A 1.2 Nucleic Acids
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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SL and HL Content
Learning Objectives
A1.2.1—DNA as the Genetic Material
Discuss why DNA is the genetic material in all living organisms.
Explain why some viruses use RNA instead of DNA.
Debate why viruses are not considered living organisms.
Deoxyribonucleic Acid (DNA) is a molecule composed of two long chains (strands) coiled around each other to form a double helix.
It carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses.
Structure of DNA:
DNA is made up of nucleotides, each consisting of:
a phosphate group
a sugar molecule (deoxyribose)
a nitrogenous base (adenine [A], thymine [T], cytosine [C], or guanine [G])
The sequence of these bases encodes genetic information.
Function of DNA:
DNA holds the instructions for the synthesis of proteins, which are essential for cell structure and function.
Genes, segments of DNA, are transcribed into RNA and then translated into proteins.
Universal Genetic Code:
The genetic code is nearly universal, with the same codons coding for the same amino acids in almost all organisms, demonstrating the common ancestry of life.
RNA in Viruses:
Viruses are infectious agents that replicate only inside the living cells of an organism.
Some viruses use RNA (Ribonucleic Acid) instead of DNA as their genetic material.
RNA viruses can have single-stranded or double-stranded RNA genomes.
Examples of RNA Viruses:
Influenza virus, HIV, and coronaviruses (e.g., SARS-CoV-2) are examples of RNA viruses.
A1.2.2—Components of a Nucleotide
Identify and describe the three components of a nucleotide: phosphates, pentose sugars, and nitrogenous bases.
Discuss the use of circles, pentagons, and rectangles in diagrams to represent these components.
A1.2.3—Sugar–Phosphate Bonding
Explain how sugar-phosphate bonds form the backbone of DNA and RNA.
Discuss the significance of the continuous chain of covalently bonded atoms in nucleotides.
A1.2.4—Nitrogenous Bases
List the names of the nitrogenous bases in nucleic acids.
Discuss the role of these bases in the genetic code.
A1.2.5—RNA Structure
Describe how RNA is formed by the condensation of nucleotide monomers.
Draw and recognize diagrams of single nucleotides and RNA polymers.
A1.2.6—DNA Structure
Explain the structure of DNA as a double helix with antiparallel strands.
Discuss hydrogen bonding between complementary base pairs: adenine (A) with thymine (T) and guanine (G) with cytosine (C).
A1.2.7—Differences between DNA and RNA
Compare and contrast DNA and RNA in terms of strand number, types of nitrogenous bases, and type of pentose sugar.
Sketch the differences between ribose and deoxyribose sugars.
A1.2.8—Complementary Base Pairing
Discuss the role of complementary base pairing in DNA replication and expression.
Explain how hydrogen bonding is crucial for complementarity.
A1.2.9—DNA’s Capacity for Storing Information
Explain the diversity of possible DNA base sequences and their implications.
Emphasize the enormous capacity of DNA for storing genetic information.
A1.2.10—Universal Genetic Code
Discuss the conservation of the genetic code across all life forms as evidence of common ancestry.
Additional Higher Level
A1.2.11—Directionality of RNA and DNA
Explain the significance of 5’ to 3’ linkages in the sugar-phosphate backbone.
Discuss the importance of directionality for replication, transcription, and translation.
A1.2.12—Purine-to-Pyrimidine Bonding
Discuss how purine-to-pyrimidine bonding contributes to DNA helix stability.
Explain why adenine–thymine (A–T) and cytosine–guanine (C–G) pairs result in a consistent three-dimensional structure.
A1.2.13—Structure of a Nucleosome
Describe the structure of a nucleosome: DNA wrapped around histone proteins.
Use molecular visualization software to study the association between proteins and DNA within a nucleosome.
A1.2.14—Hershey–Chase Experiment
Explain the significance of the Hershey–Chase experiment in identifying DNA as the genetic material.
Discuss how technological advancements enable new experimental possibilities.
A1.2.15—Chargaff’s Data
Analyze Chargaff’s data on the relative amounts of pyrimidine and purine bases across different life forms.
Discuss how the data falsified the tetranucleotide hypothesis, addressing the “problem of induction” through “certainty of falsification”.