W4 d1 and w3 day 2Bio421_5_ER protein trafficking

What are the two types of protein transport regarding the timing of protein transport to the endoplasmic reticulum (ER)?

Co-translational and post-translational protein transport.

What is the role of the signal sequence in protein transport to the ER?

It directs the ribosome-RNA complex to the protein translocator during protein synthesis.

Name one characteristic of the ER signal sequence.

It has a hydrophobic core region.

What is the ultimate fate of water soluble proteins after translocating across the ER?

They may be secreted from the cell or stay in the ER or Golgi.

What is the function of the Sec61 complex?

It serves as the ER translocator that forms a water-filled pore through the ER membrane.

What happens to the signal peptide after protein synthesis is complete in the ER?

Signal peptidase cleaves the signal peptide, releasing the protein into the ER lumen.

What defines single-pass transmembrane proteins during their translocation process?

They begin similarly to soluble ER proteins, but translation pauses until the ribosome is brought to the ER membrane.

What defines multi-pass transmembrane proteins?

They have multiple transmembrane domains and contain multiple start and stop transfer signals.

How can we predict the number of transmembrane domains in a protein?

By looking at the hydrophobic regions within the protein structure.

What distinguishes N-terminal signal sequences from internal signal sequences in transmembrane protein targeting?

N-terminal signal sequences get cleaved by signal peptidase, but internal signal sequences do not.

What are the two types of protein transport regarding the timing of protein transport to the endoplasmic reticulum (ER)?

Co-translational and post-translational protein transport.

What is the role of the signal sequence in protein transport to the ER?

It directs the ribosome-RNA complex to the protein translocator during protein synthesis.

Name one characteristic of the ER signal sequence.

It has a hydrophobic core region.

What is the ultimate fate of water soluble proteins after translocating across the ER?

They may be secreted from the cell or stay in the ER or Golgi.

What is the function of the Sec61 complex?

It serves as the ER translocator that forms a water-filled pore through the ER membrane.

What happens to the signal peptide after protein synthesis is complete in the ER?

Signal peptidase cleaves the signal peptide, releasing the protein into the ER lumen.

What defines single-pass transmembrane proteins during their translocation process?

They begin similarly to soluble ER proteins, but translation pauses until the ribosome is brought to the ER membrane.

What defines multi-pass transmembrane proteins?

They have multiple transmembrane domains and contain multiple start and stop transfer signals.

How can we predict the number of transmembrane domains in a protein?

By looking at the hydrophobic regions within the protein structure.

What distinguishes N-terminal signal sequences from internal signal sequences in transmembrane protein targeting?

N-terminal signal sequences get cleaved by signal peptidase, but internal signal sequences do not.

What is a signal peptide in protein transport?

A short peptide that tells the cell to direct the protein to the ER.

What happens during co-translational translocation?

Proteins are translocated into the ER while they are still being synthesized by ribosomes.

What dietary component can affect the composition of the signal sequence?

The amino acid composition can vary based on dietary intake.

How do ribosomes know where to begin protein synthesis?

The ribosome recognizes the start codon of the mRNA.

What is the significance of hydrophobic amino acids in signal sequences?

They help anchor the protein in the lipid bilayer of membranes.

What is required to initiate the translocation of proteins across the ER membrane?

The ribosome must be recruited to the protein translocator.

What role does the Golgi apparatus play after protein translocation?

It modifies, sorts, and packages proteins for secretion or delivery to other organelles.

What defines the ER lumen?

The interior space of the endoplasmic reticulum where proteins are folded and modified.

Why are signal sequences important for protein targeting?

They ensure proteins reach their correct destinations within the cell.

What are ER-resident proteins?

Proteins that function within the endoplasmic reticulum and are retained there.

How is protein maturation achieved in the ER?

Through proper folding and post-translational modifications such as glycosylation.

What is the relationship between the signal sequence and the ribosome?

The signal sequence is recognized by the ribosome during the synthesis of proteins destined for the ER.

What does post-translational modification include?

Chemical modifications made to proteins after they have been synthesized.

What are the consequences of improper signal sequence recognition?

Proteins may be misdirected and fail to reach their intended compartments.

What factor contributes to the stability of transmembrane proteins?

The presence of hydrophobic and charged residues in specific regions of the protein.

Why are start and stop transfer signals important?

They control the orientation and number of times a protein crosses the membrane.

What is the role of chaperone proteins in the ER?

They assist in the proper folding of newly synthesized proteins.

What occurs during glycosylation in the ER?

Sugar molecules are added to proteins, which is crucial for protein stability and function.

What triggers the export of proteins from the ER to the Golgi apparatus?

The presence of signals that mark proteins for transport.

How does the hydrophobicity of a signal sequence influence its function?

More hydrophobic sequences tend to integrate better into the membrane.

How do cells ensure that only properly folded proteins leave the ER?

By utilizing quality control mechanisms that eliminate misfolded proteins.

What is a potential outcome of mutations in signal sequences?

They can lead to diseases due to improper protein localization.

How does the endoplasmic reticulum contribute to cellular communication?

By assisting in the production of signaling proteins that can be secreted.

What is the main difference between the rough and smooth ER?

Rough ER is studded with ribosomes, while smooth ER is involved in lipid synthesis and detoxification.

What process allows proteins to pass through the ER membrane?

Translocation during protein synthesis and subsequent folding.

What is the role of the nuclear signal sequence?

It directs proteins into the nucleus through nuclear pores.

What happens to proteins that are misfolded in the ER?

They are typically targeted for degradation through the ER-associated degradation pathway.