Nucleic Acids and Chargaff's Rule

Nucleic Acids

• Nucleic acids are macromolecules that store genetic information and enable protein production (DNA & RNA)
• Nucleotides are the monomers of nucleic acids
• Nucleotides consist of:
  • Nitrogenous bases (Purines & Pyrimidines)
  • Sugar (Ribose or Deoxyribose)
  • Phosphate group

Chargaff's Rule

• In all cellular DNA, regardless of the species, the number of adenine residues equals the number of thymine residues, and the number of guanine residues equals the number of cytosine residues.
• The sum of purine residues equals the sum of pyrimidine residues (A + G = T + C)

Nucleic Acid Structure ("Base Pairing")

• DNA base pairing is antiparallel
• In DNA, A pairs with T, and G pairs with C
• RNA (usually) exists as a single-stranded polymer
• DNA exists as a double-stranded polymer
• DNA's double strand is formed by hydrogen bonds between complementary nucleotides.
• Nucleotides always bind to complementary nucleotides

Polymerize Nucleotides

• Nucleotides are linked by phosphodiester linkages to form DNA or RNA strand.
• The 5' phosphate of one nucleotide is linked to the 3' hydroxyl group of the next nucleotide.

Nucleic Acid Structure - Polymerization

• The hydrophilic backbones of alternating deoxyribose and phosphate groups are on the outside of the double helix, facing the surrounding water.

• The sequence of bases along a DNA strand is important for the function of DNA.

DNA is Right-handed double helix

• DNA consists of two helical DNA chains wound around the same axis to form a right-handed double helix.

The Double Helix

• 3.4 Å per base pair
• 10 base pairs per turn
• 10-11 in aqueous solution
• 2 anti-parallel strands
• 36 Å major groove
• 20 Å minor groove

Formation of phosphodiester bond

• The formation of a phosphodiester bond connects nucleotides to form a polynucleotide chain. This linkage is a condensation reaction releasing a molecule of water.

Where is it located?

• Most DNA is located in the cell nucleus (called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (called mitochondrial DNA or mtDNA).

RNA

• RNA = ribonucleic acid
• RNA is a single-stranded polymer
• Each RNA nucleotide consists of:
  • A pentose sugar (ribose)
  • A phosphate group
  • A base (adenine, cytosine, guanine, uracil instead of thymine)

Types of RNA

• Ribosomal RNA (rRNA): Major component of the ribosomes.
• Messenger RNA (mRNA): Carries information for protein synthesis from the DNA in the nucleus to the ribosomes.
• Transfer RNA (tRNA): Brings amino acids to the ribosomes for protein synthesis.

The denaturation of DNA (melting)

• Denaturation: Double-stranded DNA can be separated into two component strands in solution by increasing the temperature or pH (alkali)
• Phosphodiester bonds are not broken by this treatment.
• Renaturation: Separated strands of DNA will renature when physiologic temp and pH are achieved.

Structural forms of the double helix

• There are three major structural forms of DNA:
  • The B form, described by Watson and Crick in 1953
  • The A form
  • The Z form

Melting temperature (Tm)

• When DNA is heated, the temperature at which one half of the helical structure is lost is defined as the melting temperature (Tm).

DNA can From Three Types of Helices

• The different forms (A, B, and Z) of DNA have different diameters, numbers of base pairs per turn, and groove sizes. This also affects the amount of water the DNA helix can interact with.

Explore the fascinating world of nucleic acids, including DNA and RNA, their structures, and the fundamental rules governing base pairing. This quiz covers nucleotides, Chargaff's Rule, and the properties of DNA and RNA. Test your understanding of the concepts that are crucial for genetics and molecular biology.