Question

Compare DNA and RNA is these ways. (a) Monosaccharide units (b) Principal purine and pyrimidine bases (c) Primary structure (d) Location in the cell (e) Function in the cell

Short answer

Answer: The monosaccharide in DNA is called deoxyribose, while in RNA it is called ribose. The difference between the two sugars is the presence of a hydroxyl group (-OH) at carbon 2', on the ribose sugar in RNA, whereas the same position in deoxyribose has a hydrogen atom (-H).

Step-by-step solution

(a) Monosaccharide units

DNA and RNA are both composed of nucleotides as their monomer units. A nucleotide consists of a monosaccharide, a nitrogenous base, and a phosphate group. The monosaccharide in DNA is called deoxyribose, while in RNA it is called ribose. The difference between the two sugars is the presence of a hydroxyl group (-OH) at carbon 2', on the ribose sugar in RNA, whereas the same position in deoxyribose has a hydrogen atom (-H).

(b) Principal purine and pyrimidine bases

Both DNA and RNA contain four principal nitrogenous bases: two purines and two pyrimidines. In DNA, the purines are adenine (A) and guanine (G), and the pyrimidines are cytosine (C) and thymine (T). However, in RNA, thymine is replaced by uracil (U), so the principal bases in RNA are adenine (A), guanine (G), cytosine (C), and uracil (U).

(c) Primary structure

The primary structure of DNA and RNA refers to the linear sequence of nucleotides. In DNA, the nucleotides form a double helix structure, with the two strands being antiparallel and complementary. In RNA, the nucleotides predominantly form a single-stranded structure, although they can fold back on themselves to create secondary structures, such as loops and stems.

(d) Location in the cell

The location of DNA and RNA in the cell is different. DNA is mainly found in the cell nucleus, where it's packaged into chromosomes. Small amounts of DNA can also be found in the mitochondria (mitochondrial DNA). RNA, on the other hand, is synthesized in the nucleus but then exported to the cytoplasm. The different types of RNA, like messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), function in various locations within the cytoplasm.

(e) Function in the cell

The primary function of DNA is to store and transmit genetic information. It serves as the blueprint for producing all the proteins in an organism. RNA, on the other hand, has three main types, each with different functions: 1. Messenger RNA (mRNA): It carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm, where protein synthesis occurs. 2. Transfer RNA (tRNA): It assists in the process of translation, where it carries the correct amino acid to the ribosome to be added to the growing protein chain. 3. Ribosomal RNA (rRNA): It is a component of ribosomes and plays a role in catalyzing the formation of peptide bonds during the translation process.