15.1 - Intracell. Compartments & Prot. Trans. Flashcards
What is protein sorting?
The process by which proteins are directed to specific cellular locations.
What determines the destination of a protein?
A sorting signal, an amino acid sequence in the protein.
How do proteins destined for the nucleus reach their destination?
They pass through nuclear pores.
What are the two types of ER?
Rough ER and Smooth ER.
What is the function of the Signal Recognition Particle (SRP)?
It binds to the signal sequence, slows protein synthesis, and directs the ribosome to the SRP receptor on the ER
What are the two types of proteins in the ER?
Soluble proteins and membrane proteins
What is glycosylation?
The process of attaching oligosaccharides to proteins, converting them into glycoproteins
What are the functions of glycosylation?
Protect proteins from degradation, guide proteins to organelles, and promote cell recognition
What happens to misfolded proteins in the ER?
They are either folded correctly by chaperones or degraded if folding fails
What is the cis face of the Golgi apparatus?
The entry side of the Golgi where proteins arrive from the ER.
What are the two types of protein secretion?
Unregulated secretion and regulated secretion.
What is an example of regulated secretion?
Insulin release based on blood glucose levels.
Cells undergo translation to produce _____
polypeptides
What happens to polypeptides after translation?
They are modified and transported within the cell to perform their functions
What determines where a protein is sent in the cell?
A sorting signal (amino acid sequence) directs the protein to the correct location
What are the destinations of proteins within a cell?
Nucleus (via nuclear pores).
Chloroplasts, mitochondria, peroxisomes, and ER (via translocators).
Other destinations (via vesicles from the ER).
How does the sorting signal guide proteins?
It is a specific amino acid sequence that directs proteins to their appropriate locations.
What are the structural differences between rough and smooth ER?
Rough ER has ribosomes attached to its surface, while smooth ER does not.
What happens to proteins with an ER signal sequence?
Ribosomes synthesizing these proteins bind to the ER, and the proteins enter the ER via translocation channels
What is the role of the Signal Recognition Particle (SRP)?
It binds to the signal sequence, slows protein synthesis, and guides the ribosome to the SRP receptor on the ER.
What happens to soluble proteins in the ER?
They are released into the lumen of the ER, modified, and transported to their destinations
What happens to membrane proteins in the ER?
They remain embedded in the ER membrane and are anchored by stop-transfer sequences
What is glycosylation?
The addition of oligosaccharides to proteins, converting them into glycoproteins
What is the function of oligosaccharides in glycosylation?
- Protect proteins from degradation.
- Guide proteins to other organelles.
- Promote cell recognition
What role do chaperone proteins play in the ER?
They ensure proper folding of proteins and direct misfolded proteins for degradation if necessary
How do proteins leave the ER?
They bud off in vesicles and fuse with the Golgi apparatus.
What are the entry and exit points of the Golgi?
Entry: Cis face
Exit: Trans face
What modifications occur in the Golgi?
Proteins undergo further oligosaccharide processing and are sorted to lysosomes, the cell surface, or back to the ER
What is unregulated secretion?
Continuous delivery of membrane proteins (e.g., receptors) to the cell surface
What is regulated secretion?
Controlled release of proteins, such as insulin, in response to specific signals like blood glucose levels
How are ribosomes directed to the ER during protein synthesis?
Ribosomes synthesizing proteins with an ER signal sequence bind to the ER membrane, directing these proteins into the ER via translocation channels.
What mechanism explains how proteins destined for the ER enter the organelle?
The ER signal sequence and translocation channels guide proteins into the ER as they are synthesized.
What mechanism shows how proteins are guided to their destinations within a cell?
Signal sequences act as “addresses,” guiding proteins to their correct locations in the cell based on their specific amino acid sequence
What mechanism involves the Signal Recognition Particle (SRP) in guiding ribosomes to the ER?
SRP binds to the ER signal sequence, slows protein synthesis, and directs the ribosome to the SRP receptor on the ER membrane
How does the SRP system ensure accurate targeting of proteins to the ER?
By binding to the signal sequence, SRP pauses synthesis and interacts with the SRP receptor to ensure the ribosome attaches to the ER correctly
What mechanism explains how soluble proteins are released into the ER lumen?
Soluble proteins are guided into the ER lumen during synthesis and are released into the lumen to undergo modification and transport
How do membrane proteins anchor themselves within the ER membrane?
Stop-transfer sequences within membrane proteins interact with the ER membrane, halting translocation and embedding the protein into the membrane.
What mechanism describes how proteins are glycosylated in the ER?
Oligosaccharides are transferred from the lipid Dolichol to asparagine residues on proteins, converting them into glycoproteins. This process protects proteins, guides them to organelles, or aids in cell recognition.
What mechanism involves chaperone proteins in ensuring proper protein folding?
Chaperones fold proteins properly in the ER, and if folding fails, they direct misfolded proteins for degradation. Properly folded proteins are packaged into vesicles for transport to the Golgi apparatus.
What mechanism sorts and transports proteins through the Golgi apparatus?
Proteins enter the Golgi at the cis face, undergo further oligosaccharide modifications, and are sorted at the trans face for lysosomes, the cell surface, or recycling back to the ER.
How does the Golgi apparatus handle proteins after modification?
The trans-Golgi network directs proteins to their destinations, such as the plasma membrane, lysosomes, or secretory vesicles.
What mechanism explains how proteins are secreted from the cell?
Secretory vesicles transport proteins from the Golgi apparatus to the plasma membrane, where they are released via unregulated or regulated secretion.
How does regulated secretion work?
Proteins, such as insulin, are stored in secretory vesicles and released only in response to specific signals, like changes in blood glucose levels.
