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Molecular Biology > Protein Sorting I > Flashcards

Protein Sorting I Flashcards

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1
Q

What is the plasma membrane? What is its function?

A

outer boundary of cells, bilayer

function: protective barrier, has transporters, signaling

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2
Q

What is the nucleus? What is its function?

A

contains the genome

function: principal site for DNA and RNA synthesis

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3
Q

What is the cytoplasm? What is its function?

A

consists of cytosol and cytoplasmic organelles

function: location of intermediary metabolism

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4
Q

What is the ER? What is its function?

A

ribosomes attached to it (rough), no ribosomes (smooth)

function: involved in protein synthesis, lipid synthesis, protein folding, storage of calcium

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5
Q

What is the Golgi Apparatus? What is its function?

A

stacks of disc-like compartments

function: post-translational changes on proteins and lipids, trafficking

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6
Q

What is the mitochondria? What is its function?

A

outer and inner membrane and matrix

function: makes ATP, signaling, cell differentiation and cell death

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7
Q

What are lysosomes? What do they do?

A

contain digestive enzymes that degrade organelles and biomolecules

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8
Q

What are peroxisomes? What do they do?

A

small vesicular compartments that contain enzymes used in oxidation reactions

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9
Q

What are the three topological categories of cells?

A

nucleus and cytosol; organelles in secretory and endocytic pathways; mitochondria

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10
Q

What is the nuclear envelope?

A

space between inner nuclear membrane and outer nuclear membrane

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11
Q

What allows the lumen of each topological equivalent organelle lumen to communicate with each other and with the cell exterior?

A

budding and fusion

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12
Q

This type of transport occurs between nucleus and cytosol through nuclear pore complexes (active transport and free diffusion)

A

gated transport

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13
Q

This type of transport occurs when protein translocators directly transport specific proteins from cytosol across an organelle membrane

A

transmembrane transport

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14
Q

This type of transport occurs when membrane-enclosed transport intermediates move proteins between various compartments via vesicles

A

vesicular transport

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15
Q

Protein transfer/transport to various compartments is guided by what?

A

sorting signals

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16
Q

In regards to protein sorting signals, what is the typical length of a stretch of amino acids?

A

15-60 residues

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17
Q

How are protein sorting signals localized?

A

on N or C terminus or within protein sequence

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18
Q

In regards to protein sorting signals, multiple scattered sequences in protein may form what?

A

signal patch

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19
Q

What do signal peptidases do?

A

may remove signal after protein reaches final destination

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20
Q

What are both necessary and sufficient for protein targeting?

A

signal sequences

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21
Q

True or False?

In terms of proteins sorting signals, physical properties of the sequence are more important than the actual sequence

A

true

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22
Q

What are signal sequences recognized by?

A

complementary receptors

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23
Q

This type of transport is gated, bidirectional, and selective

A

nuclear transport

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24
Q

In terms of nuclear transport, proteins that are needed in the nucleus are imported from where?

A

the cytoplasm

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25
Q

Where are tRNA and mRNA molecules synthesized and exported to?

A

synthesized in nucleus; exported to cytosol

26
Q

What is the molecular mass of a nuclear pore complex (NPC)?

A

125 million Da.

27
Q

What are NPCs composed of?

A

30 different proteins or nucleoporins

28
Q

How are NPCs arranged?

A

in octagonal symmetry with one or more aqueous pores

29
Q

How many NPCs are in the nuclear envelope?

A

3000-4000

30
Q

What is the direction of transport molecules in the NPCs?

A

both directions

31
Q

What type of diffusion do small molecules utilize in the NPCs?

A

passive diffusion; facilitated transport

32
Q

In the NPCs, what is transport facilitated by?

A

binding of particles to fibrils extending form NPC

33
Q

What is the size of molecules that travel through the NPCs by active transport?

A

large

34
Q

What are Nuclear localization signals (NLS)? What is their function?

A

short sequences rich in positively charged amino acids lysine and arginine;
function: sorting signals that direct molecules to the nucleus (selective import)

35
Q

Where are NLS located?

A

on many different sites on protein; form loops or patches on surface

36
Q

What recognizes NLS?

A

nuclear import receptors (NIRs); recognizes a subset of cargo proteins

37
Q

Where are NIRs found?

A

cytosol

38
Q

NIRs bind to NLS on protein and to NPC proteins that are present where?

A

on fibrils that extend into the cytoplasm

39
Q

NPC proteins have phenylalanine glycine repays which serve as what?

A

binding sites for import receptors

40
Q

How do receptors + cargo traverse NPC?

A

by binding, dissociating, and re-binding to adjacent phenylalanine repeats

41
Q

Where do NIR go after cargo is released into nucleus?

A

return to cytoplasm

42
Q

In regards to nuclear import receptors, cargo proteins 1, 2, and 3 are involved in direct or indirect binding?

A

direct

43
Q

In regards to nuclear import receptors, cargo protein 4 is involved in direct or indirect binding?

A

indirect

44
Q

What does nuclear export rely on?

A

Nuclear export signals (NES) on molecules that need to go out of the nucleus; also need Nuclear export receptors (NER)

45
Q

How does nuclear export work?

A

same as nuclear import: NER binds to cargo present in nucleus and NPC proteins; binding, dissociation, re-binding facilitates transport; cargo released in cytoplasm

46
Q

Where in the cell is the GAP or GTPase activating protein located?

A

cytosol

47
Q

Where in the cell is GEF or Guanine exchange factor located?

A

nuclear

48
Q

What drives nuclear transport in appropriate direction?

A

gradient of Ran conformational states

49
Q

What does Ran-GTP bind to?

A

complex of import receptor and cargo

50
Q

What does the binding of Ran-GTP cause?

A

release of cargo

51
Q

Where do Ran-GTP and import receptor go after they release cargo?

A

leave nucleus

52
Q

What is Ran-GTP hydrolyzed by in the cytoplasm?

A

Ran-GAP

53
Q

When the receptor is released from Ran-GDP is it ready for another cycle?

A

yes

54
Q

In regards to shuttling proteins, some proteins contain what?

A

NLS and NES

55
Q

What is steady state localization of shuttling proteins dependent upon?

A

relative rate of transport

56
Q

If rate of import is greater than export, it is considered what?

A

nuclear

57
Q

Changing rate of import/export can change what?

A

location of protein

58
Q

True or False?

In terms of gene regulatory proteins, transport is loosely controlled

A

false; stringently controlled

59
Q

When do gene regulatory proteins enter the nucleus?

A

only when they’re needed

60
Q

What is transport of gene regulatory proteins controlled by?

A

NLS and NES being turned on and off

61
Q

Gene regulatory protein mechanisms include what?

A

phosphorylation, proteolysis, binding to inhibitory proteins

62
Q

How is cholesterol biosynthesis regulated?

A

feedback regulation

Molecular Biology (17 decks)

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