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An __ can act as a __ and initiate the transfer of the __ part of the protein. At some point after a __ has entered the __, the __ discharges the sequence laterally into the membrane.
If neither goes through, what is it?
- internal ER signal sequence
- start-transfer signal
- stop-transfer squence
What determines how many times the protein goes through?
on the protein itself
Which part starts moving through the membrane?
the part with the stop transfer signal
The location of a __ in the polypeptide sequence determines the ___ and the __.
In the absence of a __, what happens?
- halt transfer signal
- proportion of the molecule threaded through the membrane
- proportion that remains behind at the cytosolic face of the membrane
- halt transfer signal
- the entire protein is secreted across the membrane into the lumen
Destinations of these proteins made in the ER
- end up in the ER membrane
- - second signal after signal sequence that tells it to remain in the membrane (only a portion stays in the membrane)
What will the halt-transfer signal do?
halt-transfer will signal when to stop pushing it into the ER lumen
A __ is assembled on __ embedded within the ER membrane. The __ is then transferred intact to the amino acid __ in a newly forming polypeptide chain. Several of the sugars present in the __ are removed before the __ exits from the ER.
- 14-sugar core oligosaccharide
- dolichol phosphate
- 14-sugar oligosaccharide
- core oligosaccharide
- glycosylated protein
Structure of the dolichol pyrophoshoryl oligosaccharide precursor of N-linked oligosaccharides
-strongly hydrophobic and long enough to span a phospholipid bilayer membrane four or five times
Location of dolichol phosphate?
on the rough ER, and the sugar residues face the lumen of the organelle
The five residues--__-- are conserved in the structures of all __.
- three of mannose and two of N-acetylglucosamine
- N-linked oligosaccharides
The SER is connected to what? What can't it do? How does it account for this inability?
What can the SER do?
- the RER
- cannot make proteins
- gets it from the RER
- make lipids
Functions of the SER?
- 1) lipid synthesis
- 2) synthesis of bile acids and bile salts
- 3) steroid hormone synthesis
- 4) synthesis of phospholipids and sphingolipids
- 5) detox o drugs
- 6) processing of glycogen
- 7) stores calcium ions
- specifically, which type? (characteristic of it)
- from here, it can also make __.
- cholesterol (only one part is hydrophilic, the -OH group)
Synthesis of Bile Acids/ Salts
- what do these do?
- what is the starting point?
- what do they act like?
- what other organ does this function?
- - emulsify fats in the small intestine
- - enzymes have to get to fats, so the salts break it down
- -starting point is cholesterol
- - act like detergents
- - liver
Steroid Hormone synthesis
- cells of the __(examples)__
- steroids found in the membrane made where?
- by cytosolic, what do we mean when speaking of the SER?
- adrenal cortex, testes, ovaries, placenta, etc
- in the SER
- lumen not the actual cell cytosol
Synthesis of Phospholipids
- (what kinds)
- made where? what happens?
- where do the phospholipids move?
- sphingolipids (initial steps, ends?)
- PE, PS, PI, PC
- -made on the cytosolic side of the membrane and gets flipped over
- probs to the RER
- - initial steps begin in the SER (cytosolic side)
- -synthesis ends in the Golgi
Detox of Drugs
- in which cells?
- which other organelle does this?
- what kind of drugs
- what does it do? why?
- -liver cells predominant
- - barbiturates
- - makes them hydrophilic so it can be flushed out of the body
If you give an aniimal barbiturates (phenobarbitol), which organelle will proliferate first?
- RER because enzymes are required to be able to allow detox. Then, SER proliferates
- (SER lacks enzymes)
Processing of Glycogen
- if a call goes out that glucose is needed, they get it from where?
- abridged version of conversion
- glycogen--> glucose-1-phosphate (enzyme for this in cytosol) glucose can't leave cell like that--> glucose-6-phosphate--> glucose-6-phosphatase--> glucose
Where is glucose-6-phosphatase carried?
involved in what?
- out in the SER in final step
- involved in maintaining homeostatic maintenance of glucose
Stores Calcium ions
-in connection with this function, the SER has a different name: __
- specialized SER
- explain it
- sarcoplasmic reticulum
- -nerve impulse--> potential carried deep into cell--> ACTION POTENTIAL-- Ca channels open up--> calcium out--> CONTRACTION--> relaxation--> active transport of Ca2+ back into the reticulum
Function of the SER depends on what?
the kind of cell and its activity