DNA replication

• When does DNA replication occur in the cell cycle?

  Before cell division during interphase
• What phase of the cell cycle is specifically associated with DNA replication?

  S phase
• Why is DNA replication necessary?

  To ensure new cells have full DNA copies
• What does semi-conservative replication mean?

  One strand is parental, one is new
• What are the two types of DNA referred to in replication?

  Parental DNA and daughter DNA
• What are the four nitrogenous bases in DNA?

  Adenine, cytosine, guanine, thymine
• Which bases pair together in DNA?

  Adenine with thymine, cytosine with guanine
• Why is complementary base pairing important in DNA replication?

  It enables identical DNA copies and reduces errors
• What are the two key enzymes involved in DNA replication?

  DNA helicase and DNA polymerase
• What is the function of DNA helicase?

  To break hydrogen bonds between DNA bases
• What happens to the double helix during DNA replication?

  It unwinds and separates into two strands
• What do the separated DNA strands act as during replication?

  Templates for new DNA synthesis
• What are free-floating DNA nucleotides attracted to during replication?

  Complementary bases on template strands
• What is formed when adjacent nucleotides are joined together?

  A polynucleotide chain
• What type of reaction joins nucleotides together?

  Condensation reaction
• What bond is formed between nucleotides during DNA replication?

  Phosphodiester bond
• What is the role of DNA polymerase?

  To join adjacent nucleotides together
• How does DNA replication relate to the concept of semi-conservative replication?

  New DNA has one original and one new strand
• What are the key steps in DNA replication?

  1. DNA helicase breaks hydrogen bonds.
  2. Strands unwind and separate.
  3. Free nucleotides align with complementary bases.
  4. DNA polymerase joins nucleotides via condensation reactions.
• What is the significance of the Meselson and Stahl experiment?

  It proved the semi-conservative replication process
• What type of replication does Mrs. Anand Starr's experiment provide evidence for?

  Semiconservative replication
• Who discovered the structure of DNA in 1953?

  Watson and Crick
• What significant contribution did Rosalind Franklin make to DNA research?

  Research on x-ray diffraction
• What are the two key hypotheses about DNA replication proposed by Watson and Crick?

  • Conservative replication
  • Semiconservative replication
• What is semiconservative replication?

  One original strand and one new strand
• What is conservative replication?

  Original DNA remains intact, new DNA forms
• What was the purpose of Meselson and Stahl's experiment?

  To determine the type of DNA replication
• What are the nitrogenous bases in DNA?

  Adenine, thymine, cytosine, guanine
• What isotopes of nitrogen were used in the experiment?

  14N and 15N isotopes
• How do isotopes differ?

  Same protons, different neutrons
• What is required for bacteria to grow?

  Growth medium with nutrients
• What happens to bacteria grown in 14N medium?

  All DNA contains 14N isotope
• What happens to bacteria grown in 15N medium?

  All DNA contains 15N isotope
• What is the result of centrifuging DNA from 15N bacteria?

  DNA settles at the bottom
• What is the result of centrifuging DNA from 14N bacteria?

  DNA settles higher in the tube
• What are the steps of Meselson and Stahl's experiment?

  1. Grow E. coli in 15N medium
  2. Transfer to 14N medium
  3. Allow one round of division
  4. Centrifuge to analyze DNA density
• What happens after one round of division in 14N medium?

  One band of mixed density DNA
• What happens after two rounds of division in 14N medium?

  Two bands of DNA with different densities
• What is the expected result if replication were conservative?

  Two bands: one 14N, one 15N
• How did Meselson and Stahl disprove conservative replication?

  Found only one band of mixed density