File Name: structure and functions of dna and rna .zip
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- The Expanding World of DNA and RNA
- Understanding biochemistry: structure and function of nucleic acids
- DNA structure and function
The Expanding World of DNA and RNA
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. Analysis of these RNAs has revealed that they are highly structured.
Unlike DNA, their structures do not consist of long double helices, but rather collections of short helices packed together into structures akin to proteins.
In this fashion, RNAs can achieve chemical catalysis like enzymes. Each nucleotide in RNA contains a ribose sugar, with carbons numbered 1' through 5'. A base is attached to the 1' position, in general, adenine A , cytosine C , guanine G , or uracil U. Adenine and guanine are purines , cytosine and uracil are pyrimidines.
A phosphate group is attached to the 3' position of one ribose and the 5' position of the next. The phosphate groups have a negative charge each, making RNA a charged molecule polyanion. The bases form hydrogen bonds between cytosine and guanine, between adenine and uracil and between guanine and uracil. An important structural component of RNA that distinguishes it from DNA is the presence of a hydroxyl group at the 2' position of the ribose sugar.
The presence of this functional group causes the helix to mostly take the A-form geometry ,  although in single strand dinucleotide contexts, RNA can rarely also adopt the B-form most commonly observed in DNA.
RNA is transcribed with only four bases adenine, cytosine, guanine and uracil ,  but these bases and attached sugars can be modified in numerous ways as the RNAs mature. Inosine plays a key role in the wobble hypothesis of the genetic code. There are more than other naturally occurring modified nucleosides. However, it is notable that, in ribosomal RNA, many of the post-transcriptional modifications occur in highly functional regions, such as the peptidyl transferase center and the subunit interface, implying that they are important for normal function.
The functional form of single-stranded RNA molecules, just like proteins, frequently requires a specific tertiary structure. The scaffold for this structure is provided by secondary structural elements that are hydrogen bonds within the molecule.
This leads to several recognizable "domains" of secondary structure like hairpin loops , bulges, and internal loops. All chirality centers are located in the D -ribose.
Like other structured biopolymers such as proteins, one can define topology of a folded RNA molecule. This is often done based on arrangement of intra-chain contacts within a folded RNA, termed as circuit topology. Initiation of transcription begins with the binding of the enzyme to a promoter sequence in the DNA usually found "upstream" of a gene. The DNA double helix is unwound by the helicase activity of the enzyme.
Primary transcript RNAs are often modified by enzymes after transcription. For example, a poly A tail and a 5' cap are added to eukaryotic pre-mRNA and introns are removed by the spliceosome. For instance, a number of RNA viruses such as poliovirus use this type of enzyme to replicate their genetic material.
The coding sequence of the mRNA determines the amino acid sequence in the protein that is produced. Certain RNAs are able to catalyse chemical reactions such as cutting and ligating other RNA molecules,  and the catalysis of peptide bond formation in the ribosome ;  these are known as ribozymes.
Small RNAs mainly include 5. Messenger RNA mRNA carries information about a protein sequence to the ribosomes , the protein synthesis factories in the cell. It is coded so that every three nucleotides a codon corresponds to one amino acid.
This removes its introns —non-coding sections of the pre-mRNA. The mRNA is then exported from the nucleus to the cytoplasm, where it is bound to ribosomes and translated into its corresponding protein form with the help of tRNA. In prokaryotic cells, which do not have nucleus and cytoplasm compartments, mRNA can bind to ribosomes while it is being transcribed from DNA. After a certain amount of time, the message degrades into its component nucleotides with the assistance of ribonucleases.
Transfer RNA tRNA is a small RNA chain of about 80 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.
Three of the rRNA molecules are synthesized in the nucleolus , and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time.
It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling. The earliest known regulators of gene expression were proteins known as repressors and activators — regulators with specific short binding sites within enhancer regions near the genes to be regulated. There are several kinds of RNA-dependent processes in eukaryotes regulating the expression of genes at various points, such as RNAi repressing genes post-transcriptionally , long non-coding RNAs shutting down blocks of chromatin epigenetically , and enhancer RNAs inducing increased gene expression.
Once the base pairing occurs, other proteins direct the mRNA to be destroyed by nucleases. Next to be linked to regulation were Xist and other long noncoding RNAs associated with X chromosome inactivation.
Their roles, at first mysterious, were shown by Jeannie T. Lee and others to be the silencing of blocks of chromatin via recruitment of Polycomb complex so that messenger RNA could not be transcribed from them. In any case, they are transcribed from enhancers , which are known regulatory sites in the DNA near genes they regulate. At first, regulatory RNA was thought to be a eukaryotic phenomenon, a part of the explanation for why so much more transcription in higher organisms was seen than had been predicted.
They are cis-acting regulatory RNA sequences acting allosterically. They change shape when they bind metabolites so that they gain or lose the ability to bind chromatin to regulate expression of genes. Archaea also have systems of regulatory RNA. Introns are spliced out of pre-mRNA by spliceosomes , which contain several small nuclear RNAs snRNA ,  or the introns can be ribozymes that are spliced by themselves.
