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Biology notes 120: Enzymes, feedback inhibition , cellular respiration)

by: Jamisha Evans

Biology notes 120: Enzymes, feedback inhibition , cellular respiration) BIO 120

Marketplace > Western Kentucky University > Biology > BIO 120 > Biology notes 120 Enzymes feedback inhibition cellular respiration
Jamisha Evans
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This is part of the notes from chapter 7. Part of the study guide will be uploaded soon so everyone can get a head start on studying.
Sahi, Shivendra
Class Notes
Biology 120 notes: Enzymes, Feedback inhibition, cellular respiration)
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This 4 page Class Notes was uploaded by Jamisha Evans on Friday March 25, 2016. The Class Notes belongs to BIO 120 at Western Kentucky University taught by Sahi, Shivendra in Winter 2016. Since its upload, it has received 24 views. For similar materials see BIOL CONC CELLS METAB GENETICS in Biology at Western Kentucky University.


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Date Created: 03/25/16
Biology Notes: Chapter 7  Enzymes: biological catalysts • Most enzymes are proteins • The shape of an enzyme stabilizes a temporary association between substrates • Enzymes are not changed or consumed in a reaction  ATP • ATP (adenosine triphosphate): the cellular currency for energy. It transports chemical energy within cells for metabolism • Consists of three phosphate groups, ribose and adenine  Methods of producing ATP • Substrate level phosphorylation: occurs when ATP is produced by the enzyme catalyzed transfer of a phosphate group from an intermediate substrate to ADP ◊ This is how ATP is produced in glycolysis and the citric acid cycle (mentioned in detail later) • Oxidative phosphorylation: the membrane protein ATP synthase uses energy from the electron transport chain to phosphorylate ADP to ATP  Redox reactions • An atom is REDUCED when it GAINS an electron. • An atom is OXIDIZED when it LOOSES an electron. • Oxidation and reduction are always coupled, if one atom gains an electron, another has to lose it.  Glucose oxidation • The carbon atoms of glucose are oxidized to form carbon dioxide • The oxygen atoms are reduced to form water. • Glucose is oxidized through a long series of controlled redox reactions. The resulting change in free energy is used to create ATP from ADP and PiADP+Pi+free energy→ATP+H2O. ◊ Together these reactions comprise cellular respiration.  Cellular respiration overview • Glucose is used to make ATP through cellular respiration or fermentation • Cellular respiration produces ATP from a molecule with high potential energy- usually glucose. • Each of the four steps in cellular respiration consist of a series of chemical reactions, a distinctive starting molecule and characteristic set of products.  The steps of cellular respiration • Cellular respiration: Any suit of reactions that produces ATP in an electron transport chain. • Cellular respiration has four steps: ◊ Glycolysis- glucose(6 Carbon) is broken down to pyruvate (3 Carbon) ◊ Pyruvate processing- pyruvate is oxidized to form acetyl CoA ◊ Citric acid cycle- Acetyl CoA is oxidized to CO2 ◊ Electron transport and chemiosmosis.- series of compounds that transfer electron donors to electron receiver via redox reactions. • Glycolysis ◊ First step in glucose oxidation ◊ Feedback inhibition regulates glycolysis ♦ Feedback inhibition: occurs when an enzyme in a pathway is inhibited by the product of that pathway. ♦ Cells that can stop glycolic reactions when ATP is abundant can conserve their stores of glucose for times when ATP is scarce. ◊ Glycolysis occurs in the cytoplasm. ◊ 6 Carbon (glucose) is broken down to 3 Carbon (pyruvate). The potential energy released is used to phosphorylate ADP into ATP. ♦ The glucose molecule is broken down to 2 molecules of pyruvate. Each molecule of pyruvate consists of 3 carbon. ◊ The remaining reactions occur in the Mitochondria ♦ Pyruvate produced during glycolysis is transported from the cytosol (part of the cytoplasm) into the mitochondria. ◊ Consists of an energy investment phase and an energy payoff phase ♦ Energy investment phase: ◊ 2 molecules are consumed and glucose is phosphorylated twice. ♦ Energy payoff phase: • glucose is split to form 2 molecules of pyruvate • 2 molecules of NAD +are reduced to NADH. (in other words, NADH is synthesized + (produced) from NAD ) • 4 molecules of ATP are formed by substrate-level phosphorylation (net gain is ATP) • Pyruvate processing ◊ Second step in glucose oxidation ◊ Catalyzed by the enzyme pyruvate dehydrogenase in the mitochondrial matrix ◊ In the presence of oxygen, pyruvate undergoes a series of reactions that result in the product molecule acetyl coenzyme A (CoA). ♦ Remember, during glycolysis, glucose (6C) is broken down to 2 molecules of pyruvate each consisting of (3C). So therefore pyruvate processing results in 2 molecules of acetyl (CoA) ◊ During these reactions another NADH molecule is synthesized • Citric acid cycle ( also known as Krebs cycle) ◊ Third step in glucose oxidation ◊ The acetyl CoA produced by pyruvate processing enters the citric acid cycle ◊ Located in mitochondrial matrix ♦ Each acetyl CoA is oxidized to two molecules of CO 2 ◊ Some of the potential energy release is used to: ♦ Reduce NAD to NADH ♦ Reduce FAD ( Flavin…) to FADH 2(electron carrier) ♦ Phosphorylate GDP to GTP which is later converted to ATP ◊ The first reaction of the citric acid cycle is catalyzed by the enzyme citrate synthase. ♦ During this, oxaloacetate is joined with acetyl CoA to form citrate. Once the two molecules are joined, a water molecule attacks the acetyl leading to the release of coenzyme A from the complex (Remember, in order for a bond to break water has to be added; Hydrolysis reaction). ♦ Citrate is the first molecule in the citric acid cycle ♦ The citric acid cycle completes glucose oxidation • The energy released by the oxidation of one acetyl CoA molecule is used to produce 3 NADH, 1 FADH 2and 1 GTP (GTP is then later converted to ATP) • For 1 glucose, the citric acid cycle has to run twice (because in glycolysis, 2 pyruvate were made but only one pyruvate can go through the citric acid cycle). ◊ Acetyl CoA is the molecule that powers the citric acid cycle ◊ The citric acid cycle can be turned off at multiple times through several different mechanisms of feedback inhibition ◊ To summarize… ♦ The citric acid cycle begins with acetyl CoA and ends with CO 2 ♦ The potential energy that is released is used to produce NADH and FADH and 2TP ♦ When energy supplies are high the cycle slows down. • Free energy changes NADH and FADH 2 ◊ For each glucose molecule that is oxidized to 6 CO2, the cell reduces 10 molecules of NAD + to NADH and 2 molecules of FAD to FADH 2 and produces molecules of ATP by substrate- level phosphorylation. ◊ The ATP can be used directly for cellular work. However most of glucose’s original energy is contained in the electrons transferred to NADH and FADH 2, which then carry them to oxygen (the final acceptor of electron transport system) • The electron transport chain ◊ Fourth step in cellular respiration ◊ Occurs in the cristae (the inner mitochondrial membrane) ◊ The high potential energy of the electrons carried by NADH and FADH is 2radually decreased as they move through a series of redox reaction ◊ The proteins involved in these reactions make up what is called an electron transport chain ◊ Oxygen is the final electron acceptor in the electron transport chain (receives final electron) ◊ The transfer of electrons along with protons to oxygen forms water.


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