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Transcript
Energy Functions of ATP • Chemical work – synthesizing compounds • Transport work – moving substances across the plasma membrane • Mechanical work – moving cell structures and cells •Energy coupling: use of an exergonic process to drive and endergonic process •ATP mediates most energy coupling in cells ATP • Consist of – a sugar called ribose – N containing Adenine – Three phosphate groups Unstable w/3 PO4• All negative charge-repel each other ADP is more stable A change from a less stable molecule to a more stable molecule always releases energy. The structure and hydrolysis of ATP All are negatively charged – crowded and repel, creating instability When bonds are broken from ATP to ADP (hydrolysis), 7.3 kcal/mol of energy is released (exergonic) Phosphorylation Recipient of phosphate group when ATP loses it. Done by Kinases The ATP cycle ATP is a renewable resource that can be regenerated… FAST – working muscle cell recycles its entire ATP pool once each minute; -Turnover represents 10 million molecules of ATP generated per second in a cell. • The energy can then be used to drive other reactions – ATP “carries” Energy • Photosynthesis is the process by which plants and other organisms use sunlight, CO2 & H20 to produce high energy carbohydrates such as sugars and starches. • Prokaryotesphotosynthetic capability is present within five major groups of bacteria. Where Photosynth esis Occurs The Internal Structure of a Leaf Section 23-4 CO2 enters through the stomata Epidermis Chloroplasts Stomata Guard cells • Chloroplasts are only found in photosynthetic, eukaryotic cells. Chloroplasts are capable of harnessing energy from the sun's rays of light. •Using this energy from the sunlight, chloroplasts are able to form ATP as well as synthesizing sugars from water and carbon dioxide. Things to know about Chloroplasts • have a double membrane • have their own DNA (carries the info to make enzymes) • have their own ribosomes (more like the ribosomes of prokaryotes) -used to synthesize proteins • make their own enzymes required for photosynthesis • require CO2 and H2Oproduce C6H12O6 • contain chlorophyll (green chemical "traps" sunlight energy) • The chloroplast is made up of 3 types of membrane: 1.A smooth outer membrane which is freely permeable to molecules. 2.A smooth inner membrane which contains many transporters 3.A system of thylakoid membranes Chloroplast • Organelle where photosynthesis takes place. Stroma Outer Membrane Inner Membrane Thylakoid Granum Thylakoid Thylakoid Membrane Granum Thylakoid Space Light and Pigments In addition to water and carbon dioxide, photosynthesis requires light and CHLOROPHYLL and Accessory Pigments Light – radiant energy from the sun, travels in waves (light energy is measured in units called photons) amplitude Crest – high point Baseline amplitude One wavelength Trough – low point • Amplitude – height of wave; distance between crest and/or trough (must use a reference point from which to start…) • Wavelength – distance between where waves begin to repeat themselves • Frequency – how many waves pass a certain point in a given amount of time (high frequency vs. low frequency) Sunlight is a mixture of many different wavelengths… ROYGBIV • Colors in visible light spectrum • Each of these has a different wavelength… Chlorophyll A and B • Absorb red, blue, and violet range. b a Chlorophyll Light Absorption Photosynthetic Pigments -absorb light and use it to provide energy to carry out photosynthesis • Plants absorb certain wavelengths of light • 2 major groups of pigments. • Chlorophylls (green) and carotenoids (yellow, orange and red.) Pigments • Substances in organisms that can absorb light (remember – light must be absorbed before it can be converted and used by living systems…) • The color that you see is the one being REFLECTED • CHLOROPHYLL is the major photosynthetic pigment in plants • 2 types: chlorophyll a – directly involved in transformation of photons to chemical energy chlorophyll b – helps trap other wavelengths and transfers it to chlorophyll a Location and structure of chlorophyll molecules in plants The pigment molecules have a large head section that is exposed