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IB Biology Topic A1.2 Nucleic Acids Revision Notes… | RevisionDojo

A1.1 Water

A1.2 Nucleic acids

A2.1 Origins of cells (HL)

A2.2 Cell structure

A2.3 Viruses (HL)

A3.1 Diversity of organisms

A3.2 Classification and cladistics (HL)

A4.1 Evolution and speciation

A4.2 Conservation of biodiversity

B1.1 Carbohydrates and lipids

B1.2 Proteins

B2.1 Membranes and membrane transport

B2.2 Organelles and compartmentalization

B2.3 Cell specialization

B3.1 Gas exchange

B3.2 Transport

B3.3 Muscle and motility (HL)

B4.1 Adaptation to environment

B4.2 Ecological niches

C1.1 Enzymes and metabolism

C1.2 Cell respiration

C1.3 Photosynthesis

C2.1 Chemical signalling (HL)

C2.2 Neural signalling

C3.1 Integration of body systems

C3.2 Defense against disease

C4.1 Populations and communities

C4.2 Transfer of energy and matter

D1.1 DNA replication

D1.2 Protein synthesis

D1.3 Mutations and gene editing

D2.1 Cell and nuclear division

D2.2 Gene expression (HL)

D2.3 Water potential

D3.1 Reproduction

D3.2 Inheritance

D3.3 Homeostasis

D4.1 Natural selection

D4.2 Sustainability and change

D4.3 Climate change

IB
A1.2 Nucleic acids

A1.2D Classic DNA experiments: Hershey–Chase and Chargaff's data (HL)

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Subtopics and learning objectives

A1.2.14 Evidence from the Hershey–Chase experiment for DNA as the genetic material (HL only)

A1.2C Directionality, helix stability and nucleosomes (HL)

The Hershey-Chase Experiment Showed DNA Is the Genetic Material

In the 1950s, scientists were debating one big question: which molecule carries the genetic instructions for life?
Was it protein, known for its complexity, or DNA, a simpler molecule?
Alfred Hershey and Martha Chase settled the debate with a clever experiment.

Tracing DNA and Protein With Radioactive Labels

They used two radioactive isotopes to label the two molecules separately.
1. Phosphorus-32 (³²P) labelled DNA, because DNA contains phosphorus but no sulfur.
2. Sulfur-35 (³⁵S) labelled protein, because protein contains sulfur but no phosphorus.
They grew bacteriophages so that one batch had labelled DNA and the other had labelled protein coats.

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A1.2.14 Evidence from the Hershey–Chase experiment for DNA as the genetic material (HL only)
A1.2.15 Chargaff’s data on pyrimidine and purine bases across diverse life forms (HL only)

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