Question

What are the rungs of the “DNA ladder” made of?

Answer 1

Hint: DNA is a group of molecules that is responsible for carrying the hereditary materials or the instructions from parents to offspring. DNA also helps in the production of proteins. The structure of DNA resembles a twisted ladder with sides and rungs. The DNA ladder is made up of many smaller molecules known as the nucleotides. Each nucleotide consists of a phosphate group, a sugar molecule and a nitrogenous base.

Complete answer:
The structure of DNA is made of sides and rungs. The sides or the backbone of DNA consists of sugar molecules and a phosphate group. The rungs or steps of the DNA consist of nitrogenous bases. The nitrogenous bases are of four types namely adenine, guanine, thymine and cytosine. Adenine and guanine are known as purines whereas thymine and cytosine are known as pyrimidines.
Adenine always joins with thymine and guanine with cytosine. The two strands of DNA run in opposite directions so that they are always complementary to each other. The strands are held together by a hydrogen bond that is present between the two complementary nitrogenous bases. The strands are helically twisted forming a right-handed coil. A single turn is made up of ten nucleotides.
Since the bases are complementary to each other, a cell requires approximately equal amounts of purine and pyrimidines to maintain a balance.

Note:
The order of the nucleotides in a DNA is called the DNA sequence. The DNA sequence determines which instructions are encoded in the DNA molecule. Nucleotides are linked tightly together by phosphodiester bonds, which are formed between the carbon atoms of two sugar molecules. The structure of DNA is in antiparallel orientation which means the two strands of the double helix run in opposite directions to one another. This orientation is essential for successful DNA replication.