structure and function of rna pdf

Structure And Function Of Rna Pdf

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However, whereas DNA molecules are typically long and double stranded, RNA molecules are much shorter and are typically single stranded.

Gray, Michael W. Beyer, Ann L.

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RNA, in one form or another, touches nearly everything in a cell. RNA carries out a broad range of functions, from translating genetic information into the molecular machines and structures of the cell to regulating the activity of genes during development, cellular differentiation, and changing environments.

RNA is a unique polymer. It can also bind specific proteins or small molecules, and, remarkably, RNA can catalyze chemical reactions, including joining amino acids to make proteins. Genes that are copied—"transcribed"—into the instructions for making individual proteins are often referred to as "coding genes. Several key classes of RNA molecules help convert the information contained in the cell's DNA into functional gene products like proteins.

Messenger RNAs mRNAs are copies of individual protein-coding genes, and serve as an amplified read-out of each gene's nucleic acid sequence. Ribosomal RNA rRNA constitutes the core structural and enzymatic framework of the ribosome, the machine that synthesizes proteins according to the instructions contained in the sequence of an mRNA.

Transfer RNAs tRNAs use complementary base pairing to decode the three-letter "words" in the mRNA, each corresponding to an amino acid to be sequentially incorporated into a growing protein chain. Most RNA molecules, once transcribed from the chromosomal DNA, require structural or chemical modifications before they can function.

Spliceosomal RNAs help discard intervening sequences introns from pre-mRNA transcripts and splice together the mRNA segments exons to create what can be a complex assortment of distinct protein-coding mRNAs from a single gene. Many noncoding RNAs also require post-transcriptional modifications. For instance, ribosomal RNAs receive numerous chemical modifications that are required for proper ribosome assembly and function.

Regulation of the production of proteins from coding genes is the basis for much of cellular and organismal structure, differentiation, and physiology. Diverse classes of noncoding RNAs participate in gene regulation at many levels, affecting the production, stability, or translation of specific mRNA gene products. In prokaryotes for example, bacteria , small antisense RNAs exert a variety of gene regulatory activities by base pairing specifically to their target mRNAs.

Also common in prokaryotes are riboswitches, noncoding RNA sequences that usually function as regulatory domains contained within longer mRNAs. Riboswitches regulate the activity of their host mRNAs by binding to small molecules such as nucleotides or amino acids, sensing the abundance of those small molecules and regulating the genes that make or use them accordingly.

For example, microRNAs miRNAs are regulatory RNAs approximately 22 nt long that are produced from longer transcripts that contain a certain kind of double-stranded "hairpin" structure. There are hundreds of miRNA genes in plants and animals, and each miRNA can regulate the activity of hundreds of protein-coding genes.

Therefore, miRNAs individually and collectively have a profound impact on the development and physiology of multicellular eukaryotes. Unlike miRNAs, which are produced from specific genetic loci that have evolved to regulate mRNAs, siRNAs can derive from essentially any transcribed region of the genome. A major role for certain classes of small noncoding RNAs is defense of the cell against viruses, transposons, and other nucleic acid sequences that pose a potential threat to cellular homeostasis or genome stability.

The response of some cells against viral infection includes the production of siRNAs complementary to the virus.

Many endogenous siRNAs in eukaryotic cells specify the silencing of transposons and repeat sequences that are already resident in the genome. Another class of regulatory RNA consists of diverse kinds of longer noncoding transcripts that generally function to regulate the expression of distant genetic loci, often by suppressing or promoting their transcription. For example, the rox RNAs of the fruit fly seems to facilitate the remodeling of chromosome structure to allow the male X chromosome to be transcribed at twice the rate as a single X chromosome in females, which have two X's.

Similarly, the Xist RNA in mammals helps inactivate one of the two X chromosomes in females, allowing males and females to have equivalent levels of gene expression from the X chromosome. RNA molecules regulate gene expression Regulation of the production of proteins from coding genes is the basis for much of cellular and organismal structure, differentiation, and physiology.

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However, whereas DNA molecules are typically long and double stranded, RNA molecules are much shorter and are typically single stranded. RNA molecules perform a variety of roles in the cell but are mainly involved in the process of protein synthesis translation and its regulation. RNA is typically single stranded and is made of ribonucleotides that are linked by phosphodiester bonds. A ribonucleotide in the RNA chain contains ribose the pentose sugar , one of the four nitrogenous bases A, U, G, and C , and a phosphate group. The subtle structural difference between the sugars gives DNA added stability, making DNA more suitable for storage of genetic information, whereas the relative instability of RNA makes it more suitable for its more short-term functions. The RNA-specific pyrimidine uracil forms a complementary base pair with adenine and is used instead of the thymine used in DNA. Even though RNA is single stranded, most types of RNA molecules show extensive intramolecular base pairing between complementary sequences within the RNA strand, creating a predictable three-dimensional structure essential for their function Figure

Ribonucleic acid RNA is a polymeric molecule essential in various biological roles in coding , decoding , regulation and expression of genes. Along with lipids , proteins , and carbohydrates , nucleic acids constitute one of the four major macromolecules essential for all known forms of life. Cellular organisms use messenger RNA mRNA to convey genetic information using the nitrogenous bases of guanine , uracil , adenine , and cytosine , denoted by the letters G, U, A, and C that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome. Some RNA molecules play an active role within cells by catalyzing biological reactions, controlling gene expression , or sensing and communicating responses to cellular signals. One of these active processes is protein synthesis , a universal function in which RNA molecules direct the synthesis of proteins on ribosomes.

RNA , abbreviation of ribonucleic acid , complex compound of high molecular weight that functions in cellular protein synthesis and replaces DNA deoxyribonucleic acid as a carrier of genetic codes in some viruses. RNA consists of ribose nucleotides nitrogenous bases appended to a ribose sugar attached by phosphodiester bonds, forming strands of varying lengths. The ribose sugar of RNA is a cyclical structure consisting of five carbons and one oxygen. The structure of the RNA molecule was described by R. Holley in


RNA is central to the synthesis of proteins. Here, a type of RNA called messenger RNA carries information from DNA to structures called ribosomes. These.


Role of RNA in Biology

RNA, in one form or another, touches nearly everything in a cell. RNA carries out a broad range of functions, from translating genetic information into the molecular machines and structures of the cell to regulating the activity of genes during development, cellular differentiation, and changing environments. RNA is a unique polymer. It can also bind specific proteins or small molecules, and, remarkably, RNA can catalyze chemical reactions, including joining amino acids to make proteins. Genes that are copied—"transcribed"—into the instructions for making individual proteins are often referred to as "coding genes.

Different types of RNAs and their functions

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