Lecture 9 Generating Energy. Adenosine Triphosphate (ATP) The energy currency or coin of the cell.The energy currency or coin of the cell. Transfers energy.
<ul><li> Slide 1 </li> <li> Lecture 9 Generating Energy </li> <li> Slide 2 </li> <li> Adenosine Triphosphate (ATP) The energy currency or coin of the cell.The energy currency or coin of the cell. Transfers energy from chemical bonds to endergonic (energy absorbing) reactions within the cell.Transfers energy from chemical bonds to endergonic (energy absorbing) reactions within the cell. ATP consists of a ribose sugar, adenine base, and 3 phosphate groups, PO 4 -2.ATP consists of a ribose sugar, adenine base, and 3 phosphate groups, PO 4 -2. </li> <li> Slide 3 </li> <li> ATP Energy is stored in the covalent bonds between phosphates. The greatest amount of energy is in the bond between the second and third phosphate groups. This covalent bond is known as a pyrophosphate bond. When the terminal (third) phosphate is cut loose, ATP becomes ADP (Adenosine diphosphate), and the stored energy is released for some biological process to utilize. The input of additional energy (plus a phosphate group) "recharges" ADP into ATP </li> <li> Slide 4 </li> <li> ATP Shuttles Energy From Exergonic Reactions to Endergonic Reactions </li> <li> Slide 5 </li> <li> New Terms Dehydrogenase: Is an enzyme that removes hydrogen atoms (with their electrons) from organic molecules and transfers them to an electron carrier. Electron Carrier Molecules: Molecules that accept and transfer H atoms and high energy electrons released by reactions. E.g (1)NADH: (Nicotinamide adenine dinucleotide). (2)FADH 2 (Flavin adenine dinucleotide): A secondary H carrier, related to NADH. </li> <li> Slide 6 </li> <li> Synthesis of ATP-1 Two mechanisms exist that generate ATP i) substrate level phosphorylation and ii) oxidative phosphorylation (chemiosmosis). Cellular respiration process that utilises both mechanisms to generate ATP during its different stages. There are 3 stages of cellular respiration: 1. Glycolysis 2. The Krebs Cycle 3. Oxidative Phosphorylation </li> <li> Slide 7 </li> <li> ATP Synthesis by: 1. Substrate-level phosphorylation Simple process, does not require membranes.Simple process, does not require membranes. Phosphate group is directly transferred from an organic molecule to ADP to make ATP.Phosphate group is directly transferred from an organic molecule to ADP to make ATP. Generates a small amount of ATP during cellular respiration.Generates a small amount of ATP during cellular respiration. Occurs in first two stages of aerobic respiration:Occurs in first two stages of aerobic respiration: 1.Glycolysis 2.Krebs cycle </li> <li> Slide 8 </li> <li> ATP Synthesis by: 2. Oxidative phosphorylation (Chemiosmosis) Complex process, requires mitochondrial membranes.Complex process, requires mitochondrial membranes. Generates most of ATP made during cellular respiration.Generates most of ATP made during cellular respiration. Electrons are passed from one membrane-bound enzyme to another, losing some energy with each transfer known as the electron transport chain. This "lost" energy allows for the pumping of hydrogen ions against the concentration gradient (there are fewer hydrogen ions outside the confined space than there are inside the confined space). ATP is made by ATP synthase on mitochondrial membranes, as H + flow down concentration gradient. Occurs in last stage of aerobic respiration.ATP is made by ATP synthase on mitochondrial membranes, as H + flow down concentration gradient. Occurs in last stage of aerobic respiration. Requires the presence of OXYGENRequires the presence of OXYGEN </li> <li> Slide 9 </li> <li> Two Mechanisms of ATP Synthesis: Oxidative and Substrate Level Phosphorylation </li> <li> Slide 10 </li> <li> Three Stages of Aerobic Respiration </li> <li> Slide 11 </li> <li> 1. Glycolysis: Splitting sugar Occurs in the cytoplasm of the cell Does not require oxygen 9 chemical reactions Net result: Glucose molecule (6 carbons each) is split into two pyruvic acid molecules of 3 carbons each. Pyruvic acid diffuses into mitochondrial matrix where all subsequent reactions take place. </li> <li> Slide 12 </li> <li> Slide 13 </li> <li> 2. Details of Krebs Cycle </li> <li> Slide 14 </li> <li> 3. Electron Transport Chain & Chemiosmosis Most ATP is produced at this stage. Occurs on inner mitochondrial membrane. Electrons from NADH and FADH 2 are transferred to electron acceptors, which produces a proton gradient Proton gradient used to drive synthesis of ATP. Chemiosmosis: ATP synthase allows H + to flow across inner mitochondrial membrane down concentration gradient, which produces ATP. Ultimate acceptor of H + and electrons is OXYGEN, producing water. </li> <li> Slide 15 </li> <li> Electron Transport & Chemiosmosis: Generates Most ATP Produced During Cellular Respiration </li> <li> Slide 16 </li> <li> Electron Transport Chain </li> <li> Slide 17 </li> <li> Fermentation Occurs When Oxygen is Unavailable </li> <li> Slide 18 </li> <li> Photosynthesis-1 