Key Discoveries in Genetics and Molecular Biology

Posted on Feb 22, 2025 in Biology

Pioneering Scientists and Their Contributions

  • Frederick Griffith: Observed bacteria causing pneumonia.
  • Andrei Nikolaevich Belozersky: Isolated DNA in a pure state.
  • Archibald Garrod: Suggested that some inherited diseases are caused by blockages of metabolic reactions in the body.
  • Edwin Chargaff: Found that in a segment of DNA, the amounts of adenine and thymine were equal.
  • Beadle and Tatum: Searched for mutations by observing consequences.

Fundamentals of Nucleic Acids

Nucleic acids: Organic molecules that carry genetic information.

Nitrogenous bases: Polar molecules with unevenly distributed electron clouds due to the presence of atoms.

Classification of Nitrogenous Bases

  1. Pyrimidines: Formed by a hexagonal ring; examples include cytosine, uracil, and thymine.
  2. Purines: Consist of a pentagonal and a hexagonal ring; examples include guanine and adenine.

Classification of DNA

  1. Non-repetitive DNA: Includes unique gene information.
  2. Moderately repetitive DNA: Comprises genes that carry information for ribosomal RNA, essential for protein synthesis.
  3. Highly repetitive DNA: Space DNA.

DNA Packaging Levels

  1. Nucleosomes: The double helix is wound around proteins called histones. Four units of proteins surrounded by DNA are called nucleosomes.
  2. Solenoid: Nucleosomes form another coil.
  3. Domains/Loops: Solenoids fold, forming loops that remain closed at their base by histone proteins.
  4. Chromosomes: Domain loops are wound on themselves to form chromosomes.

RNA Types and Functions

  1. Messenger RNA (mRNA): Carries a copy of gene information from the nucleus to the endoplasmic reticulum.
  2. Ribosomal RNA (rRNA): Along with ribosomal proteins, composes the ribosomes.
  3. Transfer RNA (tRNA): Base pairs with itself (palindromic bases) to form a cross-shaped structure and carries amino acids to the ribosome.

Hypotheses of DNA Replication

  1. Conservative Hypothesis: Each original strand serves as a template for the synthesis of new strands.
  2. Semi-conservative Hypothesis: Original strands serve as templates, but each new double helix contains one original and one new strand.
  3. Dispersive Hypothesis: Segments of original strands are duplicated and randomly joined with new segments.

Enzymes Involved in DNA Replication

  1. Helicases and SSB: Responsible for opening and stabilizing DNA strands.
  2. RNA Polymerase (RNA pol): Synthesizes the RNA primer.
  3. DNA Polymerase (DNA pol): Synthesizes the complementary DNA strand.
  4. Repair Enzymes: Repair errors made during DNA synthesis.
  5. Ligase: Joins DNA segments.

Cellular Economy and Protein Synthesis

Cellular Economy: Information is contained in segments of genetic material, allowing a protein to be encoded by various segments.

RNA Splicing: RNA is altered to bring it into its final functional form through a process called maturation.

Amino Acids: The basic units of proteins.

Proteins: There are about 150 amino acids, of which only 20 are involved in protein synthesis in the endoplasmic reticulum.

Gene: A segment of DNA corresponding to a protein; carries information for a protein structure.

Nucleosides: The union of a sugar and a nitrogenous base.