A 45-year-old patient presents with progressive muscle weakness, exercise intolerance, and episodes of lactic acidosis. Muscle biopsy reveals decreased ATP production despite adequate oxygen availability. Dysfunction of which cellular organelle most directly explains these findings?
Lysosome
Endoplasmic reticulum
Mitochondria
Golgi apparatus
Peroxisome
The Correct Answer is C
A. Lysosome: Lysosomes contain hydrolytic enzymes responsible for degradation of cellular waste, damaged organelles, and macromolecules. Dysfunction leads to accumulation of cellular debris and lysosomal storage diseases but does not directly impair ATP production or cause lactic acidosis under aerobic conditions.
B. Endoplasmic reticulum: The endoplasmic reticulum (ER) is involved in protein synthesis, folding, and lipid metabolism. ER dysfunction can result in misfolded proteins and stress responses, but it does not directly explain decreased ATP production or exercise-induced lactic acidosis.
C. Mitochondria: Mitochondria are the site of oxidative phosphorylation, generating the majority of ATP in the cell by utilizing oxygen to drive the electron transport chain. Dysfunction impairs aerobic ATP production, forcing cells to rely on anaerobic glycolysis, which produces excess lactate, explaining the patient’s lactic acidosis, muscle weakness, and exercise intolerance.
D. Golgi apparatus: The Golgi apparatus modifies, sorts, and packages proteins and lipids for transport within or outside the cell. While essential for cellular function, Golgi dysfunction does not directly cause a reduction in ATP generation or lactic acidosis.
E. Peroxisome: Peroxisomes contain enzymes for lipid metabolism and reactive oxygen species detoxification. Defects can cause metabolic disorders such as Zellweger syndrome, but peroxisomal dysfunction does not directly impair ATP production in aerobic conditions.
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Related Questions
Correct Answer is B
Explanation
A. Viruses reproduce independently through binary fission: Binary fission is a form of asexual reproduction used by prokaryotic cells such as bacteria. Viruses cannot reproduce independently because they lack cellular machinery and rely entirely on host cells for replication.
B. Viruses are obligate intracellular parasites that require host cells to replicate: Viruses are acellular pathogens that cannot carry out metabolism, synthesize proteins, or replicate without a host cell. They invade host cells, hijack the host's transcription and translation machinery, and assemble new virions, classifying them as obligate intracellular parasites.
C. Viruses are unicellular organisms containing ribosomes: Viruses are not cells and do not contain ribosomes, cytoplasm, or any internal organelles. They are non-living particles composed primarily of nucleic acid and protein.
D. Viruses generate ATP through oxidative phosphorylation: Viruses lack mitochondria or any energy-producing machinery, so they cannot generate ATP. Energy production is entirely dependent on the host cell’s metabolic processes.
E. Viruses are classified as eukaryotic microorganisms: Viruses are not classified as eukaryotes because they do not have a nucleus, membrane-bound organelles, or independent metabolic activity. They are a distinct category of acellular infectious agents.
Correct Answer is A
Explanation
Eukaryotic cells are characterized by having a true nucleus, which houses the cell’s genetic material enclosed within a nuclear membrane. In addition, they contain various membrane-bound organelles, such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes, each performing specialized cellular functions. This organization allows compartmentalization of metabolic processes, efficient energy production, and regulated protein synthesis. In contrast, prokaryotic cells lack a nucleus and membrane-bound organelles, with DNA located in a nucleoid region. The presence of these features distinguishes eukaryotes from prokaryotes and is fundamental to understanding their structural and functional complexity.
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