Is the process by which plants, some bacteria, and some protistans use the energy from sunlight to produce sugar, which cellular respiration converts into ATP!! </li> <li> Slide 19 </li> <li> Photosynthesis-2 6CO 2 + 6H 2 O + ENERGY ---> C 6 H 12 O 6 + 6O 2 Where does the free oxygen come from? CO 2 or H 2 OWhere does the free oxygen come from? CO 2 or H 2 O Label the CO 2 or H 2 O with radioactive O 18Label the CO 2 or H 2 O with radioactive O 18 CO 2 + 2H 2 O -------> CH 2 O + H 2 O + O 2 CO 2 + 2H 2 O -------> CH 2 O + H 2 O + O 2. CO 2 + 2H 2 O -------> CH 2 O + H 2 O + O 2 CO 2 + 2H 2 O -------> CH 2 O + H 2 O + O 2. Plants produce oxygen by splitting water.Plants produce oxygen by splitting water. Water is used as a source of H and electrons to reduce CO 2Water is used as a source of H and electrons to reduce CO 2 </li> <li> Slide 20 </li> <li> Photosynthesis-3 Light reactions: Transform light energy into usable form of chemical energy (ATP and NADPH). Water is split to obtain H. Light independent reactions (Calvin cycle): Use chemical energy (ATP and NADPH) to drive the endergonic reactions of sugar synthesis.. </li> <li> Slide 21 </li> <li> Where does photosynthesis occur? Chloroplasts are site of photosynthesis in eucaryotes All green parts of a plant carry out photosynthesis. Most chloroplasts are found in leaves, specifically in mesophyll, green tissue in interior of leaves. Stomata: Pores in leaf for exchange of CO 2 and O 2 Green color is due to chlorophyll, a light absorbing pigment. In bacteria, photosynthesis occurs on extensions of the cell membrane. </li> <li> Slide 22 </li> <li> Specific Sites for Specific Reactions Thylakoids: Membrane discs arranged in stacks (grana) which contain chlorophyll and other important molecules.Site where solar energy is trapped and converted into chemical energy (light reactions).Thylakoids: Membrane discs arranged in stacks (grana) which contain chlorophyll and other important molecules.Site where solar energy is trapped and converted into chemical energy (light reactions). Thylakoid Membrane: Site of ATP synthesis.Thylakoid Membrane: Site of ATP synthesis. Stroma: Thick fluid outside thylakoid membranes, surrounded by interior membrane. Site of sugar synthesis (dark reactions).Stroma: Thick fluid outside thylakoid membranes, surrounded by interior membrane. Site of sugar synthesis (dark reactions). </li> <li> Slide 23 </li> <li> Light reactions Light reactions trap energy and electrons required to make sugar from CO 2. Require light. Convert light energy to chemical energy of ATP and reducing power of NADPH. Occur in the thylakoid membranes of chloroplast. Water is split with energy from sun into free O 2, H and electrons. Reduce NADP + to NADPH Photophosphorylation: Light energy is used to produce ATP from ADP + P i ATP synthesis is driven by chemiosmosis Input: ADP, NADP+, water, and light. Output: ATP, NADPH, and O 2. </li> <li> Slide 24 </li> <li> Light Light is a Spectrum of Different Lights Wavelength in nanometers: Visible light spectrum - Wavelength in nanometers: 380 470 520 570 610 650 VIOLET BLUE GREEN YELLOW ORANGE RED Higher Energy Lower Energy </li> <li> Slide 25 </li> <li> Chlorophyll Pigments allow plants to absorb various wavelengths of light, they are molecules that absorb light energy. Black object: All wavelengths are absorbed, White object: All wavelengths are reflected, Green object: All wavelengths BUT green are absorbed. Green light is reflected by chlorophyll Plants use different pigments to capture light energy, each has its own unique absorption spectrum: </li> <li> Slide 26 </li> <li> Structure of a Chlorophyll Molecule </li> <li> Slide 27 </li> <li> Photosystems Are arrangements of chlorophyll and other pigments packed into thylakoids. Many Prokaryotes have only one photosystem, Photosystem II (so numbered because, while it was most likely the first to evolve, it was the second one discovered). Eukaryotes have Photosystem II plus Photosystem I. Photosystem I uses chlorophyll a, in the form referred to as P700. Photosystem II uses a form of chlorophyll a known as P680. Both "active" forms of chlorophyll a function in photosynthesis due to their association with proteins in the thylakoid membrane. </li> <li> Slide 28 </li> <li> Light Dependent Reactions: Light Energy Trapped by Chlorophyll is Used to Split Water, Make NADPH & ATP </li> <li> Slide 29 </li> <li> ATP Production Requires a Proton Gradient </li> <li> Slide 30 </li> <li> Light Dependent Reactions: Light Energy Trapped by Chlorophyll is Used to Split Water, Make NADPH & ATP-1 The P680 requires an electron, which is taken from a water molecule, breaking the water into H + ions and O -2 ions. These O -2 ions combine to form the diatomic O 2 that is released. The electron is "boosted" to a higher energy state and attached to a primary electron acceptor, which begins a series of redox reactions, passing the electron through a series of electron carriers. Eventually attaching it to a molecule in Photosystem I. Light acts on a molecule