Week 7 LIFE102 Notes
Week 7 LIFE102 Notes Life 102
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This 8 page Class Notes was uploaded by Sydney Dingman on Sunday March 6, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik N Arthun in Winter 2016. Since its upload, it has received 31 views. For similar materials see Attributes of Living Systems in Biology at Colorado State University.
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Date Created: 03/06/16
Week 7 LIFE 102 Notes 2/26/16, Module 8 cont. Glycolysis: Sugar splitting, small amount of ATP is made and glucose is oxidized (loss of electrons) Reduction is the gain of electron, cannot have reduction without oxidation. Before the citric acid cycle can begin: o Pyrubate must be converted to acetyl Coenzyme A (Acetyl CoA), which links glycolysis to the citric acid cycle. Major point of digesting food is to steal electrons and those electrons are used to pump hydrogen ions across a membrane Step 2: Citric Acid Cycle o Occurs in the mitochondrial matrix o Completes the break down of pyruvate to CO2 o The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn o Pay attention to the electron shuttles; it is where the important energy is located o Fuel is oxidized in the citric acid cycle During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis o Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food o These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation o The electron transport chain is in the inner membrane (cristae) of the mitochondrion o Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O Step 3: Electron Transport Chain o Electrons are transferred from NADH or FADH2 to the electron transport chain o Electrons are passed through a number of proteins to O2 o The electron transport chain generates no ATP directly o It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts Chemiosmosis: The energy-coupling mechanism o Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space o H+ then moves back across the membrane passing through the protein ATP synthase o ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP o This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work Cells can produce ATP in alternative ways o Aerobic respiration needs O2 for ETC o If there was no oxygen, the process of glycolysis would be connected to Anaerobic respiration Uses electron transport chain with a final electron acceptor other than O2, for example sulfate Fermentation An extension of glycolysis (repeats glycolysis) Allows continuous substrate-level phosphorylation and recycles NADH NAD+ Uses substrate level phosphorylation instead of an electron transport chain to generate ATP Alcohol fermentation o Pyruvate is converted to ethanol in two steps, with the first releasing CO2 Lactic acid fermentation o Pyruvate is reduced (gaining of electrons) by NADH, forming lactate (gives somewhat sour taste) as an end product, with no release of CO2 We need empty electron shuttles 2 Only get 2 ATP, not efficient, but better than nothing o Pyruvate is a key intersection in catabolism Energy movement through ecosystems o Energy flows into ecosystems as sunlight and leaves as heat through photosynthesis and respiration 2/29/16, Chapter 10, Photosynthesis In photosynthesis light energy is converted into chemical energy CO2+H2O(light)[CH2O]+O2Carbohydrates Types of feeders o Autotrophs: Self feeders Producers of all organic compounds in the biosphere o Photoautotrophs Produce energy from light o Heterotrophs: Other feeders Consumers of organic molecules from organisms Photosynthesis o Plants, algae and some prokaryotes o Supports all life on Earth by: Converts light energy to the chemical energy of food Location of photosynthesis o Leaves: major locations of photosynthesis Green color from chlorophyll, the green pigment within chloroplasts CO2 enters and O2 exits the leaf through microscopic pores called stomata o Chloroplasts: the sites of photosynthesis in plants The chlorophyll is the membranes of thylakoids Chloroplasts also contain stroma, a dense interior fluid 3 Tracking atoms through photosynthesis o Light+6 CO 2+12 H 2OC 6H12O +6 O 2+6 H 2O o Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product o Energy flow on our planet is a cycle How does photosynthesis work? o 2 processes: Light Reactions and Calvin Cycle Light Reactions: light energy is captured in the thylakoid membrane Acts as the input of energy Calvin Cycle: CO2 is “fixed” and reduced to sugars in the stroma o Photosynthesis consists of light reactions (the photo part) and Calvin cycle (the synthesis part) The light reactions Split H2O Release O2 Reduce NADP+ to HADPH Generate ATP from ADP by photophosphorylation The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH The Calvin cycle beings with carbon fixation, incorporating CO2 into organic molecules