| Two main stages of cell division | - Nuclear division
- Cytokinesis |
| Nuclear division | - Process by which the nucleus divides
- Two types: mitosis and meiosis |
| Cytokinesis | - Follows nuclear division
- Process where whole cell divides |
| Four requirements of semi-conservative replication | - Four types of nucleotides, each with their bases
- DNA strands act as template for attachment of these nucleotides
- The enzyme DNA polymerase
- A source of chemical energy |
| The process of semi-conservative replication | - Enzyme DNA helicase breaks hydrogen bonds between the base pairs
- The strands in the double helix separates
- Free nucleotides in the nucleus bind by specific base parings as there are exposed polynucleotide strands
- Nucleotides are joined by condensation reactions, forming phosphodiester bonds, by the enzyme DNA polymerase
- Each strand retains half of the original DNA material |
| What was Meselson and Stahl's experiment | - They used a heavy isotope of nitrogen and a light isotope of nitrogen to prove that DNA replicates semi-conservatively |
| Meselson and Stahl’s Experiment | - Bacteria are grown in a heavy 15N nitrogen isotope
- A sample of DNA from the 15N culture was extracted and spun in a centrifuge
- 15N DNA was then taken out and added to the lighter 14N nitrogen
- Samples were removed, producing 3 generations |
| Results from experiment | - DNA grown in 15N medium - ALL HEAVY DNA
- First generation after transfer to 14N medium, ALL INTERMEDIATE DNA
- Second generation, 50% LIGHT, 50% INTERMEDIATE
- Third generation, 75% LIGHT, 25% INTERMEDIATE |
