Lecture Notes on Nucleic Acids

Overview of Nucleic Acids

• Nucleic acids are one of four essential macromolecules in living systems.
• They carry genetic information essential for life, primarily in the form of DNA (Deoxyribonucleic Acid).
• DNA is unique in that it is the only molecule known to carry genetic information for living organisms.
• Viruses may use RNA, but they are not classified as living organisms.

Structure of Nucleotides

• Nucleotides: Building blocks of nucleic acids.
  • Composed of a pentose sugar, a phosphate group, and a nitrogen base.
  • Pentose Sugar: Can be ribose or deoxyribose.
    • Represented as a pentagon in models due to its shape.
  • Phosphate Group: Linked to the sugar's fifth carbon, represented as a circle.
  • Nitrogen Base: Variations include adenine (A), thymine (T), guanine (G), cytosine (C).

DNA and RNA Structure

• DNA: Composed of two strands of nucleotides.

  • Strands are parallel but oriented in opposite directions.
  • Held together by hydrogen bonds between nitrogen bases.
  • Bases form the genetic code; sugar and phosphate groups form the backbone.

• RNA: Composed of a single strand of nucleotides.

  • Contains uracil (U) instead of thymine (T).
  • Uses ribose sugar instead of deoxyribose.

Differences Between DNA and RNA

1. Number of Strands:
   • DNA has two strands; RNA has one.
2. Base Composition:
   • DNA: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
   • RNA: Adenine (A), Uracil (U), Guanine (G), Cytosine (C).
3. Sugar Component:
   • DNA: Deoxyribose (lacks an oxygen on the second carbon).
   • RNA: Ribose (includes a hydroxyl group).

Formation and Function

• DNA: Stores genetic information and instructions for building organisms.

  • Universal genetic code across organisms suggests a common ancestor.
  • Capable of storing vast information due to the variety in base sequences.

• RNA: Transcribed from DNA; involved in protein synthesis.

  • RNA strands are formed via condensation reactions, similar to DNA.

Base Pairing Rules

• DNA Base Pairing:

  • Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
  • Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.

• RNA Base Pairing (during transcription):

  • Adenine (A) pairs with Uracil (U) instead of Thymine (T).

Importance of DNA

• DNA's ability to store information is vast due to multiple base combinations.
• It is compact, allowing storage of genetic material in small spaces.
• Universality across organisms provides evolutionary evidence of a common ancestor.

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These notes cover the essential points on nucleic acids, focusing on their structure, function, and differences between DNA and RNA, as discussed in the lecture.