DNA and RNA

DNA and RNA

• DNA is a deoxyribonucleic acid and is a hereditary material whereas RNA is ribonucleic acid present in all living cells. The only difference between ribose and deoxyribose is that ribose has one more -OH group than deoxyribose, which has -H attached to the second (2′) carbon in the ring.
• Both DNA and RNA is important, if either one of these polymers fails or disappear then life would cease to exist. Without these elements protein will not be able to generate which is important for life to exist and to produce energy.
• DNA is a double-stranded molecule while RNA is a single-stranded molecule.
• DNA is stable under alkaline conditions while RNA is not stable.
• DNA and RNA perform different functions in humans. DNA is responsible for storing and transferring genetic information while RNA directly codes for amino acids and as acts as a messenger between DNA and ribosomes to make proteins.
• DNA and RNA base pairing is slightly different since DNA uses the bases adenine, thymine, cytosine, and guanine; RNA uses adenine, uracil, cytosine, and guanine. Uracil differs from thymine in that it lacks a methyl group on its ring.

Comparison of DNA and RNA

S.No.	DNA	RNA
1.	Deoxyribonucleic acid	Ribonucleic acid
2.	It occurs inside the nucleus of cell and some cell organelles but it plants it is present in mitochondria and plant cell.	It is found in cytoplasm of the cell but very little is found inside the nucleus.
3.	It is a double-stranded molecule consisting of a long chain of nucleotides.	It is single-strand helix having shorter chains of nucleotides.
4.	It stores and transfers genetic information to generate new cells and organisms.	It is used to transfer genetic code from nucleus to the ribosomes to make proteins and carries DNA blueprint’s guidelines.
5.	It has two nucleotide strands consisting of phosphate group, five carbon sugar (stable deoxyribose 2) and four nitrogen bases.	It is single stranded consisting of phosphate group, five carbon sugar (less stable ribose) and four nitrogen base.
6.	Nitrogen base pairs are Adenine links to Thymine (A-T) and Cytosine links to Guanine (C-G)	Here nitrogen base pairs are Adenine links to Uracil (A-U) and Cytosine links to Guanine (C-G).
7.	DNA is self replicating	It is synthesised from DNA when needed.
8.	The DNA helix geometry is in the form of B and can be damaged by exposure of ultra-violet rays.	The RNA helix geometry is in the form of A. It is more resistant to damage by ultra-violet rays.
9.	It is a long polymer chain.	It is shorter polymer.
10.	DNA produces regular helix i.e. it is a spirally twisted.	It produces secondary helix or pseudo helix as its stranded may get folded at places.
11.	It occurs in the form of chromosomes or chromatin fibres.	It occurs in ribosomes or forms association with ribosomes.
12.	Quantity of DNA is fixed for cell.	The quantity of RNA for a cell is variable.
13.	It is of two types: intra nuclear and extra nuclear.	It is of four types: m-RNA, t-RNA and r-RNA.
14.	Life of DNA is long.	Its life is short. Some RNA’s have very shorter life but some have longer but in all its life is short.
15.	After melting its renaturation is slow.	Fast

Biological Functions of Nucleic Acids – DNA and RNA

• DNA is the chemical basis of heredity and may be regarded as the reserve of genetic information.
• DNA is exclusively responsible for maintaining the identity of different species of organisms over millions of years.
• A DNA molecule is capable of self-duplication during cell division and identical DNA strands are transferred to daughter cells.
• Another important function of nucleic acids is the protein synthesis in the cell. Actually, the proteins are synthesized by various RNA molecules in the cell but the message for the synthesis of a particular protein is present in DNA.

DNA Fingerprinting

• It is known that every individual has unique fingerprints. These occur at the tips of the fingers and have been used for identification for a long time but these can be altered by surgery.
• A sequence of bases on DNA is also unique for a person and information regarding this is called DNA fingerprinting. It is the same for every cell and cannot be altered by any known treatment.
• DNA fingerprinting is now used–
  • in forensic laboratories for the identification of criminals.
  • to determine the paternity of an individual.
  • to identify the dead bodies in any accident by comparing the DNA’s of parents or children.
  • to identify racial groups to rewrite biological evolution.

