Bsci 330 Final Exam: 4/21

Front 1

smooth or rough er lacks ribosomes?

Back 1

smooth

Front 2

typically tubular system-space inside appears continuous

Back 2

smooth ER

Front 3

cisternae

Back 3

interconnected flattened sacs

Front 4

extensive organelle composed mostly of cisternae

Back 4

rough er

Front 5

where are ribosomes on rough er attached?

Back 5

to the RER on cytosolic surface

Front 6

describe the relationship of RER and the nuclear envelope and outer membrane

Back 6

The RER is continuous with the nuclear envelope and out outer membrane

Front 7

why and how can rough and smooth vesicles be separated?

Back 7

centrifugation because they have different densities

Front 8

T/F specific funtion of SER is similar cell-to-cell.

Back 8

false....function is different cell to cell

Front 9

name 4 functions of SER

Back 9

Synthesis of steroid hormones in gonad & adrenal cortex endocrine cells

Detoxification in liver of many organic compounds (barbiturates & ethanol)

Large glycogen reserves are stored on outside of SER membranes

Storage of Ca2+ ions in smooth ER lumen; their release triggers specific cell activities
SER contains a high concentration of Ca2+-binding proteins

Regulated release of Ca2+ from SER triggers responses like skeletal muscle contraction & fusion of secretory vesicles with the plasma membrane

Front 10

main function of RER

Back 10

synthesis and initial glycosylation of proteins

-export proteins
-most integral membrane proteins

Front 11

name the 2 places that proteins can be made?

Back 11

1)ribosomes on ER cytosolic surface
2)free ribosomes

Front 12

describe functions of ribosomes on ER (3)

Back 12

-proteins secreted from cell
-integral membrane proteins
-soluble proteins that will reside within compartments of the endomembrane system (ER, Golgi complex, lysosomes, endosomes, vesicles, plant vacuoles)

Front 13

describe function of ribosomes that are free (4)

Back 13

Proteins destined to remain in cytosol (enzymes of glycolysis, cytoskeleton proteins)

Peripheral proteins of inner cell membrane surface (spectrins, ankyrins)

Proteins that are transported into the nucleus

Proteins to be incorporated into peroxisomes, chloroplasts, mitochondria

Front 14

describe co-translational import into the ER of proteins bound for secretion

Back 14

1)mRNA for protein to be secreted binds to a free ribosome in the cytosol

2)signal sequence emerges from ribosome

3)Signal recognition particle (SRP) recognizes particle

4)SRP binds to signal sequence and ribosome and blocks translation

5)SRP tag allows complex to bind to SRP receptor of protein on ER surface

6)once ribosome is bound tightly to ER membrane, signal sequence is released from the SRP and inserted into channel of translocon where a conformational change is observed (greatly widens the channel to ER lumen)

7)SRP is then released from its receptor on ER into cytosol, translation resumes and polypeptide is translocated into channel of ER lumen

-The hydrolysis of GTP catalyzes reaction
-a protein plug keeps channel closed...will be cut by signal peptidase

Front 15

describe the SRP in mammalian cells?

Back 15

consists of 6 distinct polypeptides and a small RNA molecule, 7S rna

Front 16

protein lined membrane channel of the ER

Back 16

translocon

Front 17

can ribosome subunits be reused?

Back 17

yes

Front 18

after co-translational import into ER of proteins, what will happen to channel

Back 18

reverts to original, narrow conformation

Front 19

what keeps the translocon pore closed before/after ribosome attachment?

Back 19

a protein plug in the pore lumen that is displaced by the growing polypeptide

Front 20

after co-translational import into the ER of proteins, what will the protein be bound to do?

Back 20

committed to the secretory pathway

Front 21

draw the picture of the co translational import into the ER of proteins bound for secretion from notes

Back 21

do it....do it now!!!!!!!!!!!

Front 22

how are carbohydrates added to a protein during proteins being inserted into ER from free ribosomes?

Back 22

added to protein by other enzymes residing in the ER lumen in close proximity to the translocon

Front 23

PDI

Back 23

enzyme in ER lumen that catalyzes formation of disulfide bridges between appropriate cysteine residues of the new protein

Front 24

purpose of chaperones?

Back 24

recognize and bind to unfolded or misfolded proteins and give them a chance to attain their correct 3D structure

Front 25

what will happen to misfolded proteins in the ER bound for secretion?

Back 25

1)transported out of ER into cytosol by reverse translocation
(back through translocons they passed through)

2)When in cytosol, they are destroyed in proteasomes: protein-degrading organelles

Front 26

loosely said, how are integral membrane proteins incorporated into the membrane of RER

Back 26

woven

Front 27

where are integral membrane proteins made?

Back 27

on RER membrane bound ribosomes

exception: mitochondria, chloroplasts and peroxisomes

Front 28

What happens with respect to integral membrane proteins when they leave RER

Back 28

vesicles will bud off of RER and they will carry newly synthesized integral membrane proteins with them in the vesiscles membrane and transfer them to the golgi membrane when the fuse with the golgi

Front 29

how do integral membrane proteins get from RER to the plasma membrane?

Back 29

vesicle will bud off of RER and attach to golgi... when a golgi secretory vesicle forms it will have these integral proteins.


***picture in notes may clarify

Front 30

what do integral membrane proteins contain?

Back 30

one or more hydrophobic transmembrane segment of amino acids (

Front 31

1)what is a stop transfer sequence

2)co-translational synthesis of integral membrane proteins in the RER synthesis is what?

Back 31

1)hydrophobic transmembrane segment of amino acids that block further movement into ER lumen

2)contranslationally synthesized as they are translocated.

Front 32

describe Co-translational synthesis of integral membrane proteins in the RER

Back 32

1)integral membranes are translocated into ER membrane as they are synthesized using same machinery used by secreted proteins

2)stop transfer sequence blocks further movement into ER lumen

3)ribosome continues to synthesize polypeptide on cytosolic side of membrane

4)translocon will disassemble

Front 33

synthesis of most membrane lipids is by ER enzymes with active sites where?

Back 33

on the cytoplasmic surface of the RER

Front 34

can a lipid go from RER membrane to golgi and plasma membrane?

Back 34

yes!!!!

vesicle buds from ER and fuses to golgi....golgi will then form a vesicle (buds) and will go to plasma membrane

any integral membrane proteins or lipids can then become incorporated in its new facet

Front 35

where do newly synthesized phospholipids get inserted on RER?

Back 35

outer cytoplasmic leaflet

Front 36

can lipids be found in the inner leaflet of RER?

Back 36

yes

flippase enzymes will translocate them across the bilayer

membr

Front 37

what is membrane asymmetry established by?

Back 37

flippase specificity

Front 38

why do different organelle membranes have different lipid composition?

Back 38

-enzymes that convert one phospholipid to another type

-as membranes bud, some phospholipds are preferentially included in the new vesicle, others are excluded

-Phospholipid-transfer proteins move specific phospholipids from one membrane to another through the cytosol...may move specific phospholipids from ER to other organelles