Semi-Conservational + Conservational replication: Flashcards
What is the general basis of semi-conservational replicatioN?
= the dna double helix seperates into 2 polynucleotide strands
= each strand is replicated to form a complementary new strand
= each copies has 1 of the original dna strand and 1 new strand
What is conservative replication?
= a dna double helix is formed containing 2 new strands contains none of the original
What do all DNA bases contain?
= nitrogen
How many and what isotopes does nitrogen consist of?
= 2 isotopes
= nitrogen-14 - common
= nitrogen-15-
= slightly heavier than nitrogen-14
What is the first step scientists did?
= took a sample of bacteria
= under normal conditions almost all of the nitrogen atoms in the DNA are nitrogen-14 (lighter)
How did scientists determine that replication was either semi or conservative? (1)
= took sample of bacteria + extracted the DNA
= placed the DNA in a solution and spun this at high speeds in a centrifuge
= dna moved down the solution and formed a band that the scientists could detect
What does the position of the DNA band depend on?
=how heavy or light it is
How did scientists determine that replication was either semi or conservative? (1) RESULTS
= nitrogen atoms in the DNA are almost all nitrogen-14
= formed a band at the top of the tube
How did scientists determine that replication was either semi or conservative? (2)
= scientist cultured the bacteria into a growth medium
= contained only nitrogen-15
= after the bacteria has reproduced many times- almost all of the atoms in their dna was nitrogen 15
How did scientists determine that replication was either semi or conservative? (2) RESULTS
= when the dna was extracted and centrifuged- band formed at the bottom
How did scientists determine that replication was either semi or conservative? (3)
= scientists took a sample of the bacteria- growing on nitrogen-15
= transferred these bacteria to nitrogen-14
= allowed them to replicate their DNA only once
= extracted the dna and spun the centrifuge
How did scientists determine that replication was either semi or conservative? (3) RESULTS
= DNA produced a band in between the 2 bands
= meant the DNA contained 1 strand of nitrogen-14 and one strand of nitrogen-15
= means the dna is semi-conservativley replicated
How did scientists determine that replication was either semi or conservative? (4)
= scientists allowed the bacteria to replicate 1 more time on nitrogen-14
How did scientists determine that replication was either semi or conservative? (4) RESULTS
= when the dna was extracted and spun it produced an intermediate band and another at the top
What happens if the dna replicates conservativley?
= after out first dna replication we would have a dna molecule only containing nitrogen-15 and one only containing nitrogen-14
