Protein Trafficking

Question 1

What is the difference between free ribosomes and rough ER ribosomes?

Answer 1

No difference

Question 2

What proteins are made by free ribosomes?

Answer 2

Nuclear
Peroxisomal
Mitochondrial

Question 3

What is the signal sequence for peroxisomes?

Answer 3

C-terminal sequence SKF (ser, lys, phe)

Question 4

What is the signal sequence for the mitochondrial matrix?

Answer 4

N-terminal sequence rich in positive charged amino acids (lys, ser, thr)

Question 5

What proteins are made in the rough ER?

Answer 5

Secretory
Lysosomal
Integral

Question 6

What are secretory proteins? Examples?

Answer 6

Proteins exported from the cell

Ex. Collagen, insulin

Question 7

What signals a ribosome to attach to the ER?

Answer 7

An N-terminal signal sequence on the nascent polypeptide

Question 8

How is the signal sequence removed from the secreted protein?

Answer 8

Cleavage by signal peptidase

Question 9

How long are N-terminal secretory peptide signal sequences?

Answer 9

13-26 residues

Question 10

The N-terminal secretory peptide signal has what on the amino part?

Answer 10

At least one positively charges residue

Question 11

What forms the enter of the N-terminal secretory peptide signal sequence?

Answer 11

A highly hydrophobic stretch of about 10-15 residues

Question 12

What does the residue on the amino-terminal side of the N-terminal secretory peptide signal have?

Answer 12

Small, neutral side chain (commonly alanine)

Question 13

How does synthesis of all proteins begin?

Answer 13

By free ribosomes binding to mRNA and commencing synthesis of N-terminal region of polypeptide

Question 14

What is the signal recognition particle (SRP)?

Answer 14

An RNA-protein complex that recognizes and binds to signal sequences

Question 15

What happens when SRP binds?

Answer 15

Translation by the ribosome is temporarily arrested

Question 16

What does SRP do?

Answer 16

Directs peptide to translocation complex

Question 17

Bound SRP directs the ribosome with an incomplete peptide to go where?

Answer 17

To a specific SRP receptor on the cytosolic face of the ER

Question 18

What serve as chaperones to make sure the peptide chain folds correctly?

Answer 18

The ATP-driven heat shock proteins

Question 19

Once a protein has entered the ER, can it get back into the cytosol?

Answer 19

No

Question 20

Where do glycoproteins acquire their core sugars?

Answer 20

In the ER

Question 21

In secretory proteins, what does the N-linked moiety connect to?

Answer 21

Asp

Question 22

In secretory proteins, what does the O-linked moiety connect to?

Answer 22

Ser, thr

Question 23

N-linked oligosaccharides have what common core?

Answer 23

Pentasaccharide core

Question 24

In N-linked oligosaccharides, how is the pentasaccharide core derived?

Answer 24

By trimming a 14 residue core oligosaccharide added to specific Ans residues

Question 25

What do N-linked glycoproteins use as a carrier?

Answer 25

Dolichol phosphate

Question 26

The core oligosaccharide is assembled stepwise on a dolichol phosphate carrier molecule embedded where?

Answer 26

The ER membrane

Question 27

Dolichol phosphate is a ___ derivative.

Answer 27

Isoprenoid

Question 28

Half of the core oligosaccharides are synthesized where?

Answer 28

On the cytosolic side of ER

Question 29

What are the first 7 sugars of the core oligosaccharides?

Answer 29

2 GlcNAc + 5 mannose

Question 30

What sugars are added to the core oligosaccharide in the ER lumen?

Answer 30

4 mannose + 3 glucose

Question 31

How is dolichol phosphate regenerated?

Answer 31

Recycled to dolichol phosphate by the action of a phosphatase

Question 32

What does Tunicamycin do?

Answer 32

Blocks the first step in oligosaccharide synthesis

Question 33

What does Bacitracin do?

Answer 33

Blocks phosphatase that recycles dolichol phosphate

Question 34

Proteins in the lumen of ER are tranported where? How?

Answer 34

Transported to the cis side of the golgi complex by transport vesicles

Question 35

What things are additionally modified in the Golgi?

Answer 35

Proteins and carbohydrates

Question 36

Which side of the Golgi is closest to the cell membrane?

Answer 36

The trans face

Question 37

Mannose-6-phosphate is the signal for what?

Answer 37

The protein to go to the lysosome

Question 38

Individuals with I-cell disease are deficient in what?

Answer 38

Phosphotransferase

Question 39

What are symptoms of I-cell disease?

Answer 39

Severe psychomotor retardation Skeletal deformities Early death

Question 40

Undigested glycosaminoglycans and glycolipids build up as ___ where?

Answer 40

Inclusions in lysosomes

Question 41

What does KDEL stand for?

Answer 41

Lys, Asp, Glu, Leu

Question 42

What is KDEL?

Answer 42

A carboxy-terminal sequence on ER proteins that is a "return" signal

Question 43

How do proteins get back into the ER?

Answer 43

They enter transport vesicles at the Golgi and are taken back to ER

Question 44

What is receptor-mediated endocytosis?

Answer 44

Process of import of specific proteins into a cell by protein binding to receptor in plasma membrane and inclusion into vesicles

Question 45

How are essential metabolites delivered?

Answer 45

Via receptor-mediated endocytosis

Question 46

What are most cell surface receptors?

Answer 46

Transmembrane glycoproteins

Question 47

Where are many receptors located?

Answer 47

In coated pits (in the plasma membrane)

Question 48

What coats the "coated pits"?

Answer 48

Clathrin

Question 49

How is invagination of a coated pit triggered?

Answer 49

Receptor-ligand binding

Question 50

What is the first step of endocytosis?

Answer 50

Invagination of the coated pit

Question 51

What function does clathrin play in endocytosis?

Answer 51

Forms a lattice around the coated pit Excise it from the membrane Forms a coated vesicle

Question 52

After being excised from the pit, what does the clathrin coated vesicle do?

Answer 52

Loses the clathrin shell, and fuses with an endosome

Question 53

What are endosomes?

Answer 53

Larger, often irregular vesicles with acidic lumens

Question 54

What happens to endocytosed proteins?

Answer 54

They are acidified by ATP-driven proton pumps in membranes Causes the dissociation of protein-receptor complexes Then often recycled (may be degraded or transported)

Question 55

What is an example of an endocytosed protein in which both the receptor and the protein are recycled?

Answer 55

Transferrin

Question 56

What does transferrin do?

Answer 56

Transports iron from sites of absorption and storage to sites of utilization

Question 57

What does transferrin bind to?

Answer 57

Receptor in coated pits

Question 58

How do viruses get past the cell membrane?

Answer 58

Membrane-enveloped viruses get through endocytic pathways

Question 59

How does the diptheria toxin enter cells?

Answer 59

Binds to growth factor receptor - internalized by endocytosis

Question 60

What are the 4 stable proteins that are poorly ubiquitinated?

Answer 60

Gly Ala Cys Met

Question 61

What are the 4 unstable proteins?

Answer 61

Arg His Ile Leu