RedOx and Cell Respiration Notes
RedOx and Cell Respiration Notes BIOL 1107
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Brittany Ariana Borzillo
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This 9 page Class Notes was uploaded by Brittany Ariana Borzillo on Friday September 30, 2016. The Class Notes belongs to BIOL 1107 at University of Georgia taught by Norris A. Armstrong in Fall 2015. Since its upload, it has received 3 views. For similar materials see Principles of Biology I in Biology at University of Georgia.
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Date Created: 09/30/16
RedOx and Cell Respiration RedOx allows the cell to transfer and use energy in an incremental fashion o in small packages rather than in a single, destructive burst Oxidizing o Removal of electron from a molecule o results in a decrease in potential energy in the oxidized compound o removes some potential energy o oxidizing agent oxidizes another compound Reduction o Removed electron shifted to a second compound o increases the potential energy o reducing agent reduces another compound Electron Carriers bind and carry high-energy electrons between compounds in pathways compounds can be easily reduced (that is, they accept electrons) or oxidized (they lose electrons) ATP prevents excess free energy from increasing of heat in the cell o would result in excessive thermal motion that could damage and then destroy the cell When ATP is broken down, usually by the removal of its terminal phosphate group, energy is released Structure and Function o ATP is a molecule of adenosine monophosphate (AMP), which is composed of an adenine molecule bonded to a ribose molecule and to a single phosphate group Ribose is a five-carbon sugar found in RNA, and AMP is one of the nucleotides in RNA o addition of a second phosphate group to this core molecule results in the formation of adenosine diphosphate (ADP); the addition of a third phosphate group forms adenosine triphosphate (ATP) o addition of a phosphate group to a molecule requires energy o Phosphate groups are negatively charged and thus repel one another when they are arranged in series o ADP and ATP are unstable Energy o Synthesized via hydrolysis o hydrolysis of ATP produces ADP, together with an inorganic phosphate ion (Pi), and the release of free energy o ATP is continuously broken down into ADP ADP is continuously regenerated into ATP by the reattachment of a third phosphate group o energy comes from the metabolism of glucose to synthesize ATP Phosphorylation o enzymes may bind to several substrates that react with each other on the enzyme, forming an intermediate complex intermediate complex is a temporary structure, and it allows one of the substrates (such as ATP) and reactants to more readily react with each other; in reactions involving ATP, ATP is one of the substrates and ADP is a product o refers to the addition of the phosphate o substrate phosphorylation ATP molecules generated as a direct result of the chemical reactions that occur in catabolic pathways o Oxidative phosphorylation ATP derived from chemiosmosis a process of ATP production in cellular metabolism used to generate 90 percent of the ATP made during glucose catabolism also the method used in the light reactions of photosynthesis to harness the energy of sunlight Takes place in mitochondria Cell Respiration Glycolysis Energy-Requiring Steps 1. Hexokinase phosphorylates glucose using ATP as the source of the phosphate, producing glucose-6-phosphate, a more reactive form of glucose a. catalyzed by hexokinase b. an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars c. prevents the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it can no longer leave the cell because the negatively charged phosphate will not allow it to cross the hydrophobic interior of the plasma membrane 2. isomerase converts glucose-6-phosphate into one of its isomers, fructose-6- phosphate a. isomerase is an enzyme that catalyzes the conversion of a molecule into one of its isomers b. change from phosphoglucose to phosphofructose allows the eventual split of the sugar into two three-carbon molecules 3. phosphorylation of fructose-6-phosphate a. catalyzed by the enzyme phosphofructokinase i. phosphofructokinase is a rate-limiting enzyme ii. active when the concentration of ADP is high; it is less active when ADP levels are low and the concentration of ATP is high b. second ATP molecule donates a high-energy phosphate to fructose-6- phosphate, producing fructose-1,6-bisphosphate 4. newly added high-energy phosphates further destabilize fructose-1,6- bisphosphate a. employs an enzyme, aldolase, to cleave 1,6-bisphosphate into two three-carbon isomers i. dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate 5. an isomerase transforms the dihydroxyacetone-phosphate into its isomer, glyceraldehyde-3-phosphate a. the pathway will continue with two molecules of a single isomer Energy-Releasing Steps 6. oxidizes the sugar (glyceraldehyde-3-phosphate), extracting high-energy electrons, which are picked up by the electron carrier NAD+, producing NADH a. sugar is phosphorylated by the addition of a second phosphate group, producing 1,3-bisphosphoglycerate b. second phosphate group does not require another ATP molecule c. continuation of the reaction depends upon the availability of the oxidized form of the electron carrier, NAD+ i. NADH must be continuously oxidized back into NAD+ in order to keep this step going ii. NAD+ is not available, the second half of glycolysis slows down or stops iii. NADH will be oxidized readily, though indirectly, and the high- energy electrons from the hydrogen released in this process will be used to produce ATP 7. 