Tutor profile: Kelly H.

Find the error in the sentence below: Caroline dived straight into bed. "What a long day!" She exclaimed. "I'm so ready for the weekend."

The "She" in "She exclaimed" should be a lowercase "she" because it is not the start of a new sentence. It is a part of the same phrase as "What a long day!" and should not be capitalized.

Which element is more electronegative, Cl or Br?

Cl, chlorine, is more electronegative than Br, bromine. As halogens, both elements are highly electronegative relative to other groups on the periodic table. Chlorine is even more electronegative than bromine, however, because it contains less electron shells. While a neutral atom of Cl has 17 electrons, Br has 35. Bromine's additional electrons act to shield its nucleus, decreasing the atom's ability to attract electrons (and thus giving it a lower electronegativity than Cl).

Why must DNA replication occur from the 5' to 3' direction?

New nucleotides can only be added to an existing strand of DNA at the 3' end because of the nucleotides' molecular structures. The bases adenosine, guanosine, cytidine, and thymidine triphosphates used in DNA all contain a hydroxyl (OH) group at their 3' ends and a triphosphate group at their 5' ends. In the polymerization of DNA, the 3' hydroxyl group of the last nucleotide on the existing chain must bond with the 5' phosphate of the next nucleotide to be added. This can only occur if the new nucleotides bond to the 3' end of the existing chain, so DNA replication can only occur in the 5' to 3' direction.