Nokea
When a B cell undergoes class switching it allows the cell to:
- A. Differentiate into a memory cell
- B. Make two or more antibody classes at the same time
- C. Stop making one class of antibody and begin to make another
- D. Receive costimulatory signals from any T helper cell subset
Correct Answer: C
Rationale: Rationale:
1. Class switching in B cells involves changing the class of antibody produced.
2. This allows the B cell to stop making one class of antibody and start making another.
3. This process enhances the immune response by generating antibodies with different functions.
4. Differentiating into a memory cell (choice A) is a separate process from class switching.
5. Making two or more antibody classes simultaneously (choice B) is not a characteristic of class switching.
6. Costimulatory signals from T helper cells (choice D) are important for B cell activation but not directly related to class switching.
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Which enzyme catalyzes the following reaction? Gap 5' - G G-A-T-C-C—3' ⋮ ⋮ ⋮ ⋮ ⋮ 3' - C-C-T-A-G G—5' Gap 5' - G-G-A-T-C-C—3' ⋮ ⋮ ⋮ ⋮ ⋮ 3' - C-C-T-A-G-G—5'
- A. DNA ligase
- B. DNA endonuclease
- C. None of the options are correct
- D. DNA polymerase 1
Correct Answer: A
Rationale: The correct answer is A: DNA ligase. DNA ligase catalyzes the joining of two DNA strands by forming a phosphodiester bond between the 3' hydroxyl of one nucleotide and the 5' phosphate of another. In the given reaction, the enzyme is needed to seal the nick in the DNA strands after the Okazaki fragments have been synthesized during DNA replication.
Explanation of other choices:
B: DNA endonuclease - Endonucleases cleave the phosphodiester bond within a polynucleotide chain, not join two DNA strands.
C: None of the options are correct - This is incorrect as DNA ligase is the correct enzyme for this reaction.
D: DNA polymerase 1 - DNA polymerase synthesizes new DNA strands by adding nucleotides to the 3' end of the growing chain, not joining two DNA strands.
Which patient is at the greatest risk for developing pressure ulcers?
- A. A 42-year-old obese woman with type 2 diabetes
- B. A 78-year-old man who is confused and malnourished
- C. A 30-year-old man who is comatose following a head injury
- D. A 65-year-old woman who has urge and stress incontinence
Correct Answer: C
Rationale: Comatose patients are at significant risk for pressure ulcers due to prolonged immobility, impaired sensation, and compromised circulation.
Choose the best definition for effector T cells. They are cells that
- A. Have never seen their specific antigen
- B. Have just seen their specific antigen and start to proliferate
- C. Have been energized
- D. Have been activated, expanded and are able to kill or help other cells
Correct Answer: D
Rationale: Effector T cells are fully activated, expanded, and capable of carrying out their functions, such as killing infected cells or assisting in immune responses. The correct choice (D) accurately describes the characteristics of effector T cells. They are not naïve cells (A), as they have encountered their specific antigen. They are not just starting to proliferate (B), as they have already undergone extensive proliferation. They have not only been energized (C), but have also completed the necessary steps for full activation and functionality.
What is the primary function of platelets?
- A. Producing hormones
- B. Transporting oxygen and carbon dioxide
- C. Clotting and sealing damaged blood vessels
- D. Protecting the body from foreign substances
Correct Answer: C
Rationale: Platelets primarily function in clotting and sealing damaged blood vessels. Firstly, when a blood vessel is injured, platelets rush to the site to form a plug, preventing excessive bleeding. Secondly, platelets release clotting factors to initiate the coagulation cascade, leading to the formation of a stable blood clot. This process is crucial for wound healing and preventing blood loss. Platelets do not produce hormones (choice A), transport gases (choice B), or protect the body from foreign substances (choice D). These functions are carried out by other components of the body's systems.
Lymphokines are protein substances produced in small amounts by lymphocytes and move from cell to cell carrying message through the immune system. The most common lymphokine is:
- A. Vaccine
- B. Antigen
- C. Antibody
- D. Interferon
Correct Answer: D
Rationale: Rationale for Correct Answer (D - Interferon):
1. Lymphokines are protein substances produced by lymphocytes.
2. Interferon is a type of lymphokine produced by lymphocytes during viral infections.
3. It helps in regulating the immune response and inhibiting viral replication.
4. Interferon moves from cell to cell carrying messages through the immune system.
Summary of Incorrect Choices:
A: Vaccine - Not a lymphokine, but a substance used to stimulate the immune system.
B: Antigen - Not a lymphokine, but a substance that triggers an immune response.
C: Antibody - Not a lymphokine, but a protein produced by the immune system to neutralize pathogens.