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Cell and Molecular Biology > vesicular transport > Flashcards

vesicular transport Flashcards

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1
Q

what are the 3 types of phospholipids and what are their charges?

A 
phosphatidyl-serine = negative charge
phosphatidyl-ethanolamine = neutral charge 
phosphatidyl-choline = neutral charge
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2
Q

what is the charge of sphingomyelin

A

neutral

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3
Q

what is an unsaturated fatty acid?

A

fatty acid not fully saturated by hydrogen

contain a cis double bond –> kink in fatty acid tail

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4
Q

what is the role of cholesterol in the cell membrane?

A

fills gaps between phospholipids
stabilisation of bilayer
seals plasma membrane to preserve internal molecules

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5
Q

where is phosphatidylserine found in the cell membrane?

A

inner leaflet of cell membrane

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6
Q

what is the role of phosphatidylserine during apoptosis?

A

phosphatidylserine flips to the outer surface of the cell membrane
labels dead cell and its remnants so they can be consumed by other cells

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7
Q

how do peripheral proteins interact with the cell membrane?

A

hydrophobic residues or lipid tail attaches protein to one leaflet of membrane
OR
attach to other proteins embedded in the membrane

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8
Q

receptor mediated endocytosis of cholesterol

A
  1. LDL particles carry cholesterol in the blood
  2. LDL binds to LDL receptor
  3. adaptin binds to intracellular tail of LDL receptor
  4. adaptin recruits clathrin molecules which coat the membrane to form a coated pit
  5. membrane invagination to form a coated vesicle which buds off inside the cell and takes LDL bound to LDL receptor with it
  6. coat disassembles
  7. vesicle fuses with early endosome
  8. early endosome has an acidic environment due to a proton pump - breaks LDL binding to its receptor
  9. vesicle containing receptor buds off from early endosome and returns LDL receptor to plasma membrane vesicles containing LDL fuse with lysosome
  10. lysosome digests LDL, releasing free cholesterol + amino acids and small peptides
  11. cholesterol is used for the synthesis of new membranes
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9
Q

what is the lysosome

A

highly acidic organelle containing hydrolytic enzymes

breaks down proteins, lipids and sugars

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10
Q

how can defective endocytosis cause atherosclerosis

A 
mutation in LDL receptor affecting:
- LDL binding 
- interaction with adaptor proteins 
coated pit cannot form
accumulation of lipoproteins in the blood ---> plaques blocking arteries
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11
Q

what does dynamin do?

A

dynamin pinches the vesicle off the cell membrane by hydrolysing GTP to GDP

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12
Q

which clathrin-like coat protein is used to pinch vesicles off the ER

A

COPII

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13
Q

which clathrin-like coat protein is used to pinch vesicles off the Golgi

A

COPI

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14
Q

describe the process of phagocytosis

A
  1. microbe adheres to phagocyte
  2. actin forms pseudopod which engulfs the microbe
  3. phagosome formed = vesicle containing antigen
  4. phagosome fuses with the lysosome to form a phagolysosome
  5. microbe in the phagolysosome is digested by lysosomal enzymes - leaves a residual body
    useful material released in cytosol
    indigestible + residual material removed by endocytosis
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15
Q

describe the process of autophagy

A

vesicles fuse to form a membrane around the diseased organelle
rounded structure formed which will be transported to lysosomes
lysosomes digest the diseased organelle
lipids + amino acids released into cytosol

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16
Q

what is constitutive exocytosis and provide an example

A

continuous secretion of material

e.g. secretory vesicles in mucus secreting lung cells contain mucus -> constitutively released into airways

17
Q

what is regulated exocytosis and provide an example

A

secretion in response to a stimulus

e.g. pancreatic beta cells only release insulin in response to high blood glycose

18
Q

what is the role of SNARE proteins?

A

aid fusion of vesicles with plasma membrane by forcing 2 repulsing, negatively charged membranes together
play a role in exocytosis
do this by forming a tight 4 helical coiled coil on the initial contact

19
Q

V-SNARE

A

located on vesicles

synaptobrevin/VAMP

20
Q

T-SNARE

A

located on plasma membrane

syntaxin and SNAP25

21
Q

coiled-coil formation of SNARE proteins

A

SNAP-25 contributes 2 helices
VAMP contributes 1 helix
syntaxin contributes 1 helix

22
Q

describe a typical coiled coil

A

2 alpha helices wrap around each other:

  • hydrophobic sides of each helix (containing aliphatic AAs = leucine and valine) are tightly together in the centre
  • polar sides exposed to the side
23
Q

what is NSF

A

enzyme catalysing dissociation of SNARE coils by ATP hydrolysis + use of accessory proteins

24
Q

which SNARE protein does type A botulinum neurotoxin cleave?

A

SNAP-25

25
Q

which SNARE protein does type B botulinum neurotoxin cleave?

A

synaptobrevin

26
Q

which SNARE protein does type C botulinum neurotoxin cleave?

A

syntaxin

27
Q

what is the mechanism of action for botulinum toxin?

A
  1. botulinum toxin binds to gangliosides on neuronal membranes
  2. botulinum is endocytosed into a synaptic vesicle
  3. acidification results in botulinum changing structure and releasing SNARE protease (subunit) into the synaptic cytosol
  4. cleaved SNARE protein cannot support fusion of synaptic vesicles –> blocks neurotransmission
28
Q

Botox

A

cleaves SNAP25

used for treat muscle spasms, dystonias + is a cosmetic agent

Cell and Molecular Biology (20 decks)

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