MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A patient experiences symptoms including chronic fatigue, muscle weakness, and a general inability to tolerate cold temperatures. Blood tests reveal low levels of thyroid hormones. Which of the following cellular structures or processes would be most directly affected by this deficiency, leading to the observed symptoms?
- AMitochondrial metabolic rate
- BRibosome function
- CLysosomal degradation
- DPlasma membrane fluidity
Show answer & explanationAnswer & explanation
Correct answer: A. Mitochondrial metabolic rate
Thyroid hormones play a crucial role in regulating basal metabolic rate by influencing mitochondrial activity, particularly oxidative phosphorylation. Low thyroid hormone levels would decrease mitochondrial metabolic rate, leading to reduced ATP production and heat generation, manifesting as fatigue, muscle weakness, and cold intolerance.
Why the other options are wrong
- B. Ribosome function (protein synthesis) is generally not the primary and direct target of thyroid hormone deficiency.
- C. Lysosomal degradation is involved in waste breakdown and recycling, not directly regulated by thyroid hormones as a primary metabolic rate factor.
- D. Plasma membrane fluidity is influenced by lipid composition and temperature, but not a direct primary target of thyroid hormone deficiency leading to these systemic symptoms.
Thyroid Hormone Function
Thyroid hormones (T3 and T4) are crucial regulators of basal metabolic rate, growth, and development, primarily by influencing mitochondrial activity and gene expression.
- Increase metabolic rate and oxygen consumption in most tissues.
- Stimulate ATP production and heat generation.
- Essential for normal brain development and function.
Memory trick: Low thyroid means low 'ENERGY' production.