trunk/tengDissertation/Lipid.tex

\chapter{\label{chapt:lipid}LIPID MODELING}

\section{\label{lipidSection:introduction}Introduction}

Under biologically relevant conditions, phospholipids are solvated
in aqueous solutions at a roughly 25:1 ratio. Solvation can have a
tremendous impact on transport phenomena in biological membranes
since it can affect the dynamics of ions and molecules that are
transferred across membranes. Studies suggest that because of the
directional hydrogen bonding ability of the lipid headgroups, a
small number of water molecules are strongly held around the
different parts of the headgroup and are oriented by them with
residence times for the first hydration shell being around 0.5 - 1
ns.[14] In the second solvation shell, some water molecules are
weakly bound, but are still essential for determining the properties
of the system. Transport of various molecular species into living
cells is one of the major functions of membranes. A thorough
understanding of the underlying molecular mechanism for solute
diffusion is crucial to the further studies of other related
biological processes. All transport across cell membranes takes
place by one of two fundamental processes: Passive transport is
driven by bulk or inter-diffusion of the molecules being transported
or by membrane pores which facilitate crossing. Active transport
depends upon the expenditure of cellular energy in the form of ATP
hydrolysis. As the central processes of membrane assembly,
translocation of phospholipids across membrane bilayers requires the
hydrophilic head of the phospholipid to pass through the highly
hydrophobic interior of the membrane, and for the hydrophobic tails
to be exposed to the aqueous environment.[18] A number of studies
indicate that the flipping of phospholipids occurs rapidly in the
eukaryotic ER and the bacterial cytoplasmic membrane via a
bi-directional, facilitated diffusion process requiring no metabolic
energy input. Another system of interest would be the distribution
of sites occupied by inhaled anesthetics in membrane. Although the
physiological effects of anesthetics have been extensively studied,
the controversy over their effects on lipid bilayers still
continues. Recent deuterium NMR measurements on halothane in POPC
lipid bilayers suggest the anesthetics are primarily located at the
hydrocarbon chain region.[16] Infrared spectroscopy experiments
suggest that halothane in DMPC lipid bilayers lives near the
membrane/water interface. [17]


\section{\label{lipidSection:model}Model}

\section{\label{lipidSection:methods}Methods}

\section{\label{lipidSection:resultDiscussion}Results and Discussion}
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#	User	Rev	Content
1	tim	2685	\chapter{\label{chapt:lipid}LIPID MODELING}
2
3			\section{\label{lipidSection:introduction}Introduction}
4
5	tim	2731	Under biologically relevant conditions, phospholipids are solvated
6			in aqueous solutions at a roughly 25:1 ratio. Solvation can have a
7			tremendous impact on transport phenomena in biological membranes
8			since it can affect the dynamics of ions and molecules that are
9			transferred across membranes. Studies suggest that because of the
10			directional hydrogen bonding ability of the lipid headgroups, a
11			small number of water molecules are strongly held around the
12			different parts of the headgroup and are oriented by them with
13			residence times for the first hydration shell being around 0.5 - 1
14			ns.[14] In the second solvation shell, some water molecules are
15			weakly bound, but are still essential for determining the properties
16			of the system. Transport of various molecular species into living
17			cells is one of the major functions of membranes. A thorough
18			understanding of the underlying molecular mechanism for solute
19			diffusion is crucial to the further studies of other related
20			biological processes. All transport across cell membranes takes
21			place by one of two fundamental processes: Passive transport is
22			driven by bulk or inter-diffusion of the molecules being transported
23			or by membrane pores which facilitate crossing. Active transport
24			depends upon the expenditure of cellular energy in the form of ATP
25			hydrolysis. As the central processes of membrane assembly,
26			translocation of phospholipids across membrane bilayers requires the
27			hydrophilic head of the phospholipid to pass through the highly
28			hydrophobic interior of the membrane, and for the hydrophobic tails
29			to be exposed to the aqueous environment.[18] A number of studies
30			indicate that the flipping of phospholipids occurs rapidly in the
31			eukaryotic ER and the bacterial cytoplasmic membrane via a
32			bi-directional, facilitated diffusion process requiring no metabolic
33			energy input. Another system of interest would be the distribution
34			of sites occupied by inhaled anesthetics in membrane. Although the
35			physiological effects of anesthetics have been extensively studied,
36			the controversy over their effects on lipid bilayers still
37			continues. Recent deuterium NMR measurements on halothane in POPC
38			lipid bilayers suggest the anesthetics are primarily located at the
39			hydrocarbon chain region.[16] Infrared spectroscopy experiments
40			suggest that halothane in DMPC lipid bilayers lives near the
41			membrane/water interface. [17]
42
43
44	tim	2685	\section{\label{lipidSection:model}Model}
45
46			\section{\label{lipidSection:methods}Methods}
47
48			\section{\label{lipidSection:resultDiscussion}Results and Discussion}