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ICPP > 1.1 - Cell Membrane Lipids > Flashcards

1.1 - Cell Membrane Lipids Flashcards

1
Q

Major functions of biological membranes

A
  • continuous and highly selective permeable barrier
  • control of the enclosed electrochemical environment
  • Communication
  • Signal generation in response to stimuli (electrical and chemical)
  • Recognition, signalling, adhesion proteins and immune surveillance
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2
Q

Dynamic fluid mosaic model basics

A

⁃ phospholipid belayer with proteins and add-on structures
⁃ H20
⁃ Dynamic 3D macro molecular structure
⁃ Structural stability based on highly organised regions with defined charge density and distribution
⁃ Selectively permeable to biological molecules

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3
Q

Membranes are heterogenous within + between cells

A

⁃ ie don’t look the same, vary completely
⁃ Specialisations vary depending on tissue types and developmental status
⁃ Ie for interaction with basement membranes, interaction with adjacent cells, absorption of body fluids, secretion and transport
⁃ Membranes change over time (based on developmental status or disease)
⁃ Some (eg nerves) may specialise in electrochemical signalling - so need chemical signal generation and transmission.
⁃ Membranes are highly organised structure

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4
Q

What is the composition of cell membranes

A

⁃ measure using dry weight
⁃ Approx 40% lipid
⁃ 60% protein
⁃ 1-10% carbohydrate
⁃ However, membranes are hydrated structures, and about 20% of total membrane weight is water
⁃ Water dynamically interacts with membrane, and is vital to membrane structure + function

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5
Q

Why is water important for cell membranes

A

⁃ membranes are hydrated structures, and about 20% of total membrane weight is water
⁃ Water dynamically interacts with membrane, and is vital to membrane structure + function
⁃ Water interacts with charged/polar regions, stabilising the lipid head regions
⁃ Small proportion of water molecules also enter hydrophobic region of lipid bilayer

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6
Q

What are the different types of lipids found in membranes

A

3 main groups
⁃ phospholipids - can be unsaturated or saturated
⁃ Glycolipids
⁃ Cholesterol

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7
Q

Saturated vs unsaturated fatty acids

A

⁃ unsaturated have at least one double bond and are therefore kinked
⁃ saturated have no double bonds

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8
Q

What is amphipacity (lipids in cell membranes)

A

⁃ fundamental property of membrane lipids
⁃ Means one part of molecule is hydrophilic (polar or ionic charge). This is the head
⁃ The tails (fatty acids) are hydrophobic
⁃ Property is key to the formation of the lipid bilayer

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9
Q

Formation of the lipid bilayer in the aqueous environment

A

⁃ amiphathic phospholipids (PLs) heads strongly prefer contact with water, whereas tails avoid water
⁃ Forms 2D bilayer sheets or 3D micelles
⁃ This is the structure that is the most optimally energetically stable, thermodynamically

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10
Q

Features of glycerophospholipids

A

Consists of:
⁃ phosphate (+ charged/polar head) - aka hydrophilic head
⁃ Glycerol backbone
⁃ 2 Fatty acid chains aka hydrophobic tails
Also:
⁃ because glycerol residual has single bonds, the heads and tails can swivel
⁃ Hydrophilic head phosphate is charged, meaning it can interact with water molecules
⁃ In aqueous environments, phospholipids can arrange to form two bilayer leaflets

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11
Q

Features of the fatty acid chains

A
  • Length of C12-C24
  • Can be saturated (no C=C)
  • Can be unsaturated (at least one C=C in one of the chains)
  • unsaturated cis is C=C with ‘kink’ + sticky out leg
  • saturated trans is C=C with legs straight
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12
Q

What is the reaction that forms phospholipids (ie glycerol bonding to fatty acid chains)

A

Esterification (between the acid group of the fatty acid + the alcohol group of the glycerol)

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13
Q

Polar head groups

A
  • Amines
  • Amino acids
  • Choline (most common)
  • Inositol (has key signalling role)
    ☞ the thing that makes it charged = phosphate C=O group
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14
Q

What is sphingomyelin

A
  • Also a phospholipid (but not a glycerophospholipid)
  • No glycerol backbone → instead use sphingosine molecule
  • Can have both unsaturated or saturated fatty acids (but mainly saturated)
  • Often the fatty acid tail chains are unequal in length
  • Has a key role in lipid raft formation
  • Strong interaction with cholesterol
  • High concentration in myelin (for myelin sheaths)
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15
Q

What are the two types of glycolipids (no details)

A

cerebrosides and gangliosides
Glycolipids are also sphingolipids

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16
Q

Features of cerobrosides

A
  • Polar head group is a single saccharide
  • Mainly glucose or galactose (polar head group) → therefore hydrophilic
  • Major glycoside found in CNS/PNS myelin sheath
  • Only found in external outward facing membrane leaflet (for identity or signalling)
  • Also found in lipid rafts
17
Q

Main roles of cerebrosides

A
  • Stabilising membrane
  • Cell-cell recognition and identity markers
  • Immune system: form the basis of blood groups (antigens on RBC surface)
  • found in myelin sheath
18
Q

Features of gangliosides

A
  • polar head group with an oligosaccharide chain
  • up to 9-10 saccharides
  • includes sialic acids eg NANA
  • only in external membrane leaflet
  • extend out from cell surface (wide signalling capability)
  • very important in CNS
19
Q

Main roles of gangliosides

A
  • stabilising membranes
  • cell-cell recognition/identity markers
  • immune system (form basis of blood groups, antigens on cell surface)
  • have very important role in CNS
  • form part of lipid rafts
20
Q

What are some common structural features of membrane lipids

A
  • amphipathic ie hydrophilic head and hydrophobic tail
  • FA tails are saturated or unsaturated
  • Bilayered 3D structure
    ☞ sphingomyelin and glycolipids present on outer face of membrane (concerned with cell identity)
21
Q

Features of cholesterol in cell membranes

A
  • Essential biomolecule
  • Major membrane component
  • Primary molecule in steroid hormone synthesis
  • Structurally distinct membrane lipid
  • Properties mean that it has significant biophysical interactions with other membrane lipids + proteins
22
Q

Structure of cholesterol and how is cholesterol structurally distinct

A
  • Amphipathic so hydrophobic + hydrophilic
  • hydrophilic - small OH group ‘head’
  • hydrophobic - planar steroid rings (rigid steroid rings) and smaller ‘tail’chain
  • Not very ‘wobbly’ (and short single chain)
23
Q

Main roles of cholesterol in cell membranes

A
  • Typically 30-40% of the membrane lipids
  • Enhancing/extending temperature range – for membrane fluidity + stability
  • Lipid raft formation: cholesterol is large component in this

ICPP (5 decks)

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