Chapter 15
Transmembrane Transport in Endoplasmic Reticulum and Peroxisomes
The Endoplasmic Reticulum
The endoplasmic reticulum or ER makes up for more than half of the membranes in a cell and accounts for 10% of total cell volume. It is also the primary ...
Smooth Endoplasmic Reticulum
Smooth endoplasmic reticulum or smooth ER is a sub-organelle with specialized functions in animal cells and plant cells. It is often associated with the ...
Role of ER in the Secretory Pathway
Eukaryotic cells have a special pathway that enables communication between various intracellular membrane-bound compartments and also with the ...
Directing Proteins to the Rough Endoplasmic Reticulum
The organelle-specific signaling sequences direct proteins synthesized in the cytosol to their final destination like ER, mitochondria, peroxisomes, etc. ...
Protein Translocation Machinery on the ER Membrane
The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides ...
Cotranslational Protein Translocation
Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the ...
Post-translational Translocation of Proteins to the RER
A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process ...
Insertion of Single-pass Transmembrane Proteins in the RER
Integral membrane proteins are proteins adhered to the lipid bilayer of a cell organelle or membrane. They can be of two types: transmembrane integral ...
Insertion of Multi-pass Transmembrane Proteins in the RER
The rough ER membrane synthesizes, assembles, and embeds transmembrane proteins in diverse topologies. These proteins function as transporters or channels ...
Tail-anchoring of Proteins in the ER Membrane
Tail-anchored, or TA, proteins are estimated to make up to 3-5% of membrane proteins found in the eukaryotic cell. Such proteins have a single ...
GPI Anchoring of Proteins in the ER Membrane
GPI-anchoring is a post-translational, reversible protein modification that is ubiquitous in eukaryotes. Such proteins are primarily present on the ...
Protein Modifications in the RER
Modification of secretory and transmembrane proteins entering the rough ER begins in the ER lumen. These modifications aid in protein folding and ...
Protein Folding Quality Check in the RER
ER is the primary site for the maturation and folding of soluble and transmembrane secretory proteins. The calnexin cycle is a specific chaperone system ...
Export of Misfolded Proteins out of the ER
After folding, the ER assesses the quality of secretory and membrane proteins. The correctly folded proteins are cleared by the calnexin cycle for ...
The Unfolded Protein Response
The ER is the hub of protein synthesis in a cell. It has robust systems to quality control protein folding and also for degradation of terminally ...
Regulation of the Unfolded Protein Response
Inositol-requiring kinase one or IRE1 is the most conserved eukaryotic unfolded protein response (UPR) receptor. It is a type I transmembrane protein ...
Synthesis of Phosphatidylcholine in the ER Membrane
The ER synthesizes lipids for building cell membranes and performing cellular functions such as energy storage and signaling. The lipid synthesis ...
Assembly of the Lipid Bilayer in the ER
Biological membranes are more than just a barrier separating cell cytoplasm from the outside environment. They are highly dynamic and help maintain the ...
Peroxisomes
Peroxisomes are specialized organelles present in fungi, plant, and animal cells. It can vary in number, size, morphology, and activity depending on the ...
Protein Import into the Peroxisomes
Cells contain membrane-bound organelles called peroxisomes that oxidize organic molecules by transferring hydrogen atoms to oxygen, producing hydrogen ...
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