DNA and RNA | Science & Technology for UPSC CSE PDF Download

DNA and RNA

• Composition: DNA is composed of deoxyribose sugar, while RNA is composed of ribose sugar. The only difference between these sugars is that ribose has one more -OH group than deoxyribose.
• Importance: Both DNA and RNA are essential for life as they are involved in the synthesis of proteins, which are crucial for various cellular processes and functions. Without DNA and RNA, life as we know it would not exist.
• Structure: DNA is typically double-stranded and forms a double helix, while RNA is usually single-stranded.
• Stability: DNA is relatively stable under alkaline conditions, while RNA is not as stable and can be more prone to degradation.
• Functions: DNA primarily stores and transfers genetic information, serving as the blueprint for an organism's traits. RNA has various functions, including acting as a messenger (mRNA) to carry genetic instructions from DNA to ribosomes for protein synthesis and as a carrier (tRNA) of amino acids during protein synthesis.
• Base Pairing: DNA uses the bases adenine (A), thymine (T), cytosine (C), and guanine (G) for base pairing. RNA uses adenine (A), uracil (U), cytosine (C), and guanine (G) for base pairing, with uracil replacing thymine in RNA.

Comparison of DNA and RNA

Biological Functions of Nucleic Acids – DNA and RNA

• Genetic Information: DNA serves as the chemical basis of heredity and contains the genetic information that determines the traits and characteristics of living organisms. It can be thought of as the repository of genetic data.
• Species Identity: DNA is primarily responsible for maintaining the identity and genetic makeup of different species of organisms over long periods of evolutionary time. It carries the unique genetic code that distinguishes one species from another.
• Self-Duplication: DNA possesses the remarkable ability to replicate itself during cell division. This ensures that identical DNA strands are passed on to daughter cells, maintaining genetic consistency and fidelity.
• Protein Synthesis: While proteins are synthesized by various RNA molecules within the cell, the instructions for protein synthesis are encoded in DNA. DNA carries the genetic code that specifies the sequence of amino acids in a protein, and this information is transcribed into RNA, ultimately leading to the production of proteins.

DNA Fingerprinting

• Unique Identification: Just as fingerprints are unique to each individual, a sequence of bases in DNA, often referred to as DNA fingerprinting, is also unique for each person. This information is consistent across all cells in an individual's body and remains unaltered by any known treatment.
• Applications of DNA Fingerprinting:
  • Forensic Identification: DNA fingerprinting is widely used in forensic laboratories to identify and link individuals to crimes, aiding in criminal investigations and solving cases.
  • Paternity Testing: It is employed to determine paternity or parentage, helping establish biological relationships between individuals.
  • Human Identification: In cases of accidents or disasters, DNA fingerprinting can be used to identify deceased individuals by comparing their DNA profiles with those of their parents or children.
  • Biological Evolution: DNA fingerprinting can also be used to study and identify genetic variations among different racial and ethnic groups, providing insights into human genetic diversity and evolution.

Recombinant DNA

• Discovery of DNA Structure: In 1953, scientists made a groundbreaking discovery by elucidating the structure of DNA (deoxyribonucleic acid), which laid the foundation for understanding the genetic code and its significance in living organisms.
• Development of rDNA Technology: In 1972, researchers developed a method for cutting and splicing DNA, leading to the creation of recombinant DNA (rDNA) technology. This technique allowed scientists to manipulate and recombine genetic material from different sources, resulting in sequences that may not naturally occur in an organism's genome.
• rDNA Molecules: Recombinant DNA (rDNA) molecules are generated through laboratory-based genetic recombination methods, such as molecular cloning. These techniques enable the fusion of genetic material from diverse sources, giving rise to DNA sequences that do not exist in the original genome.
• Universal DNA Structure: One of the foundational principles behind recombinant DNA technology is that DNA molecules share the same chemical structure across all organisms. The differences lie in the specific nucleotide sequences within this common structural framework.
• Normal Phenotypes: Organisms containing recombinant DNA generally exhibit normal phenotypes, which refer to their observable physical properties, behavior, and metabolic characteristics. In most cases, the introduction of recombinant DNA does not result in drastic alterations in these aspects of the organism.

