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Biomembranes > Membranes and Lipid Proteins > Flashcards

Membranes and Lipid Proteins Flashcards

- Recognise the basic types of membrane lipid and the amphipathic nature of phospholipids - Describe membrane structure in terms of the classical "fluid-mosaic" model and list evidence supporting the model - Predict the effect of variations in chemical composition (e.g. of phospholipids) on membrane properties - Differentiate between single-spanning and multiple spanning membrane proteins in terms of likely cellular function

1
Q

Functions of the cell membranes

A
  • Define cell boundary and serve as permeability barriers
  • Represent sites of specific functions
  • Regulate the transport of solutes
  • Detect and transmit electrical and chemical signals
  • Mediate cell to cell communication
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2
Q

Describe the fluid-mosaic model

A

membrane is a two-dimensional sea of mobile lipid in which proteins diffuse or float

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3
Q

Purpose of phospholipid reorganisation

A

allow for merging and release of neurotransmitter in synaptic cleft

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4
Q

Role of cholesterol in the lipid bilayer

A

helps with stability, changes fluidity of membrane

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5
Q

Diffusion of ions through plasma membrane

A

via integral proteins -> plasma membrane will not let through any large or charged molecules

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6
Q

Define lipids

A

fat-soluble substances, phospholipids and cholesterol

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7
Q

Structure of phospholipids

A
  • share a glycerol backbone and two hydroxyl groups -> esterified to fatty acid (acyl) groups
  • phosphate group attached to two carbons, which attach to nitrogen atom and oxygen atom
  • head = polar = hydrophilic
  • fatty acid chain tails = non-polar = hydrophobic
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8
Q

Formation of monolayer

A

low concentrations of phospholipids in water

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9
Q

Formation of micelles

A

higher concentration of phospholipids, but not high enough to form a bilayer

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10
Q

How is the width of the bilayer determined

A

length of fatty-acid side chains

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11
Q

Nature of head groups determines…

A

how densely packed adjacent phospholipid molecules are in each layer of membrane

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12
Q

How can phospholipids be dissolved with detergents

A

they are also amphipathic and interact through tails

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13
Q

Rate of phospholipid diffusion at high temperatures

A

rapid (sol state)

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14
Q

Rate of phospholipid diffusion at low temperatures

A

slowly (gel state)

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15
Q

Define transition temperature

A

temperature between conversion from sol state to gel state -> reducing length of fatty acid chains redicts transition temperature

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16
Q

How do modest concentrations of cholesterol influence fluidity

A

decreases fluidity by holding phospholipids together

17
Q

How do high concentrations of cholesterol influence fluidity

A

increases fluidity

18
Q

Where are integral proteins

A

embedded in cell membrane (channels and pores)

19
Q

Where are peripheral proteins

A

embedded on exterior of membrane

20
Q

What are glycoproteins

A

carbohydrates attached to proteins

21
Q

What is a glycolipid

A

carbohydrate attached to a phospholipid

22
Q

Structure of cholesterol

A

hydroxyl group and four fused rings

23
Q

Layers of cell membrane

A

plasma membrane, internal membranes, intracellular vesicles

24
Q

Membrane lipids

A
  • “barrier properties”
  • phospholipids
  • steroids
  • neutral fats
  • glycolipid
25
Q

Formation of lipid bilayer

A
  • spontaneous in aqueous solution
  • stabilised by tail-tail and head-head interactions
  • makes exocytosis and endocytosis possible
26
Q

How are transmembrane proteins arranged in membrane

A

asymmetrically, orientation is established during biosynthesis

27
Q

Single spanning proteins

A
  • e.g. receptor tyrannise kinase
  • anchoring, receptor-transducer function
28
Q

Multiple spanning proteins

A
  • e.g. pores of ion channels
  • may form aqueous pore in membrane
29
Q

Structure of cys-loop receptors (ligand-gated ion channels)

A
  • extracellular N-terminus
  • composed of five protein subunits which form a pentameric arrangement around a central pore
  • four hydrophobic transmembrane domains
  • extracellular C-terminus
30
Q

How can you find what regions of proteins are hydrophilic/hydrophobic

A

conducting hydrography analysis

31
Q

Protein regions of high charge density

A

are relatively hydrophilic

32
Q

Protein regions of low charge density

A

are relatively hydrophobic

33
Q

Evidence for structure of fluid-mosaic model

A
  • lipid area (unimolecular film) = 2 x membrane area
  • X-ray and neutron diffraction
  • transmission electron microscopy
  • freeze-etching (reveals embedded proteins in fracture faces)
34
Q

Evidence for dynamics of fluid-mosaic model

A
  • Electron-Spin-Resonance (ESR) Spectroscopy
  • Phase-Transition
  • Protein-tagging to observe protein movement
35
Q

ESR Spectroscopy

A
  • one of most efficient
  • applies spin-probe to head, allowing to track movement of phospholipids
36
Q

FRAP (Fluorescence recovery after photobleaching)

A
  • fluorescent antibody attaches to epitope that has been commonly expressed
  • antibody binds to tag
  • see movement of proteins
37
Q

Mechanisms by which substances cross membrane

A
  • diffusion (lipophilic)
  • osmosis (net water (solvent) flow)
  • transport (facilitative or active solute movement)

Biomembranes (12 decks)

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