chapter 12

Question 1

The endomembrane system

Answer 1

movement of lipids and proteins between organelles (called trafficking) must be tightly regulated

Question 2

Components of the endomembrane system

Answer 2

Golgi, ER (rough and smooth), lysosomes, endosomes, peroxisomes

Question 3

Rough endoplasmic reticulum

Answer 3

is characterized by ribosomes on the cytsolic side of the membrane

Question 4

A subdomain of rough ER, the ___ ___ (TEs), play a role in the formation of transition vesicles that shuttle lipids and proteins from the ER to the Golgi complex

Answer 4

transitional elements

Question 5

Smooth ER

Answer 5

lacks ribosomes and has other roles in the cell involving the processing and storage of nonproteins

Question 6

Rough ER membranes form (structure)

Answer 6

large flattened sheets

Question 7

Smooth ER membranes form (structure)

Answer 7

tubular

Question 8

Rough Er is the site for…(4 things)

Answer 8

• The initial steps of additoon of carbohydrates of glycoproteins
• The folding of polypeptides
• assembly of multimeric proteins
• proteins that are incorrectly folded, modified, or assembled are recognized and exported for degration

Question 9

Smooth ER is involved in (4 things)

Answer 9

drug detoxification, carbohydrate metabolism, calcium storage, and steroid biosynthesis

Question 10

Transition elements of rough Er and smooth ER…

Answer 10

resemble one another

Question 11

Are the rough ER and smooth ER separate organelles?

Answer 11

NO, material can travel between the rough and smooth ER without the aid of vesicles

Question 12

Cells involved in the biosynthesis of secretory proteins, such as liver cells and cells producing digestive enzymes, tend to have very prominent ____networks. On the other hand, cells producing steroid hormones, such as in the testis or ovary, contain extensive networks of ___.

Answer 12

rough ER ; smooth ER

Question 13

What does it mean by “Newly synthesized proteins enter the endomembrane system cotranslationally”?

Answer 13

They are inserted through a pore complex in the ER membrane into the rough ER lumen as the polypeptide is synthesized by the ER-bound ribosome.

Question 14

The ER is also a site for quality control, where proteins improperly modified, folded, or assembled are exported from the ER for degradation by cytosolic ____ instead of moving on to the Golgi apparatus.

Answer 14

proteasomes

Question 15

Drug detoxification often involves enzyme-catalyzed _____ because the addition of hydroxyl groups to hydrophobic drugs makes them more soluble and easier to excrete from the body.

Answer 15

hydroxylation

Question 16

Hydroxylation of organic acceptor molecules is typically catalyzed by a member of the _____ family of proteins.

Answer 16

cytochrome P-450

Question 17

hepatocytes

Answer 17

liver cells

Question 18

The Smooth ER plays a central role in the biosynthesis of

Answer 18

membranes

Question 19

What are the few exceptions to smooth er making membranes?

Answer 19

mitochondria synthesize phosphatidylethanolamine, peroxisomes synthesize cholesterol, chloroplasts contain enzymes for chloroplast specific lipids

Question 20

The golgi apparatus is a series of flattened membrane bounded ___

Answer 20

cisternae

Question 21

a series of cisternae (3-8) is called

Answer 21

golgi stack

Question 22

Anterograde

Answer 22

movement of material from the ER through the Golgi apparatus toward the plasma membrane

Question 23

Retrograde

Answer 23

flow of vesicles from Golgi cisternae back toward the ER

Question 24

CGN (cis)

Answer 24

compartment closest to the ER, a network of flattened, membrane bounded tubules
Vesicles containing newly synthesized lipids and proteins from the ER continuously arrive at the CGN, where they fuse with CGN membranes

Question 25

TGN (trans)

Answer 25

Proteins and lipids leave the golgi in transport vesicles that continuously bud from the tips of TGN cisternae

Question 26

Glycosylation

Answer 26

the addition of carbohydrate side chains to specific amino acid residues of proteins, forming glycoproteins

Question 27

N-linked glycosylation

Answer 27

involved the addition of a specific oligosaccharide unit to the nitrogen atom on the terminal amino group of certain asparagine residues

Question 28

O linked glycosylation

Answer 28

involves addition of an oligosaccharide to the oxygen atom on the hydroxyl group on serine

Question 29

The most abundant chaperone in the ER lumen is

Answer 29

BiP

Question 30

How does BiP work?

Answer 30

BiP is a helper protein in the ER that keeps new proteins from sticking together the wrong way. When a new protein starts to form, BiP grabs onto the sticky (hydrophobic) parts so they don’t clump up with other proteins. BiP then lets go for a moment, using energy from ATP, to give the protein a chance to fold properly. If the protein folds the right way, those sticky parts get tucked inside and BiP doesn't need to grab on again. But if the protein still isn’t folded right, BiP grabs it again and tries the process over. This cycle helps proteins fold correctly so they can work properly in the cell.

Question 31

protein disulfide isomerase

Answer 31

an enzyme present in the ER lumen that catalyzes the formation and breakage of disulfide bonds between cysteine residues

Question 32

Unfolded protein response (UPR)

Answer 32

uses sensor molecules in the ER membrane to detect misfolded proteins. These sensors activate signaling pathways that shut down the synthesis of most proteins while enhancinh the production of those required for protein folding and degradation

Question 33

ER associated degradation (ERAD)

Answer 33

recognizes misfolded or unassembled proteins and exports, or "retrotranslocates" tjem back acorss the ER membrane to the cytosol where they are degraded by proteasomes

Question 34

The initial steps of N-glycosylation take place on the

Answer 34

cytosolic surface of the ER membrane

Question 35

Later steps of glycosylation take place in the

Answer 35

ER lumen

Question 36

All carbohydrate side chains initially have a common ___ ___ consisting of two unites of N-acetylglucosamine, nine mannose units and three glucose units

Answer 36

core oligosaccharide