DNA and RNA structure

NUCLEIC ACID

Nucleics acid are biopolymer or large biomolecules, essential to all form of life. Nucleic acids are composed of monomer, which are nucleotides made of 3 components :

·         5-carbon sugar

·         A Phosphate group

·         A nitrogenous base

Nucleic acids are the most important of all biomolecules. They are found in all living things where its function to create and encode and then store information in the nucleus of every living cell in Earth. They function to transmit and express that information inside and outside the cell nucleus to the interior operations of the cell. The encoded information is contained and conveyed via the nucleic acid sequence which is provides the ladder-step ordering of nucleotides within the molecules of RNA and DNA.

Nucleic acid structure is often divided into 4 level : primary, secondary, tertiary and quaternary. There are 2 types of nucleic acids, namely as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Generally, nucleic acids serve as repositories and transmitters of genetic information.

FUNCTION OF NUCLEIC ACID

DNA is the chemical basis of heredity and may be regarded as the reserve bank of genetic information. DNA is responsible for maintaining the identity of different species of organisms over million years. Furthermore, DNA is controlling every aspect of cellular functions. The DNA is organized into genes the fundamental units of genetic information.

DNA          →          RNA         →       PROTEIN

Besides being the building blocks in the nucleic acid (RNA and DNA) structure, their role is as structural components of some coenzymes of B-complex vitamins in the energy reaction of cells and in the control of metabolic reactions.

COMPONENTS OF NUCLEIC ACIDS

Nucleic acids are polymer of nucleotides held by 3’ and 5’ phospate bridges. Nucleic acids are build up by the monomer unit of nucleotides.

Nucleotides are composed of : a nitrogeneous base

                                                :  a pentose sugar

                                                : a phosphate group

The term nucleoside refers to base + sugar, thus the nucleotides is nucleoside + phosphate.. The nitrogenous bases found in nucleotides are aromatic heterocyclic compounds. There are 2 types of bases which is Purines and Pyrimidines. Purines are numbered in anticlockwise direction while pyrimidine are numbered in clockwise direction (internationally accepted system).

·         DNA and RNA contain the same purines namely adenine (A) and guanine (G).

·         Pyrimidine cytosine (C) is found in both DNA and RNA

·         DNA and RNA differ with respect to the second pyrimidine base, DNA contains thymine (T) while RNA contains uracil (U).

A pentose sugar (5-carbon sugar) are found in the nucleic acid structure. DNA contain deoxyribose while RNA contain ribose. Deoxyribose and ribose are differ in structure at C2. Deoxyribose has one less oxygen at C2 compared to ribose.

The addition of a pentose sugar to base produces a nucleosides. If the sugar is deoxyribose, deoxyribo-nucleosides are produced. Adenosine, guanosine, cytidine and thymine are the deoxyribo-nucleosides of  A, G, C, T respectively. If the sugar is ribose, ribonucleosides are formed. Adenosine, guanosine, cytidine and uridine are the  ribonucleosides of  A, G, C, U respectively.

WHAT IS DNA?

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

      

DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.

      

Stands For	DeoxyriboNucleicAcid.	RiboNucleicAcid.
Definition	A nucleic acid that contains the genetic instructions used in the development and functioning of all modern living organisms. DNA's genes are expressed, or manifested, through the proteins that its nucleotides produce with the help of RNA.	The information found in DNA determines which traits are to be created, activated, or deactivated, while the various forms of RNA do the work.
Function	The blueprint of biological guidelines that a living organism must follow to exist and remain functional. Medium of long-term, stable storage and transmission of genetic information.	Helps carry out DNA's blueprint guidelines. Transfers genetic code needed for the creation of proteins from the nucleus to the ribosome.
Structure	Double-stranded. It has two nucleotide strands which consist of its phosphate group, five-carbon sugar (the stable 2-deoxyribose), and four nitrogen-containing nucleobases: adenine, thymine, cytosine, and guanine.	Single-stranded. Like DNA, RNA is composed of its phosphate group, five-carbon sugar (the less stable ribose), and 4 nitrogen-containing nucleobases: adenine, uracil (not thymine), guanine, and cytosine.
Base Pairing	Adenine links to thymine (A-T) and cytosine links to guanine (C-G).	Adenine links to uracil (A-U) and cytosine links to guanine (C-G).
Location	DNA is found in the nucleus of a cell and in mitochondria.	Depending on the type of RNA, this molecule is found in a cell's nucleus, its cytoplasm, and its ribosome.
Stability	Deoxyribose sugar in DNA is less reactive because of C-H bonds. Stable in alkaline conditions. DNA has smaller grooves, which makes it harder for enzymes to "attack."	Ribose sugar is more reactive because of C-OH (hydroxyl) bonds. Not stable in alkaline conditions. RNA has larger grooves, which makes it easier to be "attacked" by enzymes.
Propagation	DNA is self-replicating.	RNA is synthesized from DNA when needed.
Unique Features	The helix geometry of DNA is of B-Form. DNA is protected in the nucleus, as it is tightly packed. DNA can be damaged by exposure to ultra-violet rays.	The helix geometry of RNA is of A-Form. RNA strands are continually made, broken down and reused. RNA is more resistant to damage by Ultra-violet rays.

