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Cell Bio > Intracellular Compartments and the Endomembrane System > Flashcards

Intracellular Compartments and the Endomembrane System Flashcards

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Biology 101 flashcards
1
Q

how did eukaryotic cells evolve to have membrane-enclosed organelles

A

through a process of membrane expansion

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2
Q

each organelle is separated from the cytoplasm by what

A

at least one phospholipid bilayer

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3
Q

the compartments of membrane-enclosed organelles aid in what

A

the organization of metabolic processes

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4
Q

do the number and relative volumes of organelles vary between cell type

A

yes

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5
Q

organelle populations and characteristics are determined by what

A

cell specialization and function

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6
Q

organelles enclose what

A
  • specific molecules
  • including proteins which facilitate a variety of functions
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7
Q

how are ions and small molecules transported across membrane-enclosed organelles

A
  • diffusion
  • channels
  • carrier proteins
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8
Q

how are proteins created

A

transcription and translation

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9
Q

where does transcription take place

A

nucleus

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10
Q

where does translation take place

A

cytosol

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11
Q

how do proteins reach their target destination

A

protein sorting

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12
Q

proteins are transported to organelles by which 3 mechanisms

A
  • pores
  • protein translocators
  • transport vesicles
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13
Q

what are pores

A

selective gates that actively transport specific macromolecules and allow free diffusion of smaller molecules

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14
Q

what do protein translocators do

A

transport proteins (typically unfolded) into organelles

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15
Q

what do transport vesicles do

A

pinch off from the membrane of one compartment and then fuse w another

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16
Q

proteins are targeted to specific organelles by what

A

AA sequences called signal peptides or signal patches

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17
Q

what do signal peptides do

A

targets proteins to specific organelles

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18
Q

are there distinct signal sequences for each organelle

A

yes

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19
Q

what do signal sequences do

A

direct proteins to the correct destination

20
Q

what is a normal signal sequence vs a relocated signal sequence

A
  • normal Proteins destined for the ER possess an N-terminal signal sequence that directs them to that organelle, whereas those destined to remain in the cytosol lack any such signal sequence
  • relocated Recombinant DNA techniques can be used to change the destination of the two proteins: if the signal sequence is removed from an ER protein and attached to a cytosolic protein, both proteins are reassigned to the expected, inappropriate location.
21
Q

describe the structure of the nucleus

A
  • nucleus is surrounded by 2 membranes (nuclear envelope)
  • outer membrane is continuous w the ER
  • envelope is perforated by nuclear pores
22
Q

describe the structure of nuclear pores

A
  • comprised of a complex of ~30 proteins
  • they act as gates that allows small molecules through, but selectively controls the transport of larger molecules
23
Q

what travels in and out of the nucleus

A
  • RNA and ribosomal subunits need to leave nucleus
  • proteins formed in cytoplasm need to enter
24
Q

how do proteins enter the nucleus

A
  • directed by a nuclear localization signal
  • nuclear import receptors bind to the signal sequence and guide the protein through the pore
25
Q

what drives the directional transport of nuclear proteins

A

hydrolysis of GTP by Ran

26
Q

what do GTPases do

A

hydrolyze GTP into GDP and Pi

27
Q

what does Ran do

A

cycles between GDP and GTP bound forms, w the aid of other enzymes (Ran-GAP, Ran-GEF)

28
Q

what happens when GTP is hydrolyzed in protein srtingg

A
  • it is released
  • proteins w a nuclear localization signal can then bind
29
Q

what binds to the nuclear import receptor to allow the nuclear protein to be released

A

Ran-GTP (once in the nucleus)

30
Q

most mitochondrial proteins are encoded in the __________ and imported from the __________

A
  • nuclear genome
  • cytosol
31
Q

proteins are transported into the mitochondria through what

A
  • import receptor proteins
  • protein translocators embedded in the outer and inner membranes
32
Q

what are the steps to protein sorting to the mitochondria

A
  1. proteins binds to import receptors
  2. it diffuses across the outer membrane until it meets a translocator in the inner membrane
  3. proteins are then moved into the mitochondrial matrix and the signal peptide is cleaved
33
Q

what is the most extensive membrane system in a eukaryotic cell

A

the ER

34
Q

what does the ER do

A
  • involved in the sythesis of proteins (both for themself and other locations)
  • protein translocation occurs during translation at the rough ER
35
Q

what translates RNA into protein

A

ribosomes

36
Q

what happens to ribosomes that are translating proteins w an ER localization signal

A

they are directed to the ER membrane

37
Q

what is used to synthesize all proteins encoded by the nuclear genome

A

a common pool of ribosomes

38
Q

does translocating proteins w an ER signal take energy? why/why not?

A
  • no additional energy
  • because they are being translocated as theya re being made
39
Q

what does SRP stand for

A

signal recognition particle

40
Q

how does protein sorting to the ER work

A
  • SRPs bind to the signal sequence and ribosome, slowing translation
  • SPR binds to a receptor associated to the ER
  • ribosome is passed to a protein translocator and protein synthesis resumes at its normal rate
  • as the protein is synthesized, it enters the ER
  • eventually the polypeptide chain is released into the lumen as a soluble protein
  • the signal peptide is cleaved off and remains in the memebrane to be degreaded
41
Q

when do proteins enter the ER

A

while they are being synthesized by the ribosome

42
Q

how are transmembrane proteins sorted to the ER

A
  • stop transfer sequences halt the translocation of proteins resulting in it being stuck through the lipid bilayer
  • once the stop sequence enters the translocator, it discharged the sequence into the bilayer
  • the rest of the protein is translated in the cytosol
43
Q

how are multi-pass transmembrane proteins sorted to the ER

A
  • they have internal ER signal sequences
  • they contain multiple start and stop sequences
  • these sequences help anchor the protein across the membrane
44
Q

what affects localization of protein sorting to the ER

A

the presence and location of start and stop transfer sequences

45
Q
A

Cell Bio (11 decks)

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