Protein Sorting Flashcards
(18 cards)
What is protein sorting, and why is it important?
Protein sorting is the process of directing proteins to their correct cellular locations. It ensures proteins reach the right organelle, membrane, or are secreted outside the cell.
How are proteins sorted to different cellular destinations?
Proteins have signal sequences (short amino acid motifs) that are recognized by cellular machinery, directing them to the ER, mitochondria, nucleus, or elsewhere.
What is the role of the endomembrane system in the cell?
It manages the production, processing, and transport of proteins and lipids. Key components include the RER, SER, Golgi apparatus, lysosomes, vesicles, and plasma membrane.
Which organelle is responsible for protein modification and packaging?
The Golgi apparatus modifies proteins (e.g., glycosylation), sorts them, and packages them into vesicles for delivery.
Are all proteins translated on the rough ER?
No.
Proteins for secretion, membranes, or endomembrane organelles → translated on RER-bound ribosomes.
Cytosolic, nuclear, mitochondrial proteins → translated on free ribosomes in the cytoplasm.
What happens if a drug disrupts vesicle transport in the endomembrane system?
Protein trafficking fails → proteins may mislocalize, accumulate, or degrade → cell functions like secretion, membrane repair, or digestion are impaired.
How would a mutation in a signal sequence affect a protein?
It could prevent the protein from reaching its correct destination, leading to loss of function or harmful accumulation in the wrong compartment.
How can you determine where a protein was translated?
Based on its destination/function:
Secreted/membrane proteins: translated on the RER.
Cytosolic/nuclear/mitochondrial proteins: translated on free ribosomes.
What is the signal recognition particle (SRP) and its role in protein sorting?
SRP recognizes ER signal sequences on nascent peptides, pauses translation, and directs the ribosome to the ER membrane for co-translational insertion.
What is the consequence of a defective SRP or SRP receptor?
Proteins destined for secretion or membranes may not enter the ER, leading to cytosolic mislocalization and loss of function.
What is the function of the nuclear envelope?
It separates the nucleus from the cytoplasm and controls the movement of RNA and proteins in and out of the nucleus.
What is the role of the rough endoplasmic reticulum (RER)?
It synthesizes proteins destined for secretion, membranes, or organelles and helps fold and modify them.
What is the function of the smooth endoplasmic reticulum (SER)?
It synthesizes lipids, detoxifies harmful substances, and stores calcium ions.
What does the Golgi apparatus do in the cell?
It modifies, sorts, and packages proteins and lipids received from the ER for delivery to their final destinations.
What is the role of transport vesicles in the endomembrane system?
They carry proteins and lipids between the ER, Golgi, lysosomes, plasma membrane, and other organelles.
What do lysosomes do in the cell?
They digest waste materials, damaged organelles, and ingested substances using hydrolytic enzymes.
What is the function of endosomes?
They sort internalized materials from endocytosis and direct them to lysosomes or back to the membrane.
What role does the plasma membrane play in the endomembrane system?
It regulates what enters and exits the cell, participates in cell signaling, and receives proteins/lipids via exocytosis.
