Problem 154 - Objective Biology for NEET

Question

Assertion: DNA is called deoxyribonucleic acid. Reason: DNA is nucleic acid containing dcoxyribose sugar.

Step-by-Step Solution

Answer

The assertion 'DNA is called deoxyribonucleic acid' and the reason 'DNA is nucleic acid containing deoxyribose sugar' are both correct, and the reason does indeed explain the assertion. Therefore, the assertion is true because the reason is true.

Step 1: Understand the Assertion and Reason

Firstly, understand what the assertion and the reason state. The assertion says 'DNA is called deoxyribonucleic acid,' which is essentially referring to the type of acid DNA is. The reason claims that 'DNA is nucleic acid containing deoxyribose sugar,' which introduces the composition of DNA.

Step 2: Relate The Assertion to Reason

Now, relate the assertion and reason. The term 'deoxyribonucleic acid' comes from the presence of 'deoxyribose sugar,' which is an essential component of DNA. The DNA is a nucleic acid, and it got its name from this sugar. Therefore, the reason provided supports the assertion.

Step 3: Make a Conclusion

Given that the reason supports the assertion and both points are scientifically correct, it can be concluded that the assertion is true because the reason is true.

Key Concepts

Nucleic acids

Nucleic acids are a group of complex organic substances that play a crucial role in the storage and transmission of genetic information in living organisms. They are made up of chains of monomers called nucleotides.
Nucleotides consist of three components: a nitrogenous base (adenine, guanine, cytosine, or thymine in DNA), a five-carbon sugar, and a phosphate group.
These nucleotides link together to form the long strands that make up nucleic acids. There are two primary types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• DNA: Stores genetic information used for the development, functioning, and reproduction of all known living organisms and many viruses.
• RNA: Primarily involved in protein synthesis and the encapsulation of genetic messages transferred from DNA.

Both DNA and RNA are found in every cell, with DNA mainly residing in the cell nucleus and mitochondria, setting the blueprint for protein production.

Deoxyribose sugar

Deoxyribose sugar is an essential component of DNA. It is a five-carbon sugar molecule that lacks one oxygen atom (hence "deoxy-"), which distinguishes it from ribose, found in RNA.
Deoxyribose is crucial because it forms the backbone of the DNA molecule, connecting nucleotides through phosphodiester bonds.

• Structure: Deoxyribose is a pentose (five-carbon) sugar that lacks an oxygen molecule at the 2' (second prime) position, compared to ribose.
• Function: The presence of deoxyribose in DNA helps provide stability to the DNA structure. This stability is key for the preservation of genetic information.

The lack of the oxygen atom on the ribose sugar is one of the reasons DNA is more stable than RNA, making it more suitable for long-term storage of genetic material.

DNA composition

DNA composition refers to the elements that make up the DNA molecule, which stores genetic information crucial for life.
The DNA molecule is composed of:

• Nitrogenous bases: There are four types in DNA - adenine (A), thymine (T), guanine (G), and cytosine (C). These bases pair specifically (A with T and G with C) through hydrogen bonds, creating the rungs of the DNA "ladder."
• Deoxyribose sugar: This sugar forms part of the DNA's backbone, linking with phosphate groups to form the sides of the ladder.
• Phosphate group: Each phosphate group is connected to the deoxyribose of one nucleotide and the next, holding together the structure of DNA.

The unique sequence of nitrogenous bases in DNA codes for various proteins that carry out critical functions in organisms, from structural roles to enzymatic activities. The overall double helix structure of DNA—created by the phosphate-sugar backbone and the paired nitrogenous bases—ensures the efficient and accurate replication of genetic information during cell division.