Biology · Molecular Basis of Inheritance · NEET
DNA is a very long chain built from small repeating units. Each small unit is called a deoxyribonucleotide. So DNA is a long polymer of deoxyribonucleotides. It carries the instructions (genetic information) that decide the features of an organism, so NCERT calls it the genetic material of most organisms.
DNA stands for Deoxyribonucleic Acid. The name tells you two things NEET loves to test: 'Deoxyribo' means its sugar is deoxyribose (ribose sugar missing one oxygen at the 2' position), and 'nucleic acid' means it is one of the two nucleic acids in living systems, the other being RNA (Ribonucleic Acid).
No. This is a common trap. NCERT says DNA acts as the genetic material in MOST organisms, not all. In some viruses, RNA is the genetic material (for example, TMV and some bacteriophages). So the safe NEET answer is: DNA is the genetic material in most organisms, RNA in a few viruses.
DNA is the whole long molecule. A gene is only a small functional segment of that DNA that codes for a product (like a protein). One long DNA molecule contains many genes. So every gene is made of DNA, but the full DNA is much more than a single gene.
The length of DNA is defined as the number of nucleotides, or the number of base pairs (bp), present in it. This number is a characteristic of the organism. NCERT examples you must remember: bacteriophage phi X174 has 5386 nucleotides, E. coli has 4.6 x 10^6 bp, and haploid human DNA has 3.3 x 10^9 bp.
DNA is made of deoxyribonucleotides. Each deoxyribonucleotide has three parts: a nitrogenous base (Adenine, Guanine, Cytosine or Thymine), a sugar called deoxyribose, and a phosphate group. Because the sugar is deoxyribose (not ribose), the molecule is called Deoxyribonucleic Acid.
The correct statement regarding RNA and DNA, respectively is:
A molecule that can act as a genetic material must fulfill the traits given below, except
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The idea built up over several experiments. Griffith showed the 'transforming principle', Avery, MacLeod and McCarty showed the transforming principle was DNA, and Hershey and Chase (1952) gave the unequivocal (final) proof that DNA is the genetic material using bacteriophages labelled with radioactive 32P and 35S.
A polymer is a long molecule made by joining many small repeating units called monomers. In DNA, the monomers are deoxyribonucleotides. Thousands to billions of these are linked together, so DNA is correctly called a long polymer of deoxyribonucleotides.
The haploid content of human DNA is 3.3 x 10^9 base pairs. Using 0.34 nm per base pair, this stretches to about 2 metres of DNA packed inside a single tiny nucleus, which is a famous NEET calculation.
No. DNA is the molecule that carries genetic information. A chromosome is DNA packaged tightly with proteins (histones) so that a very long DNA molecule fits inside the nucleus. So a chromosome is basically highly folded DNA plus protein.
The two nucleic acids found in living systems are DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid). DNA is the genetic material in most organisms, while RNA mostly acts as a messenger, adapter, structural and sometimes catalytic molecule, and is the genetic material only in some viruses.
