BIO 181 Exam Study Guide: Cellular Respiration and Photosynthesis
BIO 181 Exam Study Guide: Cellular Respiration and Photosynthesis BIO 181
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This 12 page Study Guide was uploaded by Victoria Smith on Monday February 29, 2016. The Study Guide belongs to BIO 181 at Arizona State University taught by Stout, Chakravadanula, Farrokh, Konikoff in Spring 2016. Since its upload, it has received 100 views. For similar materials see General Biology 1 in Biochemistry at Arizona State University.
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Date Created: 02/29/16
Cellular Respiration Formula for Cellular respiratC6H12O6 + O2 = H2O + CO2 + Energy Has three steps: Glycolysis Prep steps Krebs Cycle Electron Transport Chain Before we proceed to the process of Cellular Respiration, it is important to know the concept of - REDOX REACTIONS Redox Reactions The term “redox” is short for “reduction-oxidation”. Thus it has two part to it. Reduction: this happens when a molecule gains electrons or an H atom e.g. in cellular respiration when NAD+ in glycolysis g“reduced”/ turned into NADH Oxidation:this happens when a molecule loses electrons or an H atom e.g. in cellular respiration in the Electron Transport Chain when NADH “oxidized”/turned into NAD+, we say it got oxidized In order to remember these two terms use the following acronym: OIL stands foOxidation Is Loss RIG stands forReduction Is Gain Glycolysis Is an anaerobic stage. Occurs in the cytoplasm Anaerobic means that it happens in the presence of oxygen Picture Source: Shmoop 1. Glucose enters glycolysis 2. 2 ATP molecules phosphorylate 3. This splits the glucose into two molecules called PGAL/G3P (Note the knowing the names of the abbreviated molecules is not significant but it helps to know that they exist) 4. The output is ADP (thus we say that ATP got oxidized since it lost a “P”) 5. NAD+ gets reduced with PGAL to form BPGA and NADH 6. NADH is a high energy electron carrier 7. BPGA binds with ATP to form PGA and that gives off ADP 8. ADP binds with PGA to form pyruvate and ATP This is called substrate level phosphorylation Inputs Outputs Glucose NADH 2 ATP 2 Pyruvate Which substances got oxidized and which ones got reduced during Glycolysis? Oxidized Reduction NAD+ NADH ADP ATP Kreb’s Cycle Prep Step Before we begin our Kreb’s Cycle, we need to “prepare” our pyruvate. Hence why the name is “prep step”. Key: 3C = 3 Carbon 4C = 4 Carbon 6C = 6 Carbon Picture Source: Study Blue Pyruvate binds with an enzyme called acytl CoA and NAD+ is reduced to NADH 2 CO2 are given off as a waste product of respiration The remaining substance is Acytl CoA NADH goes to the Electron Transport Chain Source: Study Blue Kreb’s Cycle/Citric Acid Cycle Source: Craig Savage Acytl CoA (2C) goes into the Kreb’s Cycle It binds with oxaloacetate (4C) to form citrate (6C) NAD+ gets reduced by binding with citrate to form intermediate 1, NADH (oxidized) and CO2 is given off NAD+ is reduced with intermediate 2 and produces NADH, CO2 and intermediate 3 ADP binds/oxidizes with intermediate 2 to form ATP This forms intermediate 3 FAD+ binds/gets reduced with intermediate 3 to form FADH2 and intermediate 4 NAD+ binds/gets reduced with intermediate 4 to form NADH and oxaloacetate Note NADH and FADH go off to the third cycle of cellular respiration called Electron Transport Chain CO2 is released as a waste product And the end result of Kreb’s cycle is back into oxaloacetate ATP is produced from ADP + P using substrate level phosphorylation And since two pyruvate molecules entered the prep step, everything doubles Inputs Output 2Pyruvate 2Acytyl CoA (not included in the final products) 6NAD+ 6NADH 2FAD+ 2FADH2 4CO2 Note: all the outputs for both glycolysis and the Kreb’s Cycle go off to the Electron Transport Chain Questions: 1. What is the difference and similarity between NADH and FADH2? They are both energy carriers. However, FAD+ carries less energy than NADH 2. What gets reduced and what gets oxidized? Oxidized Reduced NAD+ NADH FAD+ FADH2 3. How is ATP produced during Kreb’s Cycle? By the use of substrate level phosphorylation 4. During cellular respiration, where is the first carbon dioxide produced? During the prep step Electron Transport Chain Occurs in inner-membrane of mitochondria Picture Source: Biology Forums NADH gives off its high energy electron to the enzyme on the ETC Electrons give off their energy as they move across the membrane toward an enzyme called ATP synthase Energy given off pumps H+ ions from the mitochondrial matrix into the intermembrane Oxygen is the last electron acceptor As it binds with the electron, it also binds with a hydrogen ion, forming water (H2O) The H+ ions pumped to the intermembrane create a concentration gradient As such, they start flooding back through ATP synthase As they diffuse through ATP synthase, the give off energy That energy is used to bind ADP + P = ATP Approximately 32 ATP molecules are made during ETC https://www.youtube.com/watch?v=Ak17BWJ3bLg