Nokea
Which organism produces a toxin that blocks neuromuscular transmission in cholinergic motor neurons:
- A. Shigella dysenteriae
- B. Clostridium tetani
- C. Corynebacterium diphtheria
- D. Clostridium botulinum
Correct Answer: D
Rationale: The correct answer is D: Clostridium botulinum. This bacterium produces botulinum toxin, which blocks neuromuscular transmission by inhibiting the release of acetylcholine at the neuromuscular junction. This leads to muscle weakness and paralysis. Shigella dysenteriae (A) causes dysentery but does not affect neuromuscular transmission. Clostridium tetani (B) produces tetanus toxin, which affects inhibitory neurons in the spinal cord, leading to muscle spasm. Corynebacterium diphtheriae (C) produces diphtheria toxin, which affects protein synthesis in cells, not neuromuscular transmission.
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The generation time of Escherichia Coli is:
- A. 20 minutes
- B. 60 minutes
- C. 20 hours
- D. 24 hours
Correct Answer: A
Rationale: The correct answer is A: 20 minutes. Escherichia coli has a short generation time, typically around 20 minutes. This means that under ideal conditions, one bacterium can divide and produce two daughter cells every 20 minutes. This rapid growth rate is a characteristic of E. coli and is important in various fields such as microbiology and biotechnology. Choice B (60 minutes) and Choice C (20 hours) are incorrect as they do not align with the typical generation time of E. coli. Choice D (24 hours) is also incorrect as it is too long for the generation time of E. coli.
A stool sample from a patient with chronic diarrhea revealed cysts with four nuclei. What is the most likely causative agent?
- A. Entamoeba histolytica
- B. Giardia lamblia
- C. Balantidium coli
- D. Trichomonas hominis
Correct Answer: A
Rationale: The correct answer is A: Entamoeba histolytica. This is because it is a protozoan parasite known to cause amoebic dysentery, presenting with chronic diarrhea and cysts with four nuclei in the stool sample. Giardia lamblia (B) causes giardiasis with trophozoites and cysts with two nuclei. Balantidium coli (C) is a ciliated parasite causing dysentery with large trophozoites. Trichomonas hominis (D) is a non-pathogenic flagellate often found in the human intestine. Thus, based on the specific characteristics of the cysts and clinical presentation, Entamoeba histolytica is the most likely causative agent.
Enzymes that remove functional groups from a substrate without adding water, or that add functional groups to a double bond, are called
- A. oxidoreductases.
- B. transferases.
- C. hydrolases.
- D. lyases.
Correct Answer: D
Rationale: The correct answer is D: lyases. Lyases are enzymes that catalyze the breaking of chemical bonds without the addition of water. They can remove functional groups from substrates or add functional groups to double bonds without the use of water.
A: Oxidoreductases involve the transfer of electrons.
B: Transferases transfer functional groups from one molecule to another.
C: Hydrolases catalyze the breaking of bonds by adding water.
Which of the following proteins are encoded by herpesviruses and required for viral DNA replication
- A. viral DNA polymerase
- B. ribonucleotide reductase
- C. neuraminidase
- D. thymidine kinase
Correct Answer: A
Rationale: The correct answer is A: viral DNA polymerase. Herpesviruses require viral DNA polymerase for viral DNA replication. This enzyme is responsible for synthesizing new DNA strands using existing viral DNA as a template. Ribonucleotide reductase (B) is not directly involved in DNA replication but in the synthesis of deoxyribonucleotides. Neuraminidase (C) is an enzyme found in influenza viruses, not herpesviruses. Thymidine kinase (D) is involved in nucleotide metabolism but is not essential for viral DNA replication in herpesviruses.
Which bacteria are responsible for causing pneumonia?
- A. Streptococcus pneumoniae
- B. Mycobacterium tuberculosis
- C. Pseudomonas aeruginosa
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D (All of the above) because different bacteria can cause pneumonia. Streptococcus pneumoniae is the most common cause of community-acquired pneumonia. Mycobacterium tuberculosis causes tuberculosis, which can lead to pneumonia. Pseudomonas aeruginosa is a common cause of hospital-acquired pneumonia. Therefore, all three bacteria can be responsible for causing pneumonia in different contexts. Choices A, B, and C are incorrect because each bacterium individually can cause pneumonia, so selecting only one option would not cover the full spectrum of bacterial causes of pneumonia.