Watson and Crick Model of DNA

NGS-based Sequencing Methods

• Allow cancer researchers to detect rare somatic variants, tumor subclones, and circulating DNA fragments
• Used in microbiology research for environmental metagenomics studies, infectious disease surveillance, and more
• Used in complex disease research to understand autoimmune and rheumatic diseases, atherosclerosis, neurological diseases, and psychiatric disorders on a molecular level
• Used in reproductive health to deliver fast, accurate information to guide choices along the reproductive health journey

Recombinant DNA Technology for Human Insulin Production

• Steps involved:
  • Identification and isolation of genes of interest or DNA fragment to be cloned (Genes A and B for two polypeptide chains of insulin)
  • Insertion of the isolated gene into a suitable vector (A and B genes in two separate plasmids)
  • Introduction of the recombinant DNA (Human insulin gene + bacterial plasmid DNA) vector into a suitable cell/organism called the host (transformation)
  • Host can be E. coli or yeast

Nucleic Acids

• Repository of biological information
• Storage and transfer of genetic information
• Two types of nucleic acids: DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid)
• Nucleic acids are polymers of nucleotides
• Nucleotides have three components: nitrogenous base, pentose sugar, and phosphate group
• Nitrogenous base is linked to pentose sugar at C-1’ through N-1 in pyrimidines and N-9 in purines
• Phosphate is bonded to C-5’ of the pentose sugar

DNA vs RNA

• DNA contains 2’-deoxy-D-ribose as pentose sugar, whereas RNA contains D-ribose
• DNA contains 2 purine bases (Adenine and Guanine) and 2 pyrimidine bases (Cytosine and Thymine), whereas RNA contains 2 purine bases (Adenine and Guanine) and 2 pyrimidine bases (Cytosine and Uracil)
• DNA is double-stranded and contains long chain of nucleotides, whereas RNA is single-stranded and contains short chain of nucleotides

DNA/RNA Structure and Stability

• Successive nucleotides of DNA/RNA are connected by phosphodiester linkages
• The sugar-phosphate backbone of DNA is hydrophilic and negatively charged at physiological pH
• The side group nitrogenous bases are hydrophobic and present in the interior of DNA double helix
• DNA resists acid and alkali attacks in solution
• RNA undergoes rapid hydrolysis under alkaline conditions

Watson and Crick Model of DNA

• DNA comprised of two helical strands wound around the same axis to form a right-handed double helix
• Hydrophilic backbone of alternating deoxyribose and phosphate groups are on the outside of the double helix
• Furanose ring of each deoxyribose is in the C-2’ endo conformation
• Purine and pyrimidine bases of both strands are stacked inside the double helix with their hydrophobic and near planar ring structures perpendicular to long axis
• Offset pairing of two strands creates a major and minor groove
• Consistent with Chargaff’s rules, hydrogen bonding between A=T, G≡C

DNA Replication

• Avery et al. proved that DNA was the genetic material
• Martha and Hershey’s experiment confirmed DNA as the genetic material
• DNA sequencing involves using DNA as the template strand, annealing a short primer, and adding dNTPs and ddNTPs to determine the sequence
• Shotgun sequencing involves random breaking of genomic DNA and Sanger sequencing fragments individually
• Next-generation sequencing involves library preparation, cluster generation, sequencing, and alignment and data analysis by computer algorithms

Learn about the Watson and Crick model of DNA, which describes the structure of DNA as a right-handed double helix with a hydrophilic backbone of deoxyribose and phosphate groups on the outside. Understand how the purine and pyrimidine bases are stacked inside the double helix.