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RNA – Definition, Structure, Types and Functions

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  • Last Updated : 14 Jul, 2022
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RNA is a ribonucleic acid that helps in the synthesis of proteins in our body. This nucleic acid is responsible for the production of new cells in the human body. It is usually obtained from the DNA molecule. RNA resembles the same that of DNA, the only difference being that it has a single strand unlike the DNA which has two strands and it consists of only a single ribose sugar molecule in it. Hence the name Ribonucleic acid. RNA is also referred to as an enzyme as it helps in the process of chemical reactions in the body.

Central Dogma

Together, RNA, short for ribonucleic acid, and DNA, short for deoxyribonucleic acid, make up the nucleic acids, one of the three or four classes of major “macromolecules” considered crucial for life. The others are proteins and lipids. Many scientists also place carbohydrates in this group. Macromolecules are very large molecules, often consisting of repeating subunits. RNA and DNA are made up of subunits called nucleotides.  

The two nucleic acids team up to create proteins. The process of creating proteins using the genetic information in nucleic acids is so important to life that biologists call it “the central dogma” of molecular biology. The dogma, which describes the flow of genetic information in an organism, according to Oregon State University, says that DNA’s information gets written out, or “transcribed,” as RNA information, and RNA’s information gets written out, or “translated,” into protein.

RNA

 

RNA 

The ability of RNA and DNA to store and copy information depends on the molecules’ repeating nucleotide subunits. The nucleotides are organized in specific sequences, which can be read like letters in a word. Each nucleotide has three major parts: a sugar molecule, a phosphate group, and a cyclic compound called a nucleobase or base. Sugars from different nucleotide units hook up via phosphate bridges to create the repeating polymer of an RNA or DNA molecule — like a necklace made of sugar beads linked together by phosphate strings.

The nucleobases attached to the sugars constitute the sequence information needed to build proteins, as described by the National Human Genome Research Institute. RNA and DNA each have a set of four bases: adenine, guanine, cytosine, and thymine for DNA, with uracil swapping in for thymine in RNA. The four bases make up the molecules’ alphabets, and as such, are denoted as letters: A for adenine, G for guanine, and so forth. But RNA and DNA can do more than just encode “letter” sequences; they can also copy them. This works because the bases on one RNA or DNA string can stick to bases on another string,  but only in a very specific way. Bases link up only with “complementary” partners: C to G and A to U in RNA (or A to T in the case of DNA). So, DNA serves as a template to transcribe an RNA molecule, which mirrors the DNA sequence — encoding a record of it.

A type of RNA called messenger RNA (mRNA) uses this copying function to ferry genetic data from DNA to the ribosomes, the protein-producing components of the cell, according to the University of Massachusetts. Ribosomes “read” mRNA sequences to determine the order in which protein subunits (amino acids) should join a growing protein molecule. Two other RNA species complete the process: Transfer RNA (tRNA) brings amino acids specified by mRNA to the ribosomes, while ribosomal RNA (rRNA), which makes up the bulk of a ribosome, links the amino acids together.

History of RNA

Nucleic acids were discovered in 1868 by Friedrich Miescher, who called the material ‘nuclein’ since it was found in the nucleus. It was later discovered that prokaryotic cells, which do not have a nucleus, also contain nucleic acids. The role of RNA in protein synthesis was suspected already in 1939

RNA as Enzyme

Scientists consider RNA’s central dogma activities central to the molecule’s definition. But ideas about what RNA is and what it can do have greatly expanded since the 1980s when biologists Sidney Altman and Thomas R. Cech discovered that RNA can operate like a protein. (The researchers won the 1989 Nobel Prize in Chemistry for their discovery.)

Proteins are key components for most chemical reactions in the body, serving as enzymes, thanks in part to the stunning variety of shapes, or conformations, these molecules can achieve. (Enzymes are proteins that facilitate and catalyze chemical reactions.) Unlike DNA, RNA can also shape-shift to an extent, and so can serve as an RNA-based enzyme, or ribozyme. RNA’s greater flexibility over DNA comes in part from the extra oxygen on RNA’s ribose sugar, which makes the molecule less stable, biologist Merlin Crossley wrote in The Conversation. The “deoxy” in deoxyribose reference DNA’s 1-oxygen deficit.

According to some researchers, the most important RNA-based catalytic activity happens in the ribosome, where rRNA, a ribozyme, mediates amino acid addition to growing proteins. Other ribozymes include small nuclear RNAs (snRNAs), which splice mRNA into usable forms, and M1 RNA, one of the first known ribozymes, which similarly clips bacterial tRNA. 

RNA Regulator 

The ability of RNA and DNA to store and copy information depends on the molecules’ repeating nucleotide subunits. The nucleotides are organized in specific sequences, which can be read like letters in a word.

Each nucleotide has three major parts: a sugar molecule, a phosphate group, and a cyclic compound called a nucleobase or base. Sugars from different nucleotide units hook up via phosphate bridges to create the repeating polymer of an RNA or DNA molecule — like a necklace made of sugar beads linked together by phosphate strings.

The nucleobases attached to the sugars constitute the sequence information needed to build proteins, as described by the National Human Genome Research Institute. RNA and DNA each have a set of four bases: adenine, guanine, cytosine, and thymine for DNA, with uracil swapping in for thymine in RNA. The four bases make up the molecules, and as such, are denoted as letters: A for adenine, G for guanine, and so forth.

But RNA and DNA can do more than just encode “letter” sequences; they can also copy them. This works because the bases on one RNA or DNA string can stick to bases on another string,  but only in a very specific way. Bases link up only with “complementary” partners: C to G and A to U in RNA (or A to T in the case of DNA). So, DNA serves as a template to transcribe an RNA molecule, which mirrors the DNA sequence — encoding a record of it.