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming one molecule of ATP a. catalyzed by phosphoglycerate kinase i. an enzyme named for the reverse reaction b. substrate-level phosphorylation c. A carbonyl group on the 1,3-bisphosphoglycerate is oxidized to a carboxyl group, and 3-phosphoglycerate is formed 8. remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing 2-phosphoglycerate a. an isomer of 3-phosphoglycerate b. mutase catalyzes the reaction 9. causes 2-phosphoglycerate to lose water from its structure a. dehydration reaction b. resulting in the formation of a double bond that increases the potential energy in the remaining phosphate bond and produces phosphoenolpyruvate (PEP) 10.the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid a. catalyzed by the enzyme pyruvate kinase i. the enzyme in this case is named for the reverse reaction of pyruvate’s conversion into PEP Outcomes of Glycolysis starts with glucose and ends with two pyruvate molecules, a total of four ATP molecules and two molecules of NADH net gain of two ATP molecules and 2 NADH molecules for its use aerobic respiration o process in which organisms convert energy in the presence of oxygen Breakdown of Pyruvate 1. A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium a. result of this step is a two-carbon hydroxyethyl group bound to the enzyme b. first of the six carbons from the original glucose molecule to be removed c. step occurs twice for every molecule of glucose metabolized d. two of the six carbons will have been removed at the end of both steps 2. hydroxyethyl group is oxidized to an acetyl group, and the electrons are picked up by NAD+, forming NADH a. high-energy electrons from NADH will be used later to generate ATP 3. enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA Acetyl CoA to CO 2 acetyl CoA delivers its acetyl group to a four-carbon molecule, oxaloacetate, to form citrate, a six-carbon molecule with three carboxyl groups in the presence of oxygen o harvest the remainder of the extractable energy from what began as a glucose molecule referred to by three different names o citric acid cycle for the first intermediate formed (citric acid, or citrate) when acetate joins to the oxaloacetate o TCA Cycle since citric acid or citrate and isocitrate are tricarboxylic acids o Krebs Cycle after Hans Krebs, who first identified the steps in the pathway in the 1930s in pigeon flight muscles Citric Acid Cycle takes place in the matrix of mitochondria almost all of the enzymes of the citric acid cycle are soluble o exception of the enzyme succinate dehydrogenase embedded in the inner membrane of the mitochondrion last part of the pathway regenerates the compound used in the first step considered an aerobic pathway because the NADH and FADH produce2 must transfer their electrons to the next pathway in the system oxidation steps of the citric acid cycle also do not occur 1. condensation step a. Prior to the start of the first step, a transitional phase occurs during which pyruvic acid is converted to acetyl CoA b. combining the two-carbon acetyl group with a four-carbon oxaloacetate molecule to form a six-carbon molecule of citrate c. CoA is bound to a sulfhydryl group (-SH) and diffuses away to eventually combine with another acetyl group d. step is irreversible because it is highly exergonic i. rate of this reaction is controlled by negative feedback and the amount of ATP available ii. ATP levels increase, the rate of this reaction decreases 2. citrate loses one water molecule and gains another as citrate is converted into its isomer (isocitrate) 3. isocitrate is oxidized, producing a five-carbon molecule, α-ketoglutarate, together with a molecule of CO2 and two electrons, which reduce NAD+ to NADH a. regulated by negative feedback from ATP and NADH, and a positive effect of ADP b. oxidation c. decarboxylation d. release electrons that reduce NAD+ to NADH and release carboxyl groups that form CO m2lecules 4. CoA binds the succinyl group to form succinyl CoA a. oxidation b. decarboxylation c. release electrons that reduce NAD+ to NADH and release carboxyl groups that form CO m2lecules d. enzyme that catalyzes step four is regulated by feedback inhibition of ATP, succinyl CoA, and NADH 5. phosphate group is substituted for coenzyme A, and a high-energy bond is formed a. energy is used in substrate-level phosphorylation i. form either guanine triphosphate (GTP) or ATP ii. two forms of the enzyme, for this step, depending upon the type of animal tissue in which they are found 1. One form is found in tissues that use large amounts of ATP a. produces ATP 2. second form of the enzyme is found in tissues that have a high number of anabolic pathways a. produces GTP iii. GTP is energetically equivalent to ATP; however, its use is more restricted 1. protein synthesis primarily uses GTP 6. dehydration process that converts succinate into fumarate a. Two hydrogen atoms are transferred to FAD, producing FADH 2 b. energy contained in the electrons of these atoms is insufficient to reduce NAD+ but adequate to reduce FAD i. carrier remains attached to the enzyme and transfers the electrons to the electron transport chain directly ii. process is made possible by the localization of the enzyme catalyzing this step inside the inner membrane of the mitochondrion 7. Water is added to fumarate a. malate is produced b. regenerates oxaloacetate by oxidizing malate c. molecule of NADH is