ORC was first found in S. cerevisiae (where it may be called scORC), but similar complexes have now been characterized in Schizosaccharomyces pombe (spORC), Drosophila (DmORC), and Xenopus (XlORC). All of the ORC complexes bind to DNA.

TLS Online TPP Program

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#Unit 2. Cellular Organization

Linking number is topological property which is expressed as  Total No. of Base Pair/Base pair per turn.

TLS Online TPP Program

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#Unit 2. Cellular Organization

How to calculate linking number?

TLS Online TPP Program

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#Unit 2. Cellular Organization

If Lk <Lk0 and DLk is <0 means negative, then the DNA is said to be “negatively supercoiled.”

TLS Online TPP Program

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#Unit 2. Cellular Organization

Conversely, if Lk >Lk0  and DLk >0 means positive, then the DNA is “positively supercoiled.”

TLS Online TPP Program

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Superhelical Density 

TLS Online TPP Program

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#Unit 2. Cellular Organization

Circular DNA molecules purified from both bacteria and eukaryotes are usually negatively supercoiled, having values of s of approximately –0.06.