Exam 3: RR (4)

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Exam 3: RR (4)
2013-10-23 19:24:38
Required Reading

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  1. a.      Processing
                                                                  i.      as it enters the __, the nascent polypeptide is acted on by __located within either the membrane or __of the RER
    1.     __ portion containing the signal peptide is removed from most nascent polypeptides by a __, the ssignal peptidase
    • RER cistern
    • enzymes 
    • lumen 
    •  N-terminal
    • proteolytic enzyme
  2. a.      __are added to the nascent protein by the enzyme __
                                                                                                                                          i.      both the __ ande __ are integral membrane proteins associated with the __that act on nascent proteins as they enter the __
    • carbs 
    • oligosaccharyltransferase
    • signal peptidase and oligosaccharyltransferase
    • translocon 
    • ER lumen
  3.                                                               i.      the RER is a major protein processing plant and is packed with molecular __that recognize and bind to __ or __ and give them the opportunity to attain their correct 3D structure
    1.      the Er lumen also contains a number of __, such as __
    • chaperones 
    • unfolded or misfolded proteins 
    • protein-processing enzymes
    • protein disulfide isoemrase
  4.                                                               i.      proteins enter the ER lumen with their __ in the __state, but they leave the compartment with may of these residues joined to one another as __
    1.      the formation and rearrangement of __ bonds is catalyzed by __
    • cysteine residues
    • reduced 
    • oxidized disulfides
    • disulfide
    • PDI
  5. a.      disulfide bonds play an important role in __ that are present at the extraceullular surface of the plasma membrane or secreted into the extracellular space
    maintaining the stability of proteins
  6.    i.      the ER is constructed for its role as a __ for the __ of the cell
    1.      its membrane provides a __ to which many __can attach
    a.      the __of the __ provides a specialized local environment that favors the __, __, and __ of a selected subset of the cell’s proteins
    • port of entry
    • biosynthetic pathway
    • large surface area
    • ribosomes 
    • lumen 
    • ER cisternae
    • modification, folding, and assembly
  7. 1.      the segregation of these newly synthesized proteins in the __ removes them from the cytosol and allows them to be __ and __ toward their ultimate destination, whether outside the cell or within one of the cytoplasm’s membranous organelles
    • ER cisternae
    • modified and dispatched
  8. a.      Synthesis of Integral Membrane Proteins on Membrane-Bound Ribsomes
                                                                  i.      integral membrane proteins—other than those of the mitochondria and chloroplasts—are also synthesized on __

    1.      these membrane proteins are translocated into the __ as they are synthesized using the same machinery described for the synthesis of secretory and lysosomal proteins
    • membrane-bound ribosomes of the ER
    • ER membrane
  9. a.      unlike __ and __, which pass entirely through the ER membrane during __, __ contain one or more __ that are shunted directly from the channel of the __into the lipid bilayer
    • soluble secretory and lysosomal proteins
    • translocation
    • integral proteins
    • hydrophobic transmembrane segments
    • translocon
  10.                                                               i.      as a polypeptide passes through the __, it is proposed that this __ in the channel continually opens and closes, which gives each segment of the nascent polypeptide an opportunity to __itself according to its __properties into either the aqueous compartment within the __ or the surrounding __ of the lipid bilayer.
    • translocon
    • lateral “gate”
    • partition 
    • solubility 
    • translocon channel
    • hydrophobic core
  11. 1.      those segments of the nascent polypeptide that are __will spontaneously “__” into the lipid bilayer and become __ of an integral membrane protein
    a.      this concept has received strong support from an in vitro study in which __were given the opportunity to translocate custom-designed nascent proteins that contained test segments of varying __
    • hydrophobic 
    • dissolve
    • transmembrane segments
    • translocons 
    • hydrophobicity
  12. The more hydrophobic the test segment, what?
    the greater the likelihood it would pass through the wall of the translocon and become integrated as a transmembrane segment of the bilayer
  13.                                                               i.      __ membrane proteins can have an orientation with their __ facing either the cytosol or the lumen of the ER
    1.      the most common determinant of membrane protein alignment is the presence of __ flanking the __end of a __segment
    • single-spanning
    • N-terminus
    • positively charged amino acid residues
    • cytosolic 
    • transmembrane
  14. 1.      during the synthesis of membrane proteins, the inner lining of the __is thought to orient the nascent polypeptide so that the more __end faces the __
    • translocon 
    • +
    • cytosol
  15.                                                               i.      In multispanning proteins, sequential transmembrane segments have __

