DNA structure and key scientists

• DNA stores and transmits genetic information from parents to offspring.

Four DNA Bases

• The four DNA bases are:
  • Adenine
  • Thymine
  • Guanine
  • Cytosine
• DNA has antiparallel strands.
• DNA's structure includes a DNA ladder which forms a double helix.

Key Scientists and Discoveries in DNA

• 1869: Friedrich Miescher isolated a substance found in the nucleus of cells called nuclein from pus cells.
• 1930: Joachim Hammerling proved genetic material is in the nucleus through experiments on algae with distinct foot, stalk, and cap regions.
• Cutting off the cap of algae allowed regeneration, while cutting off the foot did not.
• Since the foot contains the nucleus, this confirmed the location of genetic material.
• Hammerling's experiment did not identify what the genetic material was.
• 1920: Phoebus Levene discovered DNA components: phosphate groups, nitrogenous bases, and deoxyribose (5C), disagreeing that proteins were the molecule for heredity.
• Three billion nucleotide pairs make up the human genome.
• DNA's diversity arises from just four bases: A, C, T, G.
• Frederick Griffith discovered bacterial transformation using R-S strains of pneumococcus while trying to discover fix for virus pneumonia.
• Injecting mice with the S strain resulted in pneumonia and death.
• Injecting mice with the R strain did not cause pneumonia.
• Heat-killed S strain: the mouse lived.
• Heat-killed S strain plus live R strain led to pneumonia and death, revealing DNA as the transforming principle.
• 1940: Erwin Chargaff determined A=T and G=C in DNA.
• He isolated DNA from organisms and observed the levels of each base, proposing equal amounts for each pair.
• 1951: Rosalind Franklin used X-ray crystallography to study DNA, producing photograph 51.
• Watson used Franklin's work giving it to Crick and Wilson, who were given nobel prizes, while Franklin wasn't and sadly died.
• 1952: Alfred Hershey and Martha Chase proved that viruses inject DNA into bacteria to produce new viral particles by using bacteriophages.
• Radioactive DNA was separated from protein inside the bacteria. DNA directs the production of new viruses and is the hereditary material.
• Avery, MacLeod, and McCarty identified DNA as the transforming principle.
• 1953: Watson and Crick created a DNA model; DNA is a double helix made of two DNA nucleotide stands that run in opposite directions.
• The backbone consists of alternating phosphate groups and pentose sugars, with nitrogenous bases acting as rungs.
• Complementary base pairing explains how bases pair between strands, following a pattern (X) created by Wilkins and Franklin.
• Linus Pauling used X-ray diffraction to study crystallized substances, providing information on structure.

Bonds in DNA

• Covalent bonds connect the phosphate backbone in DNA strands, linking the phosphate group to the sugar.
• Hydrogen bonds hold the strands of the double helix together (A with T, G with C).

Writing DNA and RNA Molecules

• To write a complementary DNA strand, write the opposite letters for each base.
• To write an RNA molecule, split it into triplets, replace thymine with uracil, and write the Anticodons for mRNA in triplet form.

Central Dogma

• Transcription: DNA stays in the nucleus and has the instructions to make protein. DNA information is copied into RNA and bases match as follows:
  • A → U
  • T → A
  • C → G
  • G → C
• Translation: RNA copies instructions in nucleus then arrives at ribosomes and reads three bases at a time (codons). A tRNA molecule matches each codon containing an anticodon and amino acid. Each tRNA adds its amino acid, forming a chain to create a polypeptide.