Endoplasmic Reticulum and Golgi Complex

Summary - Cell Biology and Biochemistry Aspects

Rough ER - Biosynthesis and Processing of Proteins

1. Translation / Cotranslational Import

(1) ER signal sequence: Directing the ribosome-mRNA-polypeptide complex to the surface of the rER

(2) Signal-recognition particle (SRP)
　Recognizing and binding to the ER signal sequencing in the cytosol, blocking the translation process
　-Then binding to theSRP receptor on the ER
　-GTP hydrolysis, peptide move into the pore and SRP released, elongation of translation continues

(3) Translocon
　-SRP receptor
　-Pore protein
　-Signal peptidase

2. Posttranslationally Import
　Insertion of intergral membrane proteins

Mode I : Stop-transfer sequence
Mode II: Internal start-transfer sequence

3. Posttranslational Modification

(1) Core glycosylation of N-linked oligosaccharides
*Carrier during biosynthesis: Dolichol

　Tunicamycin: Inhibitor of N-linked glycoprotein synthesis
　　　　　　　Block the reaction between UDP-GluNAc and Dol-P

　Oligosaccharyltransgerase: Transfer the products from dolichol to the peptide( Asn - X - Ser/Thr )

(2) Protein disulfide isomerase

(3) Molecular chaperone
　Prevent aggergation between unfolded polypeptides by hydrophobic interaction.
　Proteins that help fold globular proteins.

GroEL-ES complex of E. coli
　消耗近14個ATP進行協助 folding的工作

HSP70 - Chaperonin
　Stablizing, transprot and folding.

Transition vesicles

1. Bidirectional transprot between ER, Golgi complex and between Golgi complex cistenae; coated by COPI

2. Directional transprot to CGN; coated by COPII

Golgi apparatus

˙ cis-Golgi network / medical cisternae / trans-Golgi network
方向看結構

˙ Stationary cisternae model: Shuttle vesicles between cisternae
　 Cisternal maturation model: 引Procollagen releasing 為例
行為動態模型

Smooth ER

˙Cytochrome p450: Aerobic hydration

RH + NAD(P)H + H2+ + O2 --> ROH + NAD(P)+ + H2O

For drug detoxification(Hydroxylation of xenobiotics, increase their solubility for metabolism and secretion) and steroid biosynthesis.

Assisted reactions(?):
* HMG-CoA reductase (C6 intermediate Mevalonate synthesis during steroid synthesis)
* Squalene synthase (C30 intermediate Squalene synthesis during steroid synthesis)
* Acyl-ACP reductase (FA biosynthesis)

˙ Plasma membrane synthesis and its property determination (Important!)
Flippase -> membrane assymetry
Steroid biosynthesis -> membrane floidity and thickness

˙ Calcium storage

重要例子: Sarcoplasmioc reticulum in muscle cell(細生課本Fig.10-11, p.277)
　　　　 用Ryanodine receptor channel 釋放; 造成肌肉收縮

˙ Glucose metabolism (Fig.12-3 p.338)
* Glucose-6-phosphatase(Glu-6-P -> Glu)
(Recalling 生化-Catabolism of Polysaccharide Ch.13 p.471~474 glycogen mobilization)

Glycogen granule
	|	GP
GLu-1-P
	|	Phosphoglucomutase
Glu-6-P
	|	Glucose-6-phosphatase
Glucose

肝細胞藉此方可輸出糖分(Permiase)增加血糖濃度