Questions: 1. Where does the energy from glucose end up in? CO2 2. What is the difference between substrate level phosphorylation and oxidative phosphorylation? Substrate level phosphorylation does not involve an enzyme, electron and a membrane whereas oxidative phosphorylation, an enzyme (ATP synthase) needs to be present, a membrane needs to be present, protons need to be present and an electron needs to be present in order for it to occur 3. What is the last electron acceptor in cellular respiration? Oxygen 4. Which molecule(s) donate electron in the ETC? NADH and FADH2 5. What is the main role of the mitochondrial membrane in cellular respiration? It helps by creating a proton gradient thus allowing H+ ions to diffuse back to the other side of the mitochondria via ATP synthase thus synthesizing ATP Fermentation Is an alternative pathway from cellular respiration mostly used by organisms such as bacteria due to the absence of oxygen It allows us to break down glucose without oxygen and mitochondria Its anaerobic Occurs in two stages namely glycolysis and waste product formation Occurs in the cytoplasm There are different types of fermentation but for the purpose of this chapter, we are going to focus on two: Lactic Acid Fermentation and Alcohol Fermentation Chemical Formulae of Both fermentation 1. Alcohol Fermentation: Glucose = 2 Ethanol + 2 CO2 + Energy (ATP) 2. Lactic Acid = 2 Lactate + 2 ATP Alcohol Fermentation steps Glycolysis occurs Pyruvate, which is the product of glycolysis, is then turn into aldehyde and 2CO2 are released as a waste product the second stage is when NAD+ gets reduced into NADH to produce ethanol and that is called Alcohol Formation ethanol and CO2 are the waste products of Alcohol fermentation Lactic Acid Fermentation glycolysis occurs NADH gets oxidized to NAD+ to form lactate Questions: 1. What is the purpose of fermentation? 2. Why do cells opt to use a slower more complex pathway/cellular respiration, instead of fermentation? This is because the products we get from fermentation still yield a lot of energy and that energy is not produced to ATP, which is needed by cells. Thus we get more energy from cellular respiration that fermentation and that is why cells undergo cellular respiration as opposed to undergoing fermentation. Phosynthesis Light Reaction Photosynthesis occurs in the chloroplast The chemical formula of photosynthesis is 6CO2 + 6H2O + Energy (light) = C6H12O6 + 6O2 + Energy (ATP) The light reaction occurs in the thylakoid membrane There are two components in the thylakoid membrane i.e. Electron Transport Chain (ETC) and photosystems Non-Cyclic Pathway Picture source: UIC Photosystem II/P680 is used The light strikes the electron on Photosystem II The electron bounces around the photosystem up until it gets picked up by the electron carrier The electron acceptor/carrier takes the electron to the ETC The electron will move down the ETC Energy is given off to make ATP As it reaches the end of ETC, it longer has high energy The electron goes into another photosystem to get charged Here it gets hit by light and boosted into a higher energy level The electron will bounce around the photosystem up until it gets into the reaction center and gets picked up by an electron acceptor The electron gets sent into another ETC As it gets there, it gets picked up by a molecule called NADP+ which also grabs a hydrogen and becomes NADPH Photolysis/Non-Cylic Pathway…continued Light strikes water The water gets split into H+ ions, Oxygen (O2) and electrons The electrons produced by photolysis are sent to Photosystem II (P680) so that during the non-Cyclic reaction, we do not run out of electrons The H+ ion gets sent to NADP+ to form NADPH Conclusion of Non-Cyclic Pathway Inputs Outputs Mechanism Light ATP Photosystem I, Photosystem II, two ETC Water NADPH Oxygen Recall: in the light reaction, we have used light and water, we are now left with Carbon Dioxide (CO2) from the reactants side of the equation. See equation below: 6CO2 + 6H20 +Light (energy) = C6H12O6 + 6O2 + Energy (ATP) Photophosphorylation During the non-cyclic cycle, the electron gets carried by the electron acceptor and sent off to the ETC Questions: 1. Which component in the light reaction gives off energy that excites the electron? Light 2. Where is the electron that is used in the ETC found? Photosystem/Chlorophyll 3. How is oxygen produced in the light reaction? Light splits water using photolysis and separates it into oxygen, an electrons and a hydrogen proton 4. As the electron moves down the ETC, what happens to the H+ protons? They get pumped into the other side of the membrane thus creating an electron gradient 5. What is the last electron acceptor in photosynthesis? NADP+ 6. Which components get reduced and oxidized during the light reaction? NADP+ gets reduced to NADPH (oxidized) and the photosystem/choloroplast gets oxidized as it loses electron to NADP+ 7. True of False: there is no ATP production during the light reaction? False, ATP