Molecules (Unity and diversity)
- Water
- Medium for life
- First cells in water
- Most life processes aqueous
- Polarity and hydrogen bonds
- Unequal electron sharing
- O δ−, H δ+
- H bonds between molecules
- Cohesion
- Xylem transport under tension
- Surface tension habitats
- Adhesion
- Polar or charged surfaces
- Capillary action in soil
- Capillary action in cell walls
- Solvent properties
- Hydrophilic solutes dissolve
- Enzymes work in solution
- Plasma, xylem, phloem transport
- Some molecules must be hydrophobic
- Water vs air
- Buoyancy, viscosity
- Thermal conductivity
- Specific heat capacity
- Loon and ringed seal
- Water beyond Earth HL only
- Delivered by asteroids
- Retained: gravity, low temperature
- Goldilocks zone
- Medium for life
- Nucleic acids
- DNA: genetic material of life
- Some viruses use RNA
- Viruses not living
- Nucleotide
- Phosphate (circle)
- Pentose sugar (pentagon)
- Base (rectangle)
- Backbone and code
- Sugar–phosphate covalent backbone
- Base sequence is code
- RNA by condensation
- DNA double helix
- Two antiparallel strands
- A–T, G–C pairs
- Hydrogen bonds
- DNA vs RNA
- Two strands vs one
- Thymine vs uracil
- Deoxyribose vs ribose
- mRNA, tRNA, rRNA
- Information
- Base pairing: replicate, express
- 4ⁿ possible sequences
- Universal code: common ancestry
- Directionality and stability HL only
- 3' to 5' backbone links
- Built 5' to 3'
- Purine with pyrimidine
- Nucleosome HL only
- Eight-histone core
- Extra histone on linker DNA
- Key evidence HL only
- Hershey–Chase: ³²P, ³⁵S
- Chargaff: A = T, G = C
- Tetranucleotide hypothesis falsified
- DNA: genetic material of life