Why does the colour leak out of cooked beetroot?

Learning Outcome

Describe how membrane structure can be investigated practically, eg by the effect of alcohol concentration or temperature on membrane permeability. 

Introduction

The cell membrane acts as both prison and protector, it keeps what it needs to keep inside the cell, and prevents anything it doesn't want getting in from getting in. The structure is fluid and adaptable according to the needs of the cell. Some molecules will pass through the phospholipid bilayer without obstruction, and some require the help of the intramembrane channel proteins to help them. Thee way these proteins work depends on their structure, their specific shape dictates the role. A protein has a comfort zone where it works at its maximum potential. We call these optimum conditions. The right temperature, the right pH, all these factors matter to a protein. A little variation either way can make a world of difference.

Discussion

What is it that controls what comes in and out of a membrane? Is it the phospholipids? The proteins? The glycoproteins or all of the above? What was affected by the increase in heat? What does this tell you about what controls the flow of belaitins in and out of cells? What does this tell you about proteins and heat? Why did the heat have an affect and not the cold? Does low temperatures affect proteins in the same way?

Summary

• Proteins act as a gatekeeper to the cell
• Proteins work best at optimum conditions
• When the variables move away from optimum (eg pH or temperature) the proteins become denatured
• Denatured proteins in the cell membrane will not function well
• This lead to the leaking of belatins in the beetroot cells
• This is what causes problems in the epithelial cells of the lungs of people with Cystic Fibrosis

Links

• University of Texas website
• Biology4kids

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