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18 Cards in this Set

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  • Back
Proteins produced by membrane bound ribosomes can do one of three things:
1. Remain associated w/membranes (eg. nuclear, ER, Golgi, ect)
2. Are entrapped in sm vesicular organelles or
3. Are secreted fm the cell
Where are the proteins produced by free ribosomes located?
1. Nucleoplasm
2. Cytosol
3. Mitochondria/chloroplast
5. Cytoskeleton of the cell
What does the "Signal Hypothesis" hypothesis?
Since "Free" and "Bound" ribosomes are functionally equivalent, the proteins tmselves must hv info determining tr final location built into tr structure. Ex. NLS (Nuclear location sequence)
Describe the makeup of the ER
It's a collection of membranous tubules & flattened sacs tt extend trghout the cytoplasm of Euk cells. The ER membranes r continuous & enclose a "lumen" or internal channel. 2 form; Smooth (no ribosomes) and Rough (has ribosomes) ER
The RER commonly extends into a series of lg flattened sacs. In addition to binding ribosomes, the "resident" RER membrane & lumenal components r involved in numerous aspects of protein processing, wt r ty?
1. Protein "translocation" into or across the membrane
2. Protein folding
3. Protein modification-primarily glycosylation
4. Protein packaging for transport along membrane/secretory pathway
The SER is composed primarily of elongated tubular structures. Its membranes and lumen are involved in numberous protein processing activites too, wt r ty?
1. Fatty acid and phospholipid synthesis
2. Steroid & steroid hormone synthesis
3. Initial fat oxidation
4. Glycogen metabolism
5. Detoxification rxns
6. Storage of materials (ex: Ca++)
Due to lipids hydrophobic nature, new lipids can only be synthesized in membranes. What membrane are lipids primarily made in in Eukaryotes?
The membrane/lipid factory is in the SER. Many of the enzymes involved in phosphoglyceride synthesis reside here as integral or peripheral SER proteins.
What two ways can newly synthesized lipids be moved from the SER membrane to their final membrane destination?
1. Phospholipid exchange proteins
2. In bulk along w/proteins fm the RER as part of membrane vesicles tt bud fm the ER
Descrive the structure of cisternae? (of the Golgi complex)
Typically dilated or swollen at tr margins wr ty contain granular material. Surrounding the cisternae on all sides are numerous vesicles tt appear to arise fm and fuse w/the margins of the cisternae.
What do the cis, medial, and trans cisternae do in their "assembly line"?
1. Covalently couple protein and lipid components
2. Modify proteins w/sulfate, phosphate, acetyl groups, etc
3. Remove, add, and/or modify the carbohydrate components attached tomembrane/secretory proteins
4. Sort proteins for delivery to tr final cellular destination
The information that targets a protein into the membrane/secretory pathway at the ER is called the Signal Sequence. Describe the classic secretory protein signal sequence.
-string of ~30a.a.s at amino terminal (beginning) of protein
-Up to 7 polar N-terminal a.a.s, 3 of wc are + charged
-Next a string of 6-12 hydrophobic
-A peptidase recognition & cleavage site
What is the Signal Recognition Particle (SRP)(ie structure)
A ribonucleoprotein particle composed of 6 proteins and a small cytoplasmic RNA (scRNA)
Describe the structure and location of the SRP-Receptor.
Transmembrane protein resident in the RER tt has a cytoplasmic projection
Describe the characteristics of the Uncleaved Internal "Signal Anchor"
1. Like ER "signal" it has + charged a.a.s on end of string of hydrophobic a.a
2. Unlike the standard signal, its not at the N-terminal nor has a built-in cleavage site
3. Recognized by the SRP and directed to ER
4. similiar to both the "signal" and "stop transfer" sequences
What modifications does the ER resident proteins make when modifying a secretory or membrane protein?
1. Folding & formation of multi-subunit proteins, assisted by chaperones in lumen
2. Formation of disulfide bonds to maintain subunit structure if protein exposed to harsh environment outside
3. Initial addition of Carb modifying groups
4. Packaging into vesicles for transport to Golgi
What is the primary modification carried out in the Golgi? What are the two types?
Glycosylation: N-linked (to asparagine) and O-linked (to serine)
Describe N-linked glycosylation.
Begins in ER w/addition of a complex polysaccharide and adjustments (additions, deletions and modifications) of the sugar groups occurring in Golgi
Describe O-linked glycosylation.
Occurs primarily in the Golgi and involves a 3-step addition of a small polysaccharide unit