INTRODUCTION In recent years, it is not uncommon to read articles on DNA in both

Question

INTRODUCTION

In recent years, it is not uncommon to read articles on DNA in both scientific and popular magazines. DNA is regularly mentioned in the news and is often featured in TV detective or crime-scene investigation dramas. DNA, also known as DeoxyriboNucleic Acid, is a long molecule that holds the genetic information for all living beings, be it vegetable, animal or a simple microorganisms. It is capable of copying itself and can synthesize RNA (RiboNucleic Acid). In more evolved or complex forms of life, DNA is contained in the nucleus of the cells. Except for the red blood cells of mammalians, which are devoid of a nuclei, all cells of a living being have their own DNA. The cells of an organism use certain parts of the DNA molecule, or genes, to produce the proteins they need to function. For a more detailed description of DNA including its structure, its functions and the mechanism by which proteins are produced, the reader should consult the texts listed [1] the Reference section of this paper, which are well written and contain excellent illustrations. In this article, I describe a simple experiment that will allow you to extract a bit of DNA from a banana, however, you can also try it using other fruits and even vegetables. It is an experiment that can be performed both at home and in a school laboratory.

PROCEDURE

SUMMARY OF THE PROCEDURE
The procedure described below exploits the fact that the external membrane of cells and that of their nuclei are composed of fatty substances that can be broken down using a simple detergent. The first operation in this procedure is to break-up the fruit into a pulp or mush so that the cells are separated each from other as much as possible thereby exposing them to the action of the detergent. Secondly, the detergent is added to the pulp of the fruit so as to release the DNA from the cell membranes, which encapsulate it. Thirdly, it is necessary to filter the mixture to separate the nucleic acid from the remains of the cellular membranes. Finally, the DNA is precipitated in alcohol where it becomes visible. The DNA you obtain using this procedure can be observed with a microscope and can be used for other experiments like electrophoresis or other experiments.

1. What type of organisms and cells contain DNA?

2. What is the role of DNA in organisms?

3. Why would you want to extract the DNA from the organism?

4. In the procedure, why is the banana crushed or ground up into a pulp?

Explanation / Answer

1. DNA or Deoxyribonucleic Acid, is a biological macromolecule present in all living forms and is responsible for constituting the geentic make-up and heredity pattern of organisms. DNA is a double-stranded helix present in the nucleus of every cell in an organisms body, barring a few cells which are anucleated. For e.g., the mammalian red blood cells do not contain a nucleus and hence lack DNA.

2. DNA are double helical biomolecules present inside the nucleus that contain all the information required for carrying out the physiological and biochemical functions in an organism necessary for its survival. DNA moelcules are made up of pairs of nitrogenous bases (where one base of each pair belong to one strand of the double helical structure, and are bound to each other through hydrogen bonds). Specific stretches of these base-pair combinations lead to the formation of proteins via an RNA intermediate, and such stretches (which can code for proteins) are known as genes. These proteins encoded by the DNA, which include every structural protein, secretory molecules, enzymes, hormones etc. in an organism, bring about the various life functions required for survival. Therefore, the information stored in the DNA lead to the structural, physiological and biochemical features and functionalities of an organism, as well as reapir of cellular damage. DNA is also the hereditary material of living organisms which get passed on from parent to offspring through gemete formation and fusion of (parental) gametes. This leads to the transmission of genetic features across generations of organisms related to each other, and the propagation of a species.

3. DNA extraction from the cells of an organism is necessary in order to study the features of the DNA of that particular organism or species. The DNA molecules are present inside the nucleus of a cell, which is why it is not possible to study the features and functions of DNA without extracting it from the cell. The cell is lysed along with the nucleus, in order to obtain the DNA, which is then subjected to experiments designed to reveal its role in various physiological processes. The study of DNA molecules from various organismal species has led to accumulation of knowledge regarding the genetic make-up of various species, chemical nature of DNA, heredity patterns, interactions between DNA and cellular proteins and their effects on the organism, the mechanism of action of drugs, and has also led to the synthesis of artificial drugs and techniques which can target specific regions of the DNA to cure a pathological condition.

4. In the procedure stated above, the banana is crushed or ground to a pulp, so that the cells of the banana are separated from each other as much as possible. Before subjecting the cells to a lysis step using a detergent, it is necessary to separate the cells so that the cell debris do not form lumps after lysis and the cells are properly exposed to the lytic agent. As a result of crushing of the banana into pulp, the cells get amply exposed to the action of the detergent during the lysis stage. This leads to sufficient rupture of the cells causing them to release their entire DNA content, which is then used for further genetic studies.

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