The basic steps involved in Recombinant DNA Technology

• Isolation of DNA Fragment: The process begins by isolating a DNA fragment that contains the gene of interest (referred to as the "insert"). This DNA fragment is typically obtained from a source organism's genome.
• Generation of Recombinant DNA (rDNA): The isolated DNA fragment is then inserted into a carrier DNA molecule known as a vector. Common vectors include plasmids or viral DNA. The insertion of the DNA fragment into the vector creates a recombinant DNA molecule.
• Transfer of rDNA into Host Cell: The next step is the transfer of the recombinant DNA molecule into a host cell, such as Escherichia coli (E. coli). This process is often called "transformation." The host cell will serve as the vehicle for replicating and producing the recombinant DNA.
• Selection and Replication: After transformation, only those host cells that have successfully taken up the recombinant DNA will carry it. These selected host cells are allowed to multiply through cell division, which also results in the replication of the recombinant DNA molecules.
• Gene Cloning or Protein Expression: Depending on the goals of the experiment, this process can lead to either gene cloning or the production of a specific protein encoded by the insert. In gene cloning, multiple copies of the DNA fragment (gene) are generated. In protein expression, the host cell produces the protein specified by the inserted gene.
• Introduction into Suitable Host: After generating recombinant molecules, the next step is to introduce them into an appropriate host organism. The choice of host depends on factors such as the type of vector used and the intended application.
• Methods of Introduction: Various methods can be used to introduce recombinant vectors into host cells. The choice of method depends on factors like the type of vector and the host cell. Common methods include electroporation, heat shock, and viral-mediated delivery.

Some commonly used procedures are

• Transformation: Transformation is a process used primarily in bacterial cells (e.g., Escherichia coli). In this method, cells are treated with calcium ions and exposed to a heat shock or electroporation, allowing them to take up plasmid DNA from their surroundings. This DNA can then be replicated and expressed by the host cell.
• Transfection: Transfection is commonly used in eukaryotic cells. It involves the introduction of foreign DNA (e.g., plasmids or viral DNA) into the host cell using chemical methods (e.g., calcium phosphate precipitation) or lipid-based carriers (e.g., liposomes). This allows the foreign DNA to enter the cell and potentially be integrated into the host genome.
• Electroporation: Electroporation is a technique used in both prokaryotic and eukaryotic cells. It involves subjecting cells to a brief electrical pulse that creates temporary pores in the cell membrane. These pores allow foreign DNA to enter the cell. Electroporation is a highly efficient method for introducing DNA into cells.
• Microinjection: Microinjection is a method primarily used for introducing DNA into eukaryotic cells. In this technique, a fine microsyringe is used to directly inject foreign DNA into the recipient cell's cytoplasm or nucleus. This method requires considerable precision and is often used for specific applications, such as creating transgenic animals.
• Biolistics: Biolistics, also known as the gene gun method, is used primarily for introducing DNA into plant cells. In this method, microscopic particles (e.g., gold or tungsten particles) are coated with the DNA of interest. These coated particles are then shot into the plant cells using a particle gun. The DNA-coated particles penetrate the plant cell walls and deliver the foreign DNA into the nucleus.

Applications of recombinant DNA technology

• Recombinant DNA is widely used in biotechnology, medicine, and research.
• Recombinant DNA is used to identify, map, and sequence genes, and to determine their function.

Recombinant DNA is used to produce

• Human Insulin: Recombinant insulin, produced using genetically engineered bacteria or yeast, is a more cost-effective and reliable source of insulin for diabetes treatment compared to insulin extracted from animal sources (such as pigs or cows).
• Human Growth Hormone: Recombinant human growth hormone is used to treat individuals with growth hormone deficiencies. It provides a safe and consistent source of growth hormone for those whose pituitary glands do not produce enough.
• Blood Clotting Factor VIII: People with hemophilia, a genetic disorder that impairs blood clotting, benefit from recombinant factor VIII. This treatment helps control bleeding and is safer than relying on donated blood products.
• Herbicide and Insect-Resistant Crops: Genetic engineering has led to the development of crops like soybeans, sorghum, and cotton that are engineered to be resistant to specific herbicides, such as glyphosate. This resistance allows farmers to control weeds more effectively. Additionally, some genetically modified crops are engineered to produce proteins from Bacillus thuringiensis (Bt), providing natural insect resistance.
• Bacillus thuringiensis (Bt): Bt is a bacterium that naturally produces a protein toxic to certain insects. In genetic engineering, genes from Bt can be incorporated into crop plants to make them resistant to insect pests. This reduces the need for chemical insecticides, making agriculture more environmentally friendly.

