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2.1 continued & 2.2 Photosynthesis

by: Gail Chernomorets

2.1 continued & 2.2 Photosynthesis BIOL 251

Marketplace > University of Nevada - Las Vegas > BIOL 251 > 2 1 continued 2 2 Photosynthesis
Gail Chernomorets

GPA 3.2

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Week 6 notes 10.04.16 & 10.06.16
Medical Microbiology
Kurt Regner
Class Notes
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This 14 page Class Notes was uploaded by Gail Chernomorets on Saturday October 8, 2016. The Class Notes belongs to BIOL 251 at University of Nevada - Las Vegas taught by Kurt Regner in Fall 2016. Since its upload, it has received 30 views.


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Date Created: 10/08/16
10/04/16 & 10/06/16 Notes 2.1 Respiration Fermentation  Starts with glycolysis - Nets a small amount of ATP - NAD+ is reduced to NADH  Must have a method to regenerate NAD+  There is no oxygen  NADH transfers an e- to pyruvate or a pyruvate derivative  Simplest level of explaining glycolysis - Cutting it in half Glycolysis, Krebs cycle, Electron Transport  If oxygen is present, there is no fermentation & aerobic organisms perform Krebs and E.T.C  Denying the organisms oxygen is an important part of industrial fermentation Next step: Pyruvate Oxidation  Requires oxygen  1C (carboxyl group) is removed and is lost as CO 2  Pyruvate (3C)  acetyl CoA (2C)  A pair of electrons is transferred from he remaining 2C fragments to NAD+  NADH  Acetate combines with coenzyme A = acetyl CoA  Hydrolysis of the acetyl-CoA bond supplies 2C and free energy (7.5 kcal/mol) to make citric acid  *** Bond between O=C to CoA (Acetyl-CoA) is important because when it is broken the energy is used to start the next pathway (Krebs Cycle)  Pyruvic acid (O=C-OH comes from glycolysis)  Pyruvate oxidation is accomplished by a multi-enzyme system: pyruvate dehydrogenase Krebs Cycle  Completes oxidation to CO 2  Also called the Citric acid cycle  Favorable  ΔG < 0 - Exergonic - Releases free energy - Needs energy from hydrolysis of bond O=C-acetyl CoA  Cycle runs 2 times per glucose (2 pyruvates)  Acetyl-CoA (2C) combines with oxaloacetate (4C) to produce citric acid (6C)  2 CO a2e lost in the above steps (Exhale)  *** 4C oxaloacetate combine with 2C acetyl-CoA to create 6C citrate  Final products - 3 NADH + 1 FADH 2 - 1 GTP generated - Oxaloacetate (4C) is regenerated  * Do not need to know the general steps of the process - Just know carbons 4+2=6 - 2C lost to CO 2 - Free energy storedas the final products  * Do not need to know chemical structures for process  Review - Glucose (6C) is oxidized to 2 molecules of pyruvate (3C) - e-s move to NAD+ - NAD+ is reduced to NADH - Free energy of glucose is converted to ATP, NADH and some is lost as heat - Pyruvate 3C is oxidized to a 2C compound - 2C is joined to a 4C compound to make citric acid 6C - Citric acid 6C is oxidized to the 4C compound in the Krebs cycle - Krebs yields 2 ATP via substrate level phosphorylation - NAD+ is reduced to NADH - FAD is reduced to FADH 2 - Produces CO 2  Next step - Passing electrons from NADH and FADH to the 2erminal electron acceptor - Requires an electron transport chain - Electron carriers within a membrane - Bacteria and Archaea use their plasma membrane Catabolism  C6H 12+66O  62O + 6H O2 2  CH 4 O  2O + H2O 2 - Process is the same - Release free energy - Bacteria and Archaea are looking for the carbon  Energy is released upon oxidation; exergonic  Electrons are passed to a final acceptor; O 2 - Aerobic organisms  Energy of e- is stored as ATP and reduced coenzymes - NADH or FADH 2  Tearing apart something that has carbon for electrons  Bacteria and Archaea use a wide range of electron donors/fuels - ATP, NADH, FADH 2  Anaerobic organisms use a different acceptor that doesn’t