How can light energy be captured? o Light: radiation energy from the sun o Light behaves as though it is made of discrete particles called photons Interactions between leaves and light o Photons of light energy interact with chlorophyll molecules and other pigments in chloroplasts o Light is: Reflected 4 Transmitted Absorbed Plants: molecules that can absorb light Chlorophyll: photosynthetic pigment How does light absorption work? o Unit of light: photon o When a photon hits any molecule, it can push an electron into a higher energy level exited state electrons fall back, emitting heat/radiation Excitation of an e- from a chlorophyll molecule (see slide 16 of chapter 10 notes) o Chlorophyll excitation in a chloroplast does not allow the electron to fall back down after it is excited, and it is captured by another molecule (primary electron acceptor) 3/2/16, Module 10 cont. Chlorophyll excitation in a chloroplast o Electron doesn’t fall back down, but is captured by another molecule Photosystem (PS): cluster of pigment molecules working together o 2 types of photosystems: PS I and PS II Work together in photosynthesis o Each PS has: Reaction center: central Chl molecule that receives all captured light energy Primary electron acceptor: molecule that accepts excited e- from reaction center Photosystems o Consists of a reaction center complex surrounded by light- harvesting complexes o The light-harvesting complexes (pigment molecules bound to proteins) transfer the energy of photons to the reaction center o A primary electron acceptor in the reaction center accepts excited electrons and is reduced 5 o Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of light reactions Linear Electron Flow o During the light reactions, there are two possible routes for electron flow: cyclic and linear o Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH o A photon hits a pigment and its energy is passed among pigment molecules until it excites P680 o An excited electron from P680 is transferred to the primary electron acceptor o P680+ is a very strong oxidizing agent It pulls very hard on electrons o H20 is split by enzymse and the electrons are transferred from the hydrogen atoms to P680+ thus reducing it to P680 o O2 is released as a by-product o this reaction o Each electron “falls” down an electron transport chain from primary electron acceptor of the PSII and PSI o Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane o Diffusion of H+ (protons) across the membrane drives ATP o In PSI (like PSII), transferred light energy excites P700, which loses an electron to an electron acceptor o P700+ (P700 that is missing an electron) accepts an electron passed down from PSII via the electron transport chain Linear Electron Flow o Each electron “falls” down an electron transport chain from the primary electron acceptor of PSI to the protein ferredoxin (Fd) o The electrons are then transferred to NADP+ and reduce it to NADPH o The high energy electrons of NADPH are available for the reactions of the Calvin cycle o Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using light energy 6 o The electrons of NADPH are available for the reactions of the reaction cycle o KNOW HOW THE ATP IS MADE AND THE TWO PRODUCTS OF THE REACTION Comparison of Chemiosmosis in Chloroplasts and Mitochondria o Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy o Mitochondria transfer chemical energy from food to ATP o Chloroplasts transform light energy into chemical energy of ATP Summary of light reactions o Light energy Chemical energy/ NADPH and ATP o Low-energy Light energy high energy e- o Flow of high-energy e- to NADPH is via an ETC ATP produced o Oxygen formed as by-product form splitting of H2O to e- + H+ + O2 The Calvin Cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar o The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle o The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH o CO2 is fixed and reduced to sugar (CHO) o Carbon enters the cycle as CO2 and leaves as a sugar names glyceraldehyde 3-phosphate (G3P) o For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2 o The Calvin cycle has 3 phases Carbon fixation Reduction Regeneration of the CO2 acceptor o The Calvin cycle uses the chemical energy of 9 ATP and 6 NADPH to reduce CO2 to sugar Calvin cycle and Light reactions are codependent, can’t have one without the other 7 Importance of Photosynthesis o The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds o Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells o Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits o In addition to food production, photosynthesis produces O2 in our atmosphere Energy Movement through ecosystems o Energy flows into an ecosystem as sunlight leaves as heat o Photosynthesis and respiration 8
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