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Biological Chemistry > Biological Membranes > Flashcards

Biological Membranes Flashcards

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1
Q

Due to the amphipathic nature of phospholipids, different structures are formed ?

A

In water, including a surface film, micelles, bilayers and liposomes/vesicles

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2
Q

Non-polar portions aggregate so that ?

A

Fewer water molecules are ordered and entropy increases

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3
Q

What part is exposed ?

A

Only polar “head groups” are exposed

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4
Q

This hydrophobic effect powers ?

A

Membrane formation, and van der Waals interactions between the hydrophobic tails stabilise membranes

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5
Q

All cells have a cell membrane, which separates ?

A

The cell from its surroundings: sheet-like fluid structure, 30–100 Å (3–10 nm) thick

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6
Q

Main structure is composed of ?

A

Two leaflets of lipids (bilayer)

- Except archaebacteria: monolayer of bifunctional lipids

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7
Q

Eukaryotic cells have various ?

A

Compartmentalising internal membranes

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8
Q

Protein molecules span the lipid bilayer, mitigating?

A

Permeability and the transfer of information

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9
Q

what does an asymmetric membrane mean ?

A

The outer surface is always different from the inner surface

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10
Q

Some lipids are found more commonly ?

A

Inside and some outside

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11
Q

Carbohydrate moieties are attached ?

A

On the carbohydrate

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12
Q

They are usually electrically polarised due to ?

A

Ion gradients across the membrane

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13
Q

What are functions of membranes ?

A
  • Define the cell boundaries and provide compartmentalisation within it
  • Allow import and export, e.g. of nutrients and waste
  • Sense external signals and transmit information into the cell
  • Separate energy-producing reactions from energy-consuming ones
  • Keep proteolytic enzymes away from important cellular proteins
  • Produce and transmit nerve signals
  • Store energy as a proton gradient
  • Support synthesis of ATP
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14
Q

Some bacteria are surrounded by ?

A

Two membranes, with a cell wall lying between the

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15
Q

Some bacteria are enclosed by ?

A

A single membrane surrounded by a thick cell wall

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16
Q

What is Periplasm ?

A

The space between the two membranes

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17
Q

Bacteria do not have ?

A

Internal membrane-bound organelles

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18
Q

What three major classes of membrane do eukaryotic cells contain ?

A
  1. The plasma membrane, separating cell from environment
  2. Endomembrane system, transporting components through cytoplasm
  3. Mitochondrial membrane (+chloroplast in plants), which are energy conversion factories
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19
Q

Explain the Fluid Mosaic Model ?

A
  • Proposed in 1972 by Singer and Nicholson
  • Lipids form a viscous, two-dimensional solvent into which proteins are inserted and integrated more or less deeply
  • Proteins can either be embedded in or associated with the membrane
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20
Q

What are three main classes of membrane lipids?

A

All amphiphatic:

  1. Phosphoglycerides (most abundant)
  2. Glycolipids
  3. Sterols
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21
Q

Phospholipids are composed of ?

A

Four components: one or two fatty acid tails, a glycerol or sphingosine platform, a phosphate, and an alcohol

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22
Q

Glycolipids are ?

A

Carbohydrate-containing lipids derived from sphingosine

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23
Q

Cholesterol is a ?

A

Sterol that is modified on one end by the attachment of a fatty acid chain and at the other end by a hydroxyl group

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24
Q

What is Phosphatidylcholine ?

A

This is the major component of most eukaryotic cell membranes

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25
Q

What does it consist of ?

A

It consists of a hydrophilic head (choline + phosphate), two hydrophobic tails (fatty acid chains) and a connecting glycerol

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26
Q

Many prokaryotes, including E. coli, cannot ?

A

Synthesise this lipid; their membranes do not contain phosphatidylcholine

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27
Q

How are phospholipids and glycolipids distributed?

A

They are distributed asymmetrically in the lipid bilayer of an animal cell plasma membrane: note that they retain their orientations during transfer between cell compartments

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28
Q

E.g. phosphatidylcholine and sphingomyelin are concentrated in ? whereas phosphatidylserine is concentrated in ?

A

Phosphatidylcholine and sphingomyelin are concentrated in the noncytosolic monolayer, whereas phosphatidylserine is concentrated in the cytosolic monolayer

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29
Q

Glycolipids are found exclusively in ?

A

In the non-cytosolic monolayer

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30
Q

Cholesterol is evenly ?

A

Distributed

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31
Q

Cells synthesise new membranes by ?

A

The expansion of existing membrane

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32
Q

Phospholipids are made in?

A

The ER membrane

33
Q

During trafficking, what happens ?

A

During trafficking, both the lipid composition of the bilayer and the disposition of specific lipids between inner and outer leaflets change considerably

34
Q

Protein content and lipid content, and types of sterol can all vary between?

A

Species

35
Q

Bacteria do not make ?

A

Sterols

36
Q

The functional specialisation of each membrane type in a cell is reflected in ?

A

Its unique lipid composition

37
Q

Lipid composition affects ?

A

Membrane fluidity

38
Q

Archaeal membranes are built from ?

A

Ether lipids with branched chains

39
Q

Better membrane stability by ether linkages and branching

structures prevent ?

