chapter 12: endomembrane system and protein sorting

Trafficking

Movement of lipids and proteins b/w organelles

List all components of the endomembrane function and their function

*ER & golgi complex are sites for protein synthesis, processing, and sorting

*endosomes- carry and sort materials brought into cell

*Lysosomes- digest ingested materials and unneeded cellular components

What is the variation in amounts of smooth and rough ER?

Cells with synthesis of secretory proteins have prominent rough ER networks

Cells that produce steroid hormones have extensive networks of smooth ER

Rough ER is the site for:

• adding carbs to glycoproteins

• Folding polypeptides

• Recognition and removal of misfolded proteins

• Assembly of multimeric proteins

Proteasome

Protease complex made to carry out selective, efficient, and processive hydrolysis of proteins

Proteasomes VS. Lysosomes

Smooth ER function

involved in drug detoxification, carb metabolism, calcium storage, and steroid biosynthesis

Golgi Apparatus

DON’T SAY FED-EX!!!!! plays a central role in membrane and protein trafficking in eukaryotes

What is the golgi a. comprised of?

Flattened membrane bounded cisternae. Usually 3-8 is called a Golgi stack

Name the 2 faces of the Golgi stack

Cis face- oriented towards the ER, called the cis-Golgi network.

Trans face- called the trans-Golgi network

What 2 models account for the flow of Lipids and proteins from the Golgi?

Anterograde vs. Retrograde transport

A-moving material toward the plasma membrane

R-flow of vesicles from Golgi cisternae back to the ER

define glycosylation and give the 2 general kinds nitrogen

• The addition of carbohydrate side chains to proteins to make glycoproteins.

N-linked: the addition of a oligosaccharide to the nitrogen atom of certain asparganine residues

O-linked: adding oligosaccharide to the oxygen atom on the hydroxyl group of some serine, threonine, and tyrosine residues

Molecular chaperones

Proteins that assist others to fold properly during or after synthesis, refold after partial denaturation, and to translocate to cellular locations

Explain what Bi P is and how it functions

• an Hsp70 molecular chaperone

• binds to the hydrophobic region of polypeptide to stop aggregation

• Polypeptide is released, binding with ATP hydrolysis which helps the protein fold.

If folded correctly, hydrophobic regions are buried. If not, process is repeated

Protein disulfide isomerase

Enzyme that can either form or break disulfide bonds between cystenines until it reaches the most stable arrangement.

Unfolded protein response (up-r)

Detects misfolded proteins by way of sensor molecules in the ER membrane. Sensors activate signaling pathways that shut down protein production (except for folding and degradation).

ERAD

Gets rid of malfunctioning proteins by sending them to be degraded by proteasomes

define a protein “tag” and give examples

A target for proteins that ensure they go to the correct location

• amino acid sequence

• Hydrophobic domain

• Oligosaccharide side chain

• Something else

What are the 2 pathways for sorting tagged polypeptides

Endomembrane system- polypeptide is transferred the ER membrane as synthesis occurs. Cotranslational import

Organelle targeted- polypeptides transported to organelles after synthesis occurs. Post translational import

What are the 3 mechanisms by which membrane enclosed organelles import proteins?

-membrane transport (must be unfolded)

-nuclear pore transport (remains folded)

-Vesicle transport (remains unfolded)

ALL REQUIRE ENERGY

Describe nuclear transport

• protein w/ localization signal binds to receptor

• Complex enters the pore

• RanGDP is phosphorylated by GEF to become ranGTP

Precursor protein

Inactive protein or peptide that can become active by post translational modification