Cell compartments and protein sorting

What organelles are involved in protein processing?

proteins to cytosol to other organelles to nucleus/mitochondria

proteins to ER to Golgi to plasma membrane or endosomes/lysosomes for recycling to exocytosis

How does protein synthesis at the ER occur?

An N-terminal hydrophobic sequence directs ribosome to ER

this is done by signal recognition particle (SRP) which causes binding to SRP receptor in ER membrane

Causes amino acid to move into translocation channel

ER signal sequence allows channel to be open, binds to channel as protein chain is threaded through, ER signal sequence is then cleaved by signal peptidase

How does insertion of integral membrane protein to ER work?

Amino acid chain has a signal sequence but also a stop hydrophobic sequence

translocation channel stops threading protein once it reaches stop sequence by cleaving off start signal sequence

produces a protein chain with portion in ER lumen and portion outside

What types of glycosylation of proteins in the ER are there?

N-linked glycosylated protein is when polysaccharide chain branches off of amino acid side chain from a nitrogen

O-linked is the same but from oxygen

What pathway do proteins from ER ribosomes follow?

From ER to cis — medial — trans of Golgi

Then exit via exocytosis, secretory vesicle in signal mediated exocytosis or to lysosome for products via endocytosis

What are the types of endocytosis pathways?

Phagocytosis of solid particles via pseudopodium into phagosome

Pinocytosis of extracellular fluid into vesicle

Receptor-mediated endocytosis via formation of coated vesicle then early endosome and late endoscope and finally lysosome