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Andrew H.
Pre-Med Student and Undergraduate Researcher at UCI
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Organic Chemistry
TutorMe
Question:

Explain how aromaticity pertains to the basicity difference between pyrrole and pyridine.

Andrew H.
Answer:

Pyrrole and pyridine have similar structures. Both contain a nitrogen within an aromatic cyclical pi system. However, the nitrogen in pyrrole cannot be used as a basic like it can in pyridine. The difference has to do with nitrogen's electrons and their role in sustaining the aromatic pi system of the molecule. The nitrogen in pyridine has one pair of pi electrons shared with the adjacent carbon atom as well as a lone pair of electrons. This lone pair of electrons can be used to remove a proton from an acidic molecule without disrupting the aromaticity of the compound. On the other hand pyrrole does not share a pair of pi electrons with the adjacent carbon of the aromatic ring. Since it is bonded to a hydrogen, its only lone pair must be incorporated into the pi system in order for the molecule to retain its aromaticity. Using the lone pair to accept the proton of an acidic molecule would break the aromaticity of the molecule and greatly destabilize it. Therefore, pyrrole is much less basic than pyridine.

Biochemistry
TutorMe
Question:

Explain the force that drives ATP production in the mitochondria from NADH and FADH2.

Andrew H.
Answer:

The force that drives the production of ATP in the mitochondria is called the proton-motive force and it is made up of the chemical and electrical potential created in the mitochondrial matrix and intermembrane space. There are four protein pumps that are in the inner membrane of the mitochondria. When electrons from NADH and FADH2 are transferred along this protein chain, protons get pumped into the intermembrane space. Since protons are positively charged, the intermembrane space becomes positively charged and the matrix becomes negatively charged creating an electrical potential. The high concentration of protons in the intermembrane space also creates a chemical potential because with a basic matrix being basic and and an acidic intermembrane space. These two potential together make up the proton motive force that drives protons from the intermembrane space back into the matrix to restore equilibrium. The protons are forces to pass through the ATP synthase complex to get to the matrix which rotates ATP synthase complex like a water mill to power the production of ATP.

Biology
TutorMe
Question:

Explain the resulting offspring genotypes that could result from a disjunction in meiosis 1 of the father.

Andrew H.
Answer:

Complications in the sex chromosomes of offspring occur during gamete formation in the father and/or the mother. The gamete formation process is called meiosis and it contains two phases. The first phase separates chromosome pairs (known as meiosis 1) and the second phase separates sister chromatids (known as meiosis 2). During meiosis 1, the cell goes from being diploid (having two sets of each chromosome) to being haploid (having only 1 set of each chromosome). In humans this would be 46 and 23 chromosomes respectively. During meiosis 1, an error can occur called a disjunction where the chromosomes do not separate correctly. If this happens to the sex chromosomes during meiosis 1 in the father, the first resulting daughter cell will have two X chromosomes and two Y chromosomes and the second daughter cell will have no sex chromosomes because the X and Y chromosomes did not separate. In meisosis 2, sister chromatids separate (these sister chromatids were made during the replication phase of the cell cycle). If the cell mentioned above goes through meisosis 2, half of the resulting gametes will have the genotype XY and the other half will be missing sex chromosomes. Since the mother offers 1 X chromosome (given no disjunction has occured) fertilization with one of the four abnormal gametes will either produce offspring with the sex genotype XXY or just X.

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