to light in the surface of the membrane; the hydrocarbon tail anchors the pigment molecules into the lipid bilayer. Double bonds are the source of the e- that flow through the ETC Accessory Pigments • Other pigments that trap other wavelengths -found in chromoplasts • Ex. Carotenoids * xanthophyll – yellows * beta carotene – oranges • These are masked by presence of chlorophylls, except in autumn (when leaf cells stop synthesizing chlorophyll) – “fall colors” • Also is very obvious in “ripe” fruits, veggies Ex. Apple, tomato • Chlorophyll B, the carotenoids, and the phycobilins are known as antenna pigments. • They capture light and pass the enrgy along to chlorophyll A. • Chlorophyll A directly participates in the light reaction of photosynthesis. Photosystems • Light-harvesting complexes in the thylakoid membranes. (few 100 in each) • Structure: – Reaction Center- contains chlorophyll A and a region containing several 100 antenna pigments. • Two Types: – PS I and PS II – PS II acts BEFORE PS I……..go figure... PSII • 680nm range • Also referred to as P680. PS I • 700nm range • Also referred to as P700 Now that you know all of that……let’s actually look at the process of photosynthesis Photosynthesis: Quick Overview STAGE 1 Photosynthesis: Quick Overview STAGE 1 Photosynthesis: Quick Overview STAGE 1 STAGE 2 Light Independent Reaction Light Dependent Reaction The Process of Photosynthesis does NOT Happen all at Once; rather it occurs in TWO STAGES: STAGE 1: LIGHT DEPENDENT REACTIONS. – PS I and PS II capture energy from sunlight. Water is Split into Hydrogen Ions, Electrons, and Oxygen (O2). The O2 Diffuses out of the Chloroplasts (Byproduct). – The Light Energy is Converted to Chemical Energy, which is Temporarily Stored in ATP and NADPH. •Two possible routs for the e- flow: •Cyclic photophosphorylation •noncyclic Steps of Light Dependent Reaction (Noncyclic Photophosphorylation) Overview: –E- enter two electron transport chains –ATP is formed –NADPH (Nicotinamide dinucleotide phosphate) is formed Steps of Light Dependent Reaction (Noncyclic Photophosphorylation) 1. 2. 3. 4. 5. 6. • • 7. 8. 9. 10. 11. 12. 13. PSII absorbs energy. e- from double bonds in the head of ChloroA become energized and move to a higher energy level. They are captured by a primary electron acceptor. Photolysis: H2O gets split apart into 2 e- , 2 H+, and one oxygen atom.. The ereplace those lost by ChloroA. 2 oxygen molecules combine and is released into the air. H+ are released into the inner thylakoid space, which creates a higher [ H+ ] inside the thylokoid. e- from ChloroA are passes along a ETC consisting of plastoquinone (PQ)--complex of 2 cytochromes and several other proteins. This flow is exergonic and provided energy to produce ATP by chemiosmosis. (photophosphorylation) The ATP is used to power the Light Independent Reaction (Calvin Cycle)….this is a coupled reaction! The e- end up at PS I. PS I absorbs energy. e- from double bonds in the head of ChloroA become energized and move to a higher energy level. They are captured by a primary electron acceptor. E- that are lost are replaced by the e- from PSII (step7). e- from ChloroA are passes along a ETC – consisting of ferrodoxin. NADPH is produced. NADP in the stroma pick up 2 H+ and form NADPH and enter the calvin cycle. Figure 10.11 How a photosystem harvests light Chlorophyll a The light reactions and chemiosmosis: organization of the thylakoid membrane The production of ATP using the energy of sunlight is called photophosphorylation. H+ H+ H+ H+ H+ H+ H+ H+ + H+ H H+ Chemiosmosis “Chemiosmotic Theory” -Peter Mitchell -1961 • Energy coupling mechanism. – Uses potential energy stored in the form of a proton gradient to phosphorylate ADP to produce ATP. ATP synthase-The Movie Chemiosmosis Proton gradient ALSO creates a pH difference as well as a charge difference. Protons can not diffuse through the membrane. SO they must flow through the ATP synthase protein channel. 