DIFFERENCE STRUCTURE OF DNA & RNA

WHAT IS RNA?

Ribonucleic acid or RNA is one of the three major biological macromolecules that are essential for all known forms of life (along with DNA and proteins). A central tenet of molecular biology states that the flow of genetic information in a cell is from DNA through RNA to proteins: “DNA makes RNA makes protein”. Proteins are the workhorses of the cell; they play leading roles in the cell as enzymes, as structural components, and in cell signalling, to name just a few. DNA (deoxyribonucleic acid) is considered the “blueprint” of the cell; it carries all of the genetic information required for the cell to grow, to take in nutrients, and to propagate. RNA–in this role–is the “DNA photocopy” of the cell. When the cell needs to produce a certain protein, it activates the protein’s gene–the portion of DNA that codes for that protein–and produces multiple copies of that piece of DNA in the form of messenger RNA, or mRNA. The multiple copies of mRNA are then used to translate the genetic code into protein through the action of the cell’s protein manufacturing machinery, the ribosome. Thus, RNA expands the quantity of a given protein that can be made at one time from one given gene, and it provides an important control point for regulating when and how much protein gets made.

For many years RNA was believed to have only three major roles in the cell–as a DNA photocopy (mRNA), as a coupler between the genetic code and the protein building blocks (tRNA), and as a structural component of ribosome (rRNA). In recent years, however, we have begun to realize that the roles adopted by RNA are much broader and much more interesting. We now know that RNA can also act as enzymes (called ribozymes) to speed chemical reactions. In a number of clinically important viruses RNA, rather than DNA, carries the viral genetic information. RNA also plays an important role in regulating cellular processes–from cell division, differentiation and growth to cell aging and death. Defects in certain RNAs or the regulation of RNAs have been implicated in a number of important human diseases, including heart disease, some cancers, stroke and many others.

CLASSIFICATION OF RNA

RNA TYPE	SIZE	FUNCTION
tRNA	Small	Transport amino acids to site of protein synthesis
rRNA	Variable in size	Combine with protein to form ribosomes, the site of protein synthesis
mRNA	Variable	Directs amino acid sequence of proteins

TRNA

·         Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein. tRNAs function at specific sites in the ribosome during translation, which is a process that synthesizes a protein from an mRNA molecule. Proteins are built from smaller units called amino acids, which are specified by three-nucleotide mRNA sequences called codons. Each codon represents a particular amino acid, and each codon is recognized by a specific tRNA. The tRNA molecule has a distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which can recognize and decode an mRNA codon. Each tRNA has its corresponding amino acid attached to its end. When a tRNA recognizes and binds to its corresponding codon in the ribosome, the tRNA transfers the appropriate amino acid to the end of the growing amino acid chain. Then the tRNAs and ribosome continue to decode the mRNA molecule until the entire sequence is translated into a protein.

RRNA

·         Ribosomal RNA (rRNA), molecule in cells that forms part of the protein-synthesizing organelle known as a ribosome and that is exported to the cytoplasm to help translate the information in messenger RNA (mRNA) into protein. Molecules of rRNA are synthesized in a specialized region of the cell nucleus called the nucleolus, which appears as a dense area within the nucleus and contains the genes that encode rRNA. The encoded rRNAs differ in size, being distinguished as either large or small. Each ribosome contains at least one large rRNA and at least one small rRNA. In the nucleolus, the large and small rRNAs combine with ribosomal proteins to form the large and small subunits of the . Ribosomal proteins are synthesized in the cytoplasm and transported to the nucleus for subassembly in the nucleolus. The subunits are then returned to the cytoplasm for final assembly.

MRNA

·         Because information in DNA cannot be decoded directly into proteins, it is first transcribed or copied into mRNA. Each molecule of mRNA encodes the information for one protein (more than one protein in bacteria) with each sequence of three nitrogen-containing bases in the mRNA specifying the incorporation of a particular amino acid within the protein. The mRNA molecules are transported through the nuclear envelope into the cytoplasm, where they are translated by the rRNA of ribosomes. In prokaryotes, mRNAs contain an exact transcribed copy of the original DNA sequence with a terminal 5′-triphosphate group and a 3′-hydroxyl residue. In eukaryotes, the mRNA molecules are more elaborate. The 5′-triphosphate residue is further esterified, forming a structure called a cap. At the 3′ ends, eukaryotic mRNAs typically contain long runs of adenosine residues that are not encoded in the DNA but are added enzymatically after transcription. Eukaryotic mRNA molecules are usually composed of small segments of the original gene and are generated by a process of cleavage and rejoining from an original precursor RNA (pre-mRNA) molecule, which is an exact copy of the gene.

DNA TO MRNA