Grwoth factors promote cell growth by acting on –
**Core Concept**
Cell growth is a complex process regulated by various growth factors, which are proteins that bind to specific receptors on the cell surface, triggering a cascade of intracellular signaling pathways. These pathways ultimately lead to the activation of transcription factors that regulate gene expression, promoting cell proliferation and growth.
**Why the Correct Answer is Right**
The correct answer involves the action of growth factors on their respective receptors, leading to the activation of tyrosine kinases. This activation triggers the phosphorylation and activation of downstream signaling molecules, such as PI3K/AKT and MAPK/ERK pathways. These pathways ultimately lead to the activation of transcription factors like NF-κB and AP-1, which regulate the expression of genes involved in cell growth and proliferation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because growth factors primarily act on the cell surface, not on the nucleus. The nucleus is the site of gene transcription and regulation, but growth factors do not directly act on the nucleus.
* **Option B:** This is incorrect because growth factors do not primarily act on cell membranes. While some growth factors may interact with cell membranes, their primary action is on the cytoplasmic signaling pathways.
* **Option C:** This is incorrect because growth factors do not primarily act on the extracellular matrix. While the extracellular matrix provides a structural framework for cells, growth factors primarily interact with cell surface receptors.
**Clinical Pearl / High-Yield Fact**
Growth factors play a crucial role in tissue repair and regeneration. They are often used therapeutically to promote wound healing, tissue repair, and angiogenesis. Understanding the action of growth factors is essential for the development of targeted therapies for various diseases, including cancer and degenerative disorders.
**Correct Answer: C, Cell surface receptors**