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BIO230 > Lecture 9 and 10 > Flashcards

Lecture 9 and 10 Flashcards

1
Q

What is protein sorting?

A

It is the movement of proteins within cell from different compartment, into the cell of out of the cell

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2
Q

Where is protein synthesis initiated?

A

Protein synthesis is initiated on ribosomes in sytosol

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3
Q

Where do UNFOLDED proteins that were synthesized in the cytosol go

A

mitochondria and plastids

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4
Q

Where do FOLDED proteins that were synthesized in the cytosol go

A

nucleus and peroxisomes

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5
Q

Co-translational process of protein sorting and synthesis

A

They are proteins with an ER signal sequence, they are associated with the ER during protein synthesis

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6
Q

Where does gated transport occur

A

proteins moving between cytosol and nucleus

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7
Q

Transport of cargo through nuclear pore complex

A

There is transport in both directions
1. nuclear import and nuclear export

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7
Q

Nuclear Pore Complex

A
  1. There is selective transport of macromolecules
  2. Free diffusion of small molecules (<5000 daltons)
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8
Q

What is the nuclear pore complex made of?

A

Nucleoporins q

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9
Q

What is the nuclear localization signal rich in?

A

Lysine and arginine

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10
Q

What does the nuclear import receptor bind to and where does it transport into?

A

The nuclear import receptor binds to a nuclear localization signal and nucleoporins in the nuclear pore complex. it transports into the nucleus.

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11
Q

What does nuclear export receptor bind to and transport into?

A

The nuclear export receptor binds to the nuclear export signal (NES) and to nucleoporins in NPC. It transports into the cytosol.

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12
Q

What does Ran GTPase cyle between?

A

GDP bound (to nucleus by Nuclear transport factor 2) and GTP bound (to cytosol with nuclear import and export receptors).

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13
Q

What is RAN GTPase regulated by?

A

Ran-GAP (GTPase activating protein) - stimulates GTP hydrolysis by Ran

Ran-GEF (Guanine nucleotide Exchange Factor) - promotes the exchange of GDP for GTP by Ran

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14
Q

Where is Ran-GAP found?

A

Cytosol

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15
Q

Where is Ran-GEF found?

A

Nucleus

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16
Q

Where are high and low Ran-GTP found?

A

high Ran-GTP - nucleus
low Ran-GTP - cytosol

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17
Q

Nuclear import of cargo proteins

A
  1. Nuclear import receptor binds cargo in the cytosol.
  2. Receptor and cargo move to the nucleus.
  3. Ran-GTP binding: causes cargo release
  4. Empty import receptor and Ran-GTP move to the cytosol
  5. Ran Binding protein and Ran GAP promote GTP hydrolysis and release of import receptor
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18
Q

Nuclear export of cargo proteins

A
  1. Nuclear export receptor binds Ran-GTP and cargo in the nucleus
  2. Receptor, cargo and Ran GTP move to cytosol
  3. Ram Binding Portein and Ran GAP promote GTP hydrolysis, release of cargo and release of export receptor.
  4. Empty export receptor returns to the nucleus.
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19
Q

Nuclear Factor of activated T-cells
(see diagram from notes)

A

High intracellular Ca2+ - nuclear import
Low intercellular Ca2+ - nuclear export

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20
Q

Experiment with NFAT

A
  1. Express NFAT-GFP fusion protein in T cells
  2. Add calcium ionophore
  3. Monitor fluorescence
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21
Q

Transmembrane transport

A

ER, mitochondria, plastids, peroxisomes

22
Q

Protein translocators

A
  1. transport of protein across membrane
  2. protein usually unfolded
23
Q

Protein translocators in mitochondrial matrix

A

TOM and TIM23 complexes

23
Q

Sorting proteins to mitochondria and chloroplasts

A

they have their own genme and ribosomes but most proteins are nuclear encoded
1. they are translated in cytosol
2. imported into organelle - post translational, proteins remain unfolded by association with hsp70 chaperones

24
Q

Importing proteins to the mitochondrial matrix

A

Precursor protein has a mitochondrial signal sequence (peptide) N terminal amphipathic alpha helix
it binds the receptor and moves through TOM and TIM23 complexes into matrix space signal sequence cleaved

