Ribosome Cys:oic TeR of pancreatic 邃 acinar cells Ribosome A Schematic diagram B. TEM C SEM D. Confocal F Figure 8.7 The rough endoplasmic reticulum(RER)(a) dent.(e)Scanning electron micrograph of the RER in a pan- Schematic diagram showing the stacks of flattened cistemae creatic acinar cell. (d) Visualization of the ER in a whole cul hat make up the rough ER. The cytosolic surfoce of the tured cell by Laser scanning confocal microscopy. The ER brane contains bound ribosomes, which gives the cis. rae their rough appearance. ( b)Transmission electron
Microsome bynes (100-200nm) ER Homogenate Whoe cells, nucle ER Microsomes are heterogeneous mixtures of similar-sized vesicles formed from membranes of the ER and Golgi complex Microsomes retain activity during purification, allowing studies of function and composition
A. Functions of the rEr Proteins synthesized on ribosomes of rEr include secretory proteins integral membrane r roared proteins, in cytosol soluble proteins of organelles m们 COTRANSLATIONAL IMDORT POSTTRANSLATIONAL IMPORT Figure 20-14 Int either remains n the ER or is tansported va various vesides and e Golg small nbcsomal subunits associate woth each other and wit complex to anoth nal a mFNA t enters one of two altemative pathways b)if dest red for any od the compartments of the endome membrane into the lumen (cistemal space of the ER as synthesis contin clcus occurs via the nuclear pores, using a mechanism differert from nut This process s cotranslational import The completed polypeptide then ved in posttranslation uptake by ocher organelles
A. Functions of the rER v Proteins synthesized on ribosomes of rER include: Ø secretory proteins, Ø integral membrane proteins, Ø soluble proteins of organelles
.o Modification and processing of newly synthesized proteins: glycosy lation in the rER; The precursor of 14 a glucose a mannose residues is the same N-acetylglucosamine in plants, animals, cyTosoL and single-celled eukaryotes ER LUMEN ⊙ polypeptide chain then remove 3 glucoses and 1 mannose in the er lipid-linked oligosaccharide N-linked: linked to the amide nitrogen of asparagine (er) O-linked: linked to the hydroxyl group serine or threonine via GalNac (in Golgi)
v Modification and processing of newly synthesized proteins: glycosylation in the rER; N-linked: linked to the amide nitrogen of asparagine (ER) O-linked: linked to the hydroxyl group serine or threonine via GalNac (in Golgi) The precursor of 14 residues is the same in plants, animals, and single-celled eukaryotes then remove 3 glucoses and 1 mannose in the ER
.o Quality control of newly synthesized proteinS---The role of N-linked glycosylation in ER protein folding TThe lumen of rer contains. >BIP and calnexin(chaperones): that recognize and bind to unfolded or mis-folded proteins and guide them for correct conformation: i Protein disulfide isomerase(PDD >Glucosyl-transferase(monitoring enzyme) recognizes unfolded or misfolded proteins and adds a glucose to the end of oligo Quality control: ensuring that misfolded proteins do not leave er
v Quality control of newly synthesized proteins---The role of N-linked glycosylation in ER protein folding