Lecture 25

Question 1

Vesicular transport

Answer 1

• the movement of material between organelles of eukaryotic cell via membrane enclosed vesicles
• transport protein and lipids to various parts of the cell including the endomembrane system and the plasma membrane
• proteins from the ER are initially sent to the Golgi and then may be delivered to other compartments of the cell

Question 2

what are coated vesicles?

Answer 2

• membrane enclosed vesicles that wear a distinctive layer of proteins on it cytosolic surface
• helps shape the membrane into a bud and captures molecules for onward transport

Question 3

Clathrin-coated vesicles

Answer 3

• found budding from the Golgi to the plasma membrane and lysosomes via endosomes as well as from the plasma membrane to the endosomes

Question 4

COP-coated vesicles

Answer 4

• found in vesicles between the ER and Golgi, as well as from one part of the Golgi to another

Question 7

vesicles have a unique combination of which proteins

Answer 7

• Rab GTPases
• v-SNARES

Question 8

describe the process of tethering

Answer 8

• Rab proteins are recognized and bound by tethering proteins found on the target membrane bringing the two closer in proximity

Question 9

describe the process of docking

Answer 9

the v-snares on the vesicles interact with complementary t-snares to firmly dock the vesicles in place

Question 10

describe the process of fusion

Answer 10

• the vesicle fuses with the target and the cargo protein is delivered to the interior of the aircraft organelle (or secreted if at the plasma membrane)

Question 11

Docking and fusion

Answer 11

• Docking does not always lead to fusion, sometimes it requires a stimulatory signal
• The fusion membrane is energetically unfavourable
• fusion occurs when the v-snares and t-snares wrap tightly around each other, bringing the vesicle closer to the membrane

Question 12

where are proteins modified

Answer 12

• in the lumen of the ER
• for example: formation of disulphide bonds

Question 13

Why aren’t disulphide bonds added in the cytosol

Answer 13

• cytosol is a reducing environment which reduces disulfide bonds

Question 14

Glycosylation

Answer 14

• covalent attachments of short branched oligosaccharides

Question 15

glycosylation function

Answer 15

• protects against protein degradation
• hold protein in the ER
• recognition of protein for packaging or cell-cell interaction

Question 16

glycosylation is rare on the ______

Answer 16

cytosolic side

Question 17

How are oligosaccharides added

Answer 17

• they are not added one at a time they are added “en bloc” (all together)

Question 18

A _____ sugar oligosaccharide is originally attached to the lipid _________ and is transferred to the ________________________ as the peptidase is translocated

Answer 18

1. 14
2. dolichol
3. an amino group of an asparagine side chain

Question 19

Exit from the ER

Answer 19

• some proteins remain in the ER an will contain appropriate signal sequence
• if proteins escape the Golgi, they will be recognized by receptors and sent back to the ER

Question 20

exocytosis

Answer 20

• vesicles from the Golgi fuse with the plasma membrane

Question 21

what happens when to many proteins in the ER accumulate

Answer 21

• the unfolded protein response is triggered
• more chaperone proteins and quality control related proteins are produced
• may inhibit protein synthesis
• the size of the ER can be expanded to cope with the load, but if limit is exceeded the cell can die

Question 22

cisternae

Answer 22

• flattened membrane enclosed sacs

Question 23

The cis face

Answer 23

is adjacent to the ER

Question 24

the trans face

Answer 24

points towards the plasma membrane

Question 25

the medial cisterna

Answer 25

is in the middle

Question 26

vesicles from the ER enter the Golgi at the _________

Answer 26

cis Golgi network

Question 27

proteins exit from the ________

Answer 27

trans Golgi network

Question 28

proteins are further modified in the ____

Answer 28

• Golgi
• oligosaccharide chains are added, removed and modified

Question 30

constitutive exocytosis pathway

Answer 30

• supplies plasma membrane with lipids and proteins. Some proteins are secreted
• entry to this pathway does not require a specific signal sequence other than the one to enter the ER
• operates continually in all eukaryotic cells

Question 31

regulated exocytosis pathway

Answer 31

• only operates in specialized cells
• proteins are sorted and packed into the trans Golgi network which has conditions that cause proteins to aggregate (low pH, high Ca2+)
• proteins are stored in vesicles where they accumulate near the PM and wait for a signal to stimulate their fusion with the PM

Question 32

what does aggregation allow

Answer 32

• it allows secretory proteins to be at very high concentration

Question 33

What is the difference between exocytosis and endocytosis

Answer 33

• exocytosis delivers phospholipids to the PM, but is balanced by removal from endocytosis

Question 34

Endocytosis

Answer 34

• the uptake of material from the invaginations of the plasma membrane

Question 35

endocytosis can be broken down into 2 types based on size

Answer 35

• phagocytosis: ingestion of large molecules, performed by specialized phagocytic cell
• pinocytosis: ingestion of fluid and molecules via small vesicles, performed by all cells

Question 36

Why is phagocytosis important

Answer 36

• important for the uptake of food and defence against infection

Question 37

after vesicles are engulfed, they are enclosed in vesicles called _______

Answer 37

phagosomes

Question 38

Example of pinocytosis transport

Answer 38

Receptor mediated endocytosis
- LDL receptors bind to LDL and are internalized as clathrin-coated vesicles
- they fuse with endoscope and are delivered to the lysosomes
- LDL receptor recycled to PM