A

Hydrolysis and oxidation of membranes

40
Q

The lipid bilayer can be in what form ?

A

Gel or fluid phase, dependent on composition and temperature

41
Q

What does heating cause?

A

Phase transition from the gel to fluid

42
Q

Under physiological conditions, membranes are more ?

A

Fluid-like than gel-like (necessary for function)

43
Q

Explain Liquid-ordered state (i.e., “gel phase”):

A

Individual molecules do not move around

44
Q

Explain Liquid-disordered state: (i.e., “fluid phase”):

A

Individual molecules can move around

45
Q

Define melting temperature (Tm) ?

A

The temperature at which a membrane transitions from being highly ordered to very fluid

46
Q

What is Tm dependent on?

A

Tm is dependent on the length of the fatty acids in the membrane lipid and the degree of cis unsaturation.

47
Q

What does a higher and a lower temperature mean ?

A
  • higher °C: need more long, saturated fatty acids

- lower °C : need more unsaturated fatty acids

48
Q

What does cholesterol help to maintain ?

A

Cholesterol helps to maintain proper membrane fluidity in animals

49
Q

How can Protein content and lipid content, and types of sterol vary ?

A

Between species

50
Q

What does bacteria not make ?

A

Sterols

51
Q

The functional specialisation of each membrane type in a cell is reflected in its ?

A

Unique lipid composition

52
Q

What does lipid composition affect ?

A

Membrane fluidity

53
Q

How are Archaeal membranes built ?

A

From ether lipids with branched lipids

54
Q

What are the different membrane protein and what do they interact with?

A
  • Integral membrane proteins interact with the lipid bilayer Transmembrane and Monolayer-associated
  • Peripheral membrane proteins interact with the polar head groups of the lipids (amphitrophic/lipid-linked) or bind to the surfaces of integral proteins
55
Q

Spontaneous flips from one layer to another are rare because ?

A

The charged head group must cross the hydrophobic tail region

56
Q

“Flip-flop” diffusion of specific lipids is catalysed by ?

A

Enzymes such as flippases, floppases and scramblases, depending on direction of movement

57
Q

What is the use of Fluorescence recovery after photobleaching (FRAP) ?

A

It allows us to monitor lateral lipid diffusion by monitoring the rate of fluorescence return

58
Q

FRAP allows us to determine ?

A

The diffusion coefficient of a lipid/protein in the leaflet by plotting a graph of the rate of fluorescent recovery

59
Q

Biological regulation results in ?

A

Attachment to, or cleavage from, lipids

60
Q

Amphitropic proteins are conditionally attached to the membrane by ?

A

Covalent interaction with lipids or carbohydrates attached to lipids

61
Q

Cytosolic proteins may be anchored via ?

A

Acylation or Prenylation

62
Q

Extracellular proteins can be anchored by ?

A

A GPI lipid anchor

63
Q

What are some examples of transmembrane proteins ?

A
  • Bacteriorhodopsin: Crosses the membrane as seven alpha-helices (a common motif) and acts as a proton pump
  • Porin: consists of a 16-stranded β sheet curved around on itself to form a transmembrane water-filled channel. Three porin proteins associate to form a trimer with three separate channels (not shown)
64
Q

Biological regulation results in ?

A

Attachment to, or cleavage from, lipids

65
Q

Transmembrane proteins are usually composed of ?

A

Alpha helices

66
Q

Explain what the hydrophobic residues and hydrophilic parts of the polypeptide backbone do?

A

Hydrophobic residues interact with the lipid bilayer, while hydrophilic parts of the polypeptide backbone form hydrogen bonds in the helix interior

67
Q

An α helix containing about 20 amino acids is required to ?

A

Completely travel through (traverse) a cell membrane: multiple helices commonly form a pore/channel

68
Q

Hydropathy plots can predict ?

A

Hydrophobic Domains

69
Q

Detergents are amphipathic molecules that disrupt ?

A

Membranes by intercalating into phospholipid bilayers

70
Q

Og / TX-100 are gentle detergents used to ?

A

Solubilise and reconstitute functional membranes.

71
Q

SDS is a strong detergent that will ?

A

Unfold proteins as well

72
Q

Membrane proteins and phospholipids in the outer leaflet are ?

A

Glycosylated, having short chains of sugars called oligosaccharides covalently linked to them

73
Q

Caveolin forces ?

A

Inward curvature of a membrane

74
Q

Stable associations of sphingolipids and cholesterol in the outer leaflet produce ?

A
  • A microdomain, slightly thicker than other membrane regions, that is enriched with specific types of membrane proteins
  • May function in signal transduction
75
Q

Inwardly curved rafts called? and are enriched in what?

A

Inwardly curved rafts called caveolae are especially enriched in the protein caveolin

76
Q

Define Caveolae ?

A

Small invaginations of plasma membrane

77
Q

What influences the passive transport of charged solutes ?

A

Both the concentration gradient and membrane potential

78
Q

Explain with example what endocytosis and exocytosis do ?

A

Larger proteins and signaling molecules may be internalised in vesicles (endocytosis) and neurotransmitters are released via vesicles (exocytosis)

Biological Chemistry (15 decks)

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