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Lecture 5

BIOL 112 Lecture 5: Lecture 5

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McGill University
Biology (Sci)
BIOL 112
Frieder Schoeck

Lecture 5 Different type of chemical reactions in a cell: all of them are called metabolism. 2 types of metabolism: Anabolic joins simple molecules to make more complex ones (ex: making a polypeptide or a DNA molecule). It REQUIRES energy. Catabolicbreak downpolymers intomonomers. (ex:cuttingupaproteinintois originalamino acids). It RELEASES energy. Everything that we do can be described as energy conversion. Ex: At the beginning, before release, the brick has potential energy which is then transformed to kinetic energy while it’s falling and then it converts to heat. The energy content does not drive energy conversion. At the beginning you have the same amount of energy than you have at the end. Same for atoms: at the beginning you have the same amount of atoms than at the end. What does drive energy conversion? The drive of energy to become evenly distributed or dispersed. Ex: cup of hot coffee. A cup of hot coffee is essentially energy highly localized in a narrow environment. It gets colder because the molecules are bouncing around and eventually the energy disperses and becomes the same as room temperature. Same with a balloon, over time the air will diffuse/disperse out. A swimmer diving into water. Kinetic energy localized in muscles becomes distributes/dispersed into the movement of molecules in the pool when he enters the water. To understand energy dispersal you have to look at probabilities. You can say that a chemical reaction only occurs if some energy (usually heat) is dispersed in the environment. Energy conversions drive chemical reactions. The grey area is free energy (unusable energy after chemical reaction). How do we calculate the grey area (free energy)? A cell has a closed system. What options does the cell have to release free energy? 2 options 1) Do some chemical reaction that increases the disorder inside the cell (ex: breaking down a polypeptide).Breakingdownproteinintoaminoacids.DeltaSmeans:increasedisorderinside of the cell. Delta S refers only to disorder INSIDE the system. 2) Undergo a chemical reaction (ex: green molecules react with blue molecules to form green- blue molecules). This releases a lot of heat called Delta H (enthalpy). This heat disperses into the environment. In the end, it increases the disorder but just in the surrounding environment. Delta H refers to disorder OUTSIDE the system. We cannot calculate absolute energy, we just want to calculate the change in energy. Delta is used for change. If Delta G is negative, then it means that such a reaction can occur spontaneously. Every chemicalreactionwe do must have a negative delta G. If DeltaG is positive itmeans that the reaction cannot occur. The Delta H can be either positive or negative & (-T x Delta S) can either be positive or negative. 4 types of reactions: 1) The most common type of reaction: A typical catabolic reaction where Heat is released and the disorder INSIDE the system is INCREASES as well. So, Delta H and (-T x Delta S) are all negative
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