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Cellular and Molecular Biology > Lecture 35: Biological Membranes and Lipids > Flashcards

Lecture 35: Biological Membranes and Lipids Flashcards

1
Q

What is the function of membranes?

A

Semipermeable barrier

Detects and interprets changes in extracellular environment

Provide anchorage sites for extracellular proteins and cytoskeleton

Provides an alternative environment to the cytoplasm

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2
Q

What does the fluid mosaic model say about membranes?

A

That they are semi-fluid, not static

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3
Q

Do membranes have a cytoplasmic and exoplasmic side?

A

Yes

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4
Q

The lumen (inside) of the ER corresponds to the exoplasmic side of the plasma membrane.

A

Modifications done in the ER (e.g., glycosylation) appear only on the exoplasmic side after vesicle fusion.

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5
Q

How many lipids does the plasma membrane of a typical cell contain?

A

The plasma membrane of a ‘typical’ cell contains ~10^9 lipids

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6
Q

What are the different types of lipids that can be found in a plasma membrane?

A
  • Phospholipids
  • Glycolipids
  • Cholesterol
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7
Q

is it true that membranes typically don’t contain that many carbohydrates?

A

Yes

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8
Q

Is Myelin an insulator for nerve cells?

A

Yes

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9
Q

What do phospholipids consist of?

A

Phosphoglycerides and Sphingolipids

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10
Q

What do signalling molecules consist of?

A
  • Steroid hormones e.g., sex hormones and cortisol
  • Eicosanoids: short range signalling molecules involved in pain, inflammation, etc.
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11
Q

Which vitamins are important for membrane function

A

Vitamins: A, D, E and K

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12
Q

Are tryglycerides fuel for metabolism?

A

Yes

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13
Q

Because membrane lipids are very diverse in structure, what are they defined by?

A

Defined by their hydrophobicity rather than structure

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14
Q

Are lipids soluble in water?

A

No, they are only soluble in organic solvents such as chloroform

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15
Q

Glycerol would be hydrophilic if not for…

A

The fatty acid tails it has, which makes it hydrophobic

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16
Q

Describe the structure of tryglycerides

A
  • One glycerol molecule attached to 3 fatty acid chains
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17
Q

Describe the structure of phosphoglycerides (type of phospholipid)

A
  • One glycerol molecule(backbone) attached to 2 fatty acid chains, and a phosphate group
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18
Q

Describe the structure of sphingolipids

A
  • One Sphingosine molecule (backbone) attached to: One fatty acid tail attached via an amide bond (hydrophobic); A phosphate group (hydrophilic) , and a polar head group, often choline.
19
Q

Where are sphingolipids often found?

A

in the myelin sheath of nerve cells.

20
Q

What type of phospholipid makes up the bulk of our biological membranes?

A

Phosphoglycerides

21
Q

What is meant by the fact that phospholipids are amphiphilic/amphipathic?

A

They are both hydrophilic and hydrophobic

22
Q

What part of phospholipids is hydrophobic and what part is hydrophilic?

A

Fatty acid chains are hydrophobic

Polar head is hydrophilic

23
Q

Describe the key properties of lipid bilayers

A
  • Extensive: They can grow and spread.
  • Self-sealing: No edges are exposed to water due to the exclusion of hydrophobic regions.
  • Amphipathic: Lipids have both hydrophobic tails and hydrophilic heads, promoting bilayer formation.
24
Q

Describe fatty acids

A
  • They are terminated with a carboxylic acid group
  • They form the ‘tails’ of phospholipids and triglycerides
  • They are hydrophobic
  • They can be saturated or unsaturated (have a double bond)
25
Q

What are the 3 systems for numbering the carbons in fatty acids?

A

1,2,3…… Chemical numbering system

α, β, 𝛾…… Biochemical still used in metabolism

ω, ω-1, ω-2….. Used in nutrition

26
Q

Describe unsaturated fatty acids

A
  • Unsaturated fatty acids have C=C double bonds
  • Double bonds in fatty acids are usually cis, but can be trans as well
  • Trans is almost straight, but cis introduces a kink
  • Melting point decreases with increasing double bonds
  • Unsaturated fatty acids can’t be packed as closely together, this irregularity of packing resulting in more fluid membranes
27
Q

Where must essential fatty acids be obtained from?

A

Our diet

28
Q

What is the importance of essential fatty acids?

A
  • Important function in cell membrane in cell signalling
  • Serve as a precursor for other signalling molecules, such as arachidonic acid
29
Q

Key essential fatty acids

A

Linoleic acid: 18:2 C18 Δ^9,12
(ω 6 fatty acid
)

Linolenic acid: 18:3 C18^ Δ9,12,15
(ω 3 fatty acid
)

30
Q

Describe Arachidonic acid

A
  • Can be synthesised, or obtained from our diet

-20:4 C20 Δ5,8,11,14

  • Synthesised from linoleic acid
  • Precursor for eicosanoids
  • Also, important functions as part of phospholipids in membrane
  • Plays important role in inflammation
31
Q

What are Eicosanoids important for?

A

Pain and inflammation (they allow you to feel pain)

32
Q

What are Eicosanoids synthesised from?

A

Arachidonic acid

33
Q

Is it true that the Hydroxy groups (or O-)
can be further modified in phospholipids?

A

Yes, by the addition of a head group, such as choline (which will be cleaved off when signals come in)

34
Q

Is it true that phospholipids can contain either saturated or unsaturated fatty acids?

A

Yes

35
Q
A
36
Q

In sphingolipids (the second type of phoshpholipid) is one of the fatty acid chains inbuilt?

A

Yes

36
Q

What band atatches a choline molecule to a phosphate group?

A

An ester bond

37
Q

Are head groups like choline and inositol typically good signalling molecuels?

A

Yes

38
Q

What amino alcohol are Sphingolipids based on?

A

sphingosine

39
Q

Describe glycolipids

A
  • Sugar containing lipids
  • Sugar instead of phosphate group
  • Can be more than one sugar unit
  • In animal cells they are derived from sphingosine not glycerol
  • Sugar always on the outside of the cell
  • Functions include: Immune responses, cell cell recognition
    and attachment
40
Q

Is cholsesterol only present in animal membranes?

A

Yes

41
Q

Describe cholesterol

A
  • Sterol – modified steroid
  • Structure of 4 hydrocarbon rings (all steroids have this structure)
  • Rings are planar, but not completely flat
  • Present in only mammalian cell membranes
  • Has a hydrophobic tail
  • Cholesterol has important effects on membrane fluidity
42
Q

Key messages

A
  • Amphipathic lipids generating the membrane bilayer, which is semi fluid
  • There are three main types of lipids in membranes
    Phospholipids (Phosphoglycerides and sphingolipids)
    Glycolipids
    Cholesterol
  • Membrane composition differ in terms of which lipids it contains and which
    and how many proteins it contain reflecting the function
  • Lipids are not just structural but have functions in signalling as well
43
Q
A

Cellular and Molecular Biology (36 decks)

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