Medical Cell Biology Chapter 5 Endomembrane system and
《Medical Cell Biology》 Chapter 5 Endomembrane system and vesicular traffic Xiaojing Wang(王晓静), Ph. D Department of Cell Biology, School of Medicine Shandong University Email: luckingwang@sdu. edu. cn
Endoplasmic reticulum (ER, 内质网) Golgi complex (高尔基复合体) Lysosome (溶酶体) Peroxisome (过氧化物酶体) Vesicle traffic (囊泡转运)
Endomembrane system (内膜系统) Single membrane organelles are related in generating and function inside the cell. Including nuclear membrane, endoplasmic reticulum, Golgi complex, lysosome and transport vesicles. Most people consider peroxisome as a membrane of endomembrane system.
A general prokaryotic cell A eukaryotic animal cell
The significance of endomembrane system Enlarge the surface area for cell metabolisms Intracellular compartments for various metabolism Specified function and coordination。
一、Endoplasmic reticulum (ER, 内质网)
19 CC, C. Garnier ergastoplasm (动质) 1945, K. R. Porter endoplasmic reticulum(内质网) 1954, Porter and G. E. Palade:内质网是一类由大小、 形态各异的膜性囊泡所构成的细胞器。
(一) The structure and types of Endoplasmic reticulum 鼠肝细胞内质网形态结构模式图
Classfication of ER ♦According to the attached ribosomes: • Rough ER(RER) (颗粒内质网, GER) • Smooth ER(SER)(无颗粒内质网, AER) ♦The ratio of Rough ER vs Smooth ER varies from tissue to tissue, cell to cell. 如胰腺外分泌细 胞中多为粗面内质网;肌细胞中多为滑面内质网;肝细胞 中二者都有。
Rough endoplasmic reticulum and Smooth endoplasmic reticulum RER has ribosomes on the cytosolic side of continuous, flattened sacs(cisternae); SER is an interconnecting network of tubular membrane elements.
(二) Biochemical components of ER microsome(微粒体)
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.
Gangliosides(神经节苷脂) Plasmalogen(缩醛脂) Neutral lipid(中性脂) lipids 30 -40% Phosphatidylcholine(卵磷脂55%) Phosphatidylethanolamine(磷脂酰乙醇胺 20 -25%) phospholipids Phosphatidylinositol(磷脂酰肌醇5 -10%) 磷脂 Phosphatidylserine(磷脂酰丝氨酸 5 -10%) Sphingomylin (鞘磷脂4 -7%) 60 -70% 蛋白质 30 -33条,分子从15 -150 KD The ratio of lipids and protein is 1: 2
Reticulo-plasmin(网质蛋白): KDEL(lys-Asp-Glu-Leu, 赖 AA-天冬AA-谷AA-亮AA) or HDEL(His-Asp-Glu-Leu, 组 AA-天冬AA-谷AA-亮AA) as retention signal (驻留信号) (1)immunoglobulin heavy chain-binding protein(免疫 球蛋白重琏结合蛋白) (2)endoplasmin(内质蛋白) (3)calreticulin (钙网蛋白) (4)calnexin (钙连蛋白) (5)protein disulfide isomerase (蛋白质二硫键异构酶)
(三) The functions of rough ER 1、Rough ER is closely related to secretory protein synthesis , modification and transport. Secretory proteins (外输性的或分泌性的蛋白质) Protein are synthesized in RER Membrane integral protein(膜整 合蛋白) Lysosomal proteins(溶酶体蛋白) Retention proteins (构成细胞 器中驻留蛋白)(内质网,高尔 基体)
(1) It harbors ribosomes for vesicular transported proteins How can a ribosome attach to RER, and how can a newmade peptide be transported across the ER membrane into the chamber of ER? Signal peptide hypothesis
(3). Glycosylation (蛋白质的糖基化) Asn (天冬酰胺) N-linked glycosylation Target sequences: Asn-X-Ser or Asn-X-Thr dolichol
(4) Intracellular transport (蛋白质的胞内运输)
2、transmembrane protein insertion (穿膜驻留蛋白的 插入转移机制) (1) One time transmembrane protein Cotranslation insertion(共翻译插入): stop transfer sequence(停止转移序列) Internal signal peptide mediated internal starttransfer peptide insertion(由内信号肽介导的内开 始转移肽插入转移机制):
(2) More times transmembrane protein
(四) The functions of smooth ER (1) Lipid synthesis (脂类合成) (2) Metabolism of glycogen (糖原代谢) (3) Detoxification (解毒) (4) Regulation of Calcium concentration(钙调节) (5) Gut acid and bile formation(胃酸和胆汁合成)
(1)Synthesis of lipids(脂类合成 lipids ) Including: phospholipids, cholesterol, fat, steroid hormones, glycolipids, et al.
