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Ch.4 - Nucleic Acids and the RNA World
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Non è quello che usi tu?Cambia libro di testo
Capitolo 4, Problema 3

Evaluate the following statements related to the synthesis of nucleic acids. Select True or False for each statement.
T/F Ribonucleotides are added to the 3′ end of a DNA strand.
T/F Polymerization of nucleic acids occurs by the formation of phosphodiester bonds.
T/F Complementary pairing between sugars is required for copying nucleic acids.
T/F Strands in a double helix are synthesized in an antiparallel orientation.

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1
Understand the structure of nucleic acids: DNA and RNA are composed of nucleotides, which include a sugar, a phosphate group, and a nitrogenous base. DNA has deoxyribonucleotides, while RNA has ribonucleotides.
Evaluate the statement about ribonucleotides: Ribonucleotides are not added to the 3′ end of a DNA strand during DNA synthesis. Instead, deoxyribonucleotides are added to the 3′ end of a growing DNA strand. RNA synthesis involves adding ribonucleotides to the 3′ end of an RNA strand.
Consider the polymerization process: Polymerization of nucleic acids involves the formation of phosphodiester bonds between the phosphate group of one nucleotide and the hydroxyl group on the sugar of another nucleotide. This is a key mechanism in both DNA and RNA synthesis.
Analyze the statement about complementary pairing: Complementary pairing occurs between nitrogenous bases, not sugars. In DNA, adenine pairs with thymine, and cytosine pairs with guanine. In RNA, adenine pairs with uracil.
Examine the orientation of strands in a double helix: DNA strands in a double helix are synthesized in an antiparallel orientation, meaning one strand runs 5′ to 3′ and the other runs 3′ to 5′. This orientation is crucial for the replication and function of DNA.

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Nucleic Acid Synthesis

Nucleic acid synthesis involves the formation of DNA and RNA strands through the addition of nucleotides. In DNA synthesis, deoxyribonucleotides are added to the 3′ end of the growing strand, while RNA synthesis involves ribonucleotides. This process is crucial for replication and transcription, ensuring genetic information is accurately copied and expressed.
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Nucleic Acids

Phosphodiester Bonds

Phosphodiester bonds are the chemical linkages that connect nucleotides in a nucleic acid strand. These bonds form between the phosphate group of one nucleotide and the hydroxyl group on the sugar of another, creating a backbone for DNA and RNA. The formation of phosphodiester bonds is essential for the polymerization of nucleic acids, allowing for the stable and continuous structure of genetic material.
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Hydrogen Bonding

Antiparallel Orientation

In a double helix, DNA strands are oriented in an antiparallel fashion, meaning one strand runs in the 5′ to 3′ direction while the other runs 3′ to 5′. This orientation is critical for the complementary base pairing that stabilizes the double helix structure. Antiparallel synthesis ensures that each strand can serve as a template for replication, maintaining the integrity of genetic information.
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Discovering the Structure of DNA