APK 2105C Lecture Notes - Lecture 9: Cell Metabolism, Potential Energy, Endergonic Reaction
23 May 2018
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Chapter 3, Part 2
Cell Metabolism
• Work and energy
o Energy = capacity to perform work
▪ Types of energy
• Kinetic energy = energy associated with matter in motion
o Molecules have kinetic energy because they move/vibrate
randomly at any temp above absolute 0
• Potential energy = energy stored in matter than can become
kinetic energy
o Bonds between atoms contain potential energy because
they can be broken to release more energy
o Examples of work in the body
▪ Movement
▪ Urine production (pump ions in certain directions)
▪ Cellular repair and reproduction
▪ Exocytosis of neurotransmitters from axons
o All work is driven by metabolic rxns
• Laws of thermodynamics
o First law = energy can neither be created nor destroyed—just converted from one
type to another
o Second law = natural processes tend to process in the direction that spreads
energy
▪ Example: diffusion of soln from high conc to low conc
• Energy change
o All chemical rxns involve energy exchange
▪ Due to 1st law of thermodynamics—have to have same amount of energy
on both sides of the equation
▪ Molecules possess energy
▪ If a rxn releases energy it’s because the reactant molecules had more
energy than the products
• Reactants → products + energy
▪ Released energy can sometimes be used to do work
▪ Change in energy determines the direction of a reaction
o Change of energy = energy of products – energy of reactants
▪ Exergonic reactions
• Proceed spontaneously
• Release energy
• Delta E (change in energy) is negative
• Energy EXITS the reaction
• Products have less energy than reactants
▪ Endergonic reactions
• Do NOT process spontaneously
• Reactants have less energy than the
products
• Have to add energy to the system for the rxn
to proceed
• deltaE is positive
▪ Commonly expressed in units of energy/unit of mass
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