大學細胞生物學第六章基質與內膜上

1、大學細胞生物學第六章基質與內膜上大學細胞生物學第六章基質與內膜上1. The Compartmentalization in Eukaryotic CellsvMembranes divide the cytoplasm of eukaryotic cells into distinct compartments. Three categories in eukaryotic cells: (1) the endomembrane system: ER, Golgi complex, Lys., secretory vesicles. (2) the cytosol. (3) mitochon

2、dria, chloroplasts, peroxisomes, and the nucleus. vMembrane-bound structures (organelles) are found in all eukaryotic cells.大學細胞生物學第六章基質與內膜上vCytoplasmic matrix and its functionsCytoplasmic Matrix: The region of fluid content of the cytoplasm outside of the membranous organelles. Aqueous solution of

3、large and small molecules including filaments of cytoskeleton which act as organizer for some order.The Cytosol is the site of protein synthesis and degradation or modification. It also performs most of the cells intermediary metabolism. Cytoplasmic matrix (Cytosol) and Endomembrane System大學細胞生物學第六章

4、基質與內膜上Functions of cytoplasmic matrix:The protein synthesis, degradation and modification.Cells carefully monitor the amount of misfolded proteins. An accumulation of misfolded proteins in the cytosol triggers a heat-shock response, which stimulates the transcription of genes encoding cytosolic chap

5、erones that help to refold the proteins.大學細胞生物學第六章基質與內膜上大學細胞生物學第六章基質與內膜上B. Endomembrane SystemvEndomembrane System : The structural and functional relationship organelles including ER,Golgi complex, lysosome, endosomes, secretory vesicles.vMembrane-bound structures (organelles) are found in all euka

6、ryotic cells.大學細胞生物學第六章基質與內膜上Intracellular compartment % of total cell volumeCytosol 54Mittchondria 22Rough ER cisternae 9Smooth ER cisternae plus Golgi cisternae 6Nucleus 6Peroxisome 1Lysosomes 1Endosomes 1Relative volumes occupied by the major intracellular compartments in Liver Cell大學細胞生物學第六章基質與內

7、膜上C. The Dynamic Nature of the Endomembrane SystemvMost organelles are part of a dynamic system in which vesicles move between compartments.vBiosynthetic parthways move proteins, carbohydrates and lipids within the cell.vSecretory pathways discharge proteins from cells.vEndocytic parthways move mate

8、rials into cells.vSorting signals are recognized by receptors and target proteins to specific sites.大學細胞生物學第六章基質與內膜上D. A few approaches to the study of cytomembranesv Insights gained from autoradiography;v Insights gained from the biochemical analysis of subcellular fractions;vInsights gained from t

9、he study of genetic mutants;The dynamic activities of endomembrane systems are highly conserved despite the structural diversity of different cell types.大學細胞生物學第六章基質與內膜上De Duve, A.Claude and G.Palade,1974 Nobel Plrize大學細胞生物學第六章基質與內膜上2. The structure and functions of Endoplasmic Reticulum(ER)Rough en

10、doplasmic 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.大學細胞生物學第六章基質與內膜上Microsome(100-200nm)rER of pancreatic cellsMicrosomes are heterogeneous mixtures of si

11、milar-sized vesicles, formed from membranes of the ER and Golgi complex. Microsomes retain activity during purification, allowing studies of function and composition.大學細胞生物學第六章基質與內膜上A. Functions of the rERv Proteins synthesized on ribosomes of rER include: secretory proteins, integral membrane prote

12、ins, soluble proteins of organelles. 大學細胞生物學第六章基質與內膜上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 resi

13、dues is the same in plants, animals, and single-celled eukaryotesthen remove 3 glucoses and 1 mannose in the ER大學細胞生物學第六章基質與內膜上v Quality control of of newly synthesized proteins-The role of N-linked glycosylation in ER protein foldingQuality control: ensuring that misfolded proteins do not leave ERT