of P700 in Photosystem I, causing an electron to be "boosted" to a still higher potential. The electron is attached to a different primary electron acceptor (that is a different molecule from the one associated with Photosystem II). </li> <li> Slide 31 </li> <li> Light Dependent Reactions: Light Energy Trapped by Chlorophyll is Used to Split Water, Make NADPH & ATP-1 The electron is passed again through a series of redox reactions, eventually being attached to NADP + and H + to form NADPH, an energy carrier needed in the Light Independent Reaction. The electron from Photosystem II replaces the excited electron in the P700 molecule. There is thus a continuous flow of electrons from water to NADPH. This energy is used in Carbon Fixation. Cyclic Electron Flow occurs in some eukaryotes and primitive photosynthetic bacteria. No NADPH is produced, only ATP. This occurs when cells may require additional ATP, or when there is no NADP + to reduce to NADPH. In Photosystem II, the pumping to H ions into the thylakoid and the conversion of ADP + P into ATP is driven by electron gradients established in the thylakoid membrane. </li> <li> Slide 32 </li> <li> Light Independent (Dark) reactions (Calvin Cycle) make sugar from CO 2 : Uses ATP and NADPH produced by light reactions to reduce CO 2 to glyceraldehyde-3-phosphate. Occurs in the stroma of chloroplast. Dont need light directly. Carbon fixation: Process of gradually reducing CO 2 gathered from atmosphere to organic molecules. NADPH provides H and electrons to reduce CO 2 and ATP provides energy. Input: CO 2, ATP, and NADPH. Output: Sugars, ADP, and NADP+. </li> <li> Slide 33 </li> <li> Light and Dark Reactions of Photosynthesis </li> <li> Slide 34 </li> <li> Dark Reactions (or Light Independent Reactions) Also known as Carbon-Fixing Reactions. The Calvin Cycle occurs in the stroma of chloroplasts (where would it occur in a prokaryote?). Carbon dioxide is captured by the chemical ribulose bisphosphate (RuBP). RuBP is a 5-C chemical. Six molecules of carbon dioxide enter the Calvin Cycle, eventually producing one molecule of glucose. </li> <li> Slide 35 </li> <li> C4 Plants When carbon dioxide levels decline below the threshold for RuBP carboxylase, RuBP is catalyzed with oxygen instead of carbon dioxide. The product of that reaction forms glycolic acid, a chemical that can be broken down by photorespiration, producing neither NADH nor ATP, in effect dismantling the Calvin Cycle. C-4 plants evolved in the tropics and are adapted to higher temperatures than are the C-3 plants found at higher latitudes. Common C-4 plants include crabgrass, corn, and sugar cane. C-4 plants, have had to adjust to decreased levels of carbon dioxide by artificially raising the carbon dioxide concentration in certain cells to prevent photorespiration. The capture of carbon dioxide by PEP is mediated by the enzyme PEP carboxylase, it has a stronger affinity for carbon dioxide than does RuBP carboxylase. </li> <li> Slide 36 </li> <li> C4 Photosynthesis Some plants have developed a preliminary step to the Calvin Cycle - known as the C-4 pathway. While most C-fixation begins with RuBP, C-4 begins with a new molecule, phosphoenolpyruvate (PEP), a 3-C chemical that is converted into oxaloacetic acid (OAA, a 4- C chemical) when carbon dioxide is combined with PEP. The OAA is converted to Malic Acid and then transported from the mesophyll cell into the bundle-sheath cell, where OAA is broken down into PEP plus carbon dioxide. The carbon dioxide then enters the Calvin Cycle, with PEP returning to the mesophyll cell. The resulting sugars are now adjacent to the leaf veins and can readily be transported throughout the plant. C-4 photosynthesis involves the separation of carbon fixation and carbohydrate synthesis in space and time </li> <li> Slide 37 </li> <li> C4 Carbon Fixation Pathway </li> <li> Slide 38 </li> <li> Photosynthesis Helps Counteract the Greenhouse Effect The earths atmosphere contains about 0.03% of carbon dioxide. Carbon dioxide traps solar energy in the atmosphere, making the earth about 10 o C warmer than it would otherwise be. Since the mid 1800s, the atmospheric levels of carbon dioxide have risen steadily due to the burning of fuels and forests. The Greenhouse Effect refers to the global warming that is caused by increased atmospheric carbon dioxide levels. Global warming may cause polar ice caps to melt, which in turn could cause massive coastal flooding and other problems. Plants use up about half of carbon dioxide generated by humans and other organisms. </li> <li> Slide 39 </li> <li> The Carbon Cycle Plants may be viewed as carbon sinks, removing carbon dioxide from the atmosphere and oceans by fixing it into organic chemicals. Animals are carbon dioxide producers that derive their energy from carbohydrates and other chemicals produced by plants by the process of photosynthesis. The balance between the plant carbon dioxide removal and animal carbon dioxide generation is equalized also by the formation of carbonates in the oceans...</li></ul>