• While humans have 700 times more DNA content than E. coli per haploid cell, humans have approximately 25,000 genes, which is only six times of that possesed by E. coli (4300 genes).
  • Each DNA molecule in a cell has a unique base sequence.
  • Eukaryotic DNA includes many repeated sequences.
  • Eukaryotic genes include exons with amino acid sequence information and introns without amino acid sequence information.
  • When a cell proliferates, a DNA molecule in the parent cell is accurately replicated into two molecules and distributed equally to the two daughter cells formed at cell replication.
  • DNA synthesis is termed replication because of the replication of genetic information.
  • When DNA is replicated using the parent strand as a template, four types of nucleotides are sequentially added to form base pairs, thus synthesizing a daughter strand with a base sequence complementary to the parent strand.
  • Newly produced double-stranded DNA consists of one parent strand and one daughter strand. This replication method is termed semiconservative replication.
  • While DNA polymerase plays a leading role in DNA replication reactions, the reaction is complex and involves a range of enzymes and proteins.
  • DNA is continuously subjected to damage from chemical substances, radiation, and ultraviolet light, and all organisms have an enzyme system that repairs damage.

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