14、he lumen of rER contains:Bip and calnexin (chaperones) : that recognize and bind to unfolded or misfolded proteins and give them correct conformation;Protein disulfide isomerase ( PDI ) ;GT(glucosyl-transferase, monitoring enenzyme ) recognize unfolded or misfolded proteins and adds a glucose to the

15、 end of oligo. 大學細胞生物學第六章基質與內膜上vSynthesis of membrane lipids Most membrane lipids are synthesized enterly within the ER. There are two exceptions: sphingomyelin and glycolipids, (begins in ER; completed in Golgi); (2) some of the unique lipids of the Mit and Chl membranes (themself). The membranes o

16、f different 0rganelles have markedly different lipids composition.Transport by budding：ERGC、Ly、PM(1) Transport by phospholipid exchange proteins(PEP)：ERother organelles（including Mit and Chl）大學細胞生物學第六章基質與內膜上The role of phospholipid translocators in lipid bilayer synthesisphospholipid translocators =

17、Scramblase(ABC transporter Family)大學細胞生物學第六章基質與內膜上B. Functions of the sERvSynthesis of steroids in endocrine cells.vDetoxification of organic compounds in liver cells. System of oxygenases-cytochrome p450 familyvRelease of glucose 6-phosphate in liver cells.vSequestration of Ca2+. Ca2+-ATPase大學細胞生物學

18、第六章基質與內膜上3. The structure and functions of Golgi complexA.The polarity of Golgi complex大學細胞生物學第六章基質與內膜上a) Cis cisternae of Golgi complex: reduced osmium tetroxide(OsO4);b) Reaction for enzyme mannosidase II , localized in the medial;c) Reaction for enzyme nucleoside diphosphatase , localized in the

19、trans cisternae.vRegional differences in membrane composition across the Golgi stack大學細胞生物學第六章基質與內膜上B. The Functions of Golgi complexvGlycosylation in the Golgi complexGolgi complex plays a key role in the assembly of the carbohydrate component of glycoproteins and glycolipids.大學細胞生物學第六章基質與內膜上 The c

20、ore carbohydrate of N-linked oligosaccharides is assembled in the rER. Modifications to N-linked oligosaccharides are completed in the Golgi complex. O-linked oligosaccharides takes place in Golgi complex.大學細胞生物學第六章基質與內膜上Structure of typical O- and N-linked oligosaccharidesCore RegionAfter R. Kornfe

21、ld and S. Kornfeld, 1985, Annu. Rev. Biochem. 45:631大學細胞生物學第六章基質與內膜上vWhat is the purpose of glycosylation?N-linked glycosylation is prevalent in all eucaryotes, but is absent from procaryotes.It dont require a template. There is an important difference between the construction of an oligosaccharide

22、and the synthesis of DNA,RNA,and protein.Important functions: (1) 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 carbohydrate-binding lectins in guiding ER-to-Golgi transport. (2) Limit

23、the approach of other macromolecules to the protein surface, more resistant to digestion by proteases. (3) Regulatory roles in signaling through the cell-surface receptor Notch, to allows these cells to respond selectively to activating stimuli.大學細胞生物學第六章基質與內膜上vThe Golgi networks are processing and

24、sorting stations where proteins are modified, segregated and then shipped in different directions.大學細胞生物學第六章基質與內膜上vGolgi complex and cells secretionContinual,unregulated discharge of material from the cellsThe discharge of products stored in cytoplasmic granules, in response to appropriate stimuli.大

25、學細胞生物學第六章基質與內膜上v Vesivular transport within the Golgi apparatus: Two views: cisternal maturation model and vesicular transport modelTwo possible models explaining the organization of the Golgi complex and the transport from one cisterna to the next.大學細胞生物學第六章基質與內膜上十 十 十 C. Golgi BiogenesisStages of Golgi growth and division. Shown are thin section electron micrographs of T. gondii RH tachyzoites replicating by endodyogeny in HFF cells. Cells were placed in one of four categories according to the number and size of the Golgi: a, single Golgi; b, single, elongated