require O 2  Facultative anaerobes have 2 ETC;one with no O one wit2 O 2 Oxidation Ex. Methane  CH 4s fully reduced - Methane (4 C-H bonds) - Fully reduced  When biological molecules are oxidized, they lose C-H (contain electrons) - Methanol (3 C-H bonds)  When biological molecules are reduced, they gain C-H - Formaldehyde (2 C-H bonds)  Energy is released incrementally - Formic acid (1 C-H bond) - Carbon dioxide (No C-H bonds) - Fully oxidized  Each step breaks a C-H bond; done in steps or increments; would fry the cell if directly to last step  Goal is to maximize the amount of energy to protect from destruction  CO 2s the completely oxidized form of carbon Redox Potential (E ’) = electron potential Ο  Bacterial and Archaeal fuels are described by their redox potential - Measured in volts (V)  Each fuel has its own redox potential; think about octane levels  Fuel is an electron (e) donor  Reduced = a lot of electrons  Electrons flow from compounds with negative reduction potential (donor) to those with positive electron potential (acceptor)  Difference in redox potential from donor to acceptor is a measure of the amount of energy  Bigger the difference, the more energy that is released  Donor – acceptor  Difference between NADH and O is 1.12 V - Release of a lot of energy  Oxidation - Exergonic; ΔG < 0 spontaneous - Stored as ATP, NADH, FADH 2  Reduction - Endergonic; ΔG > 0 non-spontaneous - Input of energy Glycolysis and the Krebs cycle  Produce small amount of ATP  The reduced co-enzymes NADH and FADH are just a2 important as the ATP  Donate electrons to an electron transport chain ETC - Supply electrons to  Respiration = making a lot ATP via a ETC  Specific process for generating the ATP = oxidative phosphorylation - Distinguish from citric acid cycle production of ATP  NADH & FADH don2te e-s = oxidized  ADP is phosphorylated to ATP by a ATP synthase (oxidative phosphorylation) Respiration  Electron donor - Oxidized - C 6 12 6 - CH 4 - CH 3H - CH 3H O3 - C n 2n - Product: Electron transport chain; various electron carriers - H+ moved across the cell membrane and each time a little energy is lost  Pmf - Proton motive force - Lots of protons have this type of energy  Electron acceptor - Final - Aerobic, O 2 - All anaerobic use something else ** Electron donor is NADH, FADH or si2ilar reduced coenzyme - Over time there is a build up of protons - Area of high concentration to low concentration can’t travel by simple diffusion but can travel through ATP synthase Respiration requires an Electron Transport Chain  A series of electron carriers embedded within a membrane  The flow of e-s is coupled with the production of ATP  Electron flow from donors to a final electron acceptor  Aerobic organisms use O as t2e final acceptor  Anaerobic organisms use inorganic and organic compounds as a final electron acceptor In Bacteria and Archaea, the ETC is within the cell membrane  NADH and FADH are 2he source of electrons  NADH loses electrons  Electron loses some electrons  ATP synthase complex is oxidative phosphorylation  Oxidized – NADH, FADH 2  Phosphorylated – ADP Electron Transport Chain  Generates NO ATP directly - Indirectly by manipulating electrons  Protons attracted because electrons have negative charge  Movement along the electron transport chain moves H+ across the plasma membrane  Slight acidification of external surface  Exterior has (+) charge  ** pH gradient + electrochemical potential = proton motive force (pmf)  H+ wish to move back across the membrane - Proton gradient - Slightly acidic and positively charged ATP Synthase  Special protein channel  Catalyzes ATP synthesis  Oxidative phosphorylation  Distinguishes this process from ATP formation in glycolysis and Krebs - Substrate level phosphorylation - Aerobic organisms use O as the final electron acceptor 2  Makes more ATP - Works exactly