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ESA 2 Membranes and Receptors > Membrane bilayer & proteins (1) > Flashcards

Membrane bilayer & proteins (1) Flashcards

0
Q

What are the dry mass weight proportions of a membrane’s composition?

A
  • Lipid: 40%
  • Protein: 60%
  • Carbohydrate: 1-10%
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1
Q

What is the function of a membrane bilayer?

A
  • Continuous, highly selective permeability barrier
  • Controls enclosed chemical environment
  • Communication
  • Recognition (signalling, adhesion, immune surveillance)
  • Signal generation in response to stimuli
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2
Q

What proportion of a membrane bilayer’s weight is water?

A
  • 20%
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3
Q

Outline the structure of a phospholipid.

A
  • 2 FA chains: may have kinks
  • Glycerol molecule
  • Interchangeable head
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4
Q

What is the glycerol and FA chains together called?

A
  • Phosphatidyl backbone
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5
Q

What do the heads to the phospholipid have to be? Give some examples.

A
  • Polar

- Choline/serine/ethanolamine/inositol.

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6
Q

What causes the kink in the FA chain?

A
  • Cis double bond.
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7
Q

What are glycolipids?

A
  • Sugar containing lipids base on sphingomyelin backbone
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8
Q

What are the different types of glycolipids?

A
  • Cerebrosides: Head group sugar monomer

- Gangliosides: Oligosaccharides head group

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9
Q

What four types of phospholipid motion?

A
  • Flexion (dynamic vibration)
  • Rotation
  • Lateral diffusion
  • Flip-flop (rare as hydrophobic through hydrophilic environment)
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10
Q

What is the structure of cholesterol?

A
  • Polar head
  • Rigid planar steroid ring structure
  • Non-polar hydrocarbon tail
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11
Q

How does cholesterol join to other phospholipid molecules?

A
  • Via beta-OH group
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12
Q

What is the role of cholesterol in membranes?

A
  • Maintains integrity to prevent crystalline islands
  • Reduces phospholipid packing: increases fluidity
  • Reduces phospholipid chain motion: decreases fluidity (helpful at high temps as reduces vibration so less damage)
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13
Q

What is the evidence for proteins in membranes?

A
  • Facilitated diffusion
  • Ion gradients
  • Specificity of cell responses
  • Membrane fractionation and gel electrophoresis
  • Freeze fracture
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14
Q

What are the motions of proteins in a bilayer?

A
  • Conformational change
  • Rotational
  • Lateral
  • NOT flip-flop
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15
Q

Why can’t proteins in membranes flip-flop?

A
  • The energy requirement to move such a large hydrophobic molecule through a hydrophilic environment is too high
  • Too destructive to move
16
Q

What restrictions of membrane protein mobility is there?

A
  • Aggregates (greater mass harder to move)
  • Tethering (cell wall)
  • Interactions with other cells
17
Q

How are there restrictions on mobility for proteins in bilayer?

A
  • Lipid mediated effects
  • Proteins tend to separate out into fluid phase/cholesterol poor region
  • Association with extra-membranous proteins.
18
Q

What are peripheral membrane proteins?

A
  • Bound to the surface
  • Electrostatic and H bond interactions
  • Removed by changes in pH/ionic strength
19
Q

What are integral membrane proteins?

A
  • Interact extensively with hydrophobic domains of lipid bilayer
  • CAN’T be removed by pH/ionic strength
  • Removed by non-polar interactions (detergents/organic solvents)
20
Q

What are the characteristics of transmembrane domains?

A
  • Alpha helical

- R groups of AA are hydrophobic

21
Q

How can proteins be locked into place so they all face in the same direction?

A
  • Post-translational lipid modifications.
22
Q

What bands do erythropoietin proteins contain, why and where?

A
  • Band 3
  • Glycophorin
  • Flexibility
  • Adhered to inside face of cellular membrane
23
Q

What is hereditary spherocytosis?

A
  • Spectrin decreased by 40-50%
  • Erythrocytes become more rounded
  • Become less resistant to lysis
  • Cleared by spleen
24
Q

What is hereditary elliptocytosis?

A
  • Defect in Spectrin molecule
  • Unable to form heterotetramers
  • Fragile elliptoid cells
25
Q

Outline secreted protein biosynthesis.

A
  • SRP from docking protein recognises ribosomes with signal sequence.
  • Ribosomes with signal sequence pass replicated protein strands through the membrane to the ER lumen via signal sequence receptors.
  • Replicated protein joins to signal peptidase to prevent further replication.
  • Protein detaches from ribosome to ER lumen
  • Ribosomes separate and return to cytoplasm.
26
Q

How are membrane proteins biosynthesis?

A
  • After replicated protein is passed through membrane, signal sequence receptors close the pore.
  • Ribosomes continue to replicate then signal peptidase stops further replication.
  • Protein is trapped between ER lumen and cytoplasm.

ESA 2 Membranes and Receptors (11 decks)

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