A type of RNA called messenger RNA (mRNA) uses this copying function to ferry genetic data from DNA to the ribosomes, the protein-producing components of the cell, according to the University of Massachusetts. Ribosomes “read” mRNA sequences to determine the order in which protein subunits (amino acids) should join a growing protein molecule. Two other RNA species complete the process: Transfer RNA (tRNA) brings amino acids specified by mRNA to the ribosomes, while ribosomal RNA (rRNA), which makes up the bulk of a ribosome, links the amino acids together.

RNA as an Enzyme 

Scientists consider RNA’s central dogma activities central to the molecule’s definition. But ideas about what RNA is and what it can do have greatly expanded since the 1980s when biologists Sidney Altman and Thomas R. Cech discovered that RNA can operate like a protein. (The researchers won the 1989 Nobel Prize in Chemistry for their discovery.)

Proteins are key components for most chemical reactions in the body, serving as enzymes, in part to the stunning variety of shapes, or conformations, these molecules can achieve. (Enzymes are proteins that facilitate and catalyze chemical reactions.) Unlike DNA, RNA can also shape-shift to an extent, and so can serve as an RNA-based enzyme, or ribozyme. RNA’s greater flexibility over DNA comes in part from the extra oxygen on RNA’s ribose sugar, which makes the molecule less stable, biologist Merlin Crossley wrote in The Conversation. The “deoxy” in deoxyribose reference DNA’s 1-oxygen deficit.

According to some researchers, the most important RNA-based catalytic activity happens in the ribosome, where rRNA, a ribozyme, mediates amino acid addition to growing proteins. Other ribozymes include small nuclear RNAs (snRNAs), which splice mRNA into usable forms, and M1 RNA, one of the first known ribozymes, which similarly clips bacterial tRNA.

Structure of RNA 

Ribonucleic acid has all the components same as that of the DNA with only 2 main differences within it. RNA has the same nitrogen bases called adenine, Guanine, and Cytosine as that of the DNA except for the Thymine which is replaced by the uracil. Adenine and uracil are considered the major building blocks of RNA and both of them form base-pair with the help of 2 hydrogen bonds.

RNA resembles a hairpin structure and like the nucleotides in DNA, nucleotides are formed in this ribonucleic material(RNA). Nucleosides are nothing but phosphate groups which sometimes also help in the production of nucleotides in the DNA

Functions of RNA 

The ribonucleic acid – RNA, which is mainly composed of nucleic acids, is involved in a variety of functions within the cell and is found in all living organisms including bacteria, viruses, plants, and animals. These nucleic acid functions as structural molecule in cell organelles and are also involved in the catalysis of biochemical reactions. The different types of RNA are involved in a various cellular processes. The primary functions of RNA:

  • Facilitate the translation of DNA into proteins
  • Functions as an adapter molecule in  protein synthesis
  • Serves as a messenger between the DNA and the ribosomes.
  • They are the carrier of genetic information in all living cells
  • Promotes the ribosomes to choose the right amino acid which is required in building up new proteins in the body.

Types of RNA

There are various types of RNA, among which the most well-known and most commonly studied in the human body are 

tRNA – Transfer RNA

The transfer RNA is held responsible for choosing the correct protein or the amino acids required by the body in turn helping the ribosomes. It is located at the endpoints of each amino acid. This is also called soluble RNA and it forms a link between the messenger RNA and the amino acid.

rRNA-Ribosomal RNA

The rRNA is the component of the ribosome and is located within the cytoplasm of a cell, where ribosomes are found. In all living cells, the ribosomal RNA plays a fundamental role in the synthesis and translation of mRNA into proteins. The rRNA is mainly composed of cellular RNA and is the most predominant RNA within the cells of all living beings.

mRNA – Messenger RNA.

This type of RNA functions by transferring the genetic material into the ribosomes and passing the instructions about the type of proteins, required by the body cells. Based on the functions, these types of RNA are called messenger RNA. Therefore, the mRNA plays a vital role in the process of transcription or during the protein synthesis process.

RNA Genome

Like DNA, RNA can carry genetic information. RNA viruses have genomes composed of RNA that encodes a number of proteins. The viral genome is replicated by some of those proteins, while other proteins protect the genome as the virus particle moves to a new host cell. Viroids are another group of pathogens, but they consist only of RNA, do not encode any protein, and are replicated by a host plant cell’s polymerase.

Double-Stranded RNA

Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells, but with the replacement of thymine by uracil and the addition of one oxygen atom. dsRNA forms the genetic material of some viruses (double-stranded RNA viruses). Double-stranded RNA, such as viral RNA or siRNA, can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates. In Eukaryotes, Double-stranded RNA (dsRNA) plays a role in the activation of the innate immune system against viral infections.

Conceptual Questions 

Question 1: A nicked RNA molecule can be ligated by

Answer:

T4 DNA ligase

Question 2: The tertiary structure of yeast tRNA

Answer:

Involves extensive base stacking interactions, resembles the 3-dimensional structure of other tRNAs is maintained mostly by non-Watson-Crick base pairing

Question 3: Which of the following RNA characteristically contains unusual purines and pyrimidines?

Answer:

 tRNA

Question 4: The anticodon is a structure on?

Answer:

tRNA. The anticodon is present in one of the loops of t RNA, which is necessary for the translation process.

Question 5: During RNA synthesis, the DNA template sequence 5’Tp Ap Gp Cp 3′ Would be transcribed to produce which of the following RNA?

Answer:

 5′-Gp Cp Up Ap-3′

Question 6: Two features of the tRNA molecule associated, with converting the triplet codon to an amino acid, are

Answer: 

In the anticodon loop and the 3′ CCA end, which is post-translational modifications.


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