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MCBM Exam 5 Kat > Protein Trafficking > Flashcards

Protein Trafficking Flashcards

0
Q

Is there a difference between free and RER ribosomes?

A

Nope. None.

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1
Q

Where is the signal on a protein for destination located on the protein?

A

Signal may be a run of 3 to <30 amino acids at N- or C-terminal or internal
Some may be post translational modifications
Some signals may be 3D domains on protein

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2
Q

What kinds of proteins are synthesized in free ribosomes?

A

Proteins destined for peroxisomes, mitochondria (except ones made in mitochondria) and the nucleus

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3
Q

What sort of signals are used for proteins to enter the nucleus?

A

Internal nuclear localization sequences

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4
Q

What sort of signal sequences are used for proteins to enter peroxisomes?

A

C-terminal sequence SKF

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5
Q

What sort of signal sequences are used for proteins to be imported into the mitochondrial matrix?

A

N-terminal sequence rich in positive charged amino acids and serine, threonine

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6
Q

What are the 3 major classes of proteins produced in the RER?

A

Secretory proteins
Lysosomal proteins
Integral membrane proteins

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7
Q

How is a signal sequence removed from a secreted protein?

A

By signal peptidase

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8
Q

What are the common signal sequences of N-terminal secretory peptides?

A

Range in length from 13-26
Amino terminal contains at least one positively charged residue
A hydrophobic 10-15 residue stretch forms the center of the signal
Residue of the signal peptidase cleavage site has small, neutral side chain (alanine common)

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9
Q

Where 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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10
Q

What is signal recognition particle (SRP)?

A

An RNA protein compex that recognizes and binds to signal sequences

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11
Q

What doe SRP when bound to a signal sequence?

A

It temporarily arrests translation by the ribosome

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12
Q

Can a protein return to the cytosol once it enters the endoplasmic reticulum?

A

No, entry into ER is irreversible

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13
Q

What chaperones assist correct peptide chain folding?

A

ATP driven heat shock proteins

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14
Q

What do N-linked glycoproteins use as a phosphate carrier and how?

A

They use dolichol embedded in the ER membrane

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15
Q

What is dolichol phosphate?

A

An isoprenoid derivative
A lipid
Localized to membranes

16
Q

What happens to dolichol phosphate as oligosaccharides are synthesized?

A

On the cytosolic side sugar precursors are added to the phosphate group forming dolichol pyrophosphate intermediate. Once the oligosaccharide is translocated across the ER membrane into the lumen the incomplete core-dolichol pyrophosphate is released as the oligosaccharide is transferred to an Asn residue

17
Q

Where are oligosaccharides synthesized?

A

Half on cytosol side of ER, half in the ER lumen

18
Q

How is dolichol phosphate regenerated?

A

Using a phosphatase

19
Q

What are some drugs that affect the addition of sugars?

A

Tunicamycin - blocks first step in oligosaccharide surface

Bacitracin - blocks phophatase that recycles dolichol phosphate

20
Q

How is bacitracin a useful antibiotic?

A

The bacterial enzyme used to recycle an isprenoid pyrophosphate in cell wall synthesis is very sensitive to it.

21
Q

How are proteins transferred to the Golgi apparatus from the ER?

A

Via transport vesicles (transfer vesicles) to the cis side of the Golgi complex

22
Q

What happens in the Golgi apparatus to proteins and carbohydrates?

A

They are additionally modified. Proteins are then sorted and directed to their destination by transfer vesicles leaving the trans face of the Golgi

23
Q

How is lysosomes targeting conducted?

A

Phospho-N-acetyl-glucosamine added to mannose by phosphotransferase > phosphotransferase recognizes 3D motif > phosphodiesterase removes N-AC-Gln leaving mannose-6-phosphate > mannose-6-phosphate binds to receptor in Golgi membrane > vesicles targeted to lysosome

24
Q

What is the autosomal recessive disease where individuals are deficient in phosphotransferase?

A

I-cell disease (mucolipidosis II)

25
Q

What happens in I-cell disease?

A

Eight acid hydrolases are not targeted to lysosomes but secreted instead which results in glycosaminoglycans and glycolipids build up as inclusions in lysosomes

26
Q

What are the symptoms of I-cell disease?

A

Severe psychomotor retardation and skeletal deformities

27
Q

How are heat shock proteins returned to the ER after traveling to the Golgi?

A

They have KDEL (lys-asp-glu-leu) as their return signal which has them be repackaged in vesicles in the Golgi and returned to the ER.

28
Q

What disease results from disorders in receptor mediated uptake?

A

Some forms of familial hypercholesterolemia

29
Q

What kind of regions of the plasma membrane are many receptors located in?

A

Coated pits with a thick coat of the protein clathrin at the cytosolic side of the indentation

30
Q

How are endosomes different than other vesicles?

A

Endosomes are often larger, often irregular vesicles with acidic lumens

31
Q

How does endocytosis of receptors begin?

A

Invagination of the coated pit triggered by receptor-ligand binding > clathrin then forms a lattice around the coated pit forming a coated vesicle > vesicle loses clathrin shell and fuses with endosome

32
Q

What is the function of transferrin?

A

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

Two Fe3+ ions bind/apotransferrin molecule to make transferrin, the two together bind to the coated pits

33
Q

How is transferrin processed?

A

Transferrin internalized into endosome then the endosome is acidified which allows Fe3+ to dissociate from apotransferrin which remains bound to the receptor

34
Q

When the receptor is recycled how is Fe3+ recaptured?

A

By ferritin in the cytosol

35
Q

How does the semliki virus (related to yellow fever) enter cells?

A

It enter susceptible cells by binding to receptors in coated pits and is endocytosed

36
Q

How does diphtheria toxin enter cells?

A

By binding to growth factor receptors and being internalized by the endocytosis

37
Q

How are proteins turned over?

A

Ubiquity in tags proteins for destruction in eukaryotic cells.

MCBM Exam 5 Kat (15 decks)

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