Lecture on Nucleic Acids: DNA and RNA

Introduction to Nucleic Acids

• Nucleic acids are essential macromolecules found in living systems.
• Two main types: DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).
• DNA carries genetic information for living organisms.
• Viruses with RNA are not considered living organisms.

Structure of Nucleotides

• Nucleotides are the building blocks of nucleic acids.
• Consists of three components:
  • Pentose Sugar: Can be ribose or deoxyribose.
  • Phosphate Group: PO₄³⁻, connects to the fifth carbon of the sugar.
  • Nitrogen Base: Attached to the first carbon of the sugar.

DNA Structure

• DNA is made up of repeating nucleotides forming a long molecule.
• The backbone is created by bonds between the phosphate of one nucleotide and the sugar of another.
• Four nitrogen bases in DNA:
  • Adenine (A)
  • Thymine (T)
  • Guanine (G)
  • Cytosine (C)
• The order of bases constitutes the genetic code.
• DNA structure:
  • Two strands forming a double helix.
  • Strands are antiparallel (opposite directions).
  • Connected by hydrogen bonds between bases.

RNA Structure

• RNA is a single strand of nucleotides.
• Similar backbone as DNA.
• Bases in RNA:
  • Adenine (A)
  • Uracil (U)
  • Guanine (G)
  • Cytosine (C)
• Differences from DNA:
  • Single-stranded.
  • Uracil replaces Thymine.
  • Contains ribose sugar instead of deoxyribose.

Complementary Base Pairing

• DNA base pairing rules:
  • Adenine with Thymine (2 hydrogen bonds)
  • Guanine with Cytosine (3 hydrogen bonds)
• RNA complementary pairing with DNA:
  • Adenine pairs with Uracil (instead of Thymine)

DNA and Genetic Information

• DNA can store large amounts of genetic information due to four bases.
• Possible combinations:
  • 4 bases in a sequence of 4 = 256 combinations.
  • 20 base sequence = over 1 trillion combinations.
• DNA's compact size allows vast storage in nuclei.
• Universality in the genetic code across all organisms.
• Supports the theory of universal common ancestry.

Conclusion

• The structure and function of DNA and RNA are central to understanding genetics and the evolution of life on Earth.
• DNA's ability to store and replicate genetic information is key to the development of complex organisms.