DNA and RNA
What are nucleic acids?
- Nucleic acid is a naturally occurring chemical compound that is capable of being broken down to yield phosphoric acid, sugars, and a mixture of organic bases (purines and pyrimidines).
- Nucleic acids are the main information-carrying molecules of the cell.
- By directing the process of protein synthesis, they determine the inherited characteristics of every living thing.
- The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA and RNA
- DNA is the master blueprint for life and constitutes the genetic material in all free-living organisms and most viruses.
- RNA is the genetic material of certain viruses, but it is also found in all living cells, where it plays an important role in certain processes such as the making of proteins.
- Although DNA and RNA both carry genetic information, there are quite a few differences between them.
Differences
| Comparison | DNA | RNA |
| Function | DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism | RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories. |
| Structure | DNA consists of two strands, arranged in a double helix. These strands are made up of subunits called nucleotides. Each nucleotide contains a phosphate, a 5-carbon sugar molecule and a nitrogenous base. | RNA only has one strand, but like DNA, is made up of nucleotides. RNA sometimes forms a secondary double helix structure, but only intermittently. |
| Length | DNA is a much longer polymer than RNA. A chromosome, for example, is a single, long DNA molecule, which would be several centimetres in length when unravelled. | RNA molecules are variable in length, but much shorter than long DNA polymers. A large RNA molecule might only be a few thousand base pairs long. |
| Sugar | The sugar in DNA is deoxyribose, which contains one less hydroxyl group than RNA’s ribose. | RNA contains ribose sugar molecules, without the hydroxyl modifications of deoxyribose. |
| Bases | The bases in DNA are Adenine (‘A’), Thymine (‘T’), Guanine (‘G’) and Cytosine (‘C’). | RNA shares Adenine (‘A’), Guanine (‘G’) and Cytosine (‘C’) with DNA, but contains Uracil (‘U’) rather than Thymine. |
| Base Pairs | Adenine and Thymine pair (A-T)
Cytosine and Guanine pair (C-G) |
Adenine and Uracil pair (A-U)
Cytosine and Guanine pair (C-G) |
| Location | DNA is found in the nucleus, with a small amount of DNA also present in mitochondria. | RNA forms in the nucleolus, and then moves to specialised regions of the cytoplasm depending on the type of RNA formed. |
| Reactivity | DNA is a more stable molecule than RNA, which is useful for a molecule which has the task of keeping genetic information safe. | RNA is more reactive than DNA and is not stable in alkaline conditions. |
| Replication | DNA is self-replicating. | RNA is synthesized from DNA. |
- In some viruses RNA, instead of DNA carries the genetic information, which include retroviruses such as HIV and RNA viruses such as Ebola virus disease, SARS, COVID-19, rabies, common cold, influenza, hepatitis C, hepatitis E, West Nile fever, polio and measles.
Unusual DNA and RNA
- While the most common form of DNA is a double helix, there is evidence for rare cases of branched DNA, quadruplex DNA, and molecules made from triple strands.
- Scientists have found DNA in which arsenic substitutes for phosphorus.
- Double-stranded RNA (dsRNA) sometimes occurs. It is similar to DNA, except thymine is replaced by uracil.
- This type of RNA is found in some viruses. When these viruses infect eukaryotic cells, the dsRNA can interfere with normal RNA function and stimulate an interferon response.
- Circular single-strand RNA (circRNA) has been found in both animals and plants. At present, the function of this type of RNA is unknown.
Why in News?
- Researchers at the Indian Institute of Technology Madras have identified a specific microRNA (miRNAs) called ‘miR-155’ that is over-expressed in tongue cancer.
- The miRNAs affect cancer growth through inhibiting or enhancing the functions of certain proteins.
What are miRNAs?
- MicroRNAs (miRNAs) are short non‐coding RNAs containing 20–24 nucleotides that participate in virtually all biological pathways in animals.
- They have been found to play important roles in many cancers, in carcinogenesis (start of cancer), malignant transformation and metastasis — the development of secondary cancer.
- The miRNAs associated with cancer are called ‘Oncomirs’.
- Many of the Oncomirs affect cancer by suppressing the performance of tumour-suppressing agents.
- Some of them can prevent the growth and spread of cancer cells and yet others prevent tumour growth itself.
References:
https://www.britannica.com/science/nucleic-acid/Deoxyribonucleic-acid-DNA
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