考研资料:北京大学细胞生物学第六章基质与内膜(上).ppt
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1、Chapter 6,Cytoplasmic matrix, Endomembrane system, Protein Sorting and membrane trafficking,Learning objective,1. Compartmentalization in Eukaryotic Cells; The structural and functional relationship among the ER, Golgi complexes, lysosomes and plasma membranes of eukaryotic cells; The pathways of pr
2、oteins targeting and sorting, and its mechanisms; The ways of protein modifications and intracellular sites after they are synthesized; Types of vesicle transport and their functions.,1. The Compartmentalization in Eukaryotic Cells,Membranes divide the cytoplasm of eukaryotic cells into distinct com
3、partments. Three categories in eukaryotic cells: (1) the endomembrane system: ER, Golgi complex, Lys., secretory vesicles. (2) the cytosol. (3) mitochondria, chloroplasts, peroxisomes, and the nucleus.,Membrane-bound structures (organelles) are found in all eukaryotic cells.,Cytoplasmic matrix and i
4、ts functions,Cytoplasmic Matrix: The region of fluid content of the cytoplasm outside of the membranous organelles. Aqueous solution of 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
5、 modification. It also performs most of the cells intermediary metabolism.,Cytoplasmic matrix (Cytosol) and Endomembrane System,Functions of cytoplasmic matrix:,The protein synthesis, degradation and modification.,Cells carefully monitor the amount of misfolded proteins. An accumulation of misfolded
6、 proteins in the cytosol triggers a heat-shock response, which stimulates the transcription of genes encoding cytosolic chaperones that help to refold the proteins.,B. Endomembrane System,Endomembrane System : The structural and functional relationship organelles including ER,Golgi complex, lysosome
7、, endosomes, secretory vesicles. Membrane-bound structures (organelles) are found in all eukaryotic cells.,Relative volumes occupied by the major intracellular compartments in Liver Cell,C. The Dynamic Nature of the Endomembrane System,Most organelles are part of a dynamic system in which vesicles m
8、ove between compartments. Biosynthetic parthways move proteins, carbohydrates and lipids within the cell. Secretory pathways discharge proteins from cells. Endocytic parthways move materials into cells. Sorting signals are recognized by receptors and target proteins to specific sites.,D. A few appro
9、aches to the study of cytomembranes,Insights gained from autoradiography; Insights gained from the biochemical analysis of subcellular fractions; Insights gained from the study of genetic mutants; The dynamic activities of endomembrane systems are highly conserved despite the structural diversity of
10、 different cell types.,De Duve, A.Claude and G.Palade,1974 Nobel Plrize,2. The structure and functions of Endoplasmic Reticulum(ER),Rough endoplasmic reticulum and Smooth endoplasmic reticulum,RER has ribosomes on the cytosolic side of continuous, flattened sacs(cisternae); SER is an interconnecting
11、 network of tubular membrane elements.,Microsome(100-200nm),rER of pancreatic cells,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. Fun
12、ctions of the rER,Proteins synthesized on ribosomes of rER include: secretory proteins, integral membrane proteins, soluble proteins of organelles.,Modification and processing of newly synthesized proteins: glycosylation in the rER;,N-linked: linked to the amide nitrogen of asparagine (ER) O-linked:
13、 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,Quality control of of newly synthesized proteins-The role of N-linked glycosylation in ER p
14、rotein folding,Quality control: ensuring that misfolded proteins do not leave ER,The 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, mon
15、itoring enenzyme ) recognize unfolded or misfolded proteins and adds a glucose to the end of oligo,Synthesis 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 uni
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