the same - Anaerobic organism use something else  NO 3  Fe 3+ 2-  SO 4  CO 32-  Have to consume more fuel Bacteria and Archaea Terminal Electron Acceptor Couples  O2/H 2  NO 3/NO -2  Fe /Fe 2+ 2- 0  SO 4S  CO 3CH 4  Facultative anaerobes have more than 1 ETC Oxidase Test  Some bacteria contain cytochrome C oxidase which transfers electrons from cytochrome C to O 2  Aerobic organisms  Processes and makes purple  O2can be converted to highly reactive and dangerous molecules  ETC flavoprotein can bypass the next carrier and transfer electrons directly to O 2  The alternative pathway produces superoxide ion O - 2 - Reactive, dangerous  Hydrogen peroxide H O 2 2 - Byproduct of being aerobic  Bacteria that make catalase produce O bubbles2when exposed to H O 2 2 2 enzymes  Super oxide dismutase catalyzes O -  H O 2 2 2  Catalase detoxifies H O 2 2 2H 2 22H O +2O 2 Aerotolerance  Obligate aerobes - Catalase + - Grow at the top - Require oxygen  Obligate anaerobes - Catalase – - Grow at the bottom - Does not require oxygen  Facultative anaerobes - Catalase + - Grow throughout from top to bottom - Grow best with oxygen but can grow without it  Aerotolerant - Catalase – - Have enzymes that eliminate peroxidases - Do not use oxygen  Microaerophiles - Catalase + - Small amounts of oxygen used - Produce small amounts of catalase  Represents organisms ability to use or not use oxygen and if it can catalyze oxygen Diversity of Bacteria and Archaea  Trophy; Greek “nutrition”  Carbon Source - Auto: C from CO is 2ixed into organic molecules - Hetero: Organic molecules are consumed for carbon  Eating something that has carbon  Energy Source for producing ATP - Photo: Pigments absorb energy of photons from light - Chemo: Inorganic/organic compounds are oxidized  Degrade for electrons  Electron Source - Litho: Inorganic compounds supply electrons  Sulfur, iron, nitrate - Organo: Organic compounds supply electrons Autotrophs  Build biomass by fixing C from CO into 2rganic molecules  Photoautotrophy - Most common - Pigments within membranes that absorb photons - Photosynthetic - Photolysis of H O2or H S 2upplies electrons - Light energy used to fix CO = a2totrophy  Chemoautotrophy - Also called Lithotrophy and Chemolithotrophy - Electrons are derived from oxidized inorganic compounds/elements 2+ + -  Fe , H , 2 S,2NH , N4 2  Use energy from electrons - Rock eaters - Energy used to fix CO 2 - Autotrophs, but not photoautotrophs - Occurs where sunlight is not present  Soil, ocean floor - Less energy from oxidation of inorganic molecules - Redox potentials are more positive than organic molecules - Low ATP yield; oxidize more inorganic compounds - Energy yields from oxidation used is -686 kcal/mole Heterotrophs  Catabolize organic molecules for electrons and accumulate carbon for building biomass  2 types  Chemoheterotrophy - Also called Heterotrophy and Organoheterotrophy - Obtain carbon and energy for biomass solely from organic compounds - Found in sewage treatment plants  Photoheterotrophy - Use light drive ATP production, but not C fixation - So it isn’t photosynthesis - Organic compounds (C containing) are consumed to build biomass - Phototrophs, but not photoautotrophs; do not perform photosynthesis! - Pigments act as proton pump (Bacteriohodopsin) - Ex. freshwater and marine organisms **Heterotrophy only receive their carbon energy source in the dark **Photoheterotrophy receive their carbon and light energy source in the light and dark (never stop eating) Review Start | Yes --------Fixes carbon? ------- No | | Photoautotroph Yes ------Energy from light-------- Yes  Photoheterotroph | | No No | | Chemoautotroph  Yes---Energy from inorg. oxidation?