Protein Sorting I

Question 1

What is the plasma membrane? What is its function?

Answer 1

outer boundary of cells, bilayer

function: protective barrier, has transporters, signaling

Question 2

What is the nucleus? What is its function?

Answer 2

contains the genome

function: principal site for DNA and RNA synthesis

Question 3

What is the cytoplasm? What is its function?

Answer 3

consists of cytosol and cytoplasmic organelles

function: location of intermediary metabolism

Question 4

What is the ER? What is its function?

Answer 4

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

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

Question 5

What is the Golgi Apparatus? What is its function?

Answer 5

stacks of disc-like compartments

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

Question 6

What is the mitochondria? What is its function?

Answer 6

outer and inner membrane and matrix

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

Question 7

What are lysosomes? What do they do?

Answer 7

contain digestive enzymes that degrade organelles and biomolecules

Question 8

What are peroxisomes? What do they do?

Answer 8

small vesicular compartments that contain enzymes used in oxidation reactions

Question 9

What are the three topological categories of cells?

Answer 9

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

Question 10

What is the nuclear envelope?

Answer 10

space between inner nuclear membrane and outer nuclear membrane

Question 11

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

Answer 11

budding and fusion

Question 12

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

Answer 12

gated transport

Question 13

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

Answer 13

transmembrane transport

Question 14

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

Answer 14

vesicular transport

Question 15

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

Answer 15

sorting signals

Question 16

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

Answer 16

15-60 residues

Question 17

How are protein sorting signals localized?

Answer 17

on N or C terminus or within protein sequence

Question 18

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

Answer 18

signal patch

Question 19

What do signal peptidases do?

Answer 19

may remove signal after protein reaches final destination

Question 20

What are both necessary and sufficient for protein targeting?

Answer 20

signal sequences

Question 21

True or False?

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

Answer 21

true

Question 22

What are signal sequences recognized by?

Answer 22

complementary receptors

Question 23

This type of transport is gated, bidirectional, and selective

Answer 23

nuclear transport

Question 24

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

Answer 24

the cytoplasm

Question 25

Where are tRNA and mRNA molecules synthesized and exported to?

Answer 25

synthesized in nucleus; exported to cytosol

Question 26

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

Answer 26

125 million Da.

Question 27

What are NPCs composed of?

Answer 27

30 different proteins or nucleoporins

Question 28

How are NPCs arranged?

Answer 28

in octagonal symmetry with one or more aqueous pores

Question 29

How many NPCs are in the nuclear envelope?

Answer 29

3000-4000

Question 30

What is the direction of transport molecules in the NPCs?

Answer 30

both directions

Question 31

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

Answer 31

passive diffusion; facilitated transport

Question 32

In the NPCs, what is transport facilitated by?

Answer 32

binding of particles to fibrils extending form NPC

Question 33

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

Answer 33

large

Question 34

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

Answer 34

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

Question 35

Where are NLS located?

Answer 35

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

Question 36

What recognizes NLS?

Answer 36

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

Question 37

Where are NIRs found?

Answer 37

cytosol

Question 38

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

Answer 38

on fibrils that extend into the cytoplasm

Question 39

NPC proteins have phenylalanine glycine repays which serve as what?

Answer 39

binding sites for import receptors

Question 40

How do receptors + cargo traverse NPC?

Answer 40

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

Question 41

Where do NIR go after cargo is released into nucleus?

Answer 41

return to cytoplasm

Question 42

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

Answer 42

direct

Question 43

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

Answer 43

indirect

Question 44

What does nuclear export rely on?

Answer 44

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

Question 45

How does nuclear export work?

Answer 45

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

Question 46

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

Answer 46

cytosol

Question 47

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

Answer 47

nuclear

Question 48

What drives nuclear transport in appropriate direction?

Answer 48

gradient of Ran conformational states

Question 49

What does Ran-GTP bind to?

Answer 49

complex of import receptor and cargo

Question 50

What does the binding of Ran-GTP cause?

Answer 50

release of cargo

Question 51

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

Answer 51

leave nucleus

Question 52

What is Ran-GTP hydrolyzed by in the cytoplasm?

Answer 52

Ran-GAP

Question 53

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

Answer 53

yes

Question 54

In regards to shuttling proteins, some proteins contain what?

Answer 54

NLS and NES

Question 55

What is steady state localization of shuttling proteins dependent upon?

Answer 55

relative rate of transport

Question 56

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

Answer 56

nuclear

Question 57

Changing rate of import/export can change what?

Answer 57

location of protein

Question 58

True or False? | In terms of gene regulatory proteins, transport is loosely controlled

Answer 58

false; stringently controlled

Question 59

When do gene regulatory proteins enter the nucleus?

Answer 59

only when they're needed

Question 60

What is transport of gene regulatory proteins controlled by?

Answer 60

NLS and NES being turned on and off

Question 61

Gene regulatory protein mechanisms include what?

Answer 61

phosphorylation, proteolysis, binding to inhibitory proteins

Question 62

How is cholesterol biosynthesis regulated?

Answer 62

feedback regulation