90% of all ATP is produced this way. Photosynthesis: Light Dependent Reaction Clip Figure 10.13 A mechanical analogy for the light reactions A. Photosystem II -Light is absorbed by pigment. Energy is transferred to e-, which Figure 8-10 Light-Dependent go into ETC. Hydrolysis breaks water up into e-, H+, and O2 Reactions B. ETC Section moves H+ 8-3 ions from stroma into inner thylakoid. C. Photosystem I -light is absorbed by pigments, energy goes to e-, NADPH is formed D. Hydrogen movement makes inside positively charged. E. As H+ diffuses through ATP synthase, ADP is made into ATP. Photosystem II Hydrogen Ion Movement Chloroplast ATP synthase Inner Thylakoid Space Thylakoid Membrane Stroma Go to Section: Electron Transport Chain Photosystem I ATP Formation Cyclic Photophosphorylation •Periodically the chloroplasts runs low on ATP. •Does this to replenish ATP levels. •e- travel from the P680 ETC to P700 then to a primary eacceptor, then back to the cytochrome complex in the P680 ETC. • No NADPH is produced. • No O2 is released. STAGE 2: Dark Reaction /Light Independent reaction/Calvin-Benson Cycle). •The ATP and NADPH created in the light reaction is used to power the formation of Organic Compounds (Sugars), using CO2. •This is a light Independent reaction. It can happen during the daylight, it just does NOT need to light be completed. •Occurs in the stroma. •Cyclical pathway where carbon enters as CO2 and exits as PGAL (phosphoglyceraldehyde.) •Carbon is fixed into PGAL. •Called carbon fixation. •This is a reduction reaction (carbon is GAINING hydrogen) •Must repeat 6 times. C3 plants The Calvin cycle 6 CO2 attaches to a 5-C sugarRuBP.Ribulose biphosphate. This forms a 6C molecule (PGA) The Calvin cycle 6 6-C molecule breaks (PGA) down into 2 3-C molecules (3PGAL-3phosphoglycera te) 12 Catalyzes by the enzyme Rubisco. 12 12 PGAL 2 PGAL 1 PGA The Calvin cycle 6 PGAL converted to RuBP 12 12 12 PGAL Summary: H+ 6CO2 + 18 ATP + 12 NADPH + 18ADP + 18 Pi + 12NADP+ + 1 Glucose 2 PGAL 1 PGA Factors affecting Photosynthesis • Amount of water available – too little, stop photosynthesis • Temperature – best between Oo Celsius and 35o Celsius (too high, damage enzymes; too low, stop photosynthesis) • Intensity of light – up to a point, increasing light intensity increases rate • C-3 Other Pathways – Calvin cycle occurs in all photosynthetic cells-both palisade and mesophyll layers. • C-4 – Called C4 because the CO2 is first incorporated into a 4-carbon compound. – Light reaction occurs ONLY in the mesophyll cells and the calvin cycle occurs in the bundle-sheath cells. • CAM • CAM plants live in very dry condition and, unlike other plants, open their stomata to fix CO2 only at night. Figure 10.18 C4 leaf anatomy and the C4 pathway Cellular Respiration Objectives • Describe the role of ATP in coupling the cell's anabolic and catabolic processes. • Explain how chemiosmosis functions in bioenergetics. • How are organic molecules broken down by the catabolic pathways of cellular respiration? • Explain the role of oxygen in energy-yielding pathways of cellular respiration. • Explain how cells generate ATP in the absence of oxygen. Cellular Respiration • the process that occurs in cells in which cells break down sugar for ENERGY! • Occurs in cytoplasm and Mitochondria. Glycolysis Important points: • Occurs in Cytoplasm • First 3 steps are endothermic-Energy of activation = 2 ATP • Last 6 steps are exothermic; producing 4 ATPs. • 4-2= 2 ATP (net yield) • Releases less then 25% of energy from glucose. A closer look at glycolysis Step 1 Step 2 Step 4 Step 3 Step 5 Step 6 Step 7 Step 5 Step 8 Step 6 Step 9 Step 7 Cellular Respiration Overview: • We get our energy from the food we eat. • The unit for energy is the calorie. • Plants are producers and make glucose by the process of photosynthesis. • Heterotrophs breakdown glucose for energy. • There are two important ways a cell can harvest energy from food: fermentation and cellular respiration. 30 Step1: Glycolysis • • • • Means “Splitting Glucose” Both pathways start with Glycolysis. Glycolysis starts with Glucose. Glucose is broken down into 2 molecules called Pyruvate. • Happens in the Cytoplasm. 