Chp 12 Flashcards
What are the structure and functions of the rough ER?
The rough ER has ribosomes attached to its surface; it synthesizes and processes proteins for secretion or membrane insertion.
What are the structure and functions of the smooth ER?
The smooth ER lacks ribosomes; it synthesizes lipids, detoxifies chemicals, and stores calcium ions.
What are the structure and functions of the Golgi apparatus?
The Golgi apparatus modifies, sorts, and packages proteins and lipids for delivery to different destinations.
What is the primary function of the lysosome?
The lysosome digests and recycles cellular waste and foreign material.
Why do cells that produce steroid hormones contain more smooth ER than polypeptide-producing cells?
Steroid hormone-producing cells need more smooth ER for lipid and steroid synthesis.
How is membrane asymmetry established in the ER?
Membrane asymmetry is established by the orientation and modification of proteins and lipids as they are synthesized and inserted into the ER membrane.
What is the stationary cisternae model for protein movement through the Golgi apparatus?
This model proposes that Golgi cisternae remain in place and cargo is transported via vesicles between cisternae.
What is the cisternal maturation model for protein movement through the Golgi apparatus?
This model proposes that Golgi cisternae themselves mature and move forward, carrying cargo with them.
What is the difference between anterograde and retrograde movement in the Golgi and endomembrane system?
Anterograde movement is forward (ER → Golgi → plasma membrane); retrograde is backward (plasma membrane/Golgi → ER).
What are the final destinations for proteins sorted via the posttranslational import pathway?
Proteins may be targeted to organelles such as mitochondria, chloroplasts, peroxisomes, or the nucleus.
What are the final destinations for proteins sorted via the cotranslational import pathway?
Proteins are directed to the ER, Golgi, lysosomes, plasma membrane, or for secretion.
How is the polypeptide signal sequence recognized by the ER?
The signal sequence is recognized by the signal recognition particle (SRP) during translation.
What is the signal recognition particle (SRP) and what are its three active sites?
SRP is a ribonucleoprotein that recognizes the ER signal sequence; it has sites for signal sequence binding, SRP receptor binding, and GTP binding/hydrolysis.
How does the SRP mechanism of cotranslational import work?
SRP binds the signal sequence and ribosome, pauses translation, docks at the SRP receptor on the ER, and transfers the ribosome to the translocon. Components involved include SRP, ER signal sequence, translocon, SRP receptor, pore, ribosome receptor, signal peptidase, and GTP.
What are the steps involved in exocytosis and endocytosis?
Exocytosis: vesicle fuses with plasma membrane, releasing contents. Endocytosis: plasma membrane engulfs material, forming a vesicle.
What is the difference between constitutive, regulated, and polarized secretion?
Constitutive: continuous release (e.g., collagen), regulated: triggered by signals (e.g., insulin), polarized: directed to specific cell regions (e.g., neurotransmitter release).
What is the role of signal sequences, start-transfer, and stop-transfer sequences in membrane protein integration?
They direct insertion and orientation of proteins in the membrane during synthesis.
Which mechanism results in an integral membrane protein with the N-terminus in the ER lumen?
A single start-transfer sequence with no stop-transfer sequence places the N-terminus in the lumen.
Which mechanism results in an integral membrane protein with the C-terminus in the ER lumen?
A start-transfer sequence followed by a stop-transfer sequence places the C-terminus in the lumen.
How is a multipass membrane protein (e.g., GPCR) synthesized?
Multiple start-transfer and stop-transfer sequences allow the protein to span the membrane several times.
