Cell Biology

... from active transport to vesicles

endoplasmic reticulum

1. smooth endoplasmic reticulum (smooth ER)
2. cisternal space – lumen – of rough endoplasmic reticulum (rough ER) with proteins produced on exterior
3. chains of ribosomes along mRNA on membrane of rough ER, the proteins move into the lumen of the cisterna following assembly
4. cisternae of rough ER (rER)
5. nuclear membrane
6. nuclear material in nucleus (cut-away)
7. nucleolus, site of production of ribosomal components
8. strands of heterochromatin adherent to nucleolus
9. rosette-shaped nuclear pore
10. outer nuclear membrane continuous with membrane of ER
(click to enlarge image)

The luminal space within the double-layered nuclear membrane is continuous at points with the endoplasmic reticulum, whose membrane is continuous with the outer nuclear membrane (nuclear envelope). Attached to the rough endoplasmic reticulum (rER) are ribosomes (em2) executing translation of genetic coding into polypeptides and proteins. Some proteins are passed to the Golgi complex for packaging as vesicles.

Sarco(endo)plasmic reticulum calcium-ATPases (SERCAs) pump calcium from the cytoplasm of mammalian cells into organellar structures such as the sarcoplasmic reticulum (muscle) or the endoplasmic reticulum. SERCAs exhibit a threshold of activation of the order of 100-200 nM of calcium, such that they set the resting level of cytoplasmic calcium. The SERCA1 isoform is expressed at high levels in fast-twitch muscle, and it is highly concentrated in the sarcoplasmic reticulum. The key structural features of SERCA1 include a transmembrane domain (10 transmembrane alpha helices), a stalk sector (helical extensions of transmembrane helices), and cytoplasmic β-strand, phosphorylation and nucleotide binding domains attached to the stalk domain at a distance of 60 Å from the transmembrane domain. It is proposed that binding of calcium to high-affinity sites in the transmembrane domain trigger phosphorylation of SERCA1 by ATP. Phosphorylation then initiates a series of conformational changes that distort the transmembrane helices such that access of calcium shifts from the cytoplasm to the lumen while calcium binding sites are destroyed, thus releasing calcium to the lumen. [s]

Џ beautiful Flash 8 animation - Inner Life of the Cell, which shows ribosomes injecting nascent proteins through pores into the ER, and Interpretation: Inner Life of the Cell Џ

• A • adhesion • C • cell membranescellular adhesion moleculescellular signal transductioncentrioleschemotaxischloroplastciliacommunicationconcentration gradientscytokine receptorscytoplasmcytoskeleton • E • energy transducersendoplasmic reticulumendosomesexosome • G • Golgi apparatusGPCRs • H • hormones • I • ion channels • L • lysosome • M • meiosismicrotubulesmitosismitochondrion • N • Nitric Oxideneurotransmissionneuronal interconnectionsnuclear membranenuclear pore • P • pinocytosisproteasomepumps • R •receptor proteinsreceptor-mediated endocytosis • S • second messengerssignaling gradientssignal transductionspindlestructure • T • transporttwo-component systems • V • vacuolevesicle

animation - SERCA : animation - smooth endoplasmic reticulum : tour smooth ER :animation - rough ER with ribosomes : tour rough ER :zoom in on rough ER : animation - ribosomes : ribosome close-up and rough ER : Virtual Cell Textbook - Cell Biology :

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