produced in the process Products of CAC Two carbon atoms come into the citric acid cycle from each acetyl group, representing four out of the six carbons of one glucose molecule Two carbon dioxide molecules are released on each turn of the cycle o do not necessarily contain the most recently added carbon atoms two acetyl carbon atoms will eventually be released on later turns of the cycle o all six carbon atoms from the original glucose molecule are eventually incorporated into carbon dioxide Each turn of the cycle forms three NADH molecules and one FADH mole2ule o carriers will connect with the last portion of aerobic respiration to produce ATP molecules One GTP or ATP is made in each cycle Several of the intermediate compounds in the citric acid cycle can be used in synthesizing non-essential amino acids o the cycle is amphibolic both catabolic and anabolic Electron Transport Chain last component of aerobic respiration only part of glucose metabolism that uses atmospheric oxygen present in multiple copies in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes Complex I o two electrons are carried to the first complex via NADH o composed of flavin mononucleotide (FMN) and an iron-sulfur (Fe-S)- containing protein FMN one of several prosthetic groups or co-factors in the electron transport chain prosthetic group is a non-protein molecule required for the activity of a protein are organic or inorganic, non-peptide molecules bound to a protein that facilitate its function prosthetic groups include co-enzymes, which are the prosthetic groups of enzymes o enzyme in complex I is NADH dehydrogenase and is a very large protein, containing 45 amino acid chains o pump four hydrogen ions across the membrane from the matrix into the intermembrane space the hydrogen ion gradient is established o maintained between the two compartments separated by the inner mitochondrial membrane. Q and Complex II o directly receives FADH 2 which does not pass through complex I o compound connecting the first and second complexes to the third is ubiquinone (Q) lipid soluble freely moves through the hydrophobic core of the membrane o Once it is reduced, (QH 2, ubiquinone delivers its electrons to the next complex in the electron transport chain receives the electrons derived from NADH from complex I and the electrons derived from FADH f2om complex II, including succinate dehydrogenase enzyme and FADH2 form a small complex that delivers electrons directly to the electron transport chain electrons bypass and thus do not energize the proton pump in the first complex, fewer ATP molecules are made from the FADH 2 electrons o number of ATP molecules ultimately obtained is directly proportional to the number of protons pumped across the inner mitochondrial membrane Complex III o composed of cytochrome b, another Fe-S protein, Rieske center (2Fe- 2S center), and cytochrome c proteins cytochrome oxidoreductase prosthetic group of heme o heme molecule is similar to the heme in hemoglobin, but it carries electrons, not oxygen o heme molecules in the cytochromes have slightly different characteristics due to the effects of the different proteins binding them, giving slightly different characteristics to each complex o pumps protons through the membrane and passes its electrons to cytochrome c for transport to the fourth complex of proteins and enzymes cytochrome c is the acceptor of electrons from Q whereas Q carries pairs of electrons, cytochrome c can accept only one at a time Complex IV o composed of cytochrome proteins c, a, and a 3 contains two heme groups (one in each of the two cytochromes, a, and a3) and three copper ions (a pair of CuA and one CuB in cytochrome a )3 o cytochromes hold an oxygen molecule very tightly between the iron and copper ions until the oxygen is completely reduced o reduced oxygen then picks up two hydrogen ions from the surrounding medium to make water removal of the hydrogen ions from the system contributes to the ion gradient used in the process of chemiosmosis Chemiosmosis free energy from the series of redox reactions just described is used to pump hydrogen ions (protons) across the membrane uneven distribution of H+ ions across the membrane establishes both concentration and electrical gradients o owing to the hydrogen ions’ positive charge and their aggregation on one side of the membrane. o hydrogen ions in the matrix space can only pass through the inner mitochondrial membrane through an integral membrane protein called ATP synthase complex protein acts as a tiny generator, turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient o turning of parts of this molecular machine facilitates the addition of a phosphate to ADP, forming ATP, using the potential energy of the hydrogen ion gradient ATP Yield umber of ATP molecules generated from the catabolism of glucose varies o he number of hydrogen ions that the electron transport chain complexes can pump through the membrane varies between species o another source of variance stems from the shuttle of electrons across the membranes of the mitochondria electrons are picked up on the inside of mitochondria by either NAD+ or FAD+ FAD+ molecules can transport fewer ions; consequently, fewer ATP molecules are generated when FAD+ acts as a carrier o intermediate compounds in these pathways are used for other purposes Glucose catabolism connects with the pathways that build or break down all other biochemical compounds in cells, and the result is somewhat messier than the ideal situations described thus far
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