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Cell Biology > Ch.12 - Protein Sorting and Transport > Flashcards

Ch.12 - Protein Sorting and Transport Flashcards

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1
Q

What does the vesicular transport connect?

A
  • ER
  • golgi
  • endosomes
  • lysosomes
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2
Q

ER extends from what, throughout what?

A

from the nuclear membrane throughout the cytoplasm

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3
Q

ER is a network of what?

A

membrane-enclosed tubules and sacs (cisternae)

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4
Q

What is typically the largest organelle?

A

ER

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5
Q

What membrane is continuous?

A

ER

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6
Q

Which ER makes lipids?

A

smooth ER

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7
Q

What does the rough ER make?

A

transmembrane and secreted proteins

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8
Q

What is the rough ER covered by?

A

ribosomes

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9
Q

what is the role of the ER?

A

protein processing and sorting

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10
Q

The role of the ER was first demonstrated by Palade and colleagues in the ______s

A

1960s

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11
Q

What did the first demonstration of protein processing and sorting study?

A

pancreatic acinar cells that secrete digestive enzymes into the small intestine

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12
Q

What did autoradiography determine?

A

the location of radiolabeled proteins

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13
Q

After labeling the proteins in the ER experiment, what happened next?

A

a chase (incubation w/non-labeled amino acids for different lengths of time)

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14
Q

What did a chase allow the tracking of?

A

the labeled proteins throughout the ER, golgi, secretory vesicles, and then outside the cell

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15
Q

What did the experiments in the 1960s (about the ER) define?

A

secretory pathway

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16
Q

What is the secretory pathway?

A

rough ER –> golgi –> secretory vesicles –> cell exterior

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17
Q

What do proteins synthesized on free ribosomes stay in?

A

cytosol or transported to nucleus/other organelles

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18
Q

Proteins synthesized on membrane-bound ribosomes are taken where?

A

directly to the ER

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19
Q

Which type of translation uses energy from the ribosome?

A

cotranslational translation

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20
Q

Proteins moving into the ER DURING their synthesis on membrane-bound ribosomes. Which translocation is this?

A

cotranslational translocation

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21
Q

Proteins move into the ER AFTER translation has been completed on free ribosomes. Which translocation is this?

A

posttranslational translocation

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22
Q

How are ribosomes targeted to the ER?

A

by a signal sequence at the amino terminus

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23
Q

When is the signal sequence removed?

A

when the growing polypeptide chain enters the ER

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24
Q

How are signal sequences determined?

A

by in vitro preparations of rough ER

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25
Q

What happens to the ER when cells are disrupted?

A

the ER breaks up into microsomes (small vesicles)

26
Q

About how long are signal sequences?

A

20 amino acids

27
Q

Signal sequences include a stretch of what?

A

hydrophobic residues

28
Q

Where are the hydrophobic residues usually located in signal sequences?

A

at the N-terminus

29
Q

What do SRPs consist of?

A

6 polypeptides + a small cytoplasmic RNA (SRP RNA)

30
Q

What is a complex of 3 transmembrane proteins called?

A

Sec61 proteins

31
Q

What do Sec61 proteins do?

A

translocate secreted polypeptides in bacteria

32
Q

Which type of translocation is more common in yeast?

A

posttranslational

33
Q

What is the function of Hsp70 and Hsp40 chaperones ?

A

keep the peptide chains from folding so they can enter the translocon

34
Q

What is the Hsp70 chaperone that acts as a ratchet to pull the polypeptide chain through the channel into the ER

A

BiP (binding protein)

35
Q

What does BiP bind to?

A

hydrophobic regions

36
Q

Proteins destined for incorporation into membranes are initially inserted where?

A

ER membrane

37
Q

Membrane-spanning regions of integral regions of integral membrane proteins typically have __________ regions with _______ amino acids.

A

α helical regions with hydrophobic amino acids

38
Q

The ER lumen is topologically equivalents to what?

A

cell exterior

39
Q

Domains of membrane proteins that are exposed on the cell surface correspond to what?

A

regions of polypeptide chains that are translocated into the ER lumen

40
Q

How are many proteins directly inserted into the ER membrane?

A

internal transmembrane sequences

41
Q

What are the internal transmembrane sequences recognized by?

A

SRP (but not cleaved by it)

42
Q

Transmembrane α helices exit the translocon laterally and do what?

A

anchor proteins in the ER membrane

43
Q

What direction are the polypeptides oriented across the ER membrane (N and C terminus)?

A

either direction

44
Q

What does the Transmembrane α helix do?

A

Halts translocation and anchors the polypeptide in the membrane

45
Q

Where is the transmembrane α helix located in the protein?

A

middle

46
Q

Where does the carboxy terminal portion of polypeptide remain? (ER lumen or cytosol)

A

cytosol

47
Q

What does the signal peptidase do?

A

cut the signal sequence from the primary polypeptide

48
Q

Proteins that span the membrane multiple times are inserted by what?

A

an alternating series of internal signal sequences and transmembrane stop-transfer sequences (N terminus is in cytosol)

49
Q

Some proteins have a transmembrane sequence at the carboxy terminus that cannot what?

A

cannot be recognized by SRP until translation is complete

50
Q

What is the transmembrane sequence recognized by (when it is at the carboxy terminus)?

A

targeting factor TRC40

51
Q

What does the targeting factor TRC40 specifically do?

A

brings the protein to a GET1-GET2 receptor in the ER membrane

52
Q

Where does protein folding and processing occur (2 places)?

A

either during translocation across the ER membrane or in the ER lumen

53
Q

what is the primary role of lumen proteins?

A

assist folding and assembly of newly translocated peptides

54
Q

Hsp70 chaperone BiP helps proteins do what?

A

not fold

55
Q

Hsp70 chaperone BiP binds to what as they cross the ER membrane?

A

unfolded polypeptides

56
Q

Why is BiP not needed for cotranslational translocation in the ER?

A

the polypeptide is pushed through the translocator by the energy of the ribosome

57
Q

What type of bonds are important in protein folding?

A

disulfide bonds

58
Q

What type of environment is the cytosol?

A

reducing

59
Q

Most cystine residues in the cytosol are in the _____ state.

A

reduced (-SH)

60
Q

What type of environment is the ER?

A

oxidizing

61
Q

What part of the cell promotes disulfide (S-S) bond formation?

A

ER

62
Q

What facilitates the disulfide bond formation?

A

protein disulfide isomerase

Cell Biology (8 decks)

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