The endoplasmic reticulum & secretory pathway
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.
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.