Recombinant DNA

• In 1953, scientists discovered the structure of DNA, and in 1972, researchers developed a method for cutting and splicing DNA. That method became known as recombinant DNA or rDNA.
• Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory methods of genetic recombination (such as molecular cloning) to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in the genome.
• Recombinant DNA is possible because DNA molecules from all organisms share the same chemical structure. They differ only in the nucleotide sequence within that identical overall structure.
• In most cases, organisms containing recombinant DNA have apparently normal phenotypes(observable physical properties of an organism), That is, their appearance, behavior, and metabolism are usually unchanged.

The basic steps involved in Recombinant DNA Technology:

• Isolation of a DNA fragment containing a gene of interest that needs to be cloned (called as insert).
• Generation of a recombinant DNA (rDNA) molecule by insertion of the DNA fragment into a carrier DNA molecule called vector (e.g. plasmid) that can self-replicate within a host cell.
• Transfer of the rDNA into an E. coli host cell (a process called transformation).
• Selection of only those host cells carrying the rDNA and allowing them to multiply thereby multiplying the rDNA molecules.
• The whole process thus can generate either a large amount of rDNA (gene cloning) or a large amount of protein expressed by the insert.
• The first rDNA molecules to be generated using these procedures were established by the combined efforts in 1973 by the molecular biologists’ Paul Berg, Herbert Boyer, Annie Chang, and Stanley Cohen.
• The next step after a recombinant molecule has been generated is to introduce it into a suitable host.
  • There are many methods to introduce recombinant vectors and these are dependent on several factors such as the vector type and host cell.

Some commonly used procedures are:

• Transformation
• Transfection
• Electroporation
• Microinjection: In the procedure of microinjection, foreign DNA is directly injected into recipient cells using a fine microsyringe under a phase-contrast microscope to aid vision.
• Biolistics: A remarkable method that has been developed to introduce foreign DNA into mainly plant cells is by using a gene or particle gun. Microscopic particles of gold or tungsten are coated with the DNA of interest and bombarded onto cells with a device much like a particle gun. Hence the term biolistics is used.

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 is cheaper and easier when compared to insulin obtained from animal sources.
• Human growth hormone: For patients with pituitary glands generating an insufficient quantity of hormone for normal growth, this was a boon
• Blood clotting factor VIII: To help patients suffering from haemophilia.
• Herbicide and Insect-resistant crops: Commercial varieties like soya, sorghum, cotton have been developed. Such varieties integrate a recombinant gene that causes the resistance to herbicide glyph sate application
• Bacillus Thuringeinsis: is the name of the bacterium that naturally produces a protein with insecticidal properties

DNA Profiling

• DNA profiling is the process of determining an individual’s DNA characteristics.
• Modern-day DNA profiling is also called STR analysis and relies on microsatellites rather than the minisatellites used in DNA fingerprinting.
• Microsatellites, or short tandem repeats (STRs), are the shorter relatives of minisatellites usually two to five base pairs long. Like minisatellites, they are repeated many times throughout the human genome.

DNA Sequencing

• DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA.
• In this era of genomics wherein, whole genomes of species are being sequenced and compared to get a vision into the fundamental nature of DNA, the blueprint of life, the ease with which DNA is sequenced has played a major role.
• The first methods for sequencing DNA were developed in the middle 1970s by Fred Sanger, and by Walter Gilbert and Allan Maxam.
• Subsequently, Sanger developed a new method that forms the basis of most DNA sequencing today.
• Sequencing DNA means determining the order of the four chemical building blocks – called “bases” – that make up the DNA molecule.
• The sequence tells scientists the kind of genetic information that is carried in a particular DNA segment.

Benefits of DNA Sequencing:

• Forensics: To identify a particular individual because every individual has a unique sequence of DNA.
• Determine the Paternity of the child
• Medicine: Used to detect the genes which are associated with some heredity or acquired diseases. As almost all organisms have some kind of genetic material we can understand the causes of all human diseases.
• Agriculture: Specific genes of bacteria have been used to make crops resistant against insects and pests. It is also useful in the production of livestock with improved quality of meat and milk.

DNA Barcoding

• DNA barcoding is a method of species identification using a short section of DNA from a specific gene or genes.
• DNA barcoding is a system for fast and accurate species identification that makes the ecological systems more accessible by using short DNA sequences instead of whole-genome and is used for eukaryotes.
• The short DNA sequence is generated from the standard region of the genome known as a marker.
• Application
  • Identification of plant leaves even in absence of fruit
  • Identification of insect larvae
  • Identification of products in commerce
• Criticism
  • Lack of reliable information above the species level
  • Gross oversimplification of the science of taxonomy.