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Along with proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one of the four main types of macromolecules necessary for all known life forms. Nucleic acids are composed of two major macromolecules, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), which carry the genetic instructions for the development, function, growth and reproduction of all known organisms and viruses. Structure of DNA and RNA: DNA macromolecules consist of two polynucleotide strands that are intertwined to form a double helix. RNA macromolecules typically exist as single polynucleotide strands that are much shorter than comparative DNA molecules.
Structure and Function of DNA and RNA
Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of organisms. All known cellular life and some viruses contain DNA. The main role of DNA in cells is to store information for long periods of time. It is often likened to a blueprint because it contains instructions for building other components of the cell, such as proteins and RNA molecules. DNA segments that carry genetic information are called genes, but other DNA sequences have structural goals or are involved in regulating the expression of genetic information. In eukaryotes such as animals and plants, DNA is stored in the nucleus, while in prokaryotes such as bacteria and archaea, DNA is present in the cytoplasm of the cell. Apart from enzymes, DNA does not function directly on other molecules. Instead, during DNA replication, different enzymes act on the DNA and copy its information into more DNA, or transcribe it into proteins.
Other proteins such as histones are involved in DNA packaging or repairing DNA damage that leads to mutations. DNA is a long polymer made up of individual units called nucleotides, which are linked together by a backbone of sugar and phosphate groups. This backbone carries four molecules called bases, the order of which encodes information. The core function of DNA is to cypher the sequence of amino acid residues in proteins using the genetic code. To read the genetic code, cells copy a stretch of DNA into the nucleic acid RNA. These RNA copies can then be used to direct protein synthesis, but they can also be used directly as part of the ribosome or spliceosome.
The main function of RNA is to provide a copy of the DNA sequence and exit the nucleus (if the cell is eukaryotic). Once RNA is made, it performs many functions. mRNA provides a template for ribosomes to synthesise proteins with amino acid sequences corresponding to those stored in DNA;
- As rRNA, making up about half of the structure of the ribosome (the other half is made up of proteins);
- As tRNA, amino acids are transported to the ribosome for integration into the polypeptide chain being synthesised;
- Some RNAs have enzymatic activity (ribozymes) and act as enzymes;
- Certain small fragments of RNA have obvious regulatory functions on various cellular processes;
- RNA may also have other functions that we haven’t realised yet.
Chemical Structure of DNA and RNA
Chemical Structure of DNA
DNA is a polymer called a nucleotide that contains deoxyribose sugar and nitrogenous bases. Nucleotides are linked by phosphodiester bonds between their sugars. Nitrogen bases also form hydrogen bonds with each other according to predictable base pairing rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
In human DNA, there are 150 million base pairs in a single molecule, normally
There are several other nucleic acids that are synthetic or naturally occurring and somewhat similar to DNA. Those molecules that can be powerful genetic information in an organism from another planet are RNA: ribonucleic acid, TNA: threose nucleic acid, XNA: Xeno nucleic acid, and GNA: glycol nucleic acid.
There are many other synthetic molecules that can store genetic information. However, evolution never created these molecules naturally, choosing instead DNA as the genetic information for its stability. However, the stability of all molecules varies with environmental conditions, so an organism from another planet might have XNA, GNA, or TNA as its genetic information, which is more stable.
Chemical Structure of RNA
Ribonucleic acid has all components similar to DNA with only 2 major differences. RNA has the same nitrogenous bases as DNA, called adenine, guanine, and cytosine, with the exception of thymine, which has been replaced by uracil. Adenine and uracil are considered the main building blocks of RNA, and both base pairs use 2 hydrogen bonds.
RNA looks like a hairpin pattern, just like the nucleotides in DNA, where nucleotides are formed in this ribonucleic material (RNA). Nucleosides are nothing but phosphate groups that also sometimes help make nucleotides in DNA.
Like DNA, each RNA strand has the same basic unit, consisting of nitrogenous bases covalently attached to a sugar-phosphate backbone. RNA is usually a single-stranded molecule. Also, the sugar in RNA is ribose rather than deoxyribose (ribose has an extra hydroxyl group on the second carbon), which explains the molecule’s name. RNA exhibits four nitrogenous bases: adenine, cytosine, uracil, and guanine. Uracil is a pyrimidine that has the same structure as thymine, another type of pyrimidine found in DNA. Like thymine, uracil can mate with adenine.
Conclusion
Both DNA and RNA are made up of nucleotides, each of which contains a sugar backbone of five carbon atoms, a phosphate group, and a nitrogenous base. DNA provides the code for cellular activity, while RNA translates this code into proteins to perform cellular functions.
DNA and RNA each have four nitrogenous bases, three of which are shared (cytosine, adenine, and guanine) and one that differs between the two (RNA has uracil, while DNA has thymine). DNA stores all genetic information and helps pass it on to form new cells. The main function of RNA is to transport copies of amino acids from genes to the sites where proteins are assembled on the ribosome. This is basically done by mRNA.
