Hershey and Chase used and experiment in which they traced viruses’ infection of the host cell and using radioactive markers determined that nucleotides not proteins were the genetic materials. Watson and Crick can up with the model of the structure and pairing of the DNA in large part due to the discoveries and use of X-ray crystallography by Franklin and Wilkins who saw that the DNA formed a double helix. The Watson and Crick model stated that DNA was a double helix, that A paired with T and C paired with G because they were purines and prymadines and two of the same kind couldn’t pair together without making the structure too large. Also DNA arranged itself in an anti-parallel manner.
What is the difference between DNA replication of the leading strand and the lagging strand?
The leading strand is copied in the 5’ to 3’ direction towards the replication bubble in one long strand with no interruption. The lagging strand is moving in the wrong direction technically so it has to replicate in smaller segments called okazaki fragments in 5’ to 3’ direction and each segment has to be primed and then reconnected by DNA ligase. Even though it would seem the lagging strand would be slower in actuality both strands replicate at an even pace.
How does DNA replication guard against error?
The fact that each base will only pair with one other base makes the room for error smaller. DNA has functions such as mismatch repair, which will replace a incorrectly placed base with the right base. Nucleotide excision repair is when chunks of incorrectly coded DNA are removed and the correct sequence is spliced back in. Also telomeres are long strands of noncoding DNA placed at the end of every strand of DNA so that each time the strand shortens it doesn’t cut out DNA that actually codes for anything.
Facts:
- When DNA replicates the new strand has one daughter strand and one strand from the original so that both of the new strands are half of the original
- Cytosine and thymine are pyrimidines and Adenosine and Guanine are purines
- The helix of DNA makes a turn about every 3.4 nm
- Helicase unwinds the DNA before and after the replication fork so that it doesn’t wind to tightly and tear
- DNA polymerase 3 synthesizes the new strands of DNA
This shows the base pairing that occurs along with the double helix and anti-parallel structure that a DNA molecule has. Also showing how the bases are attached to the sugar phosphate backbone, which allows them to stay stable.
Summary: Understanding that DNA is the genetic material is relatively recent within the study of biology but much is now known about DNA. DNA replicates by attaching the 5’ end of a strand with DNA polymerase 3 after primer helps it bind it then creates a complimentary strand that has a sequence opposite the replicated one. The DNA of non-eukaryotes is simpler and doesn’t take as much time to replicate because it is circular eukaryotes are more complicated because some genes are more tightly packed as to not be replicated ect.
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