Chapter 7, Problem 2STP

Summary Introduction

To determine:

Effect of having the polar and non-polar ends of phospholipid molecules orientation.

Introduction:

The cell membrane is the outer membrane of most of the organism’s cells and it separate the outer environment from the inner components of the cell.

Answer to Problem 2STP

It helps in the orientation of other cellular components such as membrane proteins surface sugar moieties.

It protects cell from dehydration.

It maintains contact with the environment.

It regulates the transfer of important molecules to and fro the membrane.

Explanation of Solution

The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules.

Lipids are arranged within the membrane with the polar head towards outer sides and the hydrophobic tails towards the inner part. This ensures the non-polar tail of saturated hydrocarbons is protected from the outer aqueous environment. The lipid component of the membrane is mainly composed of phosphoglycerides.

The most accepted model for the structure of cell membrane is widely accepted fluid mosaic model, proposed by singer and Nicolson in 1972. This model explains that the quasi-fluid nature of lipid bilayer enables the lateral movement of proteins across the membrane.

Phospholipids consist of a glycerol molecule, two fatty acids, and a phosphate group that is modified by an alcohol.

The phosphate group is the negatively-charged polar head, which is hydrophilic.

The fatty acid chains are the uncharged, nonpolar tails, which are hydrophobic.

The tails are hydrophobic, they face the inside, away from the water and meet in the inner region of the membrane.

The heads are hydrophilic, they face outward and are attracted to the intracellular and extracellular fluid.

If phospholipids are placed in water, they form into micelles, which are lipid molecules that arrange themselves in a spherical form in aqueous solutions.