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Chapter 8-9 ((((((((((image), Free Energy, Stability, and Equilibrium,…
Chapter 8-9
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Free Energy, Stability, and Equilibrium
when a process occurs spontaneously in a system, we can be sure that G is negative
G represents the difference between the free energy of the final state and the free state of the initial state
G can only be negative when the process involves a loss of free energy during the change from initial state to final state
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free energy is the portion of a system's energy that can perform work when temperature and pressure are uniform throughout the system, as a living cell
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an isolated system is unable to exchange either energy or matter with its surroundings outside the thermos (ex: such as that approximated by liquid in a thermos bottle
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the energy of the universe is constant: energy can be transferred and transformed, but it cannot be created or destroyed
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the more randomly arranged a collection of matter is, the greater its entropy
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THERMAL - is kinetic energy associated with the random movement of atoms or molecules; thermal energy in transfer from one object to another is called heat
POTENTIAL - energy that matter possesses because of its location or structure, example: water behind a dam
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begins with a specific molecule, which is then altered in a series of defined steps, resulting in a certain product
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a major pathway of this is cellular respiration, in which the sugar glucose and other organic fuels are broken down in the presence of oxygen to carbon dioxide and water
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upon entering the mitochondrion via active transport, pyruvate is first converted to a compound called acetyl coenzyme A (acetyl CoA) THIS STEP LINKS GLYCOLYSIS AND THE CITRIC ACID CYCLE TOGETHER
a complex of several enzymes catalyzes the three numbered steps. the acetyl group of acetyl CoA will enter the citric acid cycle. the CO2 molecule will diffuse out of the cell
at the start of the citric acid cycle, acetyl CoA adds its two-carbon acetyl group to oxaloacetate, producing citrate. the citrate is then converted to its isomer, isocitrate, by removal of one water molecule and addition of another. isocitrate is oxidized, reducing NAD+ to NADH and then the resulting compound loses a CO2 molecule.
another CO2 is lost, and the resulting compound is oxidized, reducing NAD+ to NADH. the remaining molecule is then attached to coenzyme A by an unstable bond. CoA is displaced by a phosphate group, which is transferred to GDP, forming GTP, a molecule with functions similar to ATP. GTP can also be used to generate ATP
two hydrogens are transferred to FAD, forming FADH2 and oxidizing succinate. addition of a water molecule rearranges bonds in the substrate. the substrate is oxidized, reducing NAD+ to NADH and regenerating oxaloacetate
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during glycolysis, each glucose molecules is broken down into 2 molecules of pyruvate. the pyruvate then enters the mitochondrion where it is then oxidized to acetyl CoA, which will be further oxidized to CO2 in the citric acid cycle.
the electron carriers NADH and FADH2 transfer electrons derived from glucose to electron transport chains. during oxidative phosphorylation, electron transport chains convert chemical energy to a form used for ATP synthesis in the process called chemiosmosis
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consists of a number of molecules (mostly proteins) built into the inner membrane of the mitochondria of eukaryotic cells
electrons removed from glucose are shuttled by NADH to the "top", higher-energy end of the chain. at the "bottom". lower-energy end, O2 captures these electrons along with hydrogen nuclei and forms water
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occurs in the cytostol, begins the degradation process by breaking glucose into two molecules of a compound called pyruvate
in eukaryotes, pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA, which then goes into the citric acid cycle
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the loss of electrons from one substance is called oxidation and the addition of electrons to another substance is known as reduction
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in addition to calories, food must also provide the carbon skeletons that cells require to make their own molecules. some organic monomers obtained from digestion can be used directly
for example: amino acids from the hydrolysis of proteins in food can be incorporated into the organism's own proteins. however, the body needs specific molecules that are not present as such in food. compounds formed as intermediates of glycolysis and the citric acid cycle can be diverted into anabolic pathways as precursors from which the cell can synthesize the molecules it requires
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in the digestive tract, starch is hydrolyzed to glucose, which can then be broken down in the cells by glycolysis and the citric acid cycle. similarly, glycogen (the polysaccharide that humans and many other animals store in their liver and muscle cells) can be hydrolyzed to glucose between meals as fuel for respiration
catabolism can harvest energy stored in fats obtained either from food or from fat cells in the body. after fats are digested to glycerol and fatty acids, the glycerol is converted to glyceraldehyde 3-phosphate, an intermediate of glycolysis. most of the energy of a fat is stored in the fatty acids. metabolic sequence called beta oxidation breaks the fatty acids down to two-carbon fragments, which enter the citric acid cycle as acetyl CoA
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pyruvate is converted to ethanol in two steps. the first steps releases carbon dioxide from the pyruvate, which is converted to the two-carbon compound acetaldehyde. in the second step, acetaldehyde is reduced by NADH to ethanol. this regenerates the supply of NAD+ needed for the continuation of glycolysis.
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pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of CO2
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CHEMIOSMOSIS IS WHEN ENERGY IS STORED IN THE FORM OF A HYDROGEN ION GRADIENT ACROSS A MEMBRANE AND IS USED TO DRIVE CELLULAR WORK SUCH AS THE SYNTHESIS OF ATP
- NADH and FADH2 shuttle high-energy electrons extracted from food during glycolysis and the citric acid cycle into an electron transport chain built into the inner mitochondrial membrane. the electrons are passed to a terminal acceptor at the "downhill" end of the chain, forming water. 2 mobile carriers Q and Cyt c move rapidly. as these complexes shuttle electrons, they pump protons from the mitochondrial matrix into the intermembrane space. FADH2 deposits it electrons via complex 2 and so results in fewer protons being pumped into the intermembrane space than others with NADH.
- during chemiosmosis, the protons flow back down their gradient via ATP synthase, which is built into the membrane nearby. the ATP synthase harnesses the protonmotive force to phosphorylate ADP, forming ATP. together, electron transport and chemiosmosis make up oxidative phosphorylation
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an enzyme is a macro molecule that acts as a catalyst and speeds up a reaction without being consumed by the reaction
without regulation by enzymes, chemical traffic through the pathways of metabolism would be congested b/c many chemical reactions would take forever
the energy required to contort the reactant molecules so the bonds can break is known as activation energy
activation energy is often supplied in the heat in the form of thermal energy that the reactant molecules absorb from the surroundings
when the molecules have absorbed enough energy for the bonds to break, the reactants are in an unstable condition known as the transition state
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ATP contains the sugar ribose, with the nitrogenous base adenine and a chain of 3 phosphate groups bonded to it
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- CHEMICAL WORK - the pushing of endergonic reactions that would not occur spontaneously (the synthesis of polymers from monomers)
- TRANSPORT WORK - the pumping of substances across membranes against the direction of spontaneous movement
- MECHANICAL WORK - such as the beating of cilia, the contraction of muscle cells, and the movement of chromosomes during cellular reproduction
