DNA replication

living cells replace dead cells, new cells need to be 100% identical to old, dna needs to be copied inside the nucleus.

three models of dna replication: semi-conservative, conservative, dispersive.

semi-conservative: one strand of original DNA and one strand of new DNA.

conservative: original DNA and new molecule of DNA.

dispersive: two molecules of DNA, chunks of new DNA and chunks of old.

experiment:

different types of nitrogen exist due to mass

the larger number of nitrogen, the heavier the nitrogen as more neutrons.

meselson and stahl used n-14 and n-15 in experiment

used centrifuge, used to seperate substance based on weight.

heavier molecules will go to bottom as a pellet, lighter will still be a solution at top.

grew bacteria with just n-15, put into environment with n-14. any new dna formed would be used with n-14. two dna molecules will contain one strand of n-14 and n-15. waited until dna replicated once, took sample, placed in solution and centrifuged. found that dna gathered into a single band, each new dna molecule must contain both n-14 and n-15. supports semi-conservative and dispersive.

roles of nitrogen: create organism’s DNA, provide the necessary building blocks for nucleotides. essential for huge range of organisms. nitrogen is taken from an organism’s environment. plants get nitrogen from soil, we get nitrogen from these plants. type of nitrogen absorbed by plant is the type of nitrogen that we will absorb and will in turn determine the type of nitrogen available in our body to build new DNA molecules.