(4)Ca 2+ storage and regulation As in muscle , it is specified as sarcoplasmic reticulum (肌细胞中的肌浆网——特化的SER) ( • It invovles in regulation of calcium concentration in muscle contraction. ( 参与肌原纤维收缩中的钙离子浓度 调节) • Releasing or storing calcium as signaling molecules( 储存钙离子,作为细胞内信号物质。) (5)Roles on synthesis and secretion of gut acid and bile (胃酸、胆汁的合成与分泌) ü 胃壁腺上皮细胞中,参与胃酸形成 ü 肝细胞中参与胆汁的合成与分泌
二、Golgi complex (高尔基复合体) It was identified in 1897 by the Italian physician Camillo Golgi and named after him in 1898. Camillo Golgi (1843 -1926) Nobel prize 1906
Golgi complex under Light microscope Golgi complex under florescent microscope
Golgi complex under Electron microscope
What is Golgi complex? The Golgi complex, or Golgi apparatus, functions as a factory in which proteins received from the ER are further processed and sorted for transport to their eventual destinations: lysosomes, the plasma membrane, or secretion. In addition, glycolipids and sphingomyelin are synthesized within the Golgi. • main functions:cell secretion
(一)Structure & Chemical Components 1、structure of Golgi complex Golgi C. is constituted by cisternae, vesicles and vacuoles cisternae vesicles
Transitional vesicles Cis-Golgi network (CGN) Cis cisterna Medial cisterna Trans-Golgi network (TGN) vacuole
(1) CGN (Cis-Golgi network, 顺面高尔基网) • A complex network of tubules and vesicles closest to the nucleus and the ER • receives transport vesicles from the smooth ER
(2) Cisternae( Golgi Stack,高尔基中间膜囊) • 3 -20 flattened and stacked saclike structures called cisternae. • Each disc-shaped cisternae forms a structure that resembles a stack of plates, called a Golgi stack. • adds sugars to both lipids and proteins.
(3)TGN (Trans-Golgi network,反面高尔基网) • A complex network of tubules and vesicles near cell membrane • performs proteolysis and sorts molecules for their destination. • Secretory vesicle: involved in secretion (selective excretion)
Golgi complex structure
A striking feature of the Golgi complex is its polarity.
2、 The chemical composition of Golgi complex • Protein membrane> Golgi Complex > ER plasma Lipid plasma membrane>Golgi Complex> ER
• enzyme – glycosyl transferase, sulfotransferase, Phospholipase enzyme, Tyrosine protein kinase, mannosidase and so on. – Golgi marker enzyme: glycosyl transferase ( 糖基转移酶)
(二)The function of Golgi complex 1、Golgi complex is the transfer station of protein secretion
Continual, unregulated discharge of material from the cells The discharge of products stored in cytoplasmic granules, in response to appropriate stimuli.
• (1) Constitutive secretion • Proteins are continuously secreted from the cell regardless of environmental factors. Proteins are packaged in vesicles in the Golgi apparatus and are secreted via exocytosis, all around the cell. No external signals are needed to initiate this process.
• (2) regulated secretion – Proteins are stored in cytoplasmic granules and only secreted in response to a specific signal. – such as neural or hormonal stimulation. Cells that use the regulated secretory pathway are usually apical or polarized.
2、Golgi complex is the important place for produces synthetic(胞内物质加 合成的重要场所) (1) The produces synthetic of glycoproteins Golgi complex plays a key role in the assembly of the carbohydrate component of glycoproteins and glycolipids. N-linked glycosylation? glycans attached to a nitrogen of asparagine(天 门冬AA) or arginine(精AA) side-chains O-linked glycosylation glycans attached to the hydroxy oxygen of serine, threonine, tyrosine
N-linked glycosylation begin with addition of a 14 sugar precursor to an asparagine in the polypeptide chain of the target protein. N-glycosylation begins in the endoplasmic reticulum the protein is transferred to the Golgi apparatus where the glycans lose a variable number of mannose residues (甘露糖残基) and acquire a more complex structure during a process called ‘terminal glycosylation’.
Modifications to N-linked oligosaccharides are completed in the Golgi complex.
• O-linked glycosylation (Golgi): • These modifications take place in the Golgi complex by the sequential addition of single sugar residues. • The serine or threonine is usually linked directly to Nacetylgalactosamine(N-乙酰半乳糖胺), to which other sugars can then be added. In some cases, these sugars are further modified by the addition of sulfate groups. • Many cytoplasmic and nuclear proteins, including a variety of transcription factors, are also modified by this way.
v. What is the purpose of glycosylation? (1) Limit the approach of other macromolecules to the protein surface, more resistant to digestion by proteases. (2) One might suspect that they function to aid folding and the transport process; for example, carbohydrate as a marker during protein folding in ER and the use of carbohydratebinding lectins in guiding ER-to-Golgi transport. (3) Regulatory roles in signaling through the cell-surface receptor Notch, to allows these cells to respond selectively to activating stimuli.
(2) Protein cleavage (蛋白质的水解加 ) example:insulin ◇Proinsulin : A, B, C peptide chains; ◇Golgi complex process:cutting C peptide chain, A、B chain form active insulin by SS-Bond
3、 Protein sorting and transporting • proteins exiting from the TGN – lysosomes, – secretory vesicles – the plasma membrane
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