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Tutor profile: Dana S.

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Dana S.
Artist Who Found a Canvas in Engineering—Teaching With a Creative Perspective
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Questions

Subject: Chemistry

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Question:

In places where it snows, cities will spread salt over sidewalks and roads to melt the snow and ice in order to prevent slipping when these roadways are used. Explain the molecular phenomenon that leads to salt melting ice.

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Dana S.
Answer:

Water is a highly polar molecule, meaning it has partial but distinct positive and negative charges on either side of it due to the strong electronegativity of oxygen, which pulls electrons towards this atom. Because of this, solid water or ice has a very precise crystal structure, where partial positive charges interact with partial negative charges. Salts are ionically bonded molecules, made up of two atoms which each carry a full positive or negative charge. These charges interact with the partial charges on water molecules. Since the charges on the salt ions are stronger than the partial charges on water molecules, the salt pulls water molecules out of their crystal lattice. By disrupting the crystal structure of solid water, water shifts back into a liquid form, thus melting the ice and prevent slipping on roadways in the winter. This effect overall, increase the melting point temperature of water.

Subject: Biochemistry

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Question:

Protein A has an isoelectric point of 5.1 Protein B has an isoelectric point of 6.3 Is the charge on A positive or negative at a pH of 7.5? What about B? If we wanted to separate these two proteins using a cation-exchange column, what should we adjust the pH to? Which protein would adsorb to the column?

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Dana S.
Answer:

Both A and B are negatively charged since their pI values are both less than pH 7.5. Adjust the pH to a value between the pI values of A and B (for example, pH 5.7). At this pH, protein A will be negatively charged and protein B will be positively charged. A cation-exchange column has a negatively charged resin to capture positively charged particles. This column will adsorb protein B while protein A is repelled and elutes off the column.

Subject: Biology

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Question:

Corynebacterium diphtheriae is a bacterium that spreads through air and causes diphtheria. The bacteria produce a toxin that enters host cells, where it blocks protein production. Without proteins, the cells die very quickly, more quickly than they can be cleaned up by the body. The dead tissue accumulates and creates a large, gray mass in the throat. Symptoms include fever, bluish skin, sore throat, cough, painful swallowing, extremely swollen lymph nodes. Why is bluish skin a symptom? Why is fever a symptom? How do bacterial infections cause fever? What part of the immune system is involved in fever?

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Dana S.
Answer:

The large mass at the back of the throat can block swallowing and breathing, which in severe cases can lead to deoxygenation. Deoxygenated blood has a bluish tint rather than the richer, deep red color, the accumulation of deoxygenated blood gives skin a bluish color. Fever is part of the innate immune response. Innate immunity is the non-specific response to a pathogen. Bacteria themselves do not cause fevers, however, the presence of bacteria and other pathogens in the body initiate an innate immune response, of which fever is a key component. By increasing the body's temperature, your body puts additional stress on the invading pathogen—which has adapted to thrive at homeostatic body temperature—making easier to kill.

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