Week 9 - Protein Sorting and Modification

Question 1

What happens to a transmembrane protein moving from cytosol to ER (overview)?

Answer 1

1. Starts same as secreted proteins; mRNA codes
2. Internal signal sequence recognized by SRP
3. SRP binds ribosome to the SRP receptor at the ER membrane
   4a. N-terminus surrounded by negatives; alpha helix joins membrane
   4b. N-terminus surrounded by positives; alpha helix forms in receptor before joining membrane.

Question 2

What happens to a transmembrane protein moving from ER to Golgi apparatus (overview)?

Answer 2

1. Glycosylation of lipids and proteins; no flip-flopping.

Question 3

What is the function of the Golgi apparatus?

Answer 3

Receives proteins and lipids from the ER, modifies them, and then dispatches them to other destinations in the cell. Complex oligosaccharide processing requires for mature proteins occurs here.

Question 4

The closer the Golgi is to the ER…

Answer 4

The more interconnected the network is.

Question 5

What is Protein Glycosylation?

Answer 5

The modification of proteins by adding/modifying sugar chains.

Question 6

Where does Protein Glycosylation start?

Answer 6

It starts in the ER: a single type of oligosaccharide is attached to many proteins.

Question 7

What is the Golgi apparatus?

Answer 7

A multi-stage processing unit; different enzymes in each cisterna. Complex oligosaccharide processing requires for mature proteins occurs in it.

Question 8

How is the asymmetry of membrane proteins maintained during processing?

Answer 8

Each protein is inserted into the membrane of the ER in a specific manner; maintained through vesicular transport.

Question 9

Define Endosome.

Answer 9

Membrane-bound organelle that carries materials newly ingested by endocytosis and passes them to lysosomes for degradation.

Question 10

Define Lysosome.

Answer 10

A small sac of digestive enzymes that functions in degrading worn-out organelles, as well as macromolecules, and particles taken into the cell by endocytosis.

Question 11

Endocytosed material is found where?

Answer 11

In the early endosome.

Question 12

Lysosomal proteins are delivered in vesicles from the Golgi to what?

Answer 12

To the late endosome, for digestion of material.

Question 13

What is phagocytosis?

Answer 13

A type of endocytosis; “cell eating”. A large particle is internalized.

Question 14

A late endosome that has fully digested is called what?

Answer 14

A lysosome.

Question 15

Early endosomes have a lot of enzymes but less what?

Answer 15

Less digestion than late endosomes.

Question 16

Late endosomes digests more than an early endosome but still gets what?

Answer 16

Still gets more enzymes.

Question 17

As a lysosome has a lot of digestive enzymes, it can be fused to what?

Answer 17

It can be fused to an early or late endosome to provide them with more enzymes.

Question 18

What 2 mechanisms protect a cell from acid hydrolases?

Answer 18

1. Acid hydrolases only function in acidic environments while the cytosol is neutral or basic
2. Membrane permeability.

Question 19

Lysosomes contains approx. 40 hydrolytic enzymes. What are the enzymes?

Answer 19

These enzymes are Acid hydrolases; they require an acidic environment.

Question 20

Hydrolytic enzymes are named after what? (i.e. Nuclease).

Answer 20

They are named after what they cut; i.e. nucleases cut nucleotides.

Question 21

What are lysosomes and endosomes acidified by?

Answer 21

They are acidified by a V-type ATPase; H+ pump.

Question 22

What prevents contents of the cytosol from being digested by Lysosomes?

Answer 22

Lysosomal enzymes have a low pH requirement; won’t digest neutral or basic.

Question 23

What protects lysosomal membrane proteins from proteases in the lumen?

Answer 23

Lysosomal membrane proteins are glycosylated for protection.

Question 24

How do the products of lysosomal digestion get to the cytosol?

Answer 24

Transport proteins in the lysosomal membrane transfer the products out of the lysosome to the cytosol. (i.e. amino acids, sugars, nucleotides).

Question 25

Where else are lysosomal hydrolases, delivered from the Golgi, found?

Answer 25

In early and late endosomes.

Question 26

Plant vacuoles are involved in what 5 things?

Answer 26

1. Digestion
2. Nutrient storage
3. Waste storage
4. Increasing cell size
5. Turgor pressure

Question 27

There can be a large increase in volume of a plant cell without increasing what?

Answer 27

Without increasing volume of the cytosol; protein transport increases cell volume.

Question 28

A hypotonic solution plant cell has how much turgor pressure?

Answer 28

Normal turgor pressure.

Question 29

A hypertonic solution plant cell has how much turgor pressure?

Answer 29

No turgor pressure; cell shrinkage due to water leaving the cell (Plasmolysis).

Question 30

What is plasmolysis?

Answer 30

Plasma membrane pulling away from the cell wall; usually due to hypertonic solution.

Question 31

What do Peroxisomes do?

Answer 31

They use molecular oxygen to oxidize organic molecules, and function in the breakdown of long fatty acid chains (and detoxification); oxidative reactions produce hydrogen peroxide.

Question 32

Where must proteins be unfolded to go?

Answer 32

• mitochondria

- plastids

Question 33

Where must proteins be folded to go?

Answer 33

• nucleus

- peroxisomes

Question 34

How does a nuclear protein get into the nucleus?

Answer 34

Through nuclear pore complexes (NPC0 which are gate transport; regulated by intracellular signals.

Question 35

Gated transport involved proteins moving where?

Answer 35

Between the cytosol and nucleus; NPC’s.

Question 36

NPC’s allow for selective transport of what?

Answer 36

Selective transport of macromolecules; Proteins, RNA’s, RNP’s (ribonucleoproteins) cannot move on their own.

Question 37

Eukaryotic transcription requires what?

Answer 37

It requires transcriptional activator proteins.

Question 38

The Estrogen receptor is a ligand modulated what?

Answer 38

A ligand-modulated regulator of transcription; estrogen receptor goes to DNA first to transcribe for cell growth and proliferation.

Question 39

When the ligand that signals estradiol is not present, what happens?

Answer 39

The estrogen receptors go to the cytosol.

Question 40

When estradiol enters the cell and binds to the estrogen receptor, what happens?

Answer 40

1. The estrogen receptor activates it
2. Ligand-bound estrogen receptor moves into the nucleus through NPC’s
3. Bind to enhancer sites in the genome and activates transcription.

Question 41

What gives vesicle directionality?

Answer 41

Directed movement of transport vesicles, pulled by motor proteins associated with the cytoskeleton.