Cell Bio Chapter 11: Protein Trafficking into the Endoplasmic Reticulum

Er; golgi apparatus

The endomembrane system starts at the ____ and goes through the _____

Endosomes, lysosomes, peroxisomes, cell membrane

What are the possible end destinations of the endomembrane system?

Non-cytosolic environment

What chemical similarities does the organelle lumen and the extracellular matrix share?

Outward movement

Movement from the RNA to rough ER to Golgi to organelles and membranes is called?

Secretory Pathway

A pathway for proteins to move from the rough ER through the Golgi apparatus to the plasma membrane or secretory vesicles.

Resident proteins

What kind of proteins need to stay in the ER or Golgi and will not progress

Rough ER

Continuous with outer nuclear membrane, made of flat cisternae, site of protein synthesis, covered in ribosomes

Smooth ER

Made of tubules, site of lipid synthesis, has no ribosomes

CLIMP-63

Is a protein that goes between the sides of cisternae to hold the flat shape

N-terminus

What part of the peptide will determine the pathway for protein translation in the ER?

Signal recognition particle

What does SRP stand for?

Er signal sequence

What recruits SRP?

Blocks ribosome entrance chamber which pauses translation

What is the function of SRP?

SRP receptor passes off ribosome to translocon

First step of soluble proteins to enter the endoplasmic reticulum lumen.

When polypeptide synthesized it will be translocated to luminal side

Second step of soluble proteins to enter the endoplasmic reticulum lumen.

Signal peptidase cleaves off ER signal sequence

Third step of soluble proteins to enter the endoplasmic reticulum lumen.

Final polypeptide now in ER lumen

Fourth (last) step of soluble proteins to enter the endoplasmic reticulum lumen.

Polypeptides are translocated into the endoplasmic reticulum lumen simultaneously with their synthesis on ribosomes.

What is co-translation translocation?

Single pass proteins

One hydrophobic stop-sequence stays in the membrane, next amino acids end up in cytosol

Multi-pass proteins

Hydrophobic start and stop signal sequences weave protein into membrane

Disulfide bonds and glycosylation

What covalent modification is only found in the ER lumen?

Oxygen

What buffers molecules in cytosol but not outside the cell?

The loss of electrons

What is oxidation?

Cysteine

_____ amino acids are protected by covalent bonds between sulfurs. It protects electrons and stabilize protein structure

Oligosaccharide

Adding _____ generates a glycoprotein

Glycocalyx

What kind of barrier do glycoproteins posses?

Carbohydrates (glycans) are covalently attached to proteins or lipids in the endoplasmic reticulum (ER) and Golgi apparatus

What is glycosylation?

14-sugar oligosaccharide

What oligosaccharide will attach first in glycosylation?

Dolichol lipid on bilayer

Where does the 14-sugar oligosaccharide attach as the starting point?

Oligosaccharyl transferase; signal sequence on protein

The 14-sugar is then transferred to the protein by what and where does it attach?

ER exit sites (ERESs)

Only proteins correctly folded and modified can leave the ER via

Bip and Calnexin (chaperone proteins)

_____ and ____ bind to misfolded proteins

Hydrophobic amino acids are exposed

When do BiP and calnexin bind to misfolded proteins?

Hold back misfolded proteins

What do BiP and Calnixen do?

Go forward

Anterograde means to

Go backward

Retrograde means to

Retrograde transport

What kind of transport returns proteins to prior organelle? This transport uses ER retention signal

Unfolded protein response

If the misfolded protein rate is high ____ is triggered

BiP

What chaperone protein normally binds to Ire1 and proteins?

Dimers

When BiP is not bound to Ire1 what forms?

Signaling cascade

What causes more chaperone proteins and ER membrane to be produced?

Dislocation

Misfolded proteins are removed form ER and ubiquitinated/sent to proteosome

One lumen side and one cytosolic side

What does it mean when membrane proteins are asymmetrical?

Asymmetry

____maintenance starts in ER, maintained throughout endomembrane system

The fluid filled space inside the ER membrane

What is the lumen of the Endoplasmic Reticulum?

KDEL sequence

A specific target-retrieval signal found on proteins that are supposed to live and work permanently inside the ER (resident proteins)

Lysine

What does the K in the KDEL sequence stand for?

Aspartic Acid

What does the D in the KDEL sequence stand for?

Glutamic acid

What does the E in the KDEL sequence stand for?

Leucine

What does the L in the KDEL sequence stand for?

Acts a return address for resident proteins

What is the function of the KDEL sequence?