As the two strands of the double helix are separated, the positive supercoiling interferes with the further unwinding of DNA. Which of the following enzyme makes a break in a strand of DNA to release the supercoiling and facilitate the replication to occur?

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#Question id: 15146

#Unit 8. Inheritance Biology

You have isolated a set of five yeast mutants that form dark red colonies instead of the usual white colonies of wild-type yeast. You cross each of the mutants to a wild-type haploid strain and obtain the results shown below;

What do these results tell you about each of the mutants?

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#Question id: 2826

#Unit 2. Cellular Organization

An open reading frame (ORF) is defined as a DNA sequence that

a. begins with a start codon.               

b. ends with a stop codon.

c. contains 50 codons.   

d. contains approximately an equal frequency of A, T, G, and C.

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#Question id: 16134

#Unit 13. Methods in Biology

You obtain 6 BACs (of known order, as shown below) and 7 STSs (of unknown order) that derive from a region of mouse chromosome 16 whose genomic sequence has not yet been finished.   

 

By PCR (using 20-bp primers at either end of each STS), you test each of the 6 BACs for the presence (+) or absence (-) of each of the 7 STSs. You obtain the following results:

 

You determine the DNA sequences of PCR products obtained at STS5 using BACs B, C, D, E, and F as PCR templates. The DNA sequences of PCR products obtained using BACs B and C are identical, but they differ by several nucleotide substitutions from the DNA sequences of PCR products obtained using BACs E and F. Oddly, PCR product obtained using BAC D appears to be a mixture of two sequences – one corresponding to the BAC B/ BAC C sequence and the other corresponding to the BAC E/ BAC F sequence. Briefly account for these findings, and explain how a single PCR assay could amplify two different sequences.

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#Question id: 31195

#Unit 4. Cell Communication and Cell Signaling

Active Wnt signaling leads to:

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#Question id: 28598

#Unit 2. Cellular Organization

There are some given D cyclins in mammals, except?