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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
- C-terminal
- stop-transfer squence
- translocator
- translocator
multipass
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What determines how many times the protein goes through?
on the protein itself
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Which part starts moving through the membrane?
the part with the stop transfer signal
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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
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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)
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What will the halt-transfer signal do?
halt-transfer will signal when to stop pushing it into the ER lumen
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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
- asparagine
- core oligosaccharide
- glycosylated protein
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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
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Location of dolichol phosphate?
on the rough ER, and the sugar residues face the lumen of the organelle
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The five residues--__-- are conserved in the structures of all __.
- three of mannose and two of N-acetylglucosamine
- N-linked oligosaccharides
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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
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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
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Lipid Synthesis
- specifically, which type? (characteristic of it)
- from here, it can also make __.
- cholesterol (only one part is hydrophilic, the -OH group)
- steroids
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Synthesis of Bile Acids/ Salts
- what do these do?
- why?
- 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
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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
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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
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Detox of Drugs
- in which cells?
- which other organelle does this?
- what kind of drugs
- what does it do? why?
- -liver cells predominant
- -peroxisomes
- - barbiturates
- - makes them hydrophilic so it can be flushed out of the body
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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)
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Processing of Glycogen
- if a call goes out that glucose is needed, they get it from where?
- abridged version of conversion
- liver
- glycogen--> glucose-1-phosphate (enzyme for this in cytosol) glucose can't leave cell like that--> glucose-6-phosphate--> glucose-6-phosphatase--> glucose
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Where is glucose-6-phosphatase carried?
involved in what?
- out in the SER in final step
- involved in maintaining homeostatic maintenance of glucose
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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
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Function of the SER depends on what?
the kind of cell and its activity
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