All of the following proteins synthesised by free-ribosomes, EXCEPT
**Core Concept**
Proteins synthesized by free ribosomes are generally involved in cellular housekeeping functions, such as metabolism, DNA replication, and cell signaling. These proteins are often cytosolic and do not require secretion or membrane integration. Free ribosomes are found in the cytosol and are responsible for synthesizing proteins that remain in the cytosol or are targeted to other organelles.
**Why the Correct Answer is Right**
Proteins synthesized by free ribosomes typically include enzymes involved in glycolysis, the pentose phosphate pathway, and other metabolic pathways. These enzymes catalyze reactions that occur in the cytosol and do not require membrane integration or secretion. Examples of proteins synthesized by free ribosomes include glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not specified, but some proteins synthesized by rough endoplasmic reticulum (RER) may be transported to the Golgi apparatus and then secreted, whereas free ribosomes synthesize proteins that remain in the cytosol or are targeted to other organelles.
**Option B:** Incorrect because it is not specified, but some proteins involved in cell signaling may be synthesized by free ribosomes and targeted to the plasma membrane.
**Option C:** Incorrect because it is not specified, but some proteins synthesized by free ribosomes may be involved in DNA replication and repair.
**Clinical Pearl / High-Yield Fact**
Proteins synthesized by free ribosomes are often involved in metabolic pathways and may be targeted to other organelles, such as mitochondria or peroxisomes.
**Correct Answer:** A.