These enzymes then perform the nucleotide modification. 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. Retrotransposons also spread by copying DNA and RNA from one another,  and telomerase contains an RNA that is used as template for building the ends of eukaryotic chromosomes. In the late s, it was shown that there is a single stranded covalently closed, i.
So far the function of circRNAs is largely unknown, although for few examples a microRNA sponging activity has been demonstrated. Nucleic acids were discovered in by Friedrich Miescher , who called the material 'nuclein' since it was found in the nucleus. The role of RNA in protein synthesis was suspected already in In the early s, retroviruses and reverse transcriptase were discovered, showing for the first time that enzymes could copy RNA into DNA the opposite of the usual route for transmission of genetic information.
In , Walter Fiers and his team determined the first complete nucleotide sequence of an RNA virus genome, that of bacteriophage MS2.
In , introns and RNA splicing were discovered in both mammalian viruses and in cellular genes, resulting in a Nobel to Philip Sharp and Richard Roberts. In , it was found in Petunia that introduced genes can silence similar genes of the plant's own, now known to be a result of RNA interference. In , Carl Woese hypothesized that RNA might be catalytic and suggested that the earliest forms of life self-replicating molecules could have relied on RNA both to carry genetic information and to catalyze biochemical reactions—an RNA world.
In March , complex DNA and RNA nucleotides , including uracil , cytosine and thymine , were reportedly formed in the laboratory under outer space conditions, using starter chemicals, such as pyrimidine , an organic compound commonly found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons PAHs , is one of the most carbon-rich compounds found in the Universe and may have been formed in red giants or in interstellar dust and gas clouds.
From Wikipedia, the free encyclopedia. Family of large biological molecules. This article is about the biological macromolecule. For other uses, see RNA disambiguation. Genome Heredity Mutation. Nucleotide Variation. Outline Index. Introduction History. The chemical structure of RNA is very similar to that of DNA , but differs in three primary ways: Unlike double-stranded DNA, RNA is a single-stranded molecule  in many of its biological roles and consists of much shorter chains of nucleotides.
The hydroxyl groups in the ribose backbone make RNA more chemically labile than DNA by lowering the activation energy of hydrolysis. The complementary base to adenine in DNA is thymine , whereas in RNA, it is uracil , which is an unmethylated form of thymine. Main article: Nucleic acid structure. See also: List of RNAs. See also: RNA interference.
See also: Enhancer RNA. Main article: Circular RNA. Further information: History of RNA biology. Biology portal. University of Utah.
University of California, Los Angeles. Archived from the original PDF on Retrieved Analysis of Chromosomes.
Understanding biochemistry: structure and function of nucleic acids
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. Analysis of these RNAs has revealed that they are highly structured.
DNA and RNA are remarkable because they can both encode information and possess desired properties, including the ability to bind specific targets or catalyze specific reactions. Nucleotide modifications that do not interfere with enzymatic synthesis are now being used to bestow DNA or RNA with properties that further increase their utility, including phosphate and sugar modifications that increase nuclease resistance, nucleobase modifications that increase the range of activities possible, and even whole nucleobase replacement that results in selective pairing and the creation of unnatural base pairs that increase the information content. These modifications are increasingly being applied both in vitro and in vivo , including in efforts to create semi-synthetic organisms with altered or expanded genetic alphabets. The template-directed enzymatic synthesis of DNA and RNA makes them unique among all materials and allows them to mediate the heritable storage and retrieval of biological information. The in vitro reconstitution of these processes has revolutionized biotechnology, enabling applications ranging from sequencing and cloning to a myriad of emerging techniques based on the genome-wide analysis of DNA and RNA. When combined with the range of structures available to single-stranded DNA and RNA, which allows them to recognize specific targets aptamers and even catalyze reactions, these processes allow for the laboratory evolution of functional oligonucleotides or SELEX: systematic evolution of ligands by exponential enrichment for applications ranging from affinity reagents and diagnostics to therapeutics.
Structure of DNA. •nucleotides. -monomer of nucleic acids. -made up of: •a five-carbon sugar called deoxyribose. •a phosphate group. •a nitrogenous base.
DNA structure and function
Nucleic acids, deoxyribonucleic acid DNA and ribonucleic acid RNA , carry genetic information which is read in cells to make the RNA and proteins by which living things function. The well-known structure of the DNA double helix allows this information to be copied and passed on to the next generation. In this article we summarise the structure and function of nucleic acids. The article includes a historical perspective and summarises some of the early work which led to our understanding of this important molecule and how it functions; many of these pioneering scientists were awarded Nobel Prizes for their work.
Deoxyribonucleic acid, or DNA, is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children. DNA is made up of molecules called nucleotides.
This is a comparison of the differences between DNA versus RNA, including a quick summary and a detailed table of the differences. This table summarizes the key points:. Also, RNA is found in prokaryotes , which are believed to precede eukaryotes.
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.
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