Lecture 9

Question 1

The ubiquitin-proteasome pathway?

Answer 1

The major pathway of selective protein degradation in eukaryotic cells uses ubiquitin as a marker that targets cytosolic and nuclear proteins for rapid proteolysis.
- ubiquitin marks proteins that need to be degraded
- proteasome perform degradation

Question 2

how is ubiquitin attached to target proteins?

Answer 2

Ubiquitin (found everywhere) can be covalently attached to target proteins in a variety of ways.
- Proteins can have many issues that can lead to degradation
- They can form isopeptide bonds with the protien that they bind to

Question 3

The major form of ubiquitin does what?

Answer 3

The major form of ubiquitin addition produces polyubiquitin chains which
directs the target protein to the interior of a proteasome.
- Several ubiquitin are added to a chain that is attached to a protien, thereby marking it for proteasomal degradation

Question 4

What enzymes can handle ubiquidation?

Answer 4

E1,E2, and E3 enzymes handle ubiquitination. E3 (more specific than E1 or E2) proteins called ubiquitin ligases select the target proteins to be modified.

Question 5

Priming step of ubiquitination?

Answer 5

E1 attaches to ubiquitin using ATP hydrolysis, then this binds to E2. the ubiquitin then goes to the E2 and the E1 dissociates.
- The ubiquitin-conjuugating enzyme is primed with ubiquitin now.

Question 6

Role of E3?

Answer 6

1. degradation signal on target protein
2. target protein bound to ubiquitin ligase E3, which recognizes amino acids for degradation
3. first ubiquitin chain is added to the target protein
4. this leaves the target protein with a polyubiquitin chain (following multiple E3 additions of ubiquitin)

Question 7

What is polyubiquitination?

Answer 7

polyubiquitination is a post-translational modification that
targets proteins for degradation.
- E1 activates ubiquitin, E2 is an ubiquitin carrier and recognizes E3 which selects targets.

Question 8

What is a proteasome?

Answer 8

The Proteasome Is a Compartmentalized Protease with Sequestered Active Sites.
- There are many proteases inside the tube. The active site is hidden onside and keeps proteases from degrading everything. Degraded waste is expelled from the bottom.

Question 9

How does endocytosis work?

Answer 9

In endocytosis, the material to be ingested is progressively enclosed by a small portion of the plasma membrane, which first invaginates and then pinches off to form an endocytic vesicle containing the ingested substance or particle.

Question 10

What is pinocytosis?

Answer 10

Pinocytosis constantly forms endocytic vesicles

Question 11

What is phagocytosis?

Answer 11

Phagocytosis takes up large particles on demand in a process called cell eating. The receptors recognize that something is outside and go to eat it

Question 12

How does endocytosis work in the secretory pathway?

Answer 12

The routes that lead inward from the cell surface start with the process of
endocytosis, by which cells take up plasma membrane components, fluid, solutes, macromolecules, & particulate substances.

Question 13

Endosome role in the secretory pathway?

Answer 13

most endocytic vesicles fuse with a common receiving compartment, the early endosome, where internalized cargo is sorted:
- some cargo molecules are returned to the plasma membrane
- this is done either directly or via a recycling endosome
- others remain as the early endosome changes into a late endosome by a process termed endosome maturation

Question 14

Lysosomes contain…?

Answer 14

Lysosomes contain proteases and nucleases that degrade things.

Question 15

What two items are commonly coated in clathrin?

Answer 15

Most Membrane Invaginations and Pinocytic Vesicles Are Clathrin Coated - clathrin molecules create the invagination

Question 16

Receptor mediated endocytosis?

Answer 16

Cells Use Receptor-mediated Endocytosis to Import Selected
Extracellular Macromolecules

Question 17

How are lipids transported?

Answer 17

Lipids are transported in lipid-protein particles known as low-density lipoproteins (LDLs)

Question 18

What happens when a cell needs lipids?

Answer 18

When a cell needs lipids, it makes transmembrane receptor proteins for LDL at the plasma membrane.

Question 19

What are early endosomes?

Answer 19

Early endosomes are the main sorting stations in the endocytic pathway.

Question 20

What do we do with membrane associated/integral proteins in the early endosomes?

Answer 20

If it’s in the memrbne, we can’t degrade it without damaging the membrane as well. So, they need to make a vesicle out of it and then allow it to fuse with the late endosome, allowing its degradation.

Question 21

Where do items retreived from the early endosome go?

Answer 21

Specific Proteins Are Retrieved from Early Endosomes and Returned to the Plasma Membrane

Question 22

What are lysosomes?

Answer 22

Lysosomes are membrane-enclosed organelles filled with soluble acid
hydrolases that digest macromolecules at acidic pH.

Question 23

What do vacuolar ATPases do in the lysosome?

Answer 23

A vacuolar ATPase in the lysosome membrane uses the energy of ATP hydrolysis to pump H+ into the lysosome, thereby maintaining the lumen at its acidic pH

Question 24

Late endosomes in the formation of endolysosomes?

Answer 24

Late endosomes containing material received from the plasma membrane
by endocytosis and containing newly synthesized lysosomal hydrolases fuse with preexisting lysosomes to form structures that are referred to as endolysosomes, which then fuse with one another.

Question 25

Endosome maturation and intramural vesicles?

Answer 25

As endosomes mature, patches of their membrane invaginate to form intralumenal vesicles. They carry endocytosed membrane proteins that are to be degraded.

Question 26

What is the job of the ESCRT protein complexes?

Answer 26

ESCRT Protein Complexes Mediate the Formation of Intralumenal Vesicles in Multivesicular Bodies.

Question 27

components of ESCRT?

Answer 27

There is a membrane protein that needs to be inside something to transport it - we need to make a vesicle. - There's a ubiquitin that allows a signalling receptor with a ligand attached to be detected for degradation. ESCRT-0 forces vesicles to form. - The rest of the ESCRT complex forms an intralumenal vesicle containing our material that we needed to transport.

Question 28

Routes to lysosomes?

Answer 28

The routes to the lysosomes are diverse...

Question 29

Examples of routes to the lysosomes?

Answer 29

● the Golgi apparatus delivers ● most of the lysosome’s digestive enzymes ● Late endosome to lysosome ● autophagosome (double membrane) to lysosome ● phagosome to lysosome

Question 30

What is phagocytosis?

Answer 30

Phagocytosis is a special form of endocytosis in which a cell uses large endocytic vesicles called phagosomes to ingest large particles such as microorganisms and dead cells.

Question 31

__________ is a cargo-triggered process?

Answer 31

Phagocytosis is a cargo-triggered process. That is, it requires the activation of cell-surface receptors that transmit signals to the cell interior. - Antibodies on the bacterium, and Fc receptors attach to these antibodies and cover them with actin molecules - This makes a vesicle over the bacteriujm that effectively eats (phagocytoses) waste/bacterium

Question 32

What occurs during autophagy?

Answer 32

During autophagy, organelles are engulfed into a membrane structure called the autophagosome (2 membranes) that subsequently fuses with the lysosome.

Question 33

When is autophagy mainly used?

Answer 33

when cells experience stress or starvation, autophagy is used to recycle existing proteins and macromolecules

Question 34

how does the autophagosome form?

Answer 34

The autophagosome assembles by the fusion of small vesicles that contain ATG8-marked vesicles undergo homotypic fusion with each other.

Question 35

What do the cargo receptors do?

Answer 35

Several cargo receptors recognize the ubiquitin and other acteria-specific proteins and recruit ATG8-containing vesicles. - ubiquitinated organelles are marked for degradation.