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BL2301 Cell Biology > Membranes > Flashcards

Membranes Flashcards

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1
Q

What are the 5 roles of a cell membrane?

A
  • Define boundaries of cell/organelles
  • Separate cellular and extracellular environment
  • Control movement of molecules & signal transduction
  • Separate aqueous regions of different compositions within cells
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2
Q

Which components have a higher intracellular concentration?

A
  • K+

- H+

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3
Q

Which components have a higher extracellular concentration?

A
  • Na+
  • Mg2+
  • Ca2+
  • Cl-
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4
Q

Briefly describe the fluid mosaic model

A
  • Sea of phospholipids which is movable and flexible

- Protein molecules which are slightly more fixed but are also movable and can cross the bi-layer

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5
Q

Describe the phospholipid structure

A

Hydrophilic head composed of: choline (or others), phosphate and glycerol
2 Hydrophobic hydrocarbon tails: At least one tail always contains at least 1 C=C bond which determines fluidity

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6
Q

What 3 components can form the hydrophilic head? Which one produces a negative head?

A

Ethanolamine, Serine (-), Choline

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7
Q

What other molecule can choline form a hydrophilic head with?

A

Phosphate and sphingosine (in place of glycerol)

Produces sphingomyelin

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8
Q

What is the length range of hydrocarbon tails and how does this affect fluidity?

A

14-24 hydrocarbons long

Shorter tailed hydrocarbons are often more fluid

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9
Q

What is the primary role of sphingomyelin?

A

Forms the myelin sheath

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10
Q

What 3 characteristics define the properties of the plasma membrane?

A
  • Head components
  • Saturation
  • Length
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11
Q

What is the effect of sterols on the phospholipid membrane?

A
  • Attach themselves to the head of a phospholipid, with sterol rings interacting with hydrocarbon tail making it stiffer (ambiphilic molecules)
  • Allow lipid-soluble molecules to cross the membrane
  • Cholesterol increases the viscosity of membranes by limiting flexion, rotation and lateral diffusion
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12
Q

What is cell membrane viscosity believed to affect?

A

Cell signalling

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13
Q

What is cell thickness thought to influence?

A

Trafficking of proteins across cells

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14
Q

How does the composition of the interior and exterior cell membrane differ?

A
  • Outside composed mostly of choline and sphingomyelin, interior mostly serine
  • Causes difference in charge
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15
Q

Describe lipid microdomains

A
  • Groups of lipids aggregate together for a short time period causing a microdomain to regulate a cell function, particularly cellular vent
  • Regulates release of hormones through interactions with proteins
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16
Q

Name 6 types of transmembrane protein

A
  1. Single-pass transmembrane (alpha-helical)
  2. Multiple-pass transmembrane (alpha-helical)
  3. Beta-sheet barrel
  4. Associated with one leaflet of membrane (cytosolic) with amphiphilic alpha-helix
  5. Covalently bonded to a hydrocarbon
  6. Lipid-anchored
17
Q

Describe Glycophorin A

A

Amphiphilic alpha helical transmembrane protein, passing once with hydrophobic membrane spanning section

18
Q

Describe bacteriorhodopsin

A
  • transmembrane protein with 7 helical transmembrane regions
  • first membrane-bound protein to have its structure determined
  • oritentates itself to stay within the hydrophobic region
19
Q

Describe aquaporin

A
  • alpha helical, composed of 2 smaller proteins that span only half of the membrane
  • acts as gates for the water channel in the kidney
20
Q

Where are beta-barrel transmembrane proteins commonly found and what is their function?

A

Found in: mitochondria, chloroplasts and bacteria

Allow controlled movement of hydrophilic molecules

21
Q

How are lipid-anchored proteins attached to the phospholipid membrane?

A
  • Protein is covalently attached to lipid on extracellular side of the membrane by GPI anchor composed of inositol
  • Can be attached via amide linkage ( myristoyl anchor) or thioester linkage (palmitoyl anchor/farnesyl anchor)
22
Q

How can the fluidity of the plasma membrane be demonstrated?

A
  • Attach fluorescently tagged protein to plasma membrane (GFP)
  • Bleach area and measure recover time
  • Allows the measure of lateral mobility by diffusion constant

BL2301 Cell Biology (17 decks)

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