RNA (Ribonucleic Acid): Definition, Function, Structure

Genetic material packed within the nucleus of the cell carries the blueprint of living organisms. Genes direct the cell when and how to synthesize proteins to make skin cells, organs, gametes and everything else in the body.

Ribonucleic acid (RNA) is one of two forms of genetic information in the cell. RNA works together with deoxyribonucleic acid (DNA) to help express genes, but RNA has a distinct structure and set of functions within the cell.

Central Dogma of Molecular Biology

Nobel Prize winner Francis Crick is largely credited with discovering the central dogma of molecular biology. Crick deduced that DNA is used as the template for the transcription of RNA, which is then transported to ribosomes and translated to make the correct protein.

Heredity plays an important role in the fate of an organism. Thousands of genes control cell and organism function.

Structure of RNA

An RNA macromolecule is a type of nucleic acid. It's a single strand of genetic information made up of nucleotides. Nucleotides consist of a ribose sugar, phosphate group and a nitrogenous base. Adenine (A), uracil (U), cytosine (C) and guanine (G) are the four types (A, U, C and G) of bases found in RNA.

RNA and DNA are both key players in transmitting genetic information. However, there are also notable, and important, differences between the two.

RNA structures are distinct from DNA in terms of nucleic acid makeup and structure:

  • DNA has A, T, C and G base pairings; the T stands for thymine, which uracil replaces in RNA.
  • RNA molecules are single-stranded, unlike the double helix of DNA molecules.
  • RNA has ribose sugar; DNA has deoxyribose.

Types of RNA

Scientists still have much to learn about DNA and the types of RNA. Understand precisely how these molecules work deepens understanding of genetic diseases and possible treatments.

Three major types that students need to know include: mRNA, or messenger RNA; tRNA, or transfer RNA; and rRNA, or ribosomal RNA.

Role of Messenger RNA (mRNA)

Messenger RNA is made from a DNA template through a process called transcription that happens in the nucleus in eukaryotic cells. mRNA is the complementary “blueprint” of a gene that will carry the DNA’s encoded instructions to ribosomes in the cytoplasm. Complementary mRNA is transcribed from a gene and then processed so it can serve as the template for a polypeptide during ribosomal translation.

The role of mRNA is very important because mRNA affects gene expression. mRNA provides the template needed to create new proteins. Conveyed messages regulate gene functioning and determine whether that gene will be more or less active. After passing along the information, the work of mRNA is done and it degrades.

Role of Transfer RNA (tRNA)

Cells typically contain many ribosomes, which are organelles in the cytoplasm that synthesize protein when directed to do so. When mRNA comes upon a ribosome, encoded messages from the nucleus must first be deciphered. Transfer RNA (tRNA) is responsible for "reading" the mRNA transcript.

The role of tRNA is to translate mRNA by reading the codons in the strand (codons are three-base codes that each correspond to an amino acid). A codon of three nitrogenous bases determines which specific amino acid to make.

Transfer RNA brings the right amino acid to the ribosome according to each codon so the amino acid can be added to the growing protein strand.

Role of Ribosomal RNA (rRNA)

Chains of amino-acids are linked together in the ribosome to build proteins in accordance with instructions conveyed via mRNA. Many different proteins are present in ribosomes, including ribosomal RNA (rRNA) that makes up part of the ribosome.

Ribosomal RNA is crucial for ribosomal function and protein synthesis and is why the ribosome is referred to as the protein factory of the cell.

In many respects, rRNA serves as a “link” between mRNA and tRNA. Additionally, rRNA helps read the mRNA. rRNA recruits tRNA to bring over the proper amino acids to the ribosome.

Role of microRNA (miRNA)

microRNA (miRNA) consists of very short RNA molecules that were more recently discovered. These molecules help control gene expression because they can tag mRNA for degradation or prevent translation into new proteins.

That means miRNA has the ability to down-regulate or silence genes. Researchers of molecular biology consider miRNA important for treating genetic disorders like cancer, where gene expression can either drive or prevent disease development.


About the Author

Dr. Mary Dowd studied biology in college where she worked as a lab assistant and tutored grateful students who didn't share her love of science. Her work history includes working as a naturalist in Minnesota and Wisconsin and presenting interactive science programs to groups of all ages. She enjoys writing online articles sharing information about science and education. Currently, Dr. Dowd is a dean of students at a mid-sized university.