    their arrangement within the membrane is determined by the __
    • opposite orientations
    • direction in which the first transmembrane segment is inserted
  16. 1.      once determined, every other transmembrane segment has to rotated __before it can exit the translocon
    a.      suggestion: a translocon, by itself, is capable of what?
    • 180o 
    • properly orienting transmembrane segments
  17.     i.      it is more than a simple passageway through the ER membrane; it is a complex machine capable of __and performing complex mechanical activities
    recognizing various signal sequences
  18. a.      Membrane Biosynthesis in the ER
                                                                  i.      membranes don’t arise as __, but from __ that grow as new proteins and lipids are inserted
                                                                ii.      membrane components move from the __to virtually every other compartment in the cell
    • new entities from pools of protein and lipid that mix together
    • preexisting membranes
    • ER
  19. 1.      as the membrane moves from one compartment to the next, its proteins and lipids are __
    a.      these modifications contribute to giving each membrane compartment a __ and __
                                                                ii.      Cellular membranes are __: the two phospholipid layers of a membrane have different compositions
    • modified by enzymes that reside in the cell’s various organelles
    • unique composition and distinct identity
    • asymmetric
  20. 1.      the asymmetry is established by the __ and maintained as __
    a.      domains situated at the __surface of the ER membrane can be identified on the __ surface of __, the __surface of __, and the __ surface of the __
    • ER
    • membrane carriers bud from one compartment and fuse to the next
    • cytosolic 
    • cytosolic
    • transport vesicles
    • cytosolic 
    • Golgi cisternae
    • internal
    • plasma membrane
  21.                                                               i.      domains situated at the __ of the ER membrane maintain their __and are found at the __ of the plasma membrane
    1.      including its high __and abundance of proteins with __ and __, the lumen of the ER is a lot like the __
    • luminal surface
    • orientation 
    • external surface
    • calcium concentration 

    • disulfide bonds
    • carb chains

    extracellular space
  22.                                                               i.      Most __ are synthesized completely within the ER except for __ (synthesis begins in __and is completed in __) and some unique __ of the __ and __ membranes, which are synthesized by enzymes that reside in those membranes
    1.      the enzymes involved in the synthesis of __ are integral proteins of the ER memrbaen with their __ facing the __
    • membrane lipids
    • sphingomyelin and glycolipids
    • ER 
    • Golgi
    • lipids
    • mitochondrial and chloroplast membranes
    • phospholipids
    • active sites
    • cytosol
  23. a.      newly synthesized phospholipids are inserted into the __of the bilayer facing the cytosol
                                                                                                                                          i.      some of these are __ into the opposite leaflet through the action of enzymes called __
    lipids are carried from the __ to __ and __ as part of the __ that makes up the walls of __
    • half 
    • flipped
    • flippases
    • Er to Golgi and plasma membrane
    • bilayer
    • transport vesicles
  24.                                                               i.      membranes of different organelles have markedly different __composition, which indicates that what happens?
    • lipid 
    • changes take place as membrane flows through the cell
  25. several factors may contribute to such changes
    The first?
    a.      meost membranous organelles contain enzymes that modify lipids already present within a membrane, converting one type of phospholipid to another
  26. several factors may contribute to such changes    
    The second?
    a.      when vesicles bud from a compartment, some types of phospholipids may be preferentially included within the membrane of the forming vesicle, while other types may be left behind
  27. several factors may contribute to such changes    
    The third?
    a.      cells contain lipid-transfer proteins that can bind and transport lipids through the aqueous cytosol from one membrane compartment to another
  28.                                                                                                                                       i.      these proteins facilitate the movement of specific __from the __to other organelles without the involvement of __
    1.      __ is thought to occur at sites where the ER comes into __ to the outer membrane of other organelles
    • lipids 
    • ER
    • transfport vesicles
    • lipid transfer
    • very close proximity