Structure and function of DNA and RNA.

 

Introduction:

  • The organic components known as nucleic acids are found in all living things in the form of DNA or RNA

  • These nucleic acids are created by combining nitrogenous bases, sugar molecules, and phosphate groups that are connected by various bonds in a series of sequences

  • The fundamental genetic make-up of our body is defined by the DNA structure. 

  • The Swiss biologist Johannes Friedrich Miescher first recognized and named DNA in 1869 while conducting research on white blood cells.

  • James Watson and Francis Crick later made the discovery of the DNA molecule's double helix.

types of DNA.

  • A-DNA: 

    • The double helix is right-handed and resembles the B-DNA form.

    • DNA that has been dehydrated adopts an A form that shields it from harmful conditions like desiccation. 

    • Protein binding also removes the solvent from DNA, and the DNA takes an A form.

  • B-DNA: 

    • A right-handed helix is the most typical DNA conformation

    • The majority of DNA has a B type conformation under normal physiological conditions.

  • Z-DNA: 

    • Z-DNA is a left-handed DNA whose double helix winds zigzag-style to the left

    • Andres Wang and Alexander Rich made the discovery

    • It is thought to play a part in gene regulation because it is located before the start site of a gene.

Structure of DNA

  • DNA structure looks like a twisted ladder

  • This structure is called a double-helix, as described in the diagram above. 

  • It is a nucleic acid, and all nucleic acids are made up of nucleotides

  • The DNA molecule is composed of units called nucleotides. 

  • Nucleotides are composed of a sugar group, a phosphate group, and a nitrogen base

  • The sugar and phosphate groups link the nucleotides together to form each strand of DNA

  • Adenine (A), Thymine (T), Guanine (G)  and Cytosine (C) are four types of nitrogen bases.

  • These four nitrogenous bases pair together in a definite way: A with T, and C with G. 

  • These base pairs are essential for the DNA’s double helix structure.

  • The order of the nitrogenous bases determines the genetic code or the DNA’s instructions.

  • Sugar is one of the three structural elements of DNA that form the DNA molecule's backbone

  • It is also called deoxyribose

  • A ladder-like structure is created when the nitrogenous bases of the opposing strands form hydrogen bonds.

  • The DNA molecule consists of 4 nitrogen bases, namely adenine (A), thymine (T), cytosine (C) and Guanine (G), which ultimately form the structure of a nucleotide. 

  • The A and G are purines, and the C and T are pyrimidines.

  • The two strands of DNA run in opposite directions

  • These strands are held together by the hydrogen bond that is present between the two complementary bases. 

  • The strands are helically twisted, where each strand forms a right-handed coil, and ten nucleotides make up a single turn.

  • The pitch of each helix is 3.4 nm. Hence, the distance between two consecutive base pairs (i.e., hydrogen-bonded bases of the opposite strands) is 0.34 nm.

  • The DNA coils up, forming chromosomes, and each chromosome has a single molecule of DNA in it. 

  • Overall, human beings have around twenty-three pairs of chromosomes in the nucleus of cells.

Functions of DNA:

  1. Carries genetic information from one generation to another.

  2. Replication process.

  3. Mutation – the considerable change in the sequence of DNA is called a mutation.

  4. Gene therapy

  5. Cellular metabolism

  6. Transcription

  7. DNA fingerprinting

Structure of RNA

  • Ribonucleic acid (RNA) is a compound of high molecular weight essential for the synthesis of protein in cells.

  • Some viruses use RNA as a genetic carrier

  • Ribonucleotides (nitrogenous bases attached to ribose sugars) form RNA strands by attaching phosphodiester bonds

  • With the replacement of thymine, RNA is made of the 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

  •  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.

  • Types of RNA:

    • mRNA or Messenger RNA:

      • mRNA carries genetic information from the nucleus to the cytoplasm of the cell.

    • rRNA or Ribosomal RNA:

      • rRNA is located in the cytoplasm of a cell, where ribosomes are found. 

      • They direct the translation of mRNA into proteins.

    • tRNA or Transfer RNA:

  • Like rRNA, tRNA is located in the cellular cytoplasm and is involved in protein synthesis. 

  • Transfer RNA brings or transfers amino acids to the ribosome that correspond to each three-nucleotide codon of rRNA.

RNA functions:

  1. mRNA carries information about proteins to be synthesized by ribosomes from the nucleus.

  2. rRNA directs the process of protein synthesis.

  3. tRNA carries required amino acids from the cytoplasm to the ribosomes for protein synthesis.

  4. tRNA also carries synthesized proteins.

Commonly asked questions.

  1. Write a short note on the structure and functions of DNA and RNA.

  2. Write a short note on the structure, types and functions of DNA.

  3. Write a short note on the structure, types and functions of RNA.

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