---Yes Chemoheterotroph or organic 2.2 Photosynthesis Photosynthesis  Did not originate in either plants or algae  Originated in bacteria  Evolved in early prokaryotes Autotroph  Build biomass by fixing CO in2o organic molecules  Two types: photoautotrophs and chemoautotrophs  Photoautotrophs - Pigments that absorb photons; ex. Chlorophyll - Photon energy triggers electron transport (hits a pigment) - Photolysis of H 2 or H S2supplies electrons - Energy used to fix CO 2 - Perform a type of photosynthesis Two-step Process 1. Light Dependent  Require light  Convert solar energy to chemical energy  H 2 or an inorganic compound (H , H S2 S 2 is the energy source +  Reduce NADP to NADPH  Photophosphorylation = ATP synthesis (oxidative phosphorylation) 2. Calvin-Benson Cycle Reaction  Also known as Light Independent Reaction  Night or day  Fixation of CO 2autotrophic)  Produces a carbohydrate: G3P glyceraldehyde-3-phosphate  Requires electrons from NADPH and the hydrolysis of ATP ** Image on slide is important (Light rxns & Calvin cycle) Electromagnetic Spectrum  Smaller the λ, the more energy  Light you see is not absorbed but reflected  Infrared and near-infrared are too large, not enough energy to excite electrons  Smaller the wavelength, the more light  Has 2 natures - Wavelength - Act as particles (photon)  Photons - Packets of light energy - Properties of a particle and wave - Electromagnetic energy traveling in waves  Pigments - Absorb the energy of photons of a particular λ - Bacteria have many different pigments Photosynthetic pigments  Light harvesting pigments  Absorb light energy of different λ’s  Bacteriochlorophylls - First described in plants  Closely related to plant chlorophylls - In bacteria - Similar, nearly identical  The color of photosynthetic bacteria is due to reflected light  Cyanobacteria are blue/green: absorb the other wavelengths  Numerous chlorophylls like plants Photosynthesis requires a membrane  Lipid bilayer  Light is absorbed by electrons within the bond network  Pigments are part of the membrane  Stroma = cytoplasm  Chloroplast = photobacteria - Examples - Anabaena - Pryococcus  Thylakoid membranes are found in chloroplasts and cyanobacteria  Thylakoid; Greek thylakos “sac or pouch”  Chlorophylls usually use Magnesium (metal) because it can be oxidized or reduced (get light electrons) Excited vs. Ground State  Violent  The photon hits the pigment  Excited state - pigment molecules - electrons move from ground to excited state - absorption of photon by molecule  Ground state - energy is transferred to pigment  The difference in free energy between the excited and ground state approx. equal to the free energy of the photon  Smaller wavelength = more energy Chloroplasts are absent in bacteria  Bacteria are chloroplasts  In bacteria, pigments are integrated within the plasma and internal membranes  Chlorosomes - Specialized membranes associated with the plasma membrane - Invagination of the plasma membrane - Twisted back to provide more surface area for photosynthesis Photons strike the pigments and absorb energy  This starts a transfer of high energy from pigment to pigment molecules that reaches the reaction center  The reaction center pigment donates electrons to the photosystem; flow of electrons  Inductive residence - Transfer of energy - Excited electrons and not transfer of electrons  Final acc+ptor - NADP  NADPH  H2O, H 2 H 2, S serve to replace the electrons lost by the pigment  Molecule without electrons falls apart  Has to supply water, hydrogen, gas, etc. as a form of electrons  O2is source of electrons Photosystem  Membrane system for the absorption of light, transfer of electrons and generation of ATP  Electron source - H2O - O 2roduced  NADP reduced to NADPH  High-energy electrons are passed through a series of electron carriers in a ETC ETC  A high energy electron is transferred to NADP +  H gradient across the thylakoid membrane produces ATP via oxidative phosphorylation (photophosphorylation)  An electron transport chain