DNA Profiling

• DNA profiling, also known as DNA fingerprinting or STR analysis (Short Tandem Repeat analysis), is a technique used to determine an individual's unique genetic characteristics. While DNA profiling has evolved over time, modern methods primarily rely on analyzing short tandem repeats (STRs) rather than the minisatellites used in earlier DNA fingerprinting techniques.
• Short Tandem Repeats (STRs) are regions within the DNA that consist of short sequences of nucleotides (typically 2 to 5 base pairs in length) repeated in tandem. These repeats are found at various locations throughout the human genome, and the number of repeats at each location varies from person to person. This variation in the number of repeats creates a unique genetic profile for each individual.
• During DNA profiling, specific STR regions are targeted, and the number of repeats at each location is determined. This information is then used to create a genetic profile or "DNA fingerprint" for an individual. DNA profiles are highly accurate and can be used for various purposes, including criminal investigations, paternity testing, and establishing familial relationships.
• The use of STR analysis has become the standard in DNA profiling due to its accuracy, reliability, and the ability to analyze small and degraded DNA samples.

DNA Sequencing

• DNA sequencing is the process of determining the exact nucleic acid sequence, which refers to the specific order of nucleotides in a DNA molecule. In the era of genomics, where entire genomes of various species are being sequenced and compared, the ease and accuracy of DNA sequencing have played a pivotal role in advancing our understanding of the fundamental nature of DNA, often referred to as the "blueprint of life."
• The development of DNA sequencing methods dates back to the mid-1970s when scientists like Fred Sanger, Walter Gilbert, and Allan Maxam introduced the first techniques for sequencing DNA. Subsequently, Fred Sanger devised a new method that forms the foundation for most DNA sequencing processes used today.
• Sequencing DNA involves determining the order of the four chemical building blocks, known as "bases," that make up the DNA molecule. These bases are adenine (A), thymine (T), cytosine (C), and guanine (G). The sequence of these bases in a particular DNA segment provides valuable genetic information.

Benefits of DNA Sequencing

The benefits of DNA sequencing are vast and include:

• Forensics: DNA sequencing is employed to identify specific individuals since each person possesses a unique DNA sequence.
• Paternity Determination: DNA sequencing can be used to establish paternity or familial relationships.
• Medicine: DNA sequencing is crucial for detecting genes associated with hereditary or acquired diseases. It aids in understanding the genetic basis of various human diseases.
• Agriculture: Specific bacterial genes have been utilized to create genetically modified crops that are resistant to insects and pests. Additionally, DNA sequencing plays a role in improving livestock quality by enhancing meat and milk production.

DNA Barcoding

DNA barcoding is a species identification method that involves using a short segment of DNA from specific genes to determine the identity of a species. This approach provides a rapid and accurate way to identify species, making ecological systems more accessible by relying on short DNA sequences rather than analyzing entire genomes. DNA barcoding is primarily used for eukaryotic organisms.

Key points about DNA barcoding

• Short DNA Sequences: DNA barcoding involves the use of relatively short DNA sequences from a standard region of the genome, known as a marker.

Applications of DNA Barcoding

• Identification of Plant Leaves: DNA barcoding can be used to identify plant species even in the absence of flowers or fruit, making it useful for ecological studies and botanical research.
• Identification of Insect Larvae: It is valuable for identifying insect larvae, which can be challenging to identify based on morphology alone.
• Identification of Products in Commerce: DNA barcoding can help identify species used in various commercial products, such as food and herbal supplements, to prevent mislabeling or fraud.

Criticism of DNA Barcoding

• Lack of Reliable Information Above the Species Level: DNA barcoding is highly effective at identifying species but may not provide detailed information about relationships between species or above the species level (e.g., genera or families).
• Oversimplification of Taxonomy: Some critics argue that DNA barcoding oversimplifies the science of taxonomy by relying solely on genetic data for species identification, potentially neglecting other important aspects of species classification.