#23 BB 350 Immune System, Oncogenes, Energy - Kevin Ahern's Biochemistry Online





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Published on May 15, 2012

1. Contact me at kgahern@davincipress.com / Friend me on Facebook (kevin.g.ahern)
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9. Course materials at http://oregonstate.edu/instruct/bb350

Lecture Highlights
Immune System
1. Dendritic cells are part of the immune system that are a first line of defense. They engulf invaders, digest their proteins and then "present" the proteins on their surface for binding by other cells of the immune system.
2. T-cells are another important class of immune cells. They come in two types - killers and helpers. Killers, when bound to an infected cell will facilitate the death of that cell. Helpers, when they recognize an antigen (a presented peptide) will stimulate B-cells that bind to that antigen to divide.
3. B-cells produce antibodies.
4. Remember than antigens are what are bound by antibodies.
5. Proto-oncogenes are genes in cells that play important roles in the decision of whether or not to divide. The roles they play are varied. Some are involved in signaling. Others control transcription. When mutations disrupt their normal function, proto-oncogenes become oncogenes and uncontrolled cellular growth, cancer, can result
6. Ras is a proto-oncogene that, if mutated in one specific basepair, can become an oncogene.
7. The steps in producing a tumor are, in fact, multiple in nature, and we do not know all of the steps.
8. Some proto-oncogenes, such as p53, act as suppressors of tumors. When they lose their function, tumors are much more likely to occur. p53 is common in many cancers, but can often be found in colon cancer.
9. Colon cancers known as HNPCC are inherited and they arise from mutation in proteins involved in repair of DNA damage.
Highlights Energy
1. The free energy of a reaction (Delta G) is the energy that is available for (or required for) doing things in cells (catalyzing reactions, doing work, etc.). By examining the free energy change that occurs in a reaction, one can determine if a reaction is favorable (go forward) or not favorable (go backward). Favorable reactions have Delta G values that are negative (also called exergonic reactions). Unfavorable reactions have Delta G values that are positive (also called endergonic reactions). When the Delta G for a reaction is zero, a reaction is said to be at equilibrium. Equilibrium does NOT mean equal concentrations.
2. For a reaction A - B (note that all reactions are theoretically reversible), if the Delta G is negative, the forward reaction (A - B) is favored. If the Delta G is positive, the reverse reaction (B - A) is favored. If the Delta G is zero, there is no net change in A and B, as the system is at equilibrium.
3. The term "equilibrium" means that the relative amounts of A and B do not change in the reaction. It DOES NOT mean that the amount of A equals the amount of B.
4. The Delta G for the reaction A - B can be calculated from
Delta G = DeltaGzero + RTln ([B]/[A]). I will simplify this for our class to the following form:
Delta G = DeltaGzero + RTln ([Products]/[Reactants])
8. Note that if [Products] are greater than [Reactants], the ln term is POSITIVE. If the [Products] are less than [Reactants], the ln term is NEGATIVE. If the [Products] = [Reactants], the ln term is ZERO.
9. DeltaGzero is a constant that has a specific value for each reaction.

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