Part 5 - Nucleic acids

Nucleic Acids

• Definition: Nucleic acids are macromolecules essential for all forms of life; they encode genetic information.

• Types: There are two main types of nucleic acids: DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).

DNA and Its Role

• Genetic Code: DNA codes for proteins that determine traits in living organisms such as appearance and function.

• Genes and Chromosomes: DNA consists of segments (genes) that are organized into structures called chromosomes.

Gene Expression

• Definition: Gene expression is the process through which information from a gene is used to produce a functional product, usually a protein.

• Central Dogma of Biology:

  • Replication: DNA replicates during cell division.

  • Transcription: DNA is transcribed into messenger RNA (mRNA).

  • Translation: mRNA is translated into a protein by ribosomes.

• Example: Insulin production in response to blood sugar levels involves transcription of the insulin gene followed by translation into the insulin protein.

Structure of Nucleic Acids

• Nucleotides: The building blocks of nucleic acids, each consisting of three components:

  • Pentose Sugar: A five-carbon sugar (ribose in RNA and deoxyribose in DNA).

  • Nitrogenous Base: Four possible bases (Adenine, Thymine (or Uracil in RNA), Cytosine, Guanine).

  • Phosphate Group: Contains phosphorus bonded to four oxygen molecules.

• Differences Between DNA and RNA:

  • RNA has a hydroxyl (-OH) group on the 2' carbon of the ribose sugar; DNA does not (deoxyribose).

  • RNA uses Uracil (U) instead of Thymine (T) found in DNA.

  • DNA is typically double-stranded, forming a double helix; RNA is usually single-stranded but can fold into complex shapes.

Polymers and Bonds

• Polynucleotide Formation: Nucleotides link together through condensation reactions forming phosphodiester bonds between the 3' hydroxyl and 5' phosphate groups.

• Primary Structure: The sequence of nucleotides in the nucleic acid chain is referred to as the primary structure.

Secondary Structure of DNA

• Double Helix: DNA consists of two strands running in opposite directions (antiparallel) and twisting to form a double helix.

• Base Pairing:

  • Adenine pairs with Thymine (two hydrogen bonds).

  • Guanine pairs with Cytosine (three hydrogen bonds).

• Chargaff's Rules: The amounts of A=T and C=G in a given DNA molecule reflect base pairing rules.

Functionality of RNA

• Versatility: RNA can serve both as genetic material and as a functional molecule, capable of catalyzing reactions (limited catalytic function).

• Evolutionary Theory: Some theories suggest RNA was the original genetic material due to its dual role as both a code and an active molecule.