Structure of DNA and RNA and Their Functions

DNA

Structure of DNA

All organisms contain organic materials called nucleic acids, which are found in both DNA and RNA. A series of different bonds attach nitrogenous bases, sugar molecules, and phosphate groups in a series of sequences to form these nucleic acids. Our bodies have a genetic make-up that is highly determined by DNA. The DNA structure is an integral part of nearly all living organisms.

The DNA is referred to as Deoxyribonucleic Acid. The molecule has an unusual molecular structure. Cells of both prokaryotes and eucaryotes contain this enzyme.

Types

DNA is divided into three types:
A-DNA - It is similar to the form of B-DNA in its right-handedness. During extreme conditions such as desiccation, DNA takes on the form A, which protects it. Additionally, the binding of proteins results in DNA taking on the form of an A.

B-DNA - DNA is commonly structured in this way, which is a right-handed helix. Normal physiological conditions result in most DNA having a B type conformation.

Z-DNA - The zig-zag pattern of the double helix is characteristic of Z-DNA, a left-handed DNA. Alexander Rich and Andres Wang discovered Z-DNA.

A Swiss biologist named Johannes Friedrich Miescher identified DNA for the first time in 1869, while studying white blood cells. It was later discovered by James Watson and Francis Crick through experimental data that DNA has a double helix structure. Lastly, it was confirmed that the DNA of living organisms stores genetic information.

The diagram given below illustrates the various parts involved in DNA. DNA is made up of sugars and phosphates (guanine, cytosine, adenine, and thymine).



As a ladder, the DNA structure can be compared to DNA. Due to its structure, it is known as a double helix as shown in the figure itself. Nucleic acids are made up of nucleotides, a molecule that belongs to the class of nucleic acids. DNA molecules are made up of units called nucleotides, and each nucleotide contains three components: sugar, phosphoric acid, and nitrogen bases. DNA is built from nucleotides, which contain sugar groups, phosphate groups, and nitrogen bases. DNA is composed of nucleotides linked together by sugar and phosphate groups. There are four different types of nitrogen basis named Thymine (T), Cytosine (C), Adenine (A), and Guanine (G). These nitrogen bases are visible in the form of pairs such as C and G as well as A and T. Base pairs such as these are needed for DNA to form its double helix structure, which is similar to a ladder. Genetic code or DNA instructions are determined by the order of nitrogenous bases.



Sugar is one of the three main components present in DNA and it is considered the backbone of DNA. Deoxyribose is another name for sugar. A ladder-like structure is formed by hydrogen bonds between the nitrogenous bases of opposite strands.



With the help of nitrogen bases, a nucleotide is formed that is present in DNA. Hence, with the help of DNA a nucleotide is formed and the nitrogen bases that are involved in its formation are called to be Thymine (T), Cytosine (C), Adenine (A), and Guanine (G). Purines are A and G, and pyrimidines are C and T. Each DNA strand runs in the opposite direction. There is a hydrogen bond between these complementary bases that keeps these strands together. There are ten nucleotides in one turn since the strands are helically twisted in a right-handed coil. There is a pitch of about 3.4 nm in each helix present in DNA. The distance between consecutive hydrogen-bonded base pairs is therefore 0.34 nm (i.e., the bases on opposite strands).



In each chromosome, one molecule of DNA is found, and the DNA coils up to form chromosomes. Each human cell nucleus contains approximately 23 pairs of chromosomes. Additionally, DNA is crucial to the division of cells.

