Summary of the endoplasmic reticulum and secretory pathways
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Course
Fundamentals of the Living Cell
Institution
St Georges
The document looks into the structure, function of the endoplasmic reticulum as an organelle in the cell. It will also give information about protein synthesis. It also includes key points about the golgi apparatus.
Secretory pathway
● Schematic overview of the pathway.
Rough ER, with ribosomes in the nucleus.
● The protein is transported into vesicles & sent to Golgi apparatus.
● ER is also destination for proteins that work there, & proteins that work for the
lysosomes etc.
ER is continuous with nuclear envelope
● The nucleus is surrounded by the double
membrane nuclear envelope, continuous with the
rough ER.
● Some of the nuclear lamina fragments play a part
in transcription.
● The nuclear lamina has a role in maintaining the
structure of the nucleus & gene regulation
ER structure & function
● Reticulum = “little net”
● Continuous network of membrane tubules
● Continuous with the nuclear envelope
● Protein synthesis, glycosylation [attachment of sugar structures to proteins], folding and assembly and
multi-protein complexes
● Lipid synthesis (cholesterol, phospholipids) is initiated in the ER.
● Ca2+ sequestration [storage of Ca2+ ions, very low in the ER, conc can fluctuate to send a signal]
● Detoxification by cytochrome P450 enzymes,
● The mammalian cells are much smaller than plant cells.
● Many drugs that are prescribed, are chemically inaccurate so when swallowed they change into the
correct structure for work.
ER protein synthesis & Golgi
● Central dogma; the general flow of DNA to mRNA, and out of the nucleus for protein synthesis.
● If the protein needs to be secreted form the cell [lysosomes etc], the process of protein synthesis is
more complicated.
Co-translational protein targeting to the ER.
● The AUG is always the first codon where translation begins in the cytoplasm. The ribosome attaches
first.
● The signal sequence is present in mRNA where the proteins of the result mRNA is being transported
out of the cell. The signal sequence is specific. The signal is a sequence of hydrophobic amino acids.
The purpose is to guide the mRNA to the ribosome.
● The emergence of the signal sequence interacts with the ribosome & signal recognition particle [SRP].
This will guide the ribosome to a complex that sits at the end of the ER known as the SRP receptor.
More importantly, it helps the ribosome to bind to the translocation complex .
● When the signal sequence & SRP binded, translation stopped. But, after the molecules bind to the
translocation complex, the translation process continues.
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