| Guiding questions | |
|---|---|
| • How does the structure of nucleic acids allow hereditary information to be stored? • How does the structure of DNA facilitate accurate replication? |
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| A.1.2.1 | DNA as the genetic material of all living organisms |
| Some viruses use RNA as their genetic material but viruses are not considered to be living. | |
| A.1.2.2 | Components of a nucleotide |
| In diagrams of nucleotides use circles, pentagons and rectangles to represent relative positions of phosphates, pentose sugars and bases. | |
| A.1.2.3 | Sugar–phosphate bonding and the sugar–phosphate “backbone” of DNA and RNA |
| Sugar–phosphate bonding makes a continuous chain of covalently bonded atoms in each strand of DNA or RNA nucleotides, which forms a strong “backbone” in the molecule. | |
| A.1.2.4 | Bases in each nucleic acid that form the basis of a code |
| Students should know the names of the nitrogenous bases. | |
| A.1.2.5 | RNA as a polymer formed by condensation of nucleotide monomers |
| Students should be able to draw and recognize diagrams of the structure of single nucleotides and RNA polymers. | |
| A.1.2.6 | DNA as a double helix made of two antiparallel strands of nucleotides with two strands linked by hydrogen bonding between complementary base pairs |
| In diagrams of DNA structure, students should draw the two strands antiparallel, but are not required to draw the helical shape. Students should show adenine (A) paired with thymine (T), and guanine (G) paired with cytosine (C). Students are not required to memorize the relative lengths of the purine and pyrimidine bases, or the numbers of hydrogen bonds. | |
| A.1.2.7 | Differences between DNA and RNA |
| Include the number of strands present, the types of nitrogenous bases and the type of pentose sugar. Students should be able to sketch the difference between ribose and deoxyribose. Students should be familiar with examples of nucleic acids. | |
| A.1.2.8 | Role of complementary base pairing in allowing genetic information to be replicated and expressed |
| Students should understand that complementarity is based on hydrogen bonding. | |
| A.1.2.9 | Diversity of possible DNA base sequences and the limitless capacity of DNA for storing information |
| Explain that diversity by any length of DNA molecule and any base sequence is possible. Emphasize the enormous capacity of DNA for storing data with great economy. | |
| A.1.2.10 | Conservation of the genetic code across all life forms as evidence of universal common ancestry |
| Students are not required to memorize any specific examples. | |
| Additional higher level | |
| A.1.2.11 | Directionality of RNA and DNA |
| Include 5' to 3' linkages in the sugar–phosphate backbone and their significance for replication, transcription and translation. | |
| A.1.2.12 | 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. | |
| A.1.2.13 | 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. Application of skills: Students are required to use molecular visualization software to study the association between the proteins and DNA within a nucleosome. | |
| A.1.2.14 | 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. NOS: Students should appreciate that technological developments can open up new possibilities for experiments. When radioisotopes were made available to scientists as research tools, the Hershey–Chase experiment became possible. | |
| A.1.2.15 | Chargaff’s data on the relative amounts of pyrimidine and purine bases across diverse life forms |
| NOS: Students should understand how the “problem of induction” is addressed by the “certainty of falsification”. In this case, Chargaff’s data falsified the tetranucleotide hypothesis that there was a repeating sequence of the four bases in DNA. | |
| Linking questions | |
| • What makes RNA more likely to have been the first genetic material, rather than DNA? • How can polymerization result in emergent properties? |
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