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2.5Summary

  • All organisms have high-molecular DNA that carries genetic information. The use of this information involves high-molecular RNA.
  • DNA and RNA are both organic compounds called nucleic acids (nucleotides).
  • A nucleotide (a structural unit of DNA and RNA) consists of three components - a base, a pentose and a phosphate. High-molecular DNA and RNA are polynucleotides composed of nucleotides.
  • DNA consists of four base types - adenine (A), cytosine (C), guanine (G) and thymine (T) - and RNA consists of four base types - adenine (A), cytosine (C), guanine (G) and uracil (U).
  • The pentose that constitutes DNA is 2-deoxyribose, while that in RNA is ribose.
  • In high-molecular DNA, two long polynucleotide strands form a right-handed double helix.
  • Bases are connected between the two strands of high-molecular DNA by a hydrogen bond, creating base pairs. These are formed between adenine (A) and thymine (T) and between cytosine (C) and guanine (G).
  • Although high-molecular RNA is single-stranded, partial double strands are often formed within the molecule.
  • The structure of high-molecular nucleic acids has a particular nucleotide order characterized by its base sequence. This is called the base sequence of nucleic acids.
  • Although one human cell contains approximately 1,000 times as much DNA as E. coli, humans have approximately 26,000 genes - only six times as many as E. coli's 4,300.
  • Each DNA molecule in a cell has a unique base sequence.
  • When a cell multiplies, a DNA molecule identical to that of the parent cell is replicated, and the two molecules are equally distributed to the two daughter cells.
  • DNA synthesis is also called DNA replication because genetic information is replicated during the process.
  • When DNA is replicated using the parent strand as a template, four nucleotide types are individually added to form base pairs, thus synthesizing daughter strands with a sequence complimentary to that of the parent strand. This method is called semiconservative replication.
  • Newly synthesized double-stranded DNA consists of one parent and one daughter strand.
  • Although the main agent in the DNA replication reaction is DNA polymerase, the reaction is complex and involves many types of enzymes and proteins.

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