Nokea
Following class of restriction endonucleases is commercially available and used in recombinant DNA technology:
- A. Class 1
- B. Class 2
- C. Class 3
- D. Class 5
Correct Answer: B
Rationale: The correct answer is B: Class 2. Class 2 restriction endonucleases are commonly used in recombinant DNA technology due to their specificity for recognizing short DNA sequences and cleaving within or near these sequences. They are commercially available, easy to use, and have well-defined recognition sites, making them ideal for molecular cloning applications.
Choice A (Class 1) is incorrect because Class 1 enzymes require both ATP and S-adenosyl methionine for activity, making them less practical for routine laboratory use.
Choice C (Class 3) is incorrect because Class 3 enzymes cleave DNA at two sites, potentially leading to unwanted DNA fragmentation in recombinant DNA technology.
Choice D (Class 5) is incorrect because Class 5 restriction enzymes do not exist in the classification system of restriction endonucleases.
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What is a key difference between innate and adaptive immunity?
- A. Innate immunity develops memory
- B. Adaptive immunity is always functional
- C. Innate immunity is rapid and non-specific
- D. Adaptive immunity does not require activation
Correct Answer: C
Rationale: Correct Answer: C
Rationale:
1. Innate immunity is rapid: It provides immediate defense against pathogens.
2. Innate immunity is non-specific: It reacts in the same way to all pathogens.
3. Adaptive immunity, on the other hand, is slower and pathogen-specific.
4. Adaptive immunity develops memory to provide long-lasting protection.
Summary:
A: Innate immunity does not develop memory; adaptive immunity does.
B: Adaptive immunity may not always be functional due to various factors.
D: Adaptive immunity requires activation through exposure to specific antigens.
Rolling circle replication refers to:
- A. DNA replication in every prokaryotic cell division
- B. DNA transfer during conjugation
- C. mitosis
- D. meiosis
Correct Answer: B
Rationale: Rolling circle replication is a mechanism commonly observed in DNA transfer during bacterial conjugation. The process involves the transfer of a single strand of DNA that acts as a template for the synthesis of a complementary strand in the recipient cell. This results in the formation of a circular DNA molecule in the recipient cell. This mechanism is distinct from the semiconservative replication seen in prokaryotic cell division (Choice A), the cell division process of mitosis (Choice C), and the reduction division of meiosis (Choice D). Rolling circle replication is specific to the transfer of genetic material between bacterial cells during conjugation, making Choice B the correct answer.
The nurse is caring for a patient being tested for rheumatoid arthritis. In reviewing laboratory values, which should the nurse recognize as being diagnostic of rheumatoid arthritis?
- A. C-reactive protein = 12 mg/L
- B. Rheumatoid factor is negative.
- C. White blood cells = 6000/mm3
- D. Antinuclear antibody test is negative.
Correct Answer: A
Rationale: The correct answer is A because an elevated C-reactive protein level indicates inflammation, which is a key feature of rheumatoid arthritis. Rheumatoid factor (choice B) is positive in only 70-80% of patients with rheumatoid arthritis, so a negative result does not rule out the disease. White blood cell count (choice C) and antinuclear antibody test (choice D) are not specific to rheumatoid arthritis. In summary, an elevated C-reactive protein level is a more reliable indicator of the disease compared to the other options provided.
What structure is recognized by TLR4 in mammals?
- A. Peptidoglycan
- B. Lipopolysaccharide (LPS)
- C. Double-stranded RNA
- D. Mannose-binding lectin
Correct Answer: B
Rationale: The correct answer is B: Lipopolysaccharide (LPS). TLR4 recognizes LPS, a component of the outer membrane of Gram-negative bacteria, triggering an immune response. This recognition is crucial in detecting bacterial infections. Peptidoglycan (A) is recognized by other TLRs, not TLR4. Double-stranded RNA (C) is recognized by TLR3, not TLR4. Mannose-binding lectin (D) is a pattern recognition receptor that binds to carbohydrate structures, not specifically recognized by TLR4.
The basic structure of an antibody molecule is
- A. One light chain and one heavy chain that are covalently linked and form one antigen binding site
- B. Two identical heavy chains and two identical light chains that are covalently linked and form two antigen binding sites
- C. Two identical heavy chains and two identical light chains covalently linked to form one antigen binding site
- D. Two identical light chains that form the antigen binding site and two identical heavy chains that mediate the effector functions of antibodies
Correct Answer: B
Rationale: Rationale for Answer B:
1. Antibody structure consists of two identical heavy chains and two identical light chains.
2. These chains are covalently linked to form the Y-shaped structure of an antibody.
3. Each chain contributes to the formation of antigen-binding sites.
4. Therefore, two identical heavy chains and two identical light chains form two antigen-binding sites.
Summary of Incorrect Choices:
A: Incorrect because it describes only one antigen-binding site formed by one light chain and one heavy chain.
C: Incorrect because it describes one antigen-binding site formed by two identical heavy chains and two identical light chains.
D: Incorrect because it incorrectly describes the roles of light and heavy chains in antibody structure.