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level: 2.2 DNA replication

Questions and Answers List

level questions: 2.2 DNA replication

QuestionAnswer
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