Tutor profile: Joseph S.
Subject: Organic Chemistry
Explain the concept of enantiomers.
Enantiomers are stereoisomers (molecules where all the same atoms are connected but in a different arrangement), which are mirror images of each other. Specifically, they are mirror images that cannot be superimposed - they differ in some way even though they are mirror images. For example, the mirror image of a square is that same square that can be placed over itself. However, your hands are mirror images of each other but clearly are not interchangeable. Enantiomers in organic molecules function the same. They are mirror images that cannot be placed over one another or interchanged.
Why does DNA synthesis occur only from 5' to 3'?
DNA synthesis occurs only from 5' to 3' because the 5' of DNA is bound to high energy phosphate groups. When phosphoanhydride bonds (bonds involving phosphorus and oxygen) are broken, a large amount of energy is released. This energy is what is used to attach a new nucleotide to the growing DNA molecule. If DNA polymerase makes a mistake, it must cleave off the erroneous nucleotide in order to add a correct nucleotide. If replication occurred 3' to 5', then when the erroneous nucleotide was removed, there would be no phosphoanhydride bonds to cleave, resulting in no energy to continue replicating DNA. However, when replication occurs 5' to 3', the new nucleotide brings the appropriate phosphate groups with it, allowing for continued replication.
Explain the First Law of Thermodynamics (as follows) in your own words: "energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed, under any circumstances."
This is a specific version of the law of conservation of energy applied to thermodynamic systems. At its core, this means that the total amount of energy and matter in an isolated system remains constant for classical purposes (classical meaning typical/traditional thermodynamics as it is studied in most courses). An isolated system is a section of the universe that has no interactions at all with the rest of the universe. So, in that section of the universe, energy and matter remain conserved. Energy can, however, be transferred as heat or work. Heat is the thermal energy of the particles in a system, while work is the energy that particles use to creation motion against an opposing force. For example, more heat generally means an object will be warmer. Work may be described as rolling a ball up a hill against gravity.
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