DNA, the blueprint of life, is a complex molecule with a specific structure and function. Its components, including deoxyribose sugar, phosphate groups, and nitrogenous bases, work together to store genetic information. Understanding DNA's structure is key to grasping how it replicates and transmits hereditary traits.

Base pairing rules and the antiparallel structure of DNA are crucial for its function. These features ensure accurate replication and transcription of genetic material. The complementary nature of base pairs and the opposite orientation of DNA strands play vital roles in maintaining genetic integrity across generations.

Chemical Structure and Function of DNA

Components of DNA nucleotides

• DNA (deoxyribonucleic acid) composed of repeating units called nucleotides
  • Each nucleotide consists of three components:
    • Pentose sugar called deoxyribose contains 5 carbon atoms in a ring structure
    • Phosphate group negatively charged, contributes to the acidic nature of DNA
    • Nitrogenous base attached to the 1' carbon of the deoxyribose sugar
• Nitrogenous bases in DNA are:
  • Purines: Adenine (A) and Guanine (G) double-ringed structures
  • Pyrimidines: Thymine (T) and Cytosine (C) single-ringed structures
• Nucleotides linked together by phosphodiester bonds
  • Phosphate group of one nucleotide bonds to the 3' carbon of the deoxyribose sugar of the adjacent nucleotide
  • Forms the sugar-phosphate backbone of the DNA molecule provides structural support and stability
• Nitrogenous bases face inward, forming the rungs of the DNA ladder (double helix)
• DNA is a type of nucleic acid, a macromolecule that stores and transmits genetic information

Base pairing rules in DNA

• In double-stranded DNA, nitrogenous bases pair with each other according to specific rules
  • Adenine (A) always pairs with Thymine (T) through two hydrogen bonds
  • Guanine (G) always pairs with Cytosine (C) through three hydrogen bonds
• Base pairing stabilized by hydrogen bonds between complementary bases
  • A-T base pairs form two hydrogen bonds weaker bond
  • G-C base pairs form three hydrogen bonds stronger bond
• Specificity of base pairing ensures accurate transmission of genetic information during DNA replication
  • Each strand of the double helix serves as a template for the synthesis of a new complementary strand ensures faithful copying of genetic material
• Base pairing plays a crucial role in the transcription of DNA into RNA
  • During transcription, DNA template strand is used to synthesize a complementary RNA strand (messenger RNA or mRNA)
• Complementary base pairing allows for the storage and transmission of genetic information (genes)
• This principle of complementary base pairing is fundamental to the Watson-Crick model of DNA structure

Antiparallel structure of DNA

• Two strands of the DNA double helix run in opposite directions
  • One strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction
  • Arrangement is referred to as antiparallel opposite orientation of the two strands
• Antiparallel nature of DNA is a result of the way nucleotides are linked together
  • Phosphodiester bonds connect the 5' phosphate of one nucleotide to the 3' hydroxyl group of the adjacent nucleotide creates directionality in the DNA strands
• Antiparallel arrangement of DNA strands is essential for the proper functioning of DNA replication enzymes
  • DNA polymerases can only synthesize new DNA strands in the 5' to 3' direction adds nucleotides to the growing strand
  • Antiparallel nature allows for the simultaneous synthesis of both the leading and lagging strands during DNA replication ensures efficient and accurate replication
• Antiparallel orientation contributes to the structural stability of the DNA double helix
  • Hydrogen bonds between complementary base pairs are optimally aligned when the strands are antiparallel maximizes the strength of the base pairing interactions
• Antiparallel arrangement facilitates the separation of DNA strands during replication and transcription
  • Enzymes (helicases) can easily unwind and separate the two strands for access to the genetic information

DNA Replication and Genetic Information

• DNA replication follows the semiconservative replication model, where each new double helix contains one original strand and one newly synthesized strand
• The genetic code, stored in DNA, is a set of rules that determines how the sequence of nucleotides is translated into amino acid sequences in proteins