DNA: Genetic Traces of Life

 

Understanding DNA

DNA is the chemical basis of heredity. The experiment that proved that DNA contains genetic information was first carried out by Frederick Griffith as follows:

There are 2 strains of Streptococcus pneumoniae:

a) Virulent cells: cells that are surrounded by a capsule and when grown in a petri dish will form colonies with a soft surface.

b) Non-virulent cells: cells that are not covered by a capsule and when grown in a petri dish will form colonies with a rough surface.

Deoxyribonucleic acid , better known by its abbreviation DNA, is a type of nucleic acid that has the ability to inherit traits. The presence of deoxyribonucleic acid is found in the nucleoproteins that form the cell nucleus.

All genetic information that determines the characteristics of living things is stored in DNA. DNA is located in the cell nucleus. DNA becomes quite long. To be arranged in the small cell nucleus, DNA strands are wrapped around proteins called histone proteins. With histone proteins, DNA coils form chromatin strands. When cells divide, these chromatin strands will form chromosomes.

DNA is a polymer of nucleotides. The nucleotides in DNA are connected to each other by phosphodiester bonds, namely bonds that occur between the cathide carbon of one nucleotide consisting of a pentose sugar (deoxyribose), a phosphate, and a nitrogen base. The nitrogen base bonds to the first carbon of the deoxyribose sugar, while the phosphate bonds to the fifth carbon of the same sugar.

There are four nitrogen-base compounds that make up DNA, namely:

• Adenine (A), which always pairs with thymine (T),
• Guanine (G) pairs with cytosine (S).

Uniqueness of DNA

The discovery of the structure of DNA by James Watson and Francis Crick in 1953 was an important discovery in the development of genetics around the world. The DNA structure model resulting from Watson and Crick’s analysis is able to explain how DNA carries genetic information as a blueprint that can be copied and reproduced when cells divide, so that new cells also contain the same genetic information. This is why a person’s physical traits and characteristics come from inheritance from their parents and will later be passed on to their children and grandchildren.

10 Unique Facts About DNA:

1. DNA is our genetic material and carries all instructions from generation to generation.
2. If we collected the DNA contained in one cell and stretched it, it would be more than two meters long!
3. In order to enter the cell, DNA is compacted, packed, and folded many times before finally being packed into a chamber measuring approximately 6/1 million meters.
4. All genes are made of DNA, but not all DNA is a gene. In fact, less than 2% of our DNA is made up of genes. Genes are scattered throughout our DNA, with tons of “non-gene” DNA in between.
5. DNA is made up of “letters”, which are represented as A, T, G, and C. These letters are abbreviations for the chemical compounds it contains.
6. There are 3 billion DNA letters contained in every cell.
7. Genes are like words in the DNA alphabet. Genes always start with the same set of 3 letters (ATG). That’s how scientists know it’s a gene, and the gene can literally be read by an instrument known as a DNA sequencer.
8. We have about 25,000 genes, and these genes can be found in every cell.
9. Not all genes will be used by every cell because some of them are very organ-specific (such as the brain or heart). Epigenetics dynamically controls which genes are active and which are inactive.
10. Human DNA is divided into 23 separate pairs of units (46 total). These are known as chromosomes. Each of the 23 pairs of chromosomes is compatible and has the same set of genes, so we have two copies of each gene.

DNA Testing

DNA testing in the laboratory can use various methods, depending on the purpose of the test and the type of DNA sample being tested. Some common methods used to test DNA include the following:

1. PCR (Polymerase Chain Reaction): PCR is a technique used to amplify certain DNA fragments so that they can be tested further. This is critical in forensic testing, genetic disease identification, and many other molecular biology applications.

2. Gel Electrophoresis: Gel electrophoresis is a method of separating DNA fragments based on their size. It is used to analyze the size of DNA fragments, such as in restriction mapping, PCR fragment separation, and DNA separation in DNA fingerprinting techniques.

3. Southern Blotting : Southern blotting is a method used to transfer DNA fragments from an electrophoresis gel to a nitrocellulose membrane or nylon membrane. This is then used to detect specific DNA with radioactive or non-radioactive probes.

4. Sequencing Method: There are several DNA sequencing methods available, such as Sanger sequencing and sequencing based on various NGS (Next-Generation Sequencing) platforms, which are used to determine the sequence of nucleic acids in a genome or DNA fragments.

5. DNA Fingerprinting: This method is used to identify individuals or confirm family relationships by analyzing unique patterns of DNA fragments. Techniques such as VNTR (variable number tandem repeat) and STR (short tandem repeat) are used in DNA fingerprinting.

The method used will depend on the purpose of the test and the nature of the DNA sample being tested. The choice of these methods may also evolve over time with the emergence of new technologies in the fields of genetics and molecular biology.

What are the testing stages?

There are many techniques and methods for carrying out DNA testing in the laboratory. One of the stages of DNA testing is:

1. Sampling: DNA samples are obtained from blood, saliva, or other body tissue.
2. Process using PCR: Polymerase chain reaction is used to multiply DNA fragments.
3. Gel Electrophoresis: DNA is separated based on size through gel electrophoresis.
4. DNA Analysis: DNA is sequenced and analyzed as intended.

PCR is used to make millions of copies of DNA from biological samples. DNA amplification using PCR means that DNA analysis of biological samples only requires a small amount of sample and can be obtained from fine samples such as hair. PCR’s ability to amplify small amounts of DNA makes it possible to analyze even degraded samples. However, contamination with other biological materials must still be prevented during identification, collection, and sample preparation.

Benefits of doing a DNA test

In 1980, Alec Jeffreys succeeded in demonstrating with DNA technology that DNA has various repeating sections (sequences). This is called polymorphism, which can be used as a means of specific (individual) identification of a person. The differences in DNA prints for each person or individual are like fingerprints; these DNA prints can also be read. Unlike fingerprints on a person’s fingertips, which can be changed by surgery, DNA prints cannot be changed by anyone or by any means. In fact, DNA fingerprints are the same in every cell, tissue, and organ of every individual. Therefore, DNA printing is a very accurate identification method.

Do a DNA test for anything?

1. Paternity Testing: To verify the father-child relationship or determine the biological father.
2. Genetic Health: To assess an individual’s genetic risk for certain diseases, such as heart disease, cancer, Alzheimer’s, and other genetic diseases.
3. Safety and Security: In some cases, DNA testing is used for identification purposes in national security situations or criminal investigations.
4. Identification of Remains: In natural disaster or crime situations, DNA testing can be used to identify victims.
5. Infectious Diseases: To identify agents that cause infections, such as viruses or bacteria.
6. Determination of Therapy Success: In oncology, DNA testing can be used to determine the most effective treatment based on the patient’s genetic profile.

Reference

1. Inheritance of Traits: Genetic Material. Kompas.com
2. Priyani Nunuk. Physical and Chemical Properties of DNA. University of North Sumatra. 2004
3. Marks, DB, Marks, AD, Smith, CM 1996. Basic Medical Biochemistry. Williams & Wilkins. Baltimore
4. Kartika Ratna Pertiwi. Application of DNA Technology in Forensic Identification. UNY
5. https://learn.utoronto.ca/curiousu-blog/curiosity/23-fun-facts-about-your-dna
6. Dian Atia Ihsani, et al. DNA Microarray Classification Using Principal Component Analysis (PCA) and Artificial Neural Network (ANN). ITS ENGINEERING JOURNAL Vol. 9, no. 1, (2020)
7. Luftig, MAand Richey S. 2000. DNA and Forensic Science. New England Law Review. Vol. 35:3