pumps H ’s across a membrane as electrons are passed along a series carriers  Proton motive force (pmf) - Critical for making ATP +  Energy of H gradient  ATP synthase generates ATP as H s move back across the membrane via an ATP synthase into the cell NADPH  NADP NADPH + H + - Terminal electron acceptor - Nicotinamide adenine dinucleotide phosphate  Source of electrons for Calvin cycle Bacterial Photosynthesis  2 types 1. Anoxygenic  No O 2  Ex. Purple sulfur bacteria - Reflect purple light and absorb other wavelengths 2. Oxygenic  Release O 2  Ex. Cyanobacteria - Many species  Aquatic bacteria; both  The majority of photosynthesis on the planet is performed by bacteria  Photosynthesis can occur to a depth of ~70 m or 230 feet in the ocean Anaerobic Anoxygenic Photosynthesis  Appeared ~3.5 bya  Do not produce O 2  Major evolutionary advancement  CO 2 H S2 C H 6 12S 6 H O0 2 0  H2, H2Sor S or organic compounds serves as a source of electrons  Need electrons to fix C and produce ATP via ATP synthase 0  S or product used as terminal electron acceptor for anaerobic respiration Purple Sulfur Bacteria  Aquatic photoautotrophs - Gas is result of decomposition of plants  Anaerobes  H2S as the electron donor 0  Oxidize H S2to S  Some can use S O 2 3- (thiosulfate)  Accumulate intracellular sulfur granules  S is oxidized to SO 42-  Carbon from CO is 2ixed (autotrophs)  Cyanobacteria can live close to this  Anoxygenic - Have one photosystem - One type of reaction center - Light harvesting complex - Membrane, pigments, ETC, ATP synthase - Reducing power  Source of electrons  H S2 S  SO 42-  Anaerobic respiration - Carbon  CO  2CH O) 2 n  Calvin cycle - Energy  Phototrophs  ADP  ATP - <~~ hv  Wavelength of light symbol  Oxygenic - Have two photosystems - 1 to generate ATP - 1 to generate NADPH - 2 reaction centers - Make more ATP - Reducing power  H O2 ½ O 2  Break down of water to release electrons to oxygen - Carbon  CO  2CH O) 2 n  Calvin cycle - Energy  ADP  ATP  Photophosphorylation  Accept electrons at different wavelengths Microbial mat  Cyanobacteria and purple bacteria  CO 2 H S 2 C H O6+12 +6H O 0 2 Oxygenic Photosynthesis  ~ 2.4 bya  6H 2 + 6CO  62 + C 2 O 6 12 6  Very similar in size primarily  Evolution of a H 2 splitting enzyme  Photolysis  H 2 is a source of electrons  O 2n environment  Aerobic metabolism/cellular respiration  Development of eukaryotes  Algae and plants Calvin Benson Cycle/ Light Independent Reactions  Occurs in the cytoplasm of photosynthetic bacteria  Incorporates CO in2o a sugar  Starts with CO i2corporated into an intermediate organic molecule = carbon fixation  C from CO 2sugar  NADPH supplies electrons  Terminal electron acceptor in photosystem  ATP from light reactions powers part of the Calvin cycle  Incorrectly referred to as the dark reactions  External membrane or cell membrane come out of light reaction The primary CO -fix2ng enzyme  For autotrophic bacteria, algae, and plants  Ribulose bisphosphate carboxylase-oxygenase (rubisco)  Needs to be separated from O 2  Put into another molecule  Cyanobacteria encapsulate rubisco in micro-compartments known as carboxysomes - Becomes 2 separate  The diagram is important - Unique enzymatic steps Differences between plant and bacterial photosynthesis (Differences between oxygenic and anoxygenic photosynthesis) Oxygenic Anoxygenic bacterial Photosynthesis photosynthesis Organisms Plants, algae, Purple and green cyanobacteria bacteria Type of chlorophyll Chlorophyll a, absorbs Bacteriochlorophyll 450 & 650-750 nm absorbs 800-1000 nm Photosystem I (cyclic Present Present photophosphorylatio n) Photosystem II Present Absent (noncyclic photophosphorylatio n) Produces O 2 Yes No Photosynthetic H O H S, other sulfur 2 2 electron donor compounds or certain organic compounds


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