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MCBM Exam 5 > Protein Trafficking > Flashcards

Protein Trafficking Flashcards

1
Q

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

A

No difference

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2
Q

What proteins are made by free ribosomes?

A

Nuclear
Peroxisomal
Mitochondrial

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3
Q

What is the signal sequence for peroxisomes?

A

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

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4
Q

What is the signal sequence for the mitochondrial matrix?

A

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

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5
Q

What proteins are made in the rough ER?

A

Secretory
Lysosomal
Integral

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6
Q

What are secretory proteins? Examples?

A

Proteins exported from the cell

Ex. Collagen, insulin

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7
Q

What signals a ribosome to attach to the ER?

A

An N-terminal signal sequence on the nascent polypeptide

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8
Q

How is the signal sequence removed from the secreted protein?

A

Cleavage by signal peptidase

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9
Q

How long are N-terminal secretory peptide signal sequences?

A

13-26 residues

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10
Q

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

A

At least one positively charges residue

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11
Q

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

A

A highly hydrophobic stretch of about 10-15 residues

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12
Q

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

A

Small, neutral side chain (commonly alanine)

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13
Q

How does synthesis of all proteins begin?

A

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

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14
Q

What is the signal recognition particle (SRP)?

A

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

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15
Q

What happens when SRP binds?

A

Translation by the ribosome is temporarily arrested

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16
Q

What does SRP do?

A

Directs peptide to translocation complex

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17
Q

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

A

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

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18
Q

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

A

The ATP-driven heat shock proteins

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19
Q

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

A

No

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20
Q

Where do glycoproteins acquire their core sugars?

A

In the ER

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21
Q

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

A

Asp

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22
Q

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

A

Ser, thr

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23
Q

N-linked oligosaccharides have what common core?

A

Pentasaccharide core

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24
Q

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

A

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

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25
Q

What do N-linked glycoproteins use as a carrier?

A

Dolichol phosphate

26
Q

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

A

The ER membrane

27
Q

Dolichol phosphate is a ___ derivative.

A

Isoprenoid

28
Q

Half of the core oligosaccharides are synthesized where?

A

On the cytosolic side of ER

29
Q

What are the first 7 sugars of the core oligosaccharides?

A

2 GlcNAc + 5 mannose

30
Q

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

A

4 mannose + 3 glucose

31
Q

How is dolichol phosphate regenerated?

A

Recycled to dolichol phosphate by the action of a phosphatase

32
Q

What does Tunicamycin do?

A

Blocks the first step in oligosaccharide synthesis

33
Q

What does Bacitracin do?

A

Blocks phosphatase that recycles dolichol phosphate

34
Q

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

A

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

35
Q

What things are additionally modified in the Golgi?

A

Proteins and carbohydrates

36
Q

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

A

The trans face

37
Q

Mannose-6-phosphate is the signal for what?

A

The protein to go to the lysosome

38
Q

Individuals with I-cell disease are deficient in what?

A

Phosphotransferase

39
Q

What are symptoms of I-cell disease?

A

Severe psychomotor retardation
Skeletal deformities
Early death

40
Q

Undigested glycosaminoglycans and glycolipids build up as ___ where?

A

Inclusions in lysosomes

41
Q

What does KDEL stand for?

A

Lys, Asp, Glu, Leu

42
Q

What is KDEL?

A

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

43
Q

How do proteins get back into the ER?

A

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

44
Q

What is receptor-mediated endocytosis?

A

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

45
Q

How are essential metabolites delivered?

A

Via receptor-mediated endocytosis

46
Q

What are most cell surface receptors?

A

Transmembrane glycoproteins

47
Q

Where are many receptors located?

A

In coated pits (in the plasma membrane)

48
Q

What coats the “coated pits”?

A

Clathrin

49
Q

How is invagination of a coated pit triggered?

A

Receptor-ligand binding

50
Q

What is the first step of endocytosis?

A

Invagination of the coated pit

51
Q

What function does clathrin play in endocytosis?

A

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

52
Q

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

A

Loses the clathrin shell, and fuses with an endosome

53
Q

What are endosomes?

A

Larger, often irregular vesicles with acidic lumens

54
Q

What happens to endocytosed proteins?

A

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)

55
Q

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

A

Transferrin

56
Q

What does transferrin do?

A

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

57
Q

What does transferrin bind to?

A

Receptor in coated pits

58
Q

How do viruses get past the cell membrane?

A

Membrane-enveloped viruses get through endocytic pathways

59
Q

How does the diptheria toxin enter cells?

A

Binds to growth factor receptor - internalized by endocytosis

60
Q

What are the 4 stable proteins that are poorly ubiquitinated?

A

Gly
Ala
Cys
Met

61
Q

What are the 4 unstable proteins?

A

Arg
His
Ile
Leu

MCBM Exam 5 (11 decks)

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