What's the difference between the "present perfect" and the "present perfect subjunctive"??

LS 3

....Transcriptional Repair

yah, so it says that RNA polymerase scans for lesions. Does that mean that transcription actually provides another proofreading mechanism?

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Deutsch Eins

So...I don't get what the difference between nominative and accusative possessive adjectives is...and they're almost the same in spelling.

Vitamin C

Ok, now I want to know how Vitamin C works in your body. Like what does it do exactly to boost your immune system? yea

Ok, so the mRNA has four nuclei acids together that give the genetic code to produce a certain acid? So let's say you put a chain of mRNA together and take it from a cat and put it into a dog. Does that mean that the same protein will be produced, regardless of the animal or thing that the chain is in? Also, consider between a plant and an animal.

Carbocations

"The more highly substituted carbon atom bears the greater positive charge because it resembles the more stable carbocation."

What does this mean? Like the carbon atom with more substituents has a more positive charge??? But I thought that the substituents release electrons, thus eliminating the positive charges.

Organic Chem ?

For immiscible liquids, the total vapor pressure is a sum of the individual vapor pressures of the liquids. Also, the boiling point is lower than that of both liquids. Why?

I thought that boiling point and vapor pressure were directly proportional.