The nucleus of all living cells contain macromolecular species called chromosomes made up of proteins and another type of biomolecules called nucleic acids. The chromosomes are responsible for transmission of inherent characters called heredity. Nucleic acids are mainly two types: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). Nucleic acids are long chain polymers of nucleotides, so they are also known as polynucleotides. A nucleotide is composed of a base, a C₅-carbohydrate and phosphate group (orthophosphate, pyrophosphate or triphosphate), which are bonded in the sequence base–carbohydrate–phosphate. The carbohydrate molecule in DNA is \(\beta\)-D-2-deoxyribose, whereas in RNA it is \(\beta\)-D-ribose. The nucleotide act as a energy carrier and a cofactor or coenzyme for a redox enzymes. The removal of phosphate moiety from a nucleotide produces nucleoside. The N-glycoside of purine or pyrimidine bases with pentose sugars are known as nucleosides. DNA contains four bases, viz. two purine bases adenine and guanine and two pyrimidine bases cystosine and thyamine. RNA also contains four bases: the same two purine bases adenine and guanine and two pyrimidine bases cystosine and uracil (in the place of thyamine). In nucleic acids the nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of the pentose sugar. The primary structure of nucleic acid gives the information regarding the sequence of nucleotides in the chain. The secondary structure of DNA shows that two nucleotide chains running in opposite directions and giving a right handed helix in which the two strands are held together by hydrogen bonds at definite distances.

In the secondary structure of RNA, helices are present which are only single-stranded. RNA molecules are three types: (i) messenger RNA (m–RNA) (ii) ribosomal RNA (r–RNA) and (iii) transfer RNA (t–RNA). These perform different functions. The tertiary structure gives the information of the orientation of the planar aromatic rings of the bases causing the DNA double helix to twist about the same axis. Due to twisting, a large number of hydrogen bonds are formed. The double helix of DNA is the store house of the hereditary information of the organism. The process of synthesis of RNA involving direct copying of one DNA molecule from another DNA molecule is known as replication. The process of synthesis of RNA in which a single strand DNA can act as a template is called transcription. The proteins are synthesized by various RNA molecules in the cell but the message for the synthesis of particular protein is present in DNA. This process is known as translation. In molecular biology, transcription is used as a synonym for RNA synthesis and translation is a synonym for protein synthesis. Translation is unidirectional but transcription can sometimes be reversed, i.e., RNA is copied into DNA and is known as reverse transcription.

The main point of difference between DNA and RNA

presence of deoxyribose and thiamine in DNA, ribose and uracil in RNA

The correct answer is option 2. presence of deoxyribose and thiamine in DNA, ribose and uracil in RNA.

The main differences between DNA and RNA is:

1. Sugar Component:
DNA (deoxyribonucleic acid) contains deoxyribose sugar. Deoxyribose is a five-carbon sugar that lacks an oxygen atom at the 2' position.

RNA (ribonucleic acid), on the other hand, contains ribose sugar. Ribose is also a five-carbon sugar but has an additional oxygen atom at the 2' position.

The presence of deoxyribose in DNA and ribose in RNA is a fundamental distinction between the two nucleic acids.

2. Bases:
Both DNA and RNA consist of nucleotides, which are composed of a sugar, a phosphate group, and a nitrogenous base.

In DNA, the four bases are adenine (A), cytosine (C), guanine (G), and thymine (T). Thymine is unique to DNA and pairs specifically with adenine via hydrogen bonds.

In RNA, the four bases are adenine (A), cytosine (C), guanine (G), and uracil (U). RNA lacks thymine but instead contains uracil, which pairs with adenine in a similar manner as thymine.

3. Function:
DNA is the primary genetic material in most organisms. It carries the hereditary information and serves as the blueprint for the synthesis of RNA and proteins. DNA is typically found in the nucleus of cells.

RNA is involved in various cellular processes, including gene expression and protein synthesis. It acts as an intermediate molecule between DNA and protein synthesis. RNA can be found in the nucleus as well as in the cytoplasm of cells.

In summary, the main differences between DNA and RNA can be summarized as follows:

DNA contains deoxyribose sugar, while RNA contains ribose sugar.
DNA uses thymine (T) as one of its bases, while RNA uses uracil (U) instead of thymine.
DNA is the primary genetic material, while RNA plays a role in gene expression and protein synthesis.

These differences in sugar composition, bases, and function contribute to the unique characteristics and roles of DNA and RNA in cellular processes.