09a: Protein Trafficking

Question 1

T/F: synthesis of all proteins begins on cytoplasmic ribosomes.

Answer 1

True

Question 2

Proteins translated on cytoplasmic ribosomes are targeted to:

Answer 2

1. Cytoplasm
2. Mitochondria
3. Nucleus

Question 3

Proteins translated on RER ribosomes are targeted to:

Answer 3

1. Cell membrane
2. Lysosomes
3. Cell secretion

Question 4

What’s the power house of protein synthesis?

Answer 4

RER

Question 5

Information that determines site of a protein’s localization is found in its (primary/secondary/tertiary) structure.

Answer 5

Primary

Question 6

Cytoplasmic protein have which signal?

Answer 6

No signal

Question 7

Mitochondrial protein have which signal?

Answer 7

Pre-sequence with amiphipathic character (hydrophobic and positively-charged AA) on N-terminus

Question 8

Nuclear proteins have which signal?

Answer 8

Lys-Lys-Lys-Arg-Lys

Question 9

Membrane proteins have which signal?

Answer 9

Core of hydrophobic AA near N terminus

Question 10

Secretory proteins have which signal?

Answer 10

Core of hydrophobic AA near N terminus

Question 11

Lysosomal proteins have which signal?

Answer 11

Mannose-6-P

Question 12

SRP stands for (X) and is similar in composition to (Y).

Answer 12

X = Signal Recognition Particle
Y = snRNPs (has RNA and protein components)

Question 13

What’s the function of SRPs?

Answer 13

Bind signal peptide on secretory, membrane, lysosomal proteins that have begun translation on cytoplasmic ribosomes

Question 14

Once SRP binds (X), translation is paused until:

Answer 14

X = signal peptide

SRP binds its receptor on ER membrane

Question 15

T/F: Ribosomes on ER are fixed on the membrane.

Answer 15

False - when SRP binds signal peptide, it carries ribosome to ER to continue translation of the protein

Question 16

T/F: Signal peptide is removed from mature polypeptide chain once translation and translocation is complete.

Answer 16

True - cleaved by signal peptidase

Question 17

Simple, one-pass transmembrane proteins have (X) sequence that’s composed of (Y) AA.

Answer 17

X = stop-transfer 
Y = core of hydrophobic

Question 18

Glycosylation of Asn residues occurs in (ER/Golgi/cytoplasm).

Answer 18

ER

Question 19

Glycosylation of Ser residues occurs in (ER/Golgi/cytoplasm).

Answer 19

Golgi

Question 20

Glycosylation of Thr residues occurs in (ER/Golgi/cytoplasm).

Answer 20

Golgi

Question 21

The initial glycans added to (X) in ER have which key component?

Answer 21

X = Asn (X-Ser/Thr)

Mannose

Question 22

In ER, which regions/bonds are too difficult to assemble with chaperones alone?

Answer 22

1. Pro regions
2. Disulfide bonds

(Require additional enzymes)

Question 23

Cutting/modifying sugars on (X) residues, that were added in the ER, is done in which organelle?

Answer 23

X = Asn

Golgi

Question 24

When lysosomal hydrolase precursor enters golgi, (glucose/mannose) is attached.

Answer 24

Mannose - glucose trimmed off

Question 25

(Cis/trans) golgi is closer to RER.

Answer 25

Cis

Question 26

Lysosome precursor undergoes which change in cis golgi?

Answer 26

Addition of phosphorylated sugar to mannose

Question 27

Lysosome precursor undergoes which change in trans golgi?

Answer 27

Removal of sugar from phosphorylated sugar complex that was added to mannose in cis-golgi (uncovering signal)

Question 28

Lysosomal storage diseases are usually results of:

Answer 28

deficient or dysfunctional enzymes (thus, buildup of toxic metabolites)

Question 29

How/when do mitochondrial proteins transport into the organelle?

Answer 29

Post-translationally; signal peptide binds receptor on outer mito membrane and complex forms to translocate protein to matrix

Question 30

T/F: There are no molecules that can simply diffuse across the nuclear membrane.

Answer 30

False - very small molecules can

Question 31

(X) proteins make up nuclear pores.

Answer 31

X = Nup (nucleoporins)

Question 32

(X) form the nucleus diffusion barrier as well as the (Y).

Answer 32

``` X = FG nups Y = nuclear basket ```

Question 33

(X) bind nuclear transport receptors, aka (Y), and regulate their entry into nucleus.

Answer 33

``` X = FG nups Y = importins ```

Question 34

T/F: Importins themselves enter the nucleus to drop off cargo (nuclear protein).

Answer 34

True

Question 35

The nuclear lamina is located on (X) and made up of (Y).

Answer 35

``` X = inside of nuclear envelope Y = lamin proteins ```

Question 36

Nuclear lamina functions:

Answer 36

1. stabilize nuclear structure | 2. Anchor nuclear pores