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Semester 2 > M&R Session 1 > Flashcards

M&R Session 1 Flashcards

0
Q

Membrane composition?

A

60% protein
40% lipid
1-10% carbohydrate

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1
Q

5 main functions of biological membranes?

A
  1. Selectively permeable barrier
  2. Control chemical environment
  3. Communication
  4. Recognition
  5. Signal generation
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2
Q

Structure of phospholipids?

A

Glycerol
2 FA chains
Phosphate head group

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3
Q

What are cerebrosides?

A

Glycolipids with sugar monomer heads

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4
Q

What are gangliosides?

A

Glycolipids with oligosaccharide head groups

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5
Q

What kind of molecules are membrane lipids?

A

Amphipathic

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6
Q

Four methods of lipid mobility?

A
  1. Intra-chain motion
  2. Fast-axial rotation
  3. Fast lateral diffusion
  4. Flip-flop
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7
Q

Three modes of permitted mobility of proteins in biological membranes?

A
  1. Conformational change
  2. Rotational
  3. Lateral
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8
Q

Restraints on protein mobility in membranes?

A

Flip flop too energetic
Aggregates - movement w/in membrane slower
Tethering - cannot physically move
Interaction w/other cells - adhesion proteins fixed
Lipid mediated effects - prefer cholesterol poor regions

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9
Q

Evidence for membrane proteins?

A

Facilitated diffusion
Ion gradients
Specificity of cell responses
Membrane fracture

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10
Q

Amphipathic molecule arrangement in water?

A

Micelle or bilayer

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11
Q

How are liposomes formed?

A

Enclosure by lipid bilayer in aqueous media

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12
Q

Structure of cholesterol?

A

Polar head group
Rigid planar steroid ring
Non-polar hydrocarbon tail

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13
Q

What is the function of cholesterol in the phospholipid bilayer?

A

Abolishes endothermic phase transition (reduces melting temperature)
Reduces phospholipid chain motion (reduces fluidity)

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14
Q

How does cholesterol reduce fluidity in the CSM?

A

Beta-OH locks onto adjacent phospholipid - rigid ring obstructs packing

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15
Q

Is the flexible tail motion of a phospholipid bilayer affected by cholesterol?

A

No

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16
Q

What is the overall result of cholesterol on a phospholipid bilayer?

A

Homogenise properties to keep membrane constant over a greater range of temperatures

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17
Q

Why is there no flip-flop of membrane proteins?

A

Hydrophilic structure too large to cross hydrophobic domain - too much energy and resultant disruption to ion gradients too great

18
Q

Classifying features of peripheral membrane proteins?

A

Bound to surface (can be washed off)
Electrostatic and H bond interactions
Removed by changes in pH/ionic strength

19
Q

What type of membrane protein prefers cholesterol-rich areas?

A

Transducers of protein-protein associates

20
Q

Features of integral membrane proteins?

A

Interact extensively w/hydrophobic domains

Only removed by non-polar interaction competitors (detergents/organic solvents)

21
Q

Typical length of transmembrane polypeptides?

A

18-22 a.a.

22
Q

Typical structure of transmembrane polypeptides?

A

Hydrophobic R groups

Alpha-helical transmembrane domains

23
Q

How do glycoproteins orientate?

A

Oligosaccharides outside
Disulphide bonds outside
Transmembrane helix inside
Sulphylhydryl groups inside

24
Q

Where are dolichol phosphate-linked p.p. attached to CSM?

A

On membrane lipids on extracellular side

25
Q

What causes FA of lipids to reinsert into the bilayer?

What is the effect?

A

Post-translational modification

Restricts protein movement

26
Q

Are peripheral protein associations extracellular or in the cytosol?

A

Both - Hah!

27
Q

Why is asymmetrical orientation of membrane proteins important?

A

Receptor needs recognition site towards extracellular space

28
Q

What is the structure of spectrin?

A

Alpha and beta subunits wind together –> antiparallel heterodimer
Long, floppy, rod-like (tee hee)
Heterotetramer formed by head-to-head association of 2 molecules

29
Q

Which molecules restrict lateral mobility of membrane proteins?

A

Ankyrin

Band 4.1

30
Q

Give two examples of haemolytic anaemias.

A

Hereditary spherocytosis

Hereditary elliptocytosis

31
Q

Give an overview of hereditary spherocytosis.

A

Relatively rare
Spectrin decreased by 40-50%
Erythrocytes round up and shear through narrow lumen
RBCs less resistant to lysis –> easily fatiguable
Tx: adapt lifestyle and blood transfusion

32
Q

Give a brief overview of hereditary elliptocytosis.

A

Defect in spectrin molecule
Can’t form heterotetramers –> no mesh
Fragile, elliptoid cells

33
Q

What defines the orientation of a membrane protein?

A

Positioning of positively charged residues at N or C-terminal end of start-transfer sequence during protein synthesis

34
Q

How is a membrane protein oriented with C terminus into the ER lumen?

A

+ve residue at N terminus of start-transfer sequence

35
Q

What directs the N terminus of a membrane protein into the ER lumen?

A

+ve residue at C-terminal end of start-transfer sequence

36
Q

What is the function of the stop codon during membrane protein synthesis?

A

Clamp protein in the membrane

37
Q

What stabilises the partially folded growing p.p. in multiple transmembrane domain protein synthesis?

A

Lumenal binding proteins (related to heat-shock proteins)

38
Q

Give a one sentence description of how G-protein coupled receptors are formed.

A

Spanning domains made outside and inserted into the membrane

39
Q

Is protein orientation maintained during exocytosis?

A

Yes

40
Q

Describe the vesicle resulting from endocytosis.

A

Sealed inside-out vesicle with reversed protein orientation

41
Q

Describe the vesicle resulting from exocytosis.

A

Sealed right-side out vesicle

42
Q

What property do the precursory vesicles of both exocytosis and endocytosis share?

A

They are leaky before they become sealed

Semester 2 (45 decks)

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