Content Objective: Understand the processes involved in DNA replication, including the semi-conservative mechanism, the role of key enzymes like helicase and DNA polymerase, and the directionality of DNA and RNA. Explore how DNA stability is maintained through purine-pyrimidine bonding and nucleosome structure, and investigate experimental evidence supporting DNA as the genetic material.
Language Objective: Use scientific language to describe the mechanisms of DNA replication, including enzyme functions and differences between leading and lagging strand synthesis. Explain key concepts such as 5' to 3' directionality, Okazaki fragments, and the importance of proofreading in maintaining replication accuracy.
Syllabus Details:
A1.2.15(HL)—Chargaff’s data on the relative amounts of pyrimidine and purine bases across diverse life forms
A1.2.13 (HL)—Structure of a nucleosome - "Limit to a DNA molecule wrapped around a core of eight histone proteins held together by an additional histone protein attached to linker DNA."
D1.1.1—DNA replication as production of exact copies of DNA with identical base sequences - "Students should appreciate that DNA replication is required for reproduction and for growth and tissue replacement in multicellular organisms."
D1.1.2—Semi-conservative nature of DNA replication and role of complementary base pairing "Students should understand how these processes allow a high degree of accuracy in copying base sequences."
D1.1.3—Role of helicase and DNA polymerase in DNA replication "Limit to the role of helicase in unwinding and breaking hydrogen bonds between DNA strands and the general role of DNA polymerase."
A1.2.11 (HL)—Directionality of RNA and DNA - "Include 5' to 3' linkages in the sugar–phosphate backbone and their significance for replication, transcription and translation."
A1.2.12 (HL)—Purine-to-pyrimidine bonding as a component of DNA helix stability - "Adenine–thymine (A–T) and cytosine–guanine (C–G) pairs have equal length, so the DNA helix has the same three-dimensional structure, regardless of the base sequence."
A1.2.14 (HL)—Evidence from the Hershey–Chase experiment for DNA as the genetic material "Students should understand how the results of the experiment support the conclusion that DNA is the genetic material."
D1.1.6 (HL)—Directionality of DNA polymerases "Students should understand the difference between the 5' and 3' terminals of strands of nucleotides and that DNA polymerases add the 5' of a DNA nucleotide to the 3' end of a strand of nucleotides."
D1.1.7 (HL)—Differences between replication on the leading strand and the lagging strand -"Include the terms “continuous”, “discontinuous” and “Okazaki fragments”. Students should know that replication has to be initiated with RNA primer only once on the leading strand but repeatedly on the lagging strand."
D1.1.8 (HL)—Functions of DNA primase, DNA polymerase I, DNA polymerase III and DNA ligase in replication - Limit to the simpler, prokaryotic system.
D1.1.9 (HL)—DNA proofreading - "Limit to the action of DNA polymerase III in removing any nucleotide from the 3' terminal with a mismatched base, followed by replacement with a correctly matched nucleotide."
Activity 2
Activity 3
A. Strengthen Your Skills
B. Expand Your Knowledge