Photosynthesis.ppt.pdf

PHOTOSYNTHESIS Life’s grand device OBJECTIVES outline Photosynthesis I. Intro II. Properties of light and pigments III. Chloroplast structure and function IV. Light reactions V. “Dark” or Carbon reactions Respiration I. Energy a...

PHOTOSYNTHESIS Life’s grand device OBJECTIVES outline Photosynthesis I. Intro II. Properties of light and pigments III. Chloroplast structure and function IV. Light reactions V. “Dark” or Carbon reactions Respiration I. Energy and food chains II. Carbon Cycle  I. Introduction to photosynthesis From the Greek PHOTO = produced by light SYNTHESIS = a whole made of parts put together. Definition: PHOTOSYNTHESIS is the process whereby plants, algae, some bacteria, use the energy of the sun to synthesize organic compounds (sugars) from inorganic compounds (CO2 and water).  WHY IS PHOTOSYNTHESIS SO IMPORTANT? PHOTOSYNTHESIS is one of the most important biological process on earth! Provides the oxygen we breathe Consumes much of the CO2 Food Energy Fibers and materials  GENERAL FORMULA FOR PHOTOSYNTHESIS light * * 6 CO2 + 12 H2O ---------> C6H12O6 + 6 O2 + 6 H2O pigments, enzymes Oxygen on earth allowed for the evolution of aerobic respiration and higher life-forms. Respiration: extracting energy from compounds (sugars) C6H12O6 + O2 🡪 6 CO2 + ATP II. PROPERTIES OF LIGHT Virtually all life depends on it! Light moves in waves, in energy units called PHOTONS Energy of a PHOTON inversely proportional to its wavelength Visible light occurs in a spectrum of colors  Light is absorbed by pigments The primary pigment for photosynthesis is chlorophyll a It absorbs blue and red light, not green (green light is reflected back!) Absorption spectrum of chlorophyll a  Absorption spectrum of chlorophyll a: BLUE & RED Action spectrum of photosynthesis closely matches absorption spectrum of chlorophyll a, but not perfectly (due to accessory pigments)  Accessory pigments like chlorophyll b and carotenoids (beta-carotene, lycopene): absorb light at different wavelengths, (extending the absorption range) help transfer some energy to chlorophyll a protect cell from harmful byproducts Chlorophyll a is the primary photosynthetic pigment that drives photosynthesis. Accessory pigments absorb at different wavelengths, extending the range of light useful for photosynthesis.  LIGHT-HARVESTING COMPLEXES: ACCESSORY PIGMENTS DIFFERENT PHOTOSYNTHETIC PIGMENTS ABSORB LIGHT AT DIFFERENT FREQUENCIES – ALLOWS LIGHT TO BE ABSORBED AT ALL FREQUENCIES OF THE VISIBLE SPECTRUM LHCs CONTAIN – CHLOROPHYLL EACH CHL. HAS A RED AND A BLUE ABSORPTION BAND – “ACCESSORY” PIGMENTS: “FILL IN” THE SPECTRUM CAROTENOIDS (LIKE β-CAROTENE AND LYCOPENE) FOUND IN ALL GREEN PLANTS IN MANY PHOTOSYNTHETIC BACTERIA Where does photosynthesis occur? The plant cell  III. Chloroplast structure and function: solar chemical factory  Chloroplast structure Football shaped Double membrane Stroma stroma Thylakoid membrane Grana Grana (stacks) lumen Lumen (inside thylakoid) thylakoids Inside a Chloroplast  CHLOROPLASTS STRUCTURE IS VERY SIMILAR TO MITOCHONDRIA – PROBABLY EVOLVED FROM A CYANOBACTERIUM INCORPORATED INTO A NON-PHOTOSYNTHETIC EUKARYOTE (SYMBIOSIS) IN EUKARYOTES, THE LIGHT REACTION OCCURS IN THYLAKOID MEMBRANE IN PROKARYOTES, THE LIGHT REACTION OCCURS IN: – INNER (PLASMA) MEMBRANE – IN “CHROMATOPHORES” INVAGINATIONS OF INNER MEMBRANE IN EUKARYOTES, THE DARK REACTION OCCURS IN THE STROMA Overview of photosynthesis: Note: The Light and “Dark”or Carbon reactions happen at different sites in the chloroplast H2O CO2 LIGHT ATP “DARK” or CARBON light REACTIONS REACTIONS (Thylakoids) NADPH (Stroma) (ENERGY) O2 C6H12O6 (OXYGEN GAS) (GLUCOSE)  IV. The Light Reactions 1. Light dependent 2. Occur in the thylakoid membrane of chloroplast 3. Water is split into