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BIOM 3530 - Quiz 3 > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

What proteins are involved in vesicles knowing where to go?

A

Rabs and SNAREs

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2
Q

What are Rabs?

A

Large family of GTPases that line cytosolic surface of membranes
- Only certain Rabs are on specific membrane compartments

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3
Q

What happens when Rabs are inactive?

A

They are GDP bound
- Rab-GDP associates with the dissociation inhibitor (GDI) and stays soluble in cytoplasm

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4
Q

What happens when Rabs are active?

A

They are GTP bound
- Rab-GTP associates with membrane and interacts with Rab effectors (assist with membrane fusion and tethering)

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5
Q

How many different Rabs have been found in human cells?

A

70

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6
Q

What do Rab effectors comprise of?

A

Many different types of proteins (motor and tethering proteins)

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7
Q

What do Rab-GTP and effectors form?

A

Multi-protein complexes that form discrete membrane patches capable of receiving specific vesicles or budding new vesicles

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8
Q

Where is the subcellular location for Rab5?

A
  • Early endosomes
  • Plasma membrane
  • Clathrin-coated vesicles
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9
Q

Where is the subcellular location for Rab7?

A

Late endosomes

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10
Q

What has to occur in the ER when proteins are being transported to the Golgi in transport vesicles?

A

Quality control to ensure proteins are properly folded
- In some cases, 90% of the protein is degraded in lysosomes and only 10% makes it to the final location (e.g., acetylcholine receptors)

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11
Q

What participates in quality control?

A

Chaperones
- Some proteins bind to chaperones in the ER to ensure protein structure is maintained

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12
Q

What happens to vesicles and vesicle tubules?

A

Diffuse through cytoplasm or follow cytoskeletal tracts
- Microtubules and actin are used

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13
Q

What are SNAREs?

A

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor
- Required for membrane fusion
- Catalyze membrane fusion and provide binding specificity
- Over 35 types in mammalian cells

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14
Q

What types of SNAREs are there?

A

v-SNAREs and t-SNAREs

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15
Q

What are v-SNAREs?

A

Single polypeptide chains found on vesicle membranes
- e.g., synaptobrevin

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16
Q

What are t-SNAREs?

A

Two or three polypeptide chains found on target membranes
- e.g., SNAP25

17
Q

What do v-SNAREs and t-SNAREs do?

A

Interact and “lock” membranes together
- Forms a four helical bundle

18
Q

What does synaptotagmin do in a v-SNARE/t-SNARE complex in neuronal secretory vesicles?

A

Serves as a Ca2+ sensor to activate exocytosis

19
Q

Why do SNAREs have to dissociate?

A

To enable further rounds of fusion

20
Q

What is the key regulator in SNARE disassembly?

A

NSF

21
Q

What is NSF?

A

ATPase that uses ATP to unravel the SNARE complexes

22
Q

What are lysosomes?

A

Single membrane-enclosed organelles containing hydrolytic enzymes (acid hydrolases) that degrade proteins

23
Q

Why is pH important for lysosomes?

A

Enzymes have to be proteolytically cleaved to be activated and need acidic pH (4.5-5) for optimal activity

24
Q

How do lysosomes maintain acid pH?

A

They have a vacuolar ATPase to pump H+ into the lumen

25
Q

How are lysosomes stained by lead phosphate?

A

Acid phosphatase and glutaraldehyde

26
Q

How are lysosomes supplied with enzymes?

A

Lysosomes fuse with other vesicles that come from endocytosis (endosome) and form vesicles from Golgi (from TGN)

27
Q

How are proteins destined for the lysosome recognized in the Golgi?

A

A mannose-6-phosphate (M6P) group covalently attaches to lysosomal hydrolases in cis-Golgi

28
Q

What do M6P receptor proteins do?

A

M6P receptor proteins present in trans-Golgi bind to M6P-containing protein in the lumen of TGN
- Only bind to M6P at pH > 6.5 (pH in early endosomes)

29
Q

What happens as pH drops during endosome maturation?

A

M6P-containing proteins are released from the receptor and the phosphate group is cleaved by phosphatase

30
Q

What are some lysosomal storage disorders (LSD) due to?

A

Excess cholesterol in the membrane which locks SNARE complexes and prevents dissociation
- Some due to deficiencies in acid hydrolases or other enzyme components of the lysosome

31
Q

How many genetic (autosomal recessive) LSDs are recognized in humans?

A

50

32
Q

Who is affected by LSDs?

A

Mostly affects children and survival is short (months to a few years old)

33
Q

What is an example of an LSD?

A

Tay-Sachs disease

34
Q

What are characteristics of Tay-Sachs disease?

A
  • Mutation in HexA gene (4 bp insertion)
  • HexA encodes hexosaminidase A which degrades sphingomyelin in lysosomes
  • 1 in 2,500 births in Ashkenazi Jewish population (1 in 30 are carriers)
  • Children die by 4 years of age

BIOM 3530 - Quiz 3 (4 decks)

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