Functions

DNA is the genetic material that contains all the information that is inherited. There are 250 - 2 million base pairs in every gene, which is the smallest segment of DNA. An amino acid is represented by three nitrogenous bases in a gene code for a polypeptide molecule. With the help of folding the polypeptide chains into secondary, quaternary as well as tertiary structures, different types of proteins are formed. A variety of proteins may be formed in every organism since DNA contains several genes. Most organisms rely primarily on proteins for their functions and structural elements. Besides storing genetic information, DNA plays an important role in:

• Replication process - A cell replicates itself bypassing the genetic information between its daughters and from one generation to the next and distributing DNA equally during division.
• Mutation – the considerable change in the sequence of DNA is called a mutation.
• Gene therapy
• Cellular metabolism
• Transcription
• DNA fingerprinting

RNA

Structure of RNA

Ribonucleic acid (RNA) is a compound of high molecular weight essential for the synthesis of protein in cells, which in some viruses replaces DNA (deoxyribonucleic acid) as the carrier of genetic codes. Ribonucleotides (nitrogenous bases attached to ribose sugars) form RNA strands by attaching phosphodiester bonds. With the replacement of thymine, RNA is made of other four nitrogen bases such as adenine, cytosine, guanine, and lastly uracil whereas in DNA instead of uracil, thymine is used. RNA forms a cyclical structure that is made of one oxygen and five carbons. The second carbon group of the ribose sugar molecule is attached to an inherently hydrophilic hydroxyl group (- OH). In 1965, R.W. Holley described the structure of the RNA molecule.

A majority of RNA molecules are single-stranded biopolymers. To fold the ribonucleotide chains into the complex structural forms that are characterized by helices and bulges, a self-complementary sequence within the RNA strand mainly plays an important role in interchain pairing. RNA's three-dimensional structure is essential for its stability and function, allowing enzymes attached to the chain to attach chemical groups (e.g., methyl groups) to the ribose sugar and nitrogenous bases. RNA chain contortions occur due to these modifications, which cause chemical bonds to form between distant regions of the strand. This further stabilizes the RNA structure. Structures with weak stabilization and modification can easily be destroyed. Also known as ribonucleoproteins (RNPs), RNAs can form complexes with these molecules. It has been found that at least one RNA-containing cellular RNP acts as a biocatalyst, a function that had previously been ascribed only to proteins.

Functions

Aside from messenger RNA (mRNA) and transfer RNA (tRNA), the three types of RNA studied most extensively are ribosomal RNA (rRNA), which is present in all living organisms. Similar to enzymes, these and many other kinds of RNA are primarily involved in biochemical reactions. Some of them also play a crucial role in regulating cellular processes. In addition to playing an important role in normal cellular processes and diseases, RNA plays an important role in many regulatory processes, their abundance, and their diverse functions.

The genetic code of protein synthesis is known to be DNA that is carried by ribosomes from the nucleus to the cytoplasm again by mRNA. RRNA encodes the subunits of ribosomes, which are synthesized in the nucleolus. As key regulators of translation, they play a key role in translating mRNA into protein. Once fully assembled, they are moved into the cytoplasm. Through incorporation of three nitrogenous bases in the mRNA, it specifies the inclusion of a certain amino acid in the protein sequence. In ribosomes, amino acids are joined to form proteins by tRNA molecules (often called soluble, or activator, RNA). tRNA molecules contain fewer than 100 nucleotides.

MiRNAs play an important role. Gene expression is controlled by them in most eukaryotes. DNA strands are about 22 nucleotides in length. Their binding to target mRNA inhibits (silences) gene expression partly by inhibiting translation. Functional proteins cannot be produced if they are inhibited. The role of miRNAs in cancer and other diseases is well established. MiRNA can stimulate tumorigenesis and tumor progression, for example, by regulating cancer-initiating and tumor suppressor genes. The 26 to 31 nucleotide-long piRNAs, which are also found in most animal species, are also significant in biological functions. These molecules prevent transposons (jumping genes) from being translated into germ cells (sperm and eggs). The majority of piRNAs target specific transposons and are complementary to them.

In contrast to other RNA types, circular RNA (circRNA) has bonded ends that create a loop. In the same way that mRNAs can act as templates for protein synthesis, circRNAs are formed from many protein-encoding genes. MiRNA molecules can also bind to them, acting as "sponges" that stop miRNA molecules from interacting with their targets. Additionally, circRNA regulates genes that are derived from these circRNAs by regulating transcription and alternative splicing.

Get subject wise printable pdf documentsView Here

Share

Tweet

Share

Pin it

Share