ER

Question 1

Start of Endomembrane system

Answer 1

RER

Question 2

Polypeptides are synthesized at two location

Answer 2

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

Question 3

Protein synthesized at RER

Answer 3

• secreted proteins
• transmembrane proteins
• soluble proteins reside in Endomembrane system

Question 4

Protein synthesized on free cytosolic ribosomes

Answer 4

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

Question 5

All proteins begin synthesis in

Answer 5

Ribosomes in cytosol

Question 6

How proteins know where to go

Answer 6

ER signal sequence OR sorting signal

TIGHTLY TIE PROTEIN SEQUENCE,SYNTHESIS,TARGETING

Question 7

Translation start at

Answer 7

Cytosol

Question 8

Most polypeptide synthesis take place in

Answer 8

Cytosol

Question 9

After translation two pathways separated

Answer 9

Free ribosome vs ER-docked ribosome

Question 10

Protein sorting pathways

Answer 10

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

Question 11

Co and post translational import difference

Answer 11

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

Question 12

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

Answer 12

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

Question 13

Multiple ribosome synthesizing same mRNA

Answer 13

Polysome

Question 14

Co translational translocation of SOLUBLE PROTEIN

Answer 14

Deposit polypeptides in lumen of ER

Question 15

Signal Recognition Particle (SRP)

Answer 15

Binds ribosome-mRNA-polypeptide complex to ER membrane

SRP bind ER signal sequence to new forming polypeptide

Question 16

SRP contain

Answer 16

Protein and RNA

Question 17

Polypeptide synthesis proceed until

Answer 17

ER signal sequence has been formed

Question 18

Srp bind to signal sequence and ———

Answer 18

Block further translations

Question 19

ER signal sequence inserted into translocation once ———

Answer 19

SRP has been released

Question 20

How the channel to ER lumen opens?

Answer 20

ER signal sequence contact interior of translocon

Question 21

When polypeptide synthesis is complete

Answer 21

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

Question 22

G protein (GTPases)

Answer 22

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

Question 23

G-proteins play roles in

Answer 23

• cell signaling
• cell division
• proteins synthesis
• vesicle fusion

Question 24

SRP and SRP are

Answer 24

Both G protein

Question 25

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

Answer 25

Integral Membrane Proteins

Question 26

Transmembrane proteins can be

Answer 26

Single or multi pass

Question 27

Oligosaccharide chains are always ———

Answer 27

On non-cytosolic side

Question 28

Translocon and membrane have

Answer 28

Charge asymmetry —— more negative on cytosolic side

Question 29

Hydrophobic transmembrane domain can ——— in lipid bilayer

Answer 29

Dissolve

Question 30

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

Answer 30

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

Question 31

RER is site of

Answer 31

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

Question 32

Glycosylation in (ER and Golgi) =

Answer 32

Glycoproteins

Question 33

Most proteins synthesized in RER are glycosylated on ———

Answer 33

amide nitrogen of asparagine

Question 34

Glycosylation is then modified by

Answer 34

Golgi

Question 35

Carbohydrate groups in glycoproteins function as :

Answer 35

-macromolecule binding site -aid protein folding -increase stability

Question 36

Co-translational glycosylation

Answer 36

Oligosaccharides are added to protein during synthesis

Question 37

Processing of the N-linked oligosaccharide in ER lumen

Answer 37

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

Question 38

As polypeptides enter ER lumen

Answer 38

Fold into final shape

Question 39

Chaperones of N-linked oligosacvharides

Answer 39

Calnexin and calreticulin

Question 40

Binding of calnexin and calreticulin ———

Answer 40

Prevent aggregation and drives disulfide bond formation

Question 41

Bip

Answer 41

Binding proteins chaperone Binds to hydrophobic regions and prevent interactions

Question 42

Bip release the polypeptide chain then:

Answer 42

If fold correctly, hydrophobic region is buried in the interior If fold incorrectly, interacts with BiP again

Question 43

Disulfide bond formation enzyme

Answer 43

Protein disulfide isomerase PDI

Question 44

In eukaryotic cells, disulfide bonds are only formed in

Answer 44

ER lumen

Question 45

Disulfide bond formation occurs between

Answer 45

Adjacent cysteines

Question 46

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

Answer 46

Made faster than fold

Question 47

Higher made than fold activate

Answer 47

Unfolded Protein Response (UPR)

Question 48

UPR will

Answer 48

Sensor molecules in ER detect misfolded proteins

Question 49

When UPR is activated

Answer 49

1- phosphorylate translation factor (Inhibiting protein synthesis) 2- upregulate the expression: — er based chaperones — transport proteins out of ER — protein degradation machinery

Question 50

Component of UPR that recognize misfolded or unassembled proteins

Answer 50

ER-associated degradation (ERAD)

Question 51

What happen to misfolded proteins

Answer 51

Export to cytosol and degraded by proteasomes

Question 52

Proteasomes

Answer 52

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

Question 53

Ubiquitin is joined to target protein by

Answer 53

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

Question 54

Primary source of membrane lipid

Answer 54

ER

Question 55

Why ER is primary

Answer 55

Because other doesn’t have the required enzymes

Question 56

Except ER who can produce lipid

Answer 56

Mitochondria, chloroplasts, peroxisomes

Question 57

Fatty acids required for lipid synthesis

Answer 57

Are synthesized in cytoplasm then go to ER membrane on cytosolic side Then, transfer to lumenal side by flippases

Question 58

Most organelles have enzymes modifying lipids

Answer 58

Converting one type to another

Question 59

Exchange lipids between compartment

Answer 59

Lipid Transfer Protein