Tutor profile: Carolyn S.

Phosphorylation is the removal of a phosphate group from ATP, and the subsequent addition of this phosphate group to an amino acid residue within a protein. What are the three amino acids that are most commonly phosphorylated, and what do these three amino acids all have in common?

Serine, threonine, and tyrosine are the three amino acids that are able to be phosphorylated. Each of these amino acids have a hydroxyl (OH group) in their side chain.

Valence electrons are the electrons in the outermost shell of an atom; these electrons are involved in forming bonds with other atoms. Knowing this information, do you think the valence electrons are more important for determining the physical properties, or chemical behavior of an atom?

Because the valence electrons are involved in bonding between atoms, the valence electrons, for the most part, determine the chemical behavior of an atom.

Homeostasis is vital to the proper functioning of our cells, organs, and organ systems. Can you think of a situation in which homeostasis would temporarily be disturbed, and how our bodies respond to restore homeostasis?

There are many ways in which homeostasis would be disturbed-- one example is when our blood becomes too basic (alkalemia). Our body responds to this by increasing the acidity of our blood. It accomplishes this by slowing our respiratory rates; this way, we will retain more CO2, and by LeChatlier's Principle, this will cause a right shift in the Bicarbonate Buffer System equation, shown below. The right shift will result in more H+ production, which will decrease the pH, and restore equilibrium in our body. (Please note that the two arrows pointing towards each other are meant to symbolize that this equation is reversible). CO2 (g) + H2O (l) -> <- H2CO3 (aq) -><- H+ (aq) + HCO3- (aq) Similarly, if our blood becomes too acidic (acidemia), our respiratory rate will increase. If our respiratory rate is increased, more CO2 will be blown off. By LeChatlier's Principle, a decrease in the concentration of CO2 gas will result in a left shift in the Bicarbonate Buffer System equation, thereby causing the concentration of H+ ions to decrease. When the concentration of H+ ions decrease, the pH increases. This is yet another way our body responds to restore equilibrium.