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What mechanism translates the mRNA
Ribosomes
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What is the role of tRNA
tRNA carries the amino acid to the ribosome to be assembled into a polypeptide bond
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How many amino acids make up a protein
No more then 20
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Once the polypeptide bond exits the ribosome, what does it do next
It folds to protect the hydrophobic sections, chaperones assist by protecting these until folded
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What is the difference between co-translational protein targeting and post-translational protein targeting
- Co- Delivers to the membrane while translating
- Post- Delivers to the membrane after translating
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What are some examples of Chaperones
- hsp70 family (cytosol) BiP (ER)
- GroEL family
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How many ER are in each Cell
Only one
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What is the ER
Membrane bound compartment in the cytoplasm of Eukaryotic cells where lipids are sythesized and membrane bound proteins and secretory proteins are made
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How are the ER tubules held in place
By microtubules
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Is there seperation between rough and smooth ER
No, they are continuous
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What are the primary functions of the smooth ER
- Lipid biosythesis (cholesterol, phospholipids, ect)
- Detoxification
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What are the important enzymes in the smooth ER for detoxyfication
Cytochrome p450s
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Where are the new phospholipids inserted when produced
Into the leaflet of bilayer facing the cytosol
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What is a scramblase
A membrane bound phospholipid translocator, used to transfer phospholipids one side to the other, bidirectionally (Only works in the ER)
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Where is Flippase used, and for what purpose
In the plasma membrane to flip phosphatidylserine and phosphatidylethanolamine from the cells exterior to its interior creating an asymmetric bilayer
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How is phosphatidylserine different from the other phopholipids
It is negatively charged and is placed only on the cytosol side, creating a negative charge on the cytosol side when there are no other molecules present
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How is floppase different from flippase
Floppase moves the phospholipids from the cytosol side to the extracellular side
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If a cell required more cholesterol then normal, what would one expect
More smooth ER since this is where it is made. They can proliferate when needed however
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What are the three ways that lipids are transported
- 1. Through the smooth to the rough ER membrane
- 2. By vesicles budding off the smooth ER to fuse eith other membranes (vesicular trafficking)
- 3. By transfer proteins to those organelles that don't accept vesicular traffic from the ER (Mitochondria)
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Why would steroid synthesis engage smooth ER synthesis
Because steroid hormones are synthesized from cholesterol made there
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What is vesicular traffic
When vesicles bud off of ER for movement to other regions of the cell
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Another way lipids are delivered is by a random scattering in the cell accompanied by what
Transfer proteins
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Ingested alcohol is broken down it what different sites
Peroxisomes and Smooth ER
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What is the drug phenobarbitral used for, and how is it broken down
It is a widely used anti-convulsant, and is broken down in the smooth ER.
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How fast can the ER double in size
In a few days
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What cation is found in very high rates in the ER
Ca++ used for cellular signals
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Secretory and membrane proteins are targeted during synthesis to the rough ER by
ER signal sequence or peptide
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What is an SRP (signal recognition protein)
It pauses the co-translation and delivers it to the ER membrane to finish translation, then it leaves
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Nascent (Just born) protein is a protein signal sequence and directs ribosomes to
ER
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What is a co translation transport
Transportation while the protein is being translated. The transportation is to the ER membrane
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What is the role of the signal peptidase
It stops the co-translational coding when signaled by the stop sequence making a membrane bound protein
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In what ways can a protein that enters the ER be modified
- 1. The N- terminal is often cleaved by a signal peptidase leaving it in the membrane
- 2. Most of the proteins that end up in the ER lumen receive N linked glycosylation aiding in folding
- 3. Formation of disulfide bonds which aides in folding
- 4. Some lose transmembrane domain and gain a GPI anchor
- 5. Protein folds
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How do proteins get to be a membrane bound protein
They are threaded in like a sewing machine by a translocation channel then stopped by signal peptidase
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Multi subunit complexes like antibodies are held together by what, assembled in the ER
Disulfide bonds
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What is a GPI anchor
It helps in directing membrane bound proteins to special places in the plasma membrane like the caveolae
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Disulphide bonds of complexes of membrane proteins like an antibody are assembled where
ER
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Normal new proteins are transferred from the ER to the
Golgi
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What happens to a protein if it is not folded properly
It is sent to the cytosol and degraded
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Why is correct folding of porteins necessary
They can't leave the ER unless they are folded properly and released from chaperones
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What is a disease relating to the incorrect folding of a protein in the ER
Cystic Fibrosis
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Cystic Fibrosis is caused by mutations in the CFTCR (Cystic fibrosis transmembrane conductance regulator) which
Codes for a protein that transports chloride ions in and out of epithelial cells. Therefore the cells fill with fluid and burst creating a thick discharge. The mutant protein is misfolded and therefore stay in the ER and are degraded
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N-Linked Glycosylation is received by many proteins that enter the ER for
Assistance in correct folding
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Why is the rough ER rough, what is happening
Ribosomes are attached to it synthesizing proteins into the lumen
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