Src kinases are non-receptor tyrosine kinases that regulate essential processes including growth, survival, adhesion, and differentiation. They are generally found in the cytoplasm and transduce signals from transmembrane receptors to downstream effectors. Synthesis of src kinases is initiated at which of the following sites?
- Free-standing ribosomes
- Rough endoplasmic reticulum
- Golgi apparatus
- I only
- II only
- I and II
- I, II, and III
Click for Explanation
The question stem states that src kinases are not RTKs and are instead found in the cytoplasm, indicating that they are likely produced by freely floating ribosomes. As such, they would not be processed through the secretory pathway and would not likely be in the rough ER or the Golgi apparatus.
I. True. Translation of intracellular proteins is always initiated on free-standing ribosomes in the cytosol.
II. False. Proteins that are destined for secretion are translated on ribosomes bound to the rough endoplasmic reticulum, but proteins with an intracellular destination are synthesized on free ribosomes.
III. False. The Golgi apparatus is responsible for packaging proteins that are to be secreted by the cell.
Answer: A. See explanations above.
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