2. Fully hydrated mixtures of dipalmitoyl-phosphatidylcholine (diCteo-PC: Tm, 41

Question

2. Fully hydrated mixtures of dipalmitoyl-phosphatidylcholine (diCteo-PC: Tm, 41 C). dilinoleyl-phosphatidylcholine (diC1PC; Tm, -53 C) and cholesterol at a molar ratio of 4:3:3 can fonn nanoscale liposomes. These show bilayer organization with phase segregation of the component lipids into ordered (Lo) and disordered () domains as shown below. (Figure 1) disordered (L) ordered (L) Risselada and Marrink (2008) PNAS 105: 173667-72 Figure 1. Snapshot from molecular dynamics simulation of a typical bilayer organization in liposomes composed of diCa-PC/ diCis2-PC/cholesterol (4:3:3) at 22 °C and in a fully hydrated environment. State the relative abundance of each of the three lipid components in the (4 marks) (a) domains of the bilayer

Explanation / Answer

2.

(a)

Ordered phase occurs when the temperature is lower and disordered phase occurs when the temperature is higher.

Diplamitoyl-phosphatidylcholine has melting temperature at 41 degree C

Dilinoleyl-phosphatidylcholine has melting temperature at -53 degree C

Cholesterol has melting temperature at 148 degree C

The temperature in the experiment is 22 degree C. Diplamitoyl-phosphatidylcholine exists in ordered phase at 22 degree C as it has melting temp. at 41 degree C. Dilinoleyl-phosphatidylcholine exists in disordered phase at 22 degree C as its melting temp. is at -53 degree C. Cholesterol exists in ordered phase at 22 degree C as it has melting temp. at 148 degree C.

So, the relative abundance of these components in the disordered and ordered domains can be deduced like this.

Ordered domain as more of Diplamitoyl-phosphatidylcholine and cholesterol while the disordered domain has more of Dilinoleyl-phosphatidylcholine.

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