4: The Endomembrane System
- Page ID
- 173530
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Since the authors of this textbook both did research in the area of endomembrane biology, we must admit that we are somewhat partial to this topic. That being said, the endomembrane system is arguably the most interesting and complex of all of the cellular structures we cover. It’s also quite challenging to study, as its function is essential to cell survival. Anything in the cell that is “essential” is also difficult to study, as the cell dies quickly if that function is disrupted.
There are several membrane-bound organelles that work together to form the endomembrane system: the endoplasmic reticulum (or ER for short), the Golgi apparatus (named after a person, so its name is capitalized), endosomes, lysosomes (called vacuoles in some taxa), and the vesicles that traffic cargo from one organelle to another. This system is extensive, and it is somewhat messy to differentiate one part from another. In this chapter we do our best to create order from the chaos and highlight how we study the endomembrane system as well as what we don’t yet know.
- 4.1: The Endoplasmic Reticulum
- This page covers the endomembrane system's role in protein processing, lipid synthesis, and signaling. It highlights the endoplasmic reticulum (ER) as crucial for protein targeting, folding, and post-translational modifications, with chaperone proteins preventing misfolding and relevant diseases. The text describes protein insertion mechanisms in the ER based on specific sequences, detailing the importance of transmembrane regions and bioinformatics in mapping protein domains and their functions.
- 4.2: Vesicle Transport
- This page details the crucial stages of vesicle trafficking: budding, transport, docking, and fusion, highlighting the roles of specific proteins such as Rabs, tethers, and SNAREs that ensure cargo delivery between organelles. It explains vesicle formation with binding of cargo proteins and coat proteins like clathrin, COPI, and COPII, facilitating anterograde and retrograde transport between the ER and Golgi apparatus.
- 4.3: The Golgi Apparatus
- This page discusses the Golgi apparatus, which is essential for protein processing and localization in cells. Its structure features flattened sacs called cisternae and varies among different kingdoms. Key functions include glycosylation and polysaccharide synthesis for cell walls, especially in plants and fungi. The Trans Golgi Network (TGN) serves as a sorting center for proteins, with two proposed models explaining protein movement.
- 4.4: Pathways Through the Endomembrane System
- This page details cellular transport pathways, including secretory, lysosomal, and endocytic systems. It describes how proteins are processed from the ER to the Golgi, differentiating between constitutive and regulated secretion. The importance of the mannose-6-phosphate signal for lysosome targeting is highlighted, along with endocytosis types like phagocytosis and receptor-mediated uptake.
- 4.5: End-of-Chapter Material
- This page discusses the endomembrane system, which includes the ER, Golgi apparatus, endosomes, and lysosomes, highlighting their roles in protein sorting and processing. It details the ER's function as the protein entry point, the Golgi's processing of proteins, and the role of endosomes in cargo redirection. Additionally, it summarizes three scientific articles: Voelz et al. on Acyl-CoA binding protein, Weidman on Golgi transport, and Yuen et al.
Thumbnail: The diagram shows a endomembrane system on a Eukaryote cell. (Public Domain; LadyofHats via Wikipedia)