Tutor profile: Aj S.

Choose the word pair that best completes the following sentence: The threat of rain didn’t ________ her stroll through the grounds. Even the first drops were no ________, and she continued her walk. A. hinder … incentive B. thwart … refuge C. impede … deterrent D. permit … provocation E. prevent … enticement

The best answer is C. It's important in these types of questions to look at the context of the sentence. For example, "she continued her walk" is very important in this case because the words that fill in the blanks must agree with the fact that she walked and didn't stay inside. Then we can work backwards, and we know that the first drops shouldn't have scared her if she continued to walk, and the threat of rain was no real threat to her. Learning how to quickly find the parts of these sentences that contain the real meat can really help on test day.

Two of the most generic reactions in Organic Chemistry are substitution and elimination reactions. In which two types of reactions will you never see the formation of a carbocation intermediate?

An SN2 reaction and an E2 reaction. Both of these reactions are bimolecular, meaning the reaction rate depends on the concentrations of both molecules because it is a one step reaction. In these type of reactions, an intermediate is not formed, there is just a high energy transition state. However, in SN1 and E1 reactions, the mechanism proceeds through a carbocation intermediate. In SN1, first the leaving group leaves, then a nucleophile attacks the carbocation. In E1, the leaving group leaves, and a base removes an antiperiplanar Hydrogen, moving electrons to create a pi-bond with the empty orbital of the carbocation.

In our chromosomes, parts of the DNA are converted to protein, while other parts are interspersed, but do not correlate to the final protein. What are the portions of DNA that code for the final amino acid sequence called?

Exons