Cell Biology: Chapters 13 + 14

ER

“within the cytoplasm network”, system of tubes and sacs formed by membranes

SER

without bound ribosomes, functions in lipid synthesis, carbohydrate metabolism, drug detoxification

RER

with bound ribosomes, modifies proteins produced on the ribosomes

Role is Smooth ER

• Usually minor component

• Abundant in those cells that:

– Synthesize lipid-based compounds, e.g.

steroid hormone biosynthesis

– Detoxify lipid-soluble compounds

• liver common tissue for detoxification

• modifies lipid soluble compounds to make water soluble; then excreted in urine

starting point of the biosynthetic pathway

Rough Endoplasmic Reticulum

post-translational and co-translational

The two basic targeting pathways

cytoplasm, nucleus, and mitochondria, chloroplasts and peroxisomes

post-translational goes to

secretory pathway

co-translational goes to

N-terminal

Usual signal Location with Protein of ER

+

signal removal of ER

“Core” of 6-12 mostly hydrophobic amino acids, often preceded by one or more basic amino acids

Nature of Signal ER

sorting signal

a motif in a protein (either a short sequence of amino acids or a covalent modification) that is required for it to be incorporated into vesicles that carry it to a specific destination.