Textbook Question
One strand of a fragment of duplex DNA has the sequence 5'-ATCGACCTGATC-3'.
Which chemical groups of nucleotides react to form the bond in part (b)?
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7. DNA and Chromosome Structure
DNA Structure
1:31 minutesProblem 6
Textbook Question
The principles of complementary base pairing and antiparallel polarity of nucleic acid strands in a duplex are universal for the formation of nucleic acid duplexes. What is the chemical basis for this universality?
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Understand the concept of complementary base pairing: Complementary base pairing refers to the specific pairing of nucleotide bases in DNA and RNA. Adenine (A) pairs with thymine (T) in DNA (or uracil (U) in RNA), and cytosine (C) pairs with guanine (G). This pairing is governed by hydrogen bonding between the bases.
Examine the chemical basis of hydrogen bonding: Hydrogen bonds form between the nitrogenous bases due to their specific chemical structures. Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds. These bonds are stable and ensure the specificity of base pairing.
Analyze the antiparallel polarity of nucleic acid strands: DNA strands are antiparallel, meaning one strand runs in the 5' to 3' direction while the complementary strand runs in the 3' to 5' direction. This arrangement is due to the orientation of the sugar-phosphate backbone and ensures proper alignment for hydrogen bonding between bases.
Explore the role of the sugar-phosphate backbone: The sugar-phosphate backbone provides structural support and polarity to the DNA strands. The 5' end has a phosphate group, while the 3' end has a hydroxyl group. This polarity is crucial for the antiparallel arrangement and the formation of stable duplexes.
Conclude with the universality of these principles: The chemical basis for complementary base pairing and antiparallel polarity lies in the molecular structures of nucleotides and their ability to form stable hydrogen bonds. These principles are universal because they are dictated by the fundamental chemistry of nucleic acids, ensuring accurate replication and transcription processes in all organisms.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Complementary Base Pairing
Complementary base pairing refers to the specific hydrogen bonding between nucleotide bases in DNA and RNA. In DNA, adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G), while in RNA, adenine pairs with uracil (A-U). This specificity ensures accurate replication and transcription of genetic information, forming the basis for the double helix structure.
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Antiparallel Polarity
Antiparallel polarity describes the orientation of the two strands in a nucleic acid duplex, where one strand runs in the 5' to 3' direction and the other runs 3' to 5'. This arrangement is crucial for the proper alignment of bases for hydrogen bonding and for the enzymatic processes of replication and transcription, ensuring that nucleotides are added in the correct sequence.
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Chemical Basis of Nucleic Acids
The chemical basis of nucleic acids involves the structure of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base. The covalent bonds between the phosphate and sugar form the backbone of the nucleic acid, while the hydrogen bonds between complementary bases stabilize the double helix. This chemical architecture underpins the universality of nucleic acid duplex formation across all living organisms.
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