L31 Structure and Function of Plasma Membrane Flashcards

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1
Q

Plasma membranes have been described as having ‘a trilaminar staining pattern’. Explain this.

A

When stained with osmium there appears to be 2 dark lines separated by a lightly stained central zone.

Resembles train tracks.

Hydrophilic heads form dark layers and the middle is the hydrophobic tails (which do not stain).

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2
Q

How much of a cell membrane is made of lipid molecules?

A

30-80%

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3
Q

What lipids are found in cell membranes?

A

Phospholipids, glycolipids, sterols

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4
Q

How long are phospholipid fatty acid ‘tails’?

A

14-24 carbon atoms long

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5
Q

When surrounded by water, cone-shaped (single chain) lipid molecules aggregate to form a __?__

A

micelle

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6
Q

When surrounded by water, cylindrical-shaped (double tailed) lipid molecules aggregate to form a __?__

A

bilayer

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7
Q

What is a glycerol based phospholipid known as?

A

Phosphoglyceride

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8
Q

What are the main phosphoglycerides in the plasma membrane?

A

Phosphatidylcholine

Phosphatidylethanolamine

Phosphatidylserine (-)

Phosphatidylinositol

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9
Q

Which of these molecules has an overall negative charge?

a) Phosphatidylcholine
b) Phosphatidylethanolamine
c) Phosphatidylserine
d) Phosphatidylinositol

A

c) Phosphatidylserine

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10
Q

What is the main sphingolipid in the plasma membrane?

A

Sphingomyelin

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11
Q

What type of molecule forms the head of a phospholipid?

A

A polar molecule

e.g. choline, ethanolamine, serine, inisitol

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12
Q

In a phospholipid, the fatty acid chains need to attach to __?__

A

glycerol or sphingosine

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13
Q

How are glycolipids formed?

A

Addition of CHO group(s) to lipids.

Glycerol-based: glycolipid

Sphingosine-based: sphingolipid

Combo of glycerol and sphingosine: glycosphingolipid

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14
Q

What are the most common glycosphingolipids?

A
  • Cerebrosides

- Gangliosides

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15
Q

In what cells are glycosphingolipids prominent?

A

Nerve cells.

Think of the names of the most common glycosphingolipids:

  • Cerebroside
  • Ganglioside
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16
Q

Phosphatidylserine is a negatively charged phosphoglyceride in the plasma membrane. The other common phosphoglycerides are uncharged. What purpose does phosphatidylserine serve?

A

Phosphatidylserine is located on the inside of the membrane. During apoptosis the plasma membrane modifies a lot and internal proteins become exposed at the surface. This will now be on the outside and allow macrophages to recognise the apoptosis bodies.

17
Q

Eukaryotic plasma membranes contain large amounts of cholesterol. What is the role of cholesterol in the PM?

A
  • Maintains stability and integrity of PM
  • Decreases permeability of PM
  • Decreases fluidity
18
Q

How does the plasma membrane’s composition affect fluidity?

A
  • shorter chain length on phospholipid reduces the tendency of the tails to interact with one another
  • Cis-double bonds produce kinks in the hydrocarbon chains that make them difficult to pack together
19
Q

How does temperature affect the fluidity of the plasma membrane?

A

Movement of phospholipids decreases as the temperature drops and increases as it rises.

20
Q

In what ways can a phospholipid move within the membrane?

A

They can rotate, diffuse laterally (within their monolayer), and - rarely - they can flip into the other side of the bilayer.

21
Q

What are integral membrane proteins?

A
  • Embedded within bilayer
  • Hydrophobic segments have affinity for interior of bilayer
  • Hydrophilic regions extend into aqueous phase
22
Q

What are peripheral membrane proteins?

A
  • Lack hydrophobic segment, therefore sit on the periphery, linked to polar heads of the phospholipids.
  • Glycosylphosphatidylinositol (GPI) anchors
23
Q

What are lipid-anchored membrane proteins?

A
  • Hydrophilic, sit on surface of membrane attached to a lipid molecule in the bilayer.