Tutor profile: Maggie M.
Subject: Physics (Newtonian Mechanics)
Explain the forces acting on a object that is not moving vs. an object moving with a constant velocity.
An object that is not moving will have its forces cancel out. For example, a book sitting on a desk is not moving, because the downward gravitational force is exactly canceled out by the upward normal force exerted by the table on the book. This checks out, because there is no net force, Fnet=0N, and since Fnet=mass*acceleration, it should not have any acceleration either. An object moving with a constant velocity will have a similar force diagram, where all the forces cancel out. This is because constant velocity means an acceleration of zero, so using Fnet=m*a, Fnet=0N. Therefore, a car moving at a constant velocity would have the vertical components of gravity and normal force cancel out, and the horizontal forces of applied force by the engine and opposing horizontal force of friction would also exactly cancel out.
Describe the atomic structure of water and why it lends itself to hydrogen bonding.
Water, chemical formula H2O, is a bent molecule made of a central oxygen atom with two lone pairs of electrons and two hydrogen atoms that are 104* from each other. The two lone pairs 'push' down on the hydrogens and force them closer to each other due to charge repulsion, which is why the angle (104*) is less than the expected angle of a bent molecule (120*). Water experiences hydrogen bonding because of the partial positive charges on the hydrogens and the partial negative charge on the oxygen. The oxygen is more electronegative (greater tendency to attract electrons), so it will have more electrons more often than hydrogen in their covalent bond, giving it a partially negative charge, since electrons carry a negative charge. The hydrogens consequently will have less of a share of the electrons, giving them a partial positive charge. Hydrogen bonding then happens between a partially positive hydrogen on a water molecule, and the partially negative oxygen on a different water molecule. This bonding is responsible for many special phenomena in water, such as surface tension and lower solid density due to lattice crystal.
Explain the central dogma of molecular biology.
The central dogma describes the two-step process of creating proteins, which transcribes DNA into RNA and then translates RNA into proteins. In DNA transcription, a section of DNA is 'unzipped' and special proteins read this section of DNA, and generate a complementary strand of pre-mRNA. mRNA stands for 'messenger-RNA', because it carries the message of the desired protein product, and it must be processed in order to go from pre-mRNA to mRNA. Once the mRNA is ready, it is translated by ribosomes, which piece together the correct amino acids specified by the mRNA. These amino acids are the building blocks of proteins, and once strung together by the ribosome, undergo a folding into the final protein structure.
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