Question

Which of the following describes the synthesis of nucleic acids? a. Nucleotides are added to the 5 ' end of a single nucleic acid strand. b. Nucleic acids are polymerized by the formation of peptide bonds between nucleotides. c. Strands in a double helix are synthesized in a parallel direction such that one end of the molecule has two \(3^{\prime}\) ends and other has two \(5^{\prime}\) ends. d. Complementary pairing between bases is required for copying nucleic acids.

Short answer

Option 'd' accurately describes the synthesis of nucleic acids, as complementary pairing between bases is required for copying nucleic acids, ensuring correct replication and synthesis.

Step-by-step solution

1. Evaluate Option 'a'

Option 'a' suggests that nucleotides are added to the 5' end of a single nucleic acid strand. However, during nucleic acid synthesis, new nucleotides are added at the 3' end of the growing chain, not the 5' end. Therefore, option 'a' is incorrect.

2. Evaluate Option 'b'

Option 'b' says that nucleic acids are polymerized by the formation of peptide bonds between nucleotides. This statement is incorrect because peptide bonds are formed between amino acids during protein synthesis, not nucleic acid synthesis. Nucleic acids are polymerized through the formation of phosphodiester bonds between nucleotides.

3. Evaluate Option 'c'

Option 'c' claims that the strands in a double helix are synthesized in a parallel direction, with one end of the molecule having two 3' ends and the other having two 5' ends. This is incorrect because nucleic acid strands are synthesized in an antiparallel direction, meaning one strand runs from the 5' to 3' end and the other strand runs from the 3' to the 5' end.

4. Evaluate Option 'd'

Option 'd' indicates that complementary pairing between bases is required for copying nucleic acids. This statement is correct. During DNA synthesis, each strand serves as a template for the synthesis of a new complementary strand. Adenine (A) pairs with Thymine (T) in DNA and with Uracil (U) in RNA synthesis, and Cytosine (C) pairs with Guanine (G). This base pairing ensures accurate replication and synthesis of nucleic acids.

Conclusion

Based on the evaluation of each option, option 'd' accurately describes the synthesis of nucleic acids. Complementary pairing between bases is necessary for copying nucleic acids, ensuring correct replication and synthesis.

Key concepts

Complementary Base Pairing

In the world of DNA and RNA, complementary base pairing is a core principle for accurate genetic information transfer. It is the mechanism by which nucleic acids ensure precision during the replication and transcription processes. This concept involves specific pairing rules: in DNA, Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G). During RNA synthesis, however, Adenine pairs with Uracil (U) instead of Thymine.
These pairs are held together by hydrogen bonds, forming a stable structure essential for the double helix’s integrity. Base pairs come in specific sizes and properties, which help ensure DNA replication fidelity. For example, purines (A and G) always pair with pyrimidines (T, C, and U), maintaining a consistent width of the DNA helix.
Complementary base pairing is crucial for various cellular processes, including DNA replication, where each strand serves as a template for the creation of a new complementary strand.

• Ensures accurate DNA replication
• Maintains the structural integrity of nucleic acids
• Facilitates genetic information transfer through correct base pairing

Phosphodiester Bonds

Phosphodiester bonds are vital links within the backbone of DNA and RNA, serving as the glue holding the nucleotide chains together. These bonds form between the phosphate group of one nucleotide and the sugar portion of another. Crucially, this bond forms through a dehydration reaction, where a water molecule is released.
The connection established by phosphodiester bonds creates a repeating sugar-phosphate backbone, contributing to the structural framework of nucleic acids. This backbone is highly stable, which is essential given the crucial nature of DNA and RNA in cellular functions.
During nucleic acid polymerization, enzymes facilitate the formation of these bonds. For DNA, the enzyme DNA polymerase plays this role, adding new nucleotides to the growing strand to form the characteristic 5' to 3' direction of nucleic acid chains.

• Forms the backbone of nucleic acids
• Involves repeated sugar-phosphate links
• Essential for stable framework in DNA and RNA

Antiparallel DNA Strands

In DNA, the characteristic double helix structure consists of two strands that are antiparallel. This means each strand runs in opposite directions: one from a 5' to 3' direction, and the other from 3' to 5'. Such an arrangement is vital for the overall function and replication of DNA.
This antiparallel orientation facilitates the correct positioning of base pairs—ensuring complementary bases align for efficient bonding. The necessity of this arrangement becomes evident during replication. Enzymes such as DNA helicase and DNA polymerase work best with this structure, allowing the unwinding and synthesizing of new strands.
This setup impacts all other functions, including transcription and repair mechanisms, ensuring the integrity and transfer of genetic information is maintained accurately across cellular generations.

• Strands run in opposite directions
• Necessary for accurate DNA replication
• Supports structural and functional integrity of DNA helix