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Mbb231 > ER > Flashcards

ER Flashcards

1
Q

Start of Endomembrane system

A

RER

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2
Q

Polypeptides are synthesized at two location

A

-1/3 at RER
-2/3 on free cytosolic ribosomes

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3
Q

Protein synthesized at RER

A
  • secreted proteins
  • transmembrane proteins
  • soluble proteins reside in Endomembrane system
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4
Q

Protein synthesized on free cytosolic ribosomes

A

-proteins destined to remain in ribosomes
-peripheral proteins of cytosolic surfaces
-proteins transported to nucleus
-proteins for chloroplast/chloroplast/peroxisome

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5
Q

All proteins begin synthesis in

A

Ribosomes in cytosol

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6
Q

How proteins know where to go

A

ER signal sequence OR sorting signal

TIGHTLY TIE PROTEIN SEQUENCE,SYNTHESIS,TARGETING

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7
Q

Translation start at

A

Cytosol

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8
Q

Most polypeptide synthesis take place in

A

Cytosol

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9
Q

After translation two pathways separated

A

Free ribosome vs ER-docked ribosome

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10
Q

Protein sorting pathways

A

1- Co-translational import
2- post-translational import

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11
Q

Co and post translational import difference

A

Co:
Proteins carry ER signal sequence direct to RER
——ER signal sequence

Post:
Lack of ER signal sequence, complete synthesis on free ribosome
——sorting signal

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12
Q

The proteins are released in cytoplasm from post-translational import and ———

A

Those who have organelle-specific sorting signal are imported into organelle
**cytoplasmic proteins do not have sorting signal

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13
Q

Multiple ribosome synthesizing same mRNA

A

Polysome

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14
Q

Co translational translocation of SOLUBLE PROTEIN

A

Deposit polypeptides in lumen of ER

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15
Q

Signal Recognition Particle (SRP)

A

Binds ribosome-mRNA-polypeptide complex to ER membrane

SRP bind ER signal sequence to new forming polypeptide

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16
Q

SRP contain

A

Protein and RNA

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17
Q

Polypeptide synthesis proceed until

A

ER signal sequence has been formed

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18
Q

Srp bind to signal sequence and ———

A

Block further translations

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19
Q

ER signal sequence inserted into translocation once ———

A

SRP has been released

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20
Q

How the channel to ER lumen opens?

A

ER signal sequence contact interior of translocon

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21
Q

When polypeptide synthesis is complete

A
  • polypeptide released into lumen
  • ribosome detaches from ER membrane
    -translocon pore closes
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22
Q

G protein (GTPases)

A

Molecular switch between GTP- and GDP- bound state
Different conformations= different affinities

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23
Q

G-proteins play roles in

A
  • cell signaling
  • cell division
  • proteins synthesis
  • vesicle fusion
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24
Q

SRP and SRP are

A

Both G protein

25
Q

One mahor group of polypeptide synthesized on RER is molecules destined to be

A

Integral Membrane Proteins

26
Q

Transmembrane proteins can be

A

Single or multi pass

27
Q

Oligosaccharide chains are always ———

A

On non-cytosolic side

28
Q

Translocon and membrane have

A

Charge asymmetry
—— more negative on cytosolic side

29
Q

Hydrophobic transmembrane domain can ——— in lipid bilayer

A

Dissolve

30
Q

Orientation of multi-pass protein integral membrane protein is determined by ———

A

Charge/orientation of first transmembrane domain
—— each subsequent transmembrane domain must have opposite charge

31
Q

RER is site of

A

-Protein modification
-recognition and removal of misfolded proteins
-lipid synthesis

32
Q

Glycosylation in (ER and Golgi) =

A

Glycoproteins

33
Q

Most proteins synthesized in RER are glycosylated on ———

A

amide nitrogen of asparagine

34
Q

Glycosylation is then modified by

A

Golgi

35
Q

Carbohydrate groups in glycoproteins function as :

A

-macromolecule binding site
-aid protein folding
-increase stability

36
Q

Co-translational glycosylation

A

Oligosaccharides are added to protein during synthesis

37
Q

Processing of the N-linked oligosaccharide in ER lumen

A

Initial process when 3 glucose residue and 1 mannose are removed
WHY?
Possible sort of signal indicating

38
Q

As polypeptides enter ER lumen

A

Fold into final shape

39
Q

Chaperones of N-linked oligosacvharides

A

Calnexin and calreticulin

40
Q

Binding of calnexin and calreticulin ———

A

Prevent aggregation and drives disulfide bond formation

41
Q

Bip

A

Binding proteins chaperone
Binds to hydrophobic regions and prevent interactions

42
Q

Bip release the polypeptide chain then:

A

If fold correctly, hydrophobic region is buried in the interior

If fold incorrectly, interacts with BiP again

43
Q

Disulfide bond formation enzyme

A

Protein disulfide isomerase PDI

44
Q

In eukaryotic cells, disulfide bonds are only formed in

A

ER lumen

45
Q

Disulfide bond formation occurs between

A

Adjacent cysteines

46
Q

Proteins can be —— faster than they can be ——

A

Made faster than fold

47
Q

Higher made than fold activate

A

Unfolded Protein Response (UPR)

48
Q

UPR will

A

Sensor molecules in ER detect misfolded proteins

49
Q

When UPR is activated

A

1- phosphorylate translation factor
(Inhibiting protein synthesis)

2- upregulate the expression:
— er based chaperones
— transport proteins out of ER
— protein degradation machinery

50
Q

Component of UPR that recognize misfolded or unassembled proteins

A

ER-associated degradation (ERAD)

51
Q

What happen to misfolded proteins

A

Export to cytosol and degraded by proteasomes

52
Q

Proteasomes

A

Bind ubiquitin-labeled proteins
Remove ubiquitin
Fed the protein in central channel

53
Q

Ubiquitin is joined to target protein by

A

3enzymes
E1—— ubiquitin activating
E2—— ubiquitin conjugating
E3—— ubiquitin ligase

54
Q

Primary source of membrane lipid

A

ER

55
Q

Why ER is primary

A

Because other doesn’t have the required enzymes

56
Q

Except ER who can produce lipid

A

Mitochondria, chloroplasts, peroxisomes

57
Q

Fatty acids required for lipid synthesis

A

Are synthesized in cytoplasm then go to ER membrane on cytosolic side

Then, transfer to lumenal side by flippases

58
Q

Most organelles have enzymes modifying lipids

A

Converting one type to another

59
Q

Exchange lipids between compartment

A

Lipid Transfer Protein

Mbb231 (19 decks)

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