Life 102, Week 6
Life 102, Week 6 Life 102
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This 7 page Class Notes was uploaded by Kyra Ferguson on Saturday February 27, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik Arthun in Winter 2016. Since its upload, it has received 36 views. For similar materials see Attributes of Living Systems in Life Science at Colorado State University.
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Date Created: 02/27/16
Organization of Chemistry of Life into Metabolic Pathways metabolic pathway- begin with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme Enzymes speed up metabolic reactions by lowering energy barriers A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction An enzyme is a catalytic protein Hydrolysis of sucrose by the enzyme sucrase is an enzyme of an enzyme- catalyzed reaction Enzyme Activity Most exergonic reactions have to be activated before they proceed spontaneously Activation Energy- initial energy needed to start a reaction Enzymes lower the activation energy to start a chemical reaction Ways to overcome activation barrier 1) Heating: bonds loosened (cannot be done in the body) 2) Enzymes: proteins that speed up reaction → biological catalysts Enzymes are very specific- they accelerate one particular reaction Substrates- reactants that the enzyme uses Enzymes promote reactions by serving as a physical site upon which the reactant molecules (substrates) can be positioned for various interaction) Enzyme Substrate Interactions Active site- the actual site on the enzyme where the substrate bonds for the reaction to proceed "lock and key" fit- the active site is very specific in its shape and chemistry for the substrate The enzyme is not used up in the reaction is not part of the final product can be reused How do enzymes lower activation energy? Enzyme binds substrates in right position Enzyme can also stress atomic bonds, which makes it break easily Active site has properties that facilitate reaction (acidic/basic, hydrophobic, etc_ Side groups of amino acids may participate in reactions (and be restore) Overall: reaction is facilitated Influences on Enzymatic Reaction Rate Environmental conditions: temperature pH Each enzyme has a temperature optimum and pH optimum Activation/Inhibition by other molecules: 1) Cofactor- non protein molecule/atom required for enzyme activity(many are metals) 2) Inhibitors Competitive: binds in active site Non-competitive: bonds in allosteric (other place) site, and makes active site warp 3) Activators All "allosteric" binding, opens up an active site Reason for inhibitors and activators To regulate enzyme activity Regulate how much is formed- not too much and not too little Regulation of multimeric enzymes (enzymes with multiple active sites) only require 1 activator or inhibitor for all active sites Metabolic pathway Serves as enzymes that work together Feedback inhibition- an enzyme is inhibited by its product Less product → more made More product → less made Strategy of Metabolism Use catabolism to: o Release energy o Capture electrons (such as in food) o Liberate building blocks Drive anabolism by o spending energy o Using electrons o Using building blocks Chapter 9: Cellular Respiration & Fermentation Energy movement through ecosystems Energy flows into an ecosystem as sunlight and leaves as heat Breaking down food is stealing electrons Cellular Uses for ATP ADP + P i ATP going from low to high concentration transporting vesicles across microtubules Chemical work (creating products) Catabolic pathways yield energy by oxidizing organic fuels the breakdown of molecules is exergonic C6H12 6 + O 2 → CO 2 + H2O + energy (Cellular respiration) (Oxygen) ( Carbon Dioxide) Water The transfer of electrons during chemical reactions releases energy stored in organic molecules The released energy is ultimately used to make ATP Principle of Redox Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions In oxidation, a substance loses electrons, or is oxidized In reduction, a substance gains electrons, or is reduced (as in the amount of positive charge is reduced) OIL RIG o Oxidation is Loss, Reduction is Gain some redox reactions do not transfer electrons but change the electron sharing in covalent bonds electrons "fall" to oxygen-closer to atomic nucleus = lower energy state As electrons move closer to the nucleus of oxygen, energy is released Oxidation of organic fuel molecules during Cellular Respiration During cellular respiration, the fuel (such as glucose) is oxidized, and O 2s reduced Electrons from organic compounds are usually first transferred to NAD , a coenzyme NAD picks up a H atom and becomes NADH + Each NADH (reduced NAD ) represents stored energy that is tapped to synthesize ATP Cellular Respiration Electrons and H are transferred from glucose to oxygen High energy electrons in glucose become low energy electrons in water + CO 2 Breakdown of Glucose Glucose is broken down in little steps A little energy is released per step, small enough for a cell to handle, large enough to drive ATP