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biomedical science?

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These are protein structures I downloaded from the Protein Data Bank in the internet.

This is the picture of a gyrase.



DNA gyrase, sometimes only called gyrase, is an enzyme in the topoisomerase family that passes one double strand of DNA through another double strand of DNA. Because gyrase changes the linking number of the DNA by two in each enzymatic step, it is classified as a type II topoisomerase. Gyrase has two main activities: introducing negative supercoils and relaxing positive supercoils. The unique ability of gyrase to introduce negative supercoils into DNA is what allows bacterial DNA, but not eukaryotic DNA, to have free negative supercoils. Gyrase is only found in bacteria; it is not found in eukaryotes, a property that makes gyrase a good target for antibiotics. Two classes of antibiotics that inhibit gyrase are the coumarins, including novobiocin, and the quinolones, which include naladixic acid and ciprofloxacin (better known as Cipro). The ability of gyrase to relax positive supercoils comes into play during DNA replication. The right-handed nature of the DNA double helix causes positive supercoils to accumulate ahead of a translocating enzyme, in the case of DNA replication, a DNA polymerase. The ability of gyrase (and topoisomerase IV) to relax positive supercoils allows superhelical tension ahead of the polymerase to be released so that replication can continue.

This is the description of gyrase taken from the protein data bank.
Polymeric Molecules
Chain _
Description:Gyrase A
Fragment:59KDA FRAGMENT
Mutation:null
Formula Weight:55402.2
Entity Name:null
Entity Name:Sys n/a
RCSB_NAME:GYRASE A

This is the picture of a helicase.

Helicase is an enzyme vital to all living organisms. Its function is to temporarily separate the two strands of a DNA double helix so that DNA or RNA synthesis can take place. RNA polymerase has its own helicase activity, whereas, in DNA polymerase, the helicase is a separate subunit. Helicase is a donut-shape enzyme and is produced by the DnaB gene in prokaryotes. In conjunction with DNA primase, helicase promotes DNA unwinding by binding to the initiator proteins and loading into the DNA. Helicase then denatures (untwists) the DNA by hydrolysis of adenosine triphosphate (ATP). Continuous hydrolysis of ATP allows helicase to move along the single strand of DNA, while untwisting the double-strand DNA as it progresses. An enzyme topoisomerase binds to the double-strand DNA downstream of the unwound DNA to prevent excess strain on the helix. In other words, it separates the two strands in the double helix.

This is the description of helicase taken from the protein data bank.
Polymeric Molecules
Chain _
Description:Rho
Fragment:RNA BINDING DOMAIN, RESIDUES 1 - 130
Mutation:null
Formula Weight:14640.8
Source:Method man
Entity Name:null
Entity Name Sys n/a


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