oxygen gas (O2) and H+ 4. Use light energy (photons) to generate two chemical energy compounds: ATP & NADPH  Chemical energy compounds made in the light reactions ADP + Pi + Energy 🡪🡪 ATP adenosine inorganic adenosine diphosphate phosphate triphosphate NADP+ + 2e- + H+ 🡪🡪 NADPH Nicotinamide adenin dinucleotide phosphate Sequence of events in the Light Reactions STROMA NADP+ + H+ NADPH ADP + Pi ATP PS II e- PS I ATPS H+ 2 H2O O2 + 4 H + (gas) (protons) LUMEN (inside thylakoid)  Summary of the Light reactions 2 H2O + 2 NADP+ + 3 ADP + 3 Pi O2 + 2 NADPH + 3 ATP + 4 e- + 2 H+ (gas) Light reactions: Chemical energy compounds are made from light energy, water is split into O2 and protons V. The“Dark” or Carbon Reactions 1. Light independent (can occur in light or dark; some enzymes require activation by light) 2. Occur in the stroma of chloroplasts 3. Use the chemical energy produced in Light Reactions (ATP; NADPH) to reduce CO2 to carbohydrate (sugar). 4. CO2 is converted to sugar by entering the Calvin Cycle  The Calvin Cycle From Melvin Calvin Also known as Calvin- Benson Cycle, Light independent reaction, dark reaction CO2 enters the Calvin Cycle First product is a 3-carbon molecule: 3-PGA (phosphoglyceric acid). That’s why it’s also called C-3 cycle.  RuBP is the five carbon (C-C-C-C-C) sugar-phosphate. Rubisco is the enzyme ribulose bisphosphate carboxylase/oxygenase Enzyme RUBISCO (ribulose bisphosphate carboxylase/oxygenase) is the main enzyme that catalyzes the first reactions of the Calvin Cycle. RUBISCO: Is the most abundant protein on earth!  Glyceraldehyde 3-phosphate or G3P is the product of the Calvin cycle. It is a 3-carbon sugar that is the starting point for the synthesis of other carbohydrates. Some of this G3P is used to regenerate the RuBP to continue the cycle, but some is available for molecular synthesis and is used to make fructose diphosphate and glucose These sugars are used in respiration or as a building block in making starch and cellulose.  The Calvin Cycle Named for M. Calvin RuBP CO2 3 phases ADP Ribulose bisphosphate CO2 goes 6 cycles rubisco to produce 1 glucose ATP carboxylation regeneration 3-PGA reduction 3-phosphoglycerate ATP ADP GAP NADPH Glyceraldehyde 3-phos. sugars NADP+ Pi  Summary of Carbon Reactions 6 CO2 + 18 ATP + 12 NADPH + 12 H2O C6H12O6 + 18 ADP + 18 Pi + 12 NADP+ glucose + 6 H2O + 6 O2 Carbon reactions: Use CO2 and chemical energy (ATP & NADPH) to produce sugars by means of the Calvin Cycle  Limitations on Photosynthesis Photosynthesis is not perfect in C-3 plants, it is only 1 - 4 % efficient Low efficiency due to photorespiration Photorespiration occurs when internal CO2 concentration becomes too low (drought); rubisco begins fixing oxygen. Most plants use the Calvin Cycle to Convert CO2 into sugars. These plants are called C-3 plants  C-4 plants are more efficient C-4 plants first product is a 4-carbon molecule The C-4 plants (sugar cane, corn, etc.), are more efficient than C-3 plants – they grow in hotter climates with more light. For example, sugar cane’s photosynthetic efficiency is 7% C-4 plants have a different leaf anatomy  C-3 vs. C-4 leaf anatomy Net venation Parallel venation  VI. Summary of Photosynthesis: 1. Light energy absorbed by chlorophyll a drives the reactions of photosynthesis. 2. Converts light energy into chemical energy to make organic compounds. 3. CO2 and H2O used to produce C6H12O6 (glucose) and O2 (gas). Importance of photosynthesis and the impact that it has in all our lives. Without photosynthesis, virtually all plants and animals would become extinct.  PHOTOSYNTHESIS RESPIRATION CO2 + H2O 🡪 O2 + SUGARS SUGARS + O2 🡪 H2O + CO2 O2 CO2 CO2 O2 PLANTS, H2O ALGAE, SUGARS MOST LIVING H2O BACTERIA ORGANISMS Sunlight USEFUL CHEMICAL energy ENERGY (ATP) HOMEWORK