Membrane Permeability

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4.1 Aim

The aim of this lab session is to demonstrate the effect of different conditions on membrane permeability.

4.2 Learning Objectives

In this Lab Session, students will acquire the skills to:
- analyze the effect of different temperatures on membrane integrity. - analyze the effect of the organic solvent acetone on membrane integrity.

4.3 Introduction

Even though membranes separate cells from their surrounding environment and different organelles within the cells from the cytoplasm, there is a constant flow of selected molecules through them allowing communication across them.

Membranes consist mainly of various proteins and lipid molecules. The amphipathic phospholipid molecule is the major component of the bilayer membrane (Figure 4.1).

Figure 4.1: The structure of a phospholipid molecule, the basic component of a membrane bilayer.

Due to its composition the phospholipid bilayer will allow only the passage of small hydrophobic or uncharged molecules (Figure 4.2). The passage of large or charged molecules is hindered by the lipid bilayer. Their passage through the cell membrane and membranes surrounding the organelles is mainly through selective protein carriers or channels either through active or passive transport. The kind of proteins present in the membrane is important in controlling solute movement across the membranes.

As an experimental model, red beet roots will be used to study membrane integrity. Red beet roots contain a large amount of a reddish betacyanin pigment, called betanin. This pigment is synthesized in the cytoplasm, and then transported across the tonoplast against its concentration gradient where it is accumulated and stored in the vacuole. In healthy cells the pigment remains in the vacuole, but some treatments that alter membrane permeability causes the betanin to leak out of the cells.

4.4 Experimental Procedures

4.4.1 Factors Affecting Permeability of Red Beet Root Membranes

Cut a...
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