production Respiration uses intermediate molecules to transfer electrons NADH +nd FADH se2ve as intermediate molecules that carry electrons NAD is an empty taxicab, NADH is full NADH passes the electron to the transport chain O2pulls electrons down the chain an energy yielding tumble 3 key pathways Glycosis (makes a net 2 ATP, glucose is systematically broken down and oxidized) Citric Acid Cycle (makes a net 2 ATP, glucose is systematically broken down and oxidized) Electron transport chain (exergonic reaction, makes 28 ATP) o Oxidative phosphorylation (add phosphate group by losing electrons) accounts for almost 90% of ATP generated by cellular respiration o A smaller amount is made in glycolysis and the citric acid cycle by substrate-level phosphoylation Glycosis: Step 1 "Sugar splitting" Glucose is split in half (through 10 steps and enzymes) becomes pyruvate (if oxygen is present, will enter citric acid) Occurs in cytoplasm Occurs whether or not O i2 present o the oldest form of extraction of energy, used prior to presence of oxygen Energy Investment Phase o Spends 2 ATP Energy Payof Summary: 1 molecule of glucose, partially oxidized (in payof) o Two NAD are reduced o Net of 2 ATP produced o 2 pyurvates are end product (Starting product for citric acid cycle and fermentation) Before Citric Acid Cycle can begin: Pyruvate must be converted into acetyle coenzyme A (acetyle CoA) which links glycolysis to the citric acid cycle Citric Acid Cycle: Step 2 Citric Acid occurs in the mitochondria Acetyle CoA goes through transport protein, CO is re2eased Occurs in the mitochondrail matrix Completes the breakdown of pyruvate into CO 2 The cycle oxidizes organic fuel derivied from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH 2 per turn During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH accou2t for most of the energy extracted from food Those two electron carriers donate electrons to the electron transport chain is in the inner membrane (cristae) of the mitochondrion Electrons drop in free energy as they go down the chain and are finally passes from O 2 forming H O2 Electron Transport Chain: Step 3 Electrons are transferred from NADH or FADH to th2 etc (NADH is dropped of higher than the FADH ,2and more energy is garner from that) Electrons are passed through a number of proteins to O 2 The electron transport chain generates no ATP directly It breaks down the large free energy drop from food to O into2smaller steps to release energy in manageable amounts Chemosis: The Energy Coupling Mechanism + Electrons transfer in the electron transport chain causes protein to pump H from the mitochondrial matrix to the intermembrane space H then moves back across the membrane passing through protein ATP synthase ATP synthase uses the exergonic flow of H to drive phosphorylation of ATP This is an example of chemismosis, the use of energy in a H gradient to drive cellular work ATP Synthase + The energy stored in a H gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis + The H gradient is referred to as a protein-motive force, emphasizing its capacity to do work Accounting for ATP production by cellular respiration During cellular respiration, most energy flows in this sequence glucose → NADH→ electron transport chain → protein motive force → ATP About 34% of energy in glucose molecule is transferred to ATP during cellular respiration making about 32 ATP But pyruvate is a charged molecule and 2 ATP is used by actively transport pyruvate into mitochondrion Proteins, Carbs, and Fats, can all provide energy for ATP Carbohydrate Metabolism Complex carbohdyrates are hydrolyzed to monosaccharides which then enter into glycolysis Fat metabolism Fats are broken down into glycerol and fatty acids Glycerol is converted to glycerald hyde 3-phosphate which enters glycolysis Fatty acids are broken down by beta-oxidation to 2-carbon molecules to enter citric acid cycle Protein metabolism Proteins are broken down into amino acids Amino groups are removed, and nitrogenous waste is excreted as ammonia (NH 3 Enter respiration of glycolysis or citric acid cycle Proteins have lower energy content than glucose Anabolic Pathways (Biosynthesis) The body uses small molecules to build other substances (fats, amino acids) These small molecules may come directly from food, from glycolysis, or from citric acid cycle Intermediates from glycolysis and citric acid cycle are diverted to anabolic processes Feedback Regulation Feedback Inhibition is the most common mechanism for control If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down Control of catabolism is based mainly on regulating the activity of enzymes at strategic points on The Catabolic Pathway We can use ADP or ANP if there is not ATP, but it would requiring being in a bad enough situation that you lack ATP Cells can produce ATP in alternative ways Aerobic respiration needs O f2r electron transport chain If there is no O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP This produces less ATP, but is better than none.
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