25
Q

Importing proteins to the chloroplast

A

They have TOC and TIC translocators

the precursor protein has a chloroplast signal sequence - N terminal amphipathic alpha helix
Signal sequence cleaved in chloroplast
Different from mitochondrial signal sequence for correct targeting in plants
If targeting to thylakoid
1. hydrophobic thylakoid signal sequence
2. unmasked when chloroplast signal sequence cleaved

26
Q
A
27
Q

Sorting proteins to peroxisome

A

precursor protein
1. peroxisomal targeting signal
2. 3 amino acids at C terminus (SKL)
3. protein folded

it is transported across the membrane by a large translocator complex

28
Q

How can proteins be further sorted to other compartments or to cell surface from ER?

A

Vesicular transport

29
Q

2 major functions of the ER

A

Synthesis and modification of proteins
Synthesis of lipids

30
Q

What do proteins sorted to the ER have?

A

ER signal sequence
The proteins include soluble proteins, transmembrane proteins, proteins destined for golgi, secretion, lysosomes

31
Q

Protein sorting to ER

A
  1. mRNA + ribosomes
  2. translation starts, the ER signal sequences (hydrophobic amino acids at N terminus) emerges first
  3. The ribosomes are directed to ER membrane
  4. Co-translational translocation takes place
32
Q

What do signal recognition particles and signal recognition receptors have?

A

They have GTPase domains that bind GTP

33
Q

SRP + ribosome

A

low affinity

34
Q

SRP + ribosome + ER signal sequence

A

high affinity and binds SRP receptor

35
Q

What does ribosome form a tight seal with?

A

it forms a tight seal with the translocator to prevent diffusion of ions and small molecules

36
Q

What happens when only SRP and SRP receptor are bound?

A

There is GTP hydrolysis and the complex dissociates, and SRP is released.
here translation continues and translocation begins.

37
Q

What causes translation to slow down?

A

Binding of SRP to ribosome

38
Q

What is the ER signal sequence ?

A

N terminal start transfer sequence - hydrophobic amino acids

39
Q

What cleaves ER signal sequence?

A

Signal peptidase

40
Q

Where happens to both ER signal sequence and protein?

A

The ER signal sequence laterally diffuses into the lipid bilayer (translocator is gated in a 2nd direction) and translocated protein is released into ER

41
Q

How many types of insertions for single-pass transmembrane proteins?

A

3

42
Q

Single pass (1)

A
  1. The ER signal sequence is an (NH2) start transfer sequence.
  2. The transmembrane domain is a stop transfer signal that laterally diffuses into liid bilayer.
  3. signal peptidase cleaves start transfer.
    protein synthesis continues in cytosol with COOH end in cytosol.
43
Q

Single pass (2 and 3)

A
  1. Transmembrane domain: internal start transfer sequence that is not cleaved.
  2. this internal start transfer sequence will laterally diffuse into the lipid bilayer.
44
Q

Orientation in single pass (2 and 3)

A

The more positive side is the cytosolic side. It is determined by amino acids flanking the internal start transfer sequence.

45
Q

Example 1 of multipass transmembrane protein

A

1st transmembrane domain: internal start transfer sequence
2nd transmembrane domain: stop transfer sequence

Both N and C terminus face cytosol

46
Q

Example 2 of multipass proteins

A

RHodopsin
1st transmembrane domain: start transfer; (+) amino acids
2nd transmembrane domain: start transfer
3rd: stop 4th: start

47
Q

Membrane protein types

A

integral, lipid anchored and pripheral

47
Q

where are most transmembrane proteins glycosylated?

A

extracellulcar face

48
Q
A
49
Q

Formation of GPI-anchored proteins

A
  1. Target protein has C terminal hydrophobic domain.
  2. GP anchor is preformed in the membrane.
  3. The transmembrane domain is signal for the GPI anchor.
  4. Er enzyme transfers protein to the GPI anchor.
  5. GPI anchored protein ends up on ER luminal side and can go to cell exterior surface.
50
Q

What serves as a signal for the gpi anchor?

A

C terminal hydrophobic domain

BIO230 (6 decks)

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