is created in the ETC Light Independent Reaction/Calvin Cycle This is a carbon fixation cycle It takes the carbon dioxide in the atmosphere and "fixes" it Occurs in the stroma of the chloroplast There are 3 major steps in the Calvin Cycle Fixation, Reduction and Regeneration Picture Source: UIC CO2 enters the leave into the stroma It then finds a molecule called RuBP (Ribulose BiPhosphate/Rubisco) RuBP is a 5 carbon molecule This forms an unstable 6 carbon molecule this later breaks into 2 phosphoglycerate molecules RuBP + CO2 = 2 Phosphoglycerate (PGA) PGA gets phosphorylated by ATP (ATP which was made in the light reaction This results into the following reaction: PGA + ATP = BPGA (biphosphoglycerate) [Reduced] ADP is the released BPGA combines with NADPH (from light reaction) NADPH donates the high energy electron and hydrogen to BPGA which forms PGAL/ phosphoglyceraldehyde, releasing a phosphate and NADP+ which are recycled back into the thylakoid membrane for the light reaction This PGAL is a 3 carbon molecule But recall that we had split a 6 carbon unstable molecule into two Thus at the end we will have 2PGAL which will form a 6 Carbon molecule called Glucose/sugar But now since this is a cycle, we have to make sure that we recycle our molecules Remember from the photosystem chemical reaction: 6CO2 + 6H2O + Energy (light) = C6H12O6 + 6O2 + Energy (ATP) that we have to "fix" 6 carbon molecules? Thus the process occurs 6 times thus making 12 PGAL's made The two bind together to form glucose Then the rest of the 10 PGAL's get phosphorylated and forms 6 RuBP's Note: for the purpose of this exam, you do not need to memorise the abbreviated molecules What is being reduced? (Slide 16) Phosphoglycerate Inputs Outputs CO2 Glucose/G3P NADPH NADP+ ADP ATP Carbon Dioxide Where does the ATP and NADPH come from? Light dependent reaction What's the source of making ATP and NADPH? Light What do cells do with high energy electrons? Pass to ETC and create proton gradient Where does the electron go at the end of the ETC? Another chlorophyll to get charged Why do we eat? To get/make energy From Big to small -energy released From small to big - energy required Thermodynamics 1st Law: energy is neither created nor destroyed 2nd Law: it takes energy to impose order on a system. Where do cells get energy? Photosynthesis and Respiration Energy comes from carbohydrates Anabolism vs Catabolism Picture source: Britannica Anabolism is the combination of smaller molecules to former a bigger molecule Energy input is needed for anabolism Catabolism is the breaking down of a bigger molecule to form smaller molecules Energy is released as the output Change in G>0, the reaction is endergonic Change in G<0, the reaction is exergonic If your G is less than 0 then that means energy needs to be added into the system and vice versa Metabolism Overview What is metabolism? Sum of all total reactions Each reaction is catalyzed by an enzyme How Does ATP drive Endergonic Reactions? ATP is hydrolyzed to form ADP and a phosphate group The phosphate group is transferred to a substrate Phosphorylation: addition of a phosphate group this is called an exergonic reaction because the potential energy in ADP was much lesser than the one in the final product ADP + P = Activated Substrate The diagram below shows the difference between a reaction catalyzed by an enzyme and one which is not catalyzed by an enzyme Picture source: WikiBooks Enzymes lower the activation energy of a reaction Difference between Change in G Change in G>0, the reaction is endergonic Change in G<0, the reaction is exergonic How Do Enzymes Work? Enzymes are catalysts All enzymes end with -ase In order for reactions to occur, reactants need to collide and have enough kinetic energy Enzymes do the following: a. Bring the substrates together in the active site b. Bind using the "lock-and-key" method c. They provide lower activation energy d. Don't change the energy released in the reaction e. Enzymes do not change DELTA G f. Flexible and dynamic g. Have enough kinetic energy to withstand the repulsion forces when the electrons of substrates interact h. They are catalysts Source: Chem4kids Transition State: highest state in energy level when the substrate and enzyme bond together. It is the least stable state during the reaction Activation Energy: kinetic energy required to strain the chemical bonds between to reach a transition state. Reaction rates depend on the kinetic energy and the activation energy Three Step Process of Enzymes of Enzyme Catalysis: 1. Initiation: enzymes bring along the substrates together to the active site 2. Transition State Facilitation: the transition state is prevented thus, lowering the amount of activation energy therefore speeding up the chemical reaction. 3. Termination: because products have less affinity than reactants, they are less susceptible to the active site, thus the products are released from the active site Notes by: Victoria Smith
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