Nokea
What does the presence of carcinoembryonic antigens (CEAs) and α-fetoprotein (AFP) on cell membranes indicate has happened to the cells?
- A. They have shifted to more immature metabolic pathways and functions
- B. They have spread from areas of original development to different body tissues
- C. They produce abnormal toxins or chemicals that indicate abnormal cellular function
- D. They have become more differentiated as a result of repression of embryonic functions
Correct Answer: A
Rationale: The presence of CEAs and AFP indicates that cells have reverted to more immature metabolic pathways, characteristic of cancerous transformation.
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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 disease is an example of Type V hypersensitivity?
- A. Multiple sclerosis
- B. Grave's disease
- C. Rheumatoid arthritis
- D. Type 1 diabetes mellitus
Correct Answer: B
Rationale: The correct answer is B, Grave's disease, for Type V hypersensitivity. In Type V hypersensitivity, antibodies target cell surface receptors, leading to abnormal stimulation or blockage. In Grave's disease, antibodies target the thyroid-stimulating hormone receptor, leading to excessive thyroid hormone production. Multiple sclerosis (A) is an example of Type IV hypersensitivity involving T cell-mediated response. Rheumatoid arthritis (C) is an example of Type III hypersensitivity involving immune complex deposition. Type 1 diabetes mellitus (D) is an example of Type II hypersensitivity involving antibody-mediated destruction of cells.
Which of the following is a characteristic of the constant region of a T cell receptor?
- A. Mediates antigen binding
- B. Anchors the receptor in the T cell membrane
- C. Interacts with MHC molecules
- D. Structurally diverse amongst all T cell receptors
Correct Answer: B
Rationale: The correct answer is B: Anchors the receptor in the T cell membrane. The constant region of a T cell receptor is responsible for anchoring the receptor in the T cell membrane, providing stability and structural support. This region does not mediate antigen binding (choice A), as that function is carried out by the variable region. It also does not directly interact with MHC molecules (choice C), which is primarily the role of the variable region. Lastly, the constant region is not structurally diverse amongst T cell receptors (choice D), as it remains relatively consistent within a specific T cell subtype.
During the healing phase of inflammation, which cells would be mostly likely to regenerate?
- A. Skin
- B. Neurons
- C. Cardiac muscle
- D. Skeletal muscle
Correct Answer: A
Rationale: Skin cells are highly regenerative due to their rapid turnover rate and presence of stem cells. In contrast, neurons, cardiac muscle, and skeletal muscle have limited regenerative capacity.
the characteristic of blood types AB is
- A. a general receptor
- B. a general donor
- C. a receptor and donor
- D. neither donating nor receptor
Correct Answer: A
Rationale: The correct answer is A: a general receptor. Blood type AB individuals have both A and B antigens on their red blood cells, making them universal recipients since they can receive blood from all blood types without rejection. This is because they have no antibodies against A or B antigens. The other choices are incorrect because blood type AB individuals cannot be universal donors (choice B) as they have both A and B antigens, not making them suitable for all recipients. They are not both a receptor and donor (choice C) as they can only receive blood from all types, not donate to all. Lastly, they are not neither donating nor a receptor (choice D) since they can receive blood from all types, making them a receptor.