Activities Key Terms Quizzes Art Chapter 14 Self-Quiz
Unit 3: Genetics DNA Review
  1. DNA is the hereditary material of organisms. It is a two-stranded molecular "ladder" twisted into a . DNA is made of building blocks. Each nucleotide consists of a backbone attached to a . The sugar in DNA is a 5-carbon , with the nitrogen base attached to the 1' carbon and the phosphate group attached to the 5' carbon.
  2. The sugar-phosphate backbone forms the "sides" of the ladder with strong bonds. The 3' carbon bonds with the phosphate group of the next nucleotide. The two sides are since the sugar rings are oriented in opposite directions.
  3. The nitrogenous bases form the "rungs" that are held together by weak bonds that form between specific bases on opposite strands. There are four nitrogenous bases in DNA: (A), (T), (G), and (C). T always pairs with A, and C always pairs with G.
  4. Variation in DNA base sequences is responsible for the different of genes, and thus serves as the basis for genetic diversity and inheritance.
  5. The specific pattern of base in DNA provides the mechanism for DNA replication. An existing strand serves as a for the formation of a new strand.
  6. DNA replication requires enzymes such as which unwinds the double helix by breaking the hydrogen bonds, which "primes" the replication with starter RNA nucleotides, DNA which adds DNA nucleotides to each template strand on short fragments in the 5' to 3' direction, and which joins the fragments together to form new strands.
  7. DNA can be altered by numerous environmental factors, such as light and , or by errors during the replication process. DNA repair enzymes can correct most of the errors by removing the damaged strand and replacing that strand by base-pairing with the remaining strand.
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