Which of the following do not have ribosomes for protein synthesis
**Core Concept**
Ribosomes are small organelles found throughout the cytoplasm of eukaryotic cells and on the surface of the endoplasmic reticulum in prokaryotic cells. They are responsible for translating messenger RNA (mRNA) into specific sequences of amino acids, which are then assembled into proteins. Ribosomes are essential for protein synthesis in all cells.
**Why the Correct Answer is Right**
The correct answer is **prokaryotic cell membranes**. Prokaryotic cells, such as bacteria, do not have ribosomes attached to their cell membranes. Instead, they have ribosomes freely floating in the cytoplasm. This is because prokaryotic cells lack a true nucleus and other membrane-bound organelles found in eukaryotic cells. The absence of ribosomes on the cell membrane allows for the rapid translation of mRNA into proteins, which is essential for the rapid growth and division of prokaryotic cells.
**Why Each Wrong Option is Incorrect**
**Option A:** Mitochondria do have ribosomes, specifically 70S ribosomes, which are responsible for translating mRNA into proteins involved in the electron transport chain and other mitochondrial functions.
**Option B:** The endoplasmic reticulum (ER) has ribosomes attached to its surface, known as rough ER, which are responsible for translating mRNA into proteins that are secreted or embedded in the plasma membrane.
**Option C:** Lysosomes do not have ribosomes, but this is because they are involved in protein degradation, not synthesis. Lysosomes contain digestive enzymes that break down proteins and other molecules, but they do not produce new proteins.
**Clinical Pearl / High-Yield Fact**
It's worth noting that ribosomes are essential for protein synthesis in all cells, but the location and type of ribosomes can vary depending on the cell type and function.
**Correct Answer:** D. Lysosomes