Organelle function and intracellular protein trafficking pathways tested on USMLE Step 1.
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- What is the primary function of the rough endoplasmic reticulum (RER)?
- Synthesizes and folds proteins destined for secretion, the plasma membrane, or other organelles
- What is the primary function of the smooth endoplasmic reticulum (SER)?
- Lipid/steroid synthesis and detoxification of drugs and toxins
- Which type of cell has abundant smooth ER?
- Steroid hormone-producing cells (e.g., adrenal cortex, Leydig cells)
- Which type of cell has abundant rough ER?
- Cells that secrete large amounts of protein, such as plasma cells
- What is the general function of the Golgi apparatus?
- Modifies, sorts, and packages proteins and lipids for their final destination
- Which organelle does the cis face of the Golgi apparatus face?
- The endoplasmic reticulum
- Which structure does the trans face of the Golgi apparatus face?
- The plasma membrane
- In the Golgi, lysosomal enzymes are tagged with ____ to direct them to the lysosome.
- mannose-6-phosphate
- I-cell disease is caused by a deficiency of which enzyme?
- N-acetylglucosaminyl-1-phosphotransferase
- What happens to lysosomal enzymes in I-cell disease?
- They are secreted out of the cell instead of being delivered to lysosomes
- Proteins bearing the ____ sequence are retrieved and retained in the endoplasmic reticulum.
- KDEL
- What does the signal recognition particle (SRP) do?
- Binds a signal sequence on a nascent protein and directs the ribosome to the rough ER
- COPII-coated vesicles transport cargo in which direction?
- From the ER to the Golgi (anterograde)
- COPI-coated vesicles transport cargo in which direction?
- From the Golgi back to the ER (retrograde)
- What proteins do free (cytosolic) ribosomes synthesize?
- Proteins that stay in the cytosol or are imported into the nucleus, mitochondria, or peroxisomes