has turned pathogenic due to the acquisition of virulence factors.