Lecture 12 - Protein sorting_ Endoplasmic Reticulum (1)

What is the function of the small subunit of the ribosome during protein synthesis?

It finds a messenger RNA strand and ensures that each codon pairs with the anticodon.

Where do nearly all proteins begin their synthesis?

On ribosomes in the cytosol.

What are the main steps of the secretory pathway?

1. Translates from mRNA in ribosomes in the cytoplasm 2. Enters the ER lumen 3. Goes from the ER to the Golgi in a vesicle 4. Transits the Golgi 5. Leaves the Golgi in a vesicle 6. The vesicle fuses the cell membrane 7. It is outside.

Who received the Nobel Prize in 1974 for work related to the secretory pathway?

George Palade.

What is a signal peptide?

A short peptide (usually 16-30 amino acids long) present at the N-terminus of newly synthesized proteins destined for the secretory pathway.

What guides the ER signal sequence to the ER membrane?

A signal-recognition particle (SRP) and an SRP receptor in the ER membrane.

What is the core of the translocator called?

The Sec61 complex.

What is N-Linked Glycosylation?

The addition of a common N-Linked oligosaccharide to proteins synthesized in the Rough ER.

What role does Calnexin play in protein folding?

Calnexin binds to monoglucosylated incompletely folded proteins and retains them in the ER, aiding in proper folding.

What do chaperone proteins like Hsp70/BiP do?

They prevent protein misfolding and aggregation by protecting peptides from interacting with other misfolded proteins.