Lecture 8

Question 1

The secretory pathway?

Answer 1

1. Translates from mRNA in the
   ribosomes in the cytoplasm
2. Enters the ER lumen
3. Goes from the ER to the Golgi in a
   vesicle
4. Transits the Golgi
5. Leaves the Golgi in a vesicle
6. The vesicle fuses the cell membrane
7. It is outside

Question 2

How do transport vesicles work and what do they carry?

Answer 2

Transport vesicles bud off from one compartment and fuse with another.
As they do so, they carry material as cargo. Cargo molecules get transported into different areas in the cell.

Question 3

The secretory pathway leads what way?

Answer 3

The secretory pathway leads outward from the endoplasmic reticulum (ER) towards the Golgi apparatus and cell surface

Question 4

The endocytic pathway leads..?

Answer 4

The endoctic pathway leads inward from the plasma membrane.

Question 5

ER connections?

Answer 5

The ER is a fully interconnected space, meanign that a molecules are able to move anywhere in the ER lumen.

Question 6

Golgi Apparatus connections?

Answer 6

The Golgi apparatus is composed of not physically connected cisternae. Therefore, they cannot move from one cisternae to the next, and proteins need to be loaded into a vesicle first.

Question 7

What do transport membranes look like?

Answer 7

Most transport vesicles form from specialized, coated regions of membranes. They bud off as coated vesicles, which have a distinctive cage of extensive amounts of proteins.

Question 8

What are the four types of coated vesicles?

Answer 8

There are four well-characterized types of coated vesicles: clathrin-coated, COPI-coated, COPII-coated, and retromer-coated. Each type is used for different transport steps.

Question 9

Clathrin?

Answer 9

When a cell eats something, a vesicle will go into either an endoscope or the Golgi apparatus.

Question 10

COPI?

Answer 10

Goes from the golgi to the ER

Question 11

COPII?

Answer 11

Goes from the ER to the golgi

Question 12

Retromer?

Answer 12

Involved with the early endosome.

Question 13

COPI and COPII needed why?

Answer 13

COPI and COPII are necessaery to keep everything moving and make sure that the cell doesn’t run out of these items.

Question 14

Coats are what kind of structures?

Answer 14

Coats are geometrical structures that assemble into vesicle cages

Question 15

Rab proteins are involved with what?

Answer 15

Rab Proteins Guide Transport Vesicles to Their Target Membrane:
- All transport vesicles display surface markers that identify them and target membranes display complementary receptors .

Question 16

Steps of transport vesicles connecting with target membrane?

Answer 16

Tethering: Rab-GTP recognizes Rab effector, then docks to it
Docking: Rab effector (tethering protein) attaches the SV to the PM. The SNARE complex associates with v-SNARE.
Fusion: Associate and curl of SNARe brings vesicle close to membrane and then they fuse.

Question 17

What are SNARE proteins?

Answer 17

SNARE proteins mediate membrane fusion by putting the membranes in close proximity.
- Water is expelled between the membranes by SNARE, allowing the membranes to fuse

Question 18

how do protiens leave the ER?

Answer 18

Proteins Leave the ER in COPII-coated Transport Vesicles that form at
the ER exit site (ERES).
- There are protein recruiters that bind to the adaprtor proteins on COPII coat.
- An exit signal on the cargo receptor tells the ER to make vesicles
- Resident ER proteins are not secreted and don’t want it sent away.

Question 19

What is the function of cargo receptors?

Answer 19

Cargo receptors inside vesicles ensure they are loaded
● Cargo-specific receptors
● Activated receptors recruit adaptor proteins that recruit the coat proteins

Question 20

COPII vesicle transport vesicles…?

Answer 20

COPII vesicles transport vesicles can accommodate the large cargoes by
assembling tubes instead of vesicles.
- To do this, they aggregate in different ways to make a tube instead of a vesicle to accomodate these larger cargoes

Question 21

Camillo Golgi osmium tetroxide stain?

Answer 21

Stained sugars have sugars inside that attach to the proteins - need to be glycoslyated before secretion

Question 22

Golgi structure?

Answer 22

The Golgi consists of a collection of flattened, membrane-enclosed compartments called cisternae.
- They are not physically connected to each other

Question 23

Cis and trans face of the golgi apparatus? q

Answer 23

cis face: receives protiens from ER
trans face: send proteins out in vesicles to their destinations

Question 24

Destination tags at the Golgi?

Answer 24

Glycosylation and phosphorylations at the Golgi are a destination code
- This is the addition of carbohydrates to an amino acid or the addition of a phosphate group to a molecule
- Add sugars or modify (phosphorylate) the sugars

Question 25

Destination tags?

Answer 25

● Sugar coats serve as destination tags ● Some sugar coats are transient ● Glycosylation steps are compartmentalized in different cisternae

Question 26

Wjhat are the two methods of trnasport through the GA?

Answer 26

Vesicle transport mechanism and cisternal maturation mechanism

Question 27

Vesicle transport mechanism?

Answer 27

Vesicles transport molecules between cisternae - Doesn't work for large molecules

Question 28

Cisternal maturation mechanism?

Answer 28

Cisternae maturate from cis to trans face together alongside their cargo molecules - Works for larger proteins - New ones keep getting added to the cis face until they are able to fully mature and release their products.

Question 29

Evidence of the vesicular model?

Answer 29

Vesicles bud and fuse ● COPI vesicles surround the Golgi ( 60–90 nm ).

Question 30

Evidence of the maturation model?

Answer 30

Proto Collagen is bigger than vesicles (300nm) (huge fibres of collagen won't fit into vesicles), ● PC is not detected inside vesicles. ● It localizes to enlarged Golgi cisternae

Question 31

Fluorescent live imaging evidence?

Answer 31

Make fusion proteins , e.g., Golgi protein fused to GFP ● Track GFP through the Golgi ● See processes in real time and in different colors

Question 32

Are cisternae always stacked?

Answer 32

In some species, the Golgi cisternae are not stacked (not a highly conserved across species) * A system of dispersed cisternae in the case of the budding yeast Saccharomyces cerevisiae

Question 33

COPI vesicles?

Answer 33

COPI vesicles bring ER proteins back from the Golgi

Question 34

What is the KDEL sequence?

Answer 34

ER proteins have the KDEL sequence and KDEL receptor initiates vesicle formation. When the KDEL sequence is recognized, it recruits adaptor proteins to make the vesicles that will bring proteins back. * KDEL = Amino acid chain composed of: Lysine - Aspartic acid - Glutamic acid - Leucine

Question 35

What is in charge of secreting most protiens directly to the cell surface?

Answer 35

A nonselective constitutive secretory pathway transports most other proteins directly to the cell surface.

Question 36

Signals in the secretory pathway?

Answer 36

● No specific signal = secrete the protein (default pathway) ● Specific signals are needed to direct secretory proteins into secretory vesicles and lysosomal proteins into different specialized transport vesicles.

Question 37

The three types of secretory signal?

Answer 37

1. Signal mediated diversion to lysosomes via endosomes 2. signal mediated diversion to secretory vesicles for regulated secretion 3. constitutive secretory pathway