AP Biology Unit 3 - Cellular Energetics

bioenergetics

to carry out the processes necessary for life, cells must find a way to release the energy in these bonds when they need it and store it away when they don’t.

* every chemical reaction involves change in energy

thermodynamics

* first law, energy cannot be created or destroyed, the sum of energy in the universe is constant
* second law, energy transfers leads to less organization
* the universe tends toward disorder, entropy
* in order to power cellular processes, energy input must exceed energy loss to maintain order
* cellular processes that release needy can be coupled with cellular processes that require an input of energy
* the lack of energy flow or order results in death for an organism

exergonic reactions

those in which the products have less energy than the reactants, energy is given of during the reaction

* oxidizing molecules in mitochondria of cells, then releases the energy stored in the chemical bonds

endergonic reactions

reactions that require an input of energy, products have more energy than reactans

* plants used of CO2 and H2O to form sugars

activation energy

(exergonic reactions) the reactants must first turn into a high energy molecule (transition state), before turning into the products, in order to achieve this a certain energy is required this is the activation energy

* the hump in the graph is the activation energy, once it is reached the rest of the reaction is all downhill

enzymes

biological catalysts that speed up reactions, accomplish this by lowering the activation energy and helping the transition state to form

* enzymes do not change the energy of the starting point or the ending point of the reaction, they only lower the activation energy
* enzyme specificity, each enzyme catalyzes only one one kind of reaction
* substrates, the targeted molecules
* during a reaction the enzymes job is to bring the transition state about by helping the substrate get into position, it accomplishes this through a special region on the enzyme (active site)
* the enzyme temporarily binds one or more of the substrates to its active site and forms and enzyme-substrate complex
* shape and charge must be compatible with the active site of the enzyme in order for the enzyme-catalyzed reaction to occur
* once the reaction has occurred and the product is formed, the enzyme is released from the complex and restored to its original state (free to react again with another bunch of substrates)
* induced fit, an enzyme has to change its shape slightly to accommodate the shape of the substrates

cofactors

factors when enzymes need a little help in catalyzing reactions

* coenzymes, organic molecules
* ions, inorganic molecules
* reactions can be influenced by temperature and pH
* the rate of reaction increases with increasing temperature (frequency of collisions among the molecules)
* denatured, too much temperature can cause deprive enzymes form their ability to catalyze reactions, this is reversible if the original optimal environment conditions of the enzyme are restored
* Q10, measure of temperature sensitivity of a physiological process or enzymatic reaction rate, the more temperature dependent the higher Q10 (Q10 = 1, temperature independent)
* enzymes function best at a particular pH, at an incorrect pH hydrogen bonds can be disrupted and the structure of the enzyme can be altered

relative concentration of substrates and products

affects the rate of the reaction

* an increase in substrate concentration will initially speed up the reaction, once all of the enzyme in solution is bound by substrate, the reaction can no longer speed up
* saturation point, concentration where all of the enzyme in a reaction is bound by substrate

enzyme regulation

cell can control enzymatic activity by regulating the conditions that influence the shape of the enzyme, can be turned on or off by things that bind to them.

* these things can bind at the active site, and sometimes they bind at other sites (allosteric sites)
* competitive inhibition, if the substance has. shape that fits the active site of an enzyme it can compete with the substrate and block the substrate from getting into the active site
* allosteric inhibitor (noncompetitive inhibition), if the inhibitor binds to an allosteric site
* distorts the enzyme shape so that it cannot function

reaction and coupling and ATP

ATP, consists of a molecule of adenosine bonded to three phosphates, enormous amount of energy is packed into those phosphate bonds