Golgi Apparatus/ER

Rough ER → Golgi → secretory vesicles → cell exterior

What is the main secretory pathway of secreted proteins?

1. radioactive amino acids added to the cell (pulse)

2. amino acids absorbed by cell & added to proteins

3. after time, the non-incorporated amino acids were removed

4. non-radioactive amino acids are added to allow normal cell functioning (chase)

5. during this time, the labeled proteins were partitioned into organelles.

Describe the pulse-chaise experiment:

Smooth ER

This has no ribosomes and is involved in lipid metabolism.

Rough ER

This is covered in ribosomes on the outer surface and is a key player in protein sorting.

Endoplasmic Reticulum

This is a network of membrane-enclosed tubules and sacs
(cisternae), extending from the nuclear membrane throughout the cytoplasm.

Signal Hypothesis

This is the hypothesis that small pieces of the protein can direct protein localization. These sequences are called signal, target, or sorting sequences (Blobel).

This is a sequence of amino acids that directs the protein to the ER during translation.

N-terminus → Hydrophobic Core → Cleavage Site

Describe the ER targeting sequence:

cytoplasm

Translation begins in the _________________.

This complex recognizes signal sequences and binds them to the ER membrane where they grow and are eventually released to the ER lumen

What is an SRP Complex and how does it work?

A translocon is a channel protein that moves polypeptides across membranes.

What is a translocon?

BiP

This acts as a ratchet to pull the polypeptide chain through the channel and into the ER (molecular motor)- each BiP keeps grabbing until translocation is finished.

This is the translocon itself.

What is a Sec61 protein?

These are receptors on the translocon that are attached to BiP.

What is the Sec62/Sec63 Protein?

Brownian Motors

These motors exploit stochastic thermal fluctuations.

interior; exterior

The ER lumen is topologically equivalent to the _____________ of Golgi, lysosomes, peroxisomes and _____________ of the cell and interior

Co-translational translocation

How are proteins with an internal transmembrane sequence inserted into the membrane?