31 Products of Gylcolysis 32 33 Summary of Glycolysis • 1. One glucose (6C) converted into 2 pyruvates (3C). • Net yield of 2 ATP for use by cell. • CLIP 34 REVIEW • Glycolysis is the first step of reactions that break glucose apart to release the energy it holds in its C-H bonds. • Where did this energy come from? • Glycolysis occurs in the Cytoplasm. • Glycolysis does not need oxygen! • Glycolysis occurs in both aerobic (With oxygen) and anaerobic (without oxygen) respiration! In the presence of OXYGEN: Step 2: Krebs Cycle Step 3: Electron Transport • Happens in the Mitochondria • Starts with Pyruvate. • Pyruvate moves into the mitochondria and is broken down into CO2 , O2 and ATP. Krebs and ETC take place in a mitochondrion Double membrane Mitochondria Anatomy Krebs Cycle Overview (Citric Acid Cycle) • Occurs in the mitochondrial matrix • Pyruvate (product of glycolysis) enters the mito. and combines with coenzyme A (vitamin A) to form acetyl coenzyme A. Yields 1 NADH • Krebs starts with acetyl coA. • Cyclical series of enzyme-catalyzed reactions. • Each turn (cycle) uses 1 pyruvate and yields – 3 NADH, 1 ATP, 1 FADH – Byproduct=CO2 NAD and FAD Coenzymes that carry protons or electrons from glycolysis & krebs to the ETC • NAD: • FAD: A summary of the Krebs cycle Electron Transport • Utilizes a series of proteins called cytochromes • Made up of heme group with 4 organic rings surrounding a single iron atom (similar to hemoglobin) • But, cytochromes transfer electrons rather than oxygen…. • NADH and FADH2 provide sources of electrons for the ETC Electron Transport • The ETC is a proton pump in the inner mito membrane. • Its uses the energy released from the exergonic flow of electrons to pump protons from the matrix to the inner membrance space. • This sets up a proton gradient across the membrane=chemiosmosis. Oxidative Phosphorylation and Chemiosmosis Energy from falling e- (exergonic) is used to pump H+ across the membrane (endergonic). Oxygen is the final eacceptor!! H+ can’t get through the membrane, so they MUST pass through the channel. Phosphorlation • Substrate Level: – When an enzyme transfers a PO4- from a substrate DIRECTLY to ADP. • Oxidatative: – During Chemiosmosis. – 90% of all ATP is produced this way in the ETC – NAD & FAD lose protons (become oxidized) to the ETC…pumps protons to innermembrane space creating a gradient. This powers the phosphorlation of ADP Aerobic Respiration With oxygen Section 9-1 Respiration Glucose Glycolysis Krebs cycle Fermentation (without oxygen) With out oxygen Go to Section: Electron transport Alcohol or lactic acid 41 Figure 9.13 Free-energy change during electron transport Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis Figure 9.16 Review: how each molecule of glucose yields many ATP molecules during cellular respiration Figure 9.19 The catabolism of various food molecules • In the presence of oxygen: Pyruvate is converted into carbon dioxide and water in the Krebs cycle. • After the Krebs cycle, 36 ATP are created in the electron transport chain. 42 Section 9-2 Flowchart Cellular Respiration Reactants Glucose (C6H1206) + Oxygen (02) Final Products Glycolysis Krebs Cycle Electron Transport Chain Carbon Dioxide (CO2) + Water (H2O) 43 Go to Section: Fermentation • Without oxygen: Pyruvate is converted into Lactic Acid or Alcohol during Fermentation. • Lactic Acid-Muscle cells • Alcohol- Yeast 44 Anaerobic Respiration 45 Electrons carried in NADH Electrons carried in NADH and FADH2 Pyruvic acid Glucose Glycolysis Electron Transport Chain Krebs Cycle Cytoplasm Mitochondrion Electron Transport Hydrogen Ion Movement Channel Mitochondrion Intermembrane Space ATP synthase Inner Membrane Matrix ATP Production Lactic Acid Fermentation Section 9-1 Glucose Pyruvic acid Lactic acid 46 Go to Section: Section 9-2 Anaerobic: Fermentation Reactant Glucose (C6H1206) Products Glycolysis Fermentation Lactic Acid Or Alcohol 47 Go to Section: 48 Respiration Formula • 6____ + ___ Review Clip ___ and 6___ + 6__ + 36 ATP 49 50 35 Alternative Energy Sources • From Fats: – Enzymes cleave the bonds between the glycerol and the fatty acids, which enter the blood stream. Enzymes in the liver convert the glycerol into PGAL. – Enzymes in cells break apart the fatty acids acetylCoA. – More C-H bonds, so yields more ATP. Alternative Energy Sources • From Proteins: – Cells don’t store protein. – Enzymes breakdown proteins—into AA units, then strip of the NH3+ group. – Carbon backbone either gets converted into fats or carbohydrates. – Or, enter krebs cycle.