A1 2 Nucleic Acid

A1.2.1-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.
A1.2.2-Components of a nucleotide
In diagrams of nucleotides use circles, pentagons and rectangles to represent relative positions of phosphates, pentose sugars and bases.
A1.2.3-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.A1.2.4-Bases in each nucleic acid that form the basis of a code
Students should know the names of the nitrogenous bases.
A1.2.5-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.
A1.2.6-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.
A1.2.7-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.
A1.2.8-Role of complementary base pairing in allowing genetic information to be replicated and
expressed
Students should understand that complementarity is based on hydrogen bonding.
A1.2.9-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.
A1.2.10-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
A1.2.11-Directionality of RNA and DNA
Include 5' to 3' linkages in the sugar-phosphate backbone and their significance for replication,
transcription and translation.
A1.2.12-Purine-to-pyrimidine bonding as a component of DNA helix stability
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.
A1.2.15-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.
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.A1.2.13-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.
A1.2.14-Evidence from the Hershey-Chase experiment for DNA as the genetic material