Exam III. 1
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Quick summary of the RER
- store things
- makes proteins
- parallel, flattened, interconnected sacs
Quick summary of SER
Location of ER
How did it come into existence?
SER and RER relation?
- found in pretty much all eukaryotic cells
- we didn't know it existed because it had no biochemical signals (no signs) and can't be seen with LM; started seeing them in photos
How much in each cell?
Relation with the nuclear envelope?
- depends on activitie s of cells
- nuclear envelope continuous with some membranous system as the ER
- - comes from ER in mitosis
- variety of enzymes associated with it, especially SER (involved in biochemical pathways; ex: steroid synthesis and SER)
Protein to lipid ratio
- high protein: lipid ratio
- involved in making proteins
- little cholesterol and lipids are mainly phospholipids
2) cell fractionation?
4) take __ and do what?
- 1) can't isolate it in tact
- 2) break cells open (homogenize tissue)
- 3) isotonic sucrose solution/ use pestle
- 4) homogenate and centrifuge at a slow speed for a couple of minutes--> pellet (heavy particles) and supernatant (lot of particles)
What do you do after?
- centrifuge at higher speed and get a new pellet and supernatant
- take it again and centrifuge even higher for longer--> tiny things
You can use __ to see the function by analyzing the __.
Most organelles have __.
The one in the ER is __
- one marker that is only in that organelle
- hexose-6-phosphate dehydrogenase
Rough ER is abundant in making what? Example
- cells that make proteins, in part. proteins that will be exported
- - cells that make digestive enzymes
- protein hormones (insulin, glucagon, etc. polypeptide hormone
What are some cells with alot of rough ER?
- cells of the salviary gland
- pancreatic cells
- cartilage cells (make collagen and proteins in the ECM)
- plasma cells (antibodies)
- intestinal goblet cells (mucoprotiens and mucopolysaccharides)
Main function of the RER?
make protiens that will be exported from the cell
Explain ribosomes and the theory behind them?
- there is a large subunit and a small unit which come togher
- theory: the two subunits had to match
- reality: they all work fine; ribosomes are not different; they all work the same
- - a chem analysis disproved theory that ribosomes are different--> they're exactly alike
The info for where the protein is made is in what?
Where do ribosomes all start out?
On some amino acids, the initial portion contains a __.
the protien molecule itself= signal hypothesis
free in the cytosol and attach to mRNA, decoding info and making amino acids
The signal sequence must have a particular chemical characteristic. What is it?
- hydrophobic center and hydrophilic ends
- as long as it has this general characteristic, it will be a signal sequence
What does the signal sequence tell the cell?
Where is it located?
- if it'll go to the RER (if you have a signal sequence, you're destined to the RER.
- on the initial part of the polypeptide
What must happen if the protein is destined for the cytosol?
there is no signal sequence
What do particles in the cytosol do to the signal sequence?
particles bind to it; calle dSRP, signal recognition particle (it was a protein)
Purpose of the signal cell system?
directs protiens to a particular place; allows cell to tell exactly where a cell should end up both inside and outside the cell
One of the final destinations is where?
Next destination after the ER?
- in the membrane of the ER
- next destination is the Golgi apparatus
- - if something is transported from the ER to Golgi, vesicles will bud from the ER and eventually some membrane will be taken and may end up in plasma membrane
Where does the whole pathway begin?
in the ER: signal sequence is the first signal
Most proteins made in relation to the ER are __.
Carbs being added is calle d__.
Soluble protien sin the cytosol are not __.
in the ER, a __ is formed. __ added to it.
Explain the part in the cytoplasm and what adds this?
What happens after?
What needs to be present
- preformed carbohydrate
- 14 carbohydrates
- part made in the cytoplasm are the seven monosaccharides (5 mannose and 2 N-acetylglucosamine)= enzymes in the cytosol add this
- it is attached to a lipid called dolichol phosphate
- flippases flip it--> now in the ER lumen
what you need to have in the ER lumen is a pool of subunits
What occurs with the final subunit?
What is it always attached to?
What is needed?
the final subunit is still attached to dolichol phosphate
- always attached to asparigine residue
- - specific one is needed that must be recognized= Asp-X (any amino acid but proline)- Serine or Threonine
What is the enzyme that catalyzes this process?
What does it do?
- transfer oligosaccharides from dolichol phosphate to the polypeptide chain
Why are proteins gylcosylated at all?
identification, tag, marker
all proteins destined to places like lysosomes, need carbs to target it to a specific place
may protein proteins from proteases (may depend on carb as to a specific function)
One more function of the ER
place of storage in plasma cells, which make antibodies, and a few others
What was done to determine that antibodies were stored in the ER?
- injected an antigen called peroxidase becuase antibodies are produced in response to the antigen
- they immersed the ER cisternae in a solution of peroxidase, which, with a substrate, produced electron dense product.
- Anywhere you had peroxidase, you ahve an electron dense product
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