MCAT® ExamBiological and Biochemical Foundations of Living SystemsHard
A geneticist discovers a new gene that is expressed exclusively in the cells of the central nervous system and is crucial for neuronal development. When this gene is mutated, it leads to severe neurological defects. Which of the following terms best describes the expression pattern of this gene?
- ATissue-specific
- BInducible
- CConstitutive
- DRepressible
Show answer & explanationAnswer & explanation
Correct answer: A. Tissue-specific
The gene is described as being expressed 'exclusively in the cells of the central nervous system.' This indicates that its expression is limited to a particular tissue type, which is the definition of tissue-specific gene expression. This is a common mechanism for regulating specialized functions in multicellular organisms.
Why the other options are wrong
- B. Inducible gene expression means the gene is turned on in response to a specific stimulus, not necessarily restricted to a particular tissue type (though it can be inducible within a tissue). The key here is 'exclusively in...'.
- C. Constitutive gene expression (housekeeping genes) means the gene is expressed continuously in all cells, which contradicts 'exclusively in the central nervous system'.
- D. Repressible gene expression means the gene's expression is normally on but can be turned off by a specific molecule, which does not describe its localization of expression.
Tissue-Specific Gene Expression
The phenomenon where a particular gene is expressed or activated only in specific cell types or tissues within a multicellular organism, contributing to cellular differentiation and specialized functions.
- Restricted to certain tissues.
- Achieved by specific transcription factors.
- Crucial for cell differentiation.
- Example: hemoglobin in red blood cells.
Memory trick